JP3657793B2 - Magnetic recording medium and manufacturing method thereof - Google Patents

Description

【００７０】
上表１は、記録セルのアスペクト比は従来の磁気媒体では２０程度であるが、今後アスペクト比は小さくなる方向、つまり狭トラック化の方が狭ビットピッチ化よりも急速に進展する方向と予測されるので、アスペクトが１０の場合と１の場合（いわゆるスクエアビットとして提案されている）について示してある。ビット密度と最短セル長の関係は信号処理方法に依存するが、表１では、１／７変調方式を採用した場合の換算値を用いた。
【００７１】
前述したように、規則的磁性粒子媒体の場合には、最小記録セルは少なくとも４個の磁性粒子からなるため、低ノイズ性能を発現する上で最も好ましい粒径は最小記録セル長の１／４以下である。このため、表１では粒径はセル長の１／４としてある。
【００７２】
また、磁性粒子の密度は十分に大きな媒体信号出力を得る上で５０％以上と設定し、粒子間隔は粒子間の交換相互作用を完全に分断できるように粒子サイズ＋１ｎｍとした。また、表１において、最小記録セル中に含まれる磁性粒子数は、トラック幅と最短記録セル長の積を粒子間隔で除した値で表わされる。
【００７３】
また、規則的非磁性ポア媒体においては、ポア密度は十分に大きな媒体信号出力を得る上で５０％以下と設定した。また、ポア間隔はトラック幅以下であれば実質的に使用可能だが、表１ではポアを連結する磁壁（磁化転移）が十分な安定性を有する値として、トラック幅の０．２とした。
【００７４】
表１から、本発明の規則的磁性粒子媒体、規則的非磁性ポア媒体はともに、超高密度磁気記録媒体の候補として有用なことが明らかである。
【００７５】
＜本発明に係るマスクの製造方法＞
本発明に係る規則的磁性粒子媒体および規則的非磁性ポア媒体は、どちらも規則的に配列する開口を有するマスクを用いて製造することができる。従って、最初に、規則的に配列する開口を有するプロセスマスクの製造方法について説明する。
【００７６】
磁性層から規則的に配列する複数の磁性粒子を作製する、または非磁性マトリクス層から規則的に配列する複数の非磁性ポアを作製するためのマスクは、例えば自己組織化プロセスを利用して製造することができる。
【００７７】
自己組織化プロセスとしては、例えば、以下のものが挙げられる。
（ａ）Ｊ．Ｅｌｅｃｔｒｏｃｈｅｍ．Ｓｏｃ．１００，４１１，１９５３に開示されている、高純度Ａｌの陽極酸化法。
（ｂ）酸化物微小球の分散沈殿法。
（ｃ）酸化物微小球のガス中蒸着法。
（ｄ）応用物理第５２巻第８号、７１２，１９８３に開示されている、ステアリン酸上へのＧｅもしくはＢｉ蒸着。
（ｅ）グラファイト上へのＣｕフタロシアニンのヘテロエピタキシャル成長。
（ｆ）Ａｐｐｌ．Ｐｈｙｓ．Ｌｅｔｔ．６４（２）１９６，１９９４に開示されている、ＧａＡｓ上へのＩｎＡｓドット形成。
（ｇ）Ａｐｐｌ．Ｐｈｙｓ．Ｌｅｔｔ．６４（４）４２２，１９９４に開示されている、複合有機物上へのＡｕドット形成。
本発明においては、上述の自己組織化プロセスのどの手法も適用することが可能であり、また、自己組織化プロセスを用いない他の方法も適用可能である。
【００７８】
自己組織化プロセスを用いてマスクを製造する方法の例として、上述の（ａ）高純度Ａｌの陽極酸化法、および（ｃ）の酸化物微小球のガス中蒸着法を用いてマスクを製造する方法について説明する。
【００７９】
（Ａ）高純度Ａｌの陽極酸化法によるマスクの製造方法
Ａｌの陽極酸化による自己組織化マスクの製造は、（１）ポーラスアルマイトを形成する段階、（２）ポーラスアルマイトからマスクを作製する段階からなる。
【００８０】
以下、各段階について順次説明する。
（１）ポーラスアルマイトを形成する段階
この段階は、次の（ａ）〜（ｃ）の工程を含んでいる。
（ａ）４Ｎもしくは５Ｎグレードの高純度Ａｌ板を鏡面研磨する。
（ｂ）鏡面研磨したＡｌ板を過塩素酸化学研磨もしくは水酸化ナトリウム溶液中アルカリ研磨したのち中和する。
（ｃ）中和ののち、Ａｌ板を数％〜１０数％の陽極酸化溶液中に浸漬して、Ｐｔ、Ｃ等を負極にしてＡｌ板に正の電圧を印加して所定の時間陽極酸化する。
【００８１】
陽極酸化溶液としては、蓚酸、燐酸、硫酸、クロム酸およびこれらの混酸の水溶液を用いる。陽極酸化により、Ａｌ板の表面に連続したＡｌ₂ Ｏ₃ バリア層が形成され、さらにバリア層の上にポーラスアルマイト（Ａｌ₂ Ｏ₃ ）が形成される。ポーラスアルマイトは、規則的に配列された複数の未貫通の微小孔を有する。このような形状のポーラスアルマイトが形成されることを自己組織化という。
【００８２】
図３は、陽極酸化により形成されたバリア層、およびポーラスアルマイトを示す概略断面図である。図３に示すように、陽極酸化処理によって、高純度Ａｌ板１１の上に陽極酸化Ａｌの初期成長バリア層部１２が形成され、その上に複数の微小孔１３を有する陽極酸化Ａｌのポーラスアルマイト部１４が形成される。図３において、Ｃはポーラスアルマイトの単位セルサイズ（微小孔間隔に相当する）、Ｐは微小孔サイズ、Ｗは微小孔の周囲を囲むアルマイト壁の厚さを示す。
【００８３】
この様な自己組織化ポーラスアルマイト１４の形成機構は、陽極酸化溶液にＡｌと酸化Ａｌ（Ａｌ₂ Ｏ₃ ）の両方が溶解することに起因する。すなわち、原材料のＡｌを酸化液に浸漬して電圧を印加すると、Ａｌ表面が溶解しながら陽極酸化Ａｌ層が形成されるとともに、形成された酸化Ａｌの一部が溶液中へと溶解する。酸化Ａｌが溶解して溶液中へと流れ出た後の酸化Ａｌ表面では、電界が集中して電流密度が増加する。電流密度が増加すると、酸化Ａｌの溶解が促進されるために微小孔１３が形成される。同時に、微小孔１３の周囲には、溶解した余剰のＡｌもしく酸化Ａｌが供給されて、酸化Ａｌ壁の成長が促される。
【００８４】
以上のような酸化Ａｌの一部の溶解、すなわち局部的な溶解は、Ａｌ自体もしくはＡｌ表面に残存する自然酸化Ａｌの欠陥部において選択的に発生する。上述したように、局部溶解が発生したのち、微小孔１３が形成されて酸化Ａｌの壁が成長すると電界は弱まる。電界が弱まると、酸化Ａｌ表面上の全電界強度を保持するために、酸化Ａｌ壁の隣において電界の強い部分が再び形成されて微小孔１３が形成される。
【００８５】
陽極酸化の初期の段階では、ランダムに分布する欠陥部から微小孔１３の形成が開始される。しかし、上述したように、形成された微小孔１３の周囲に周期的かつ規則的な電界の空間分布が生ずるために、自己組織的に微小孔１３が規則的な配列をなすものと考えられる。
【００８６】
図３に示すように、Ａｌ板１１と酸化Ａｌバリア層１２との界面においては、単位セルごとに凹面が形成されている。ポーラスアルマイト１４が成長した部材を、比較的高濃度の燐酸、またはクロム酸溶液中に浸漬してポーラスアルマイト１４を除去すると、規則的に配列した凹面を有するＡｌ板１１が得られる。このＡｌ板１１に上述の陽極酸化を再び施すと、Ａｌ板１１上の凹面と凹面との間に位置する突起部が前述した欠陥部の役割を果たして、最初の陽極酸化よりもさらに規則性の良い自己組織パターンを有するポーラスアルマイト１４を得ることができる。
【００８７】
ポーラスアルマイト１４の成長速度は陽極酸化条件、主に陽極酸化電圧に依存するが、典型的には数〜１００ｎｍ／分である。また、微小孔１３の深さは陽極酸化時間で調整することができる。
【００８８】
後述する磁気媒体の試作においては、上述のようにして形成した微小孔１３のサイズが磁性粒子サイズまたは非磁性ポアサイズに対応し、微小孔１３の間隔が磁性粒子間隔または非磁性ポア間隔に対応する。また、微小孔１３の深さは磁性膜加工の特性に関連する。微小孔１３のサイズと微小孔１３間の間隔は、陽極酸化に使用する酸の種類、陽極酸化電圧、陽極酸化バス温度に依存する。
【００８９】
前述のようにポア間隔をＣ、ポア径をＰ、孔の周りに形成される酸化Ａｌ壁の厚みをＷとおき、Ａｌに印加する電圧をＥと置くと、実験的に以下の関係がある。
Ｃ＝２ＷＥ＋Ｐ ………………………（１）
ポア径Ｐ、酸化Ａｌ壁の厚みＷは、陽極酸化液の種類、濃度、バス温度に依存する。微小孔１３の径は、酸の種類、濃度、バス温度によって調整可能であり、微小孔１３の間隔は、酸の種類、濃度、バス温度、および印加電圧によって幅広く調整可能である。微小孔１３の配列の規則性、すなわち孔径分布と孔間隔分布は、Ａｌの純度、Ａｌ中へのＭｇ等の添加物の量、陽極酸化前の処理方法、陽極酸化速度、陽極酸化の回数に依存する。
【００９０】
（２）ポーラスアルマイトからマスクを作製する段階
Ａｌ上に形成したポーラスアルマイト１４からマスクを形成する方法は、例えばＪｐｎ．Ｊ．Ａｐｐｌ．Ｐｈｙｓ．３５−２（１Ｂ）Ｌ１２６，１９９６に開示されている。
【００９１】
この方法においては、次の（ａ）〜（ｅ）の工程が含まれている。
（ａ）図３に示すポーラスアルマイト１４の微小孔１３を含む表面へレジストなどの有機樹脂モールドを形成する。
（ｂ）Ａｌ板１１をエッチング除去する。
（ｃ）酸化Ａｌバリア層１２を除去する。
（ｄ）樹脂モールドへ白金などの金属を充填する。
（ｅ）樹脂モールドを除去する。
以上の一連の工程によって、貫通孔を有する白金などの金属のマスクが作製される。
【００９２】
また、Ｊｐｎ．Ｊ．Ａｐｐｌ．Ｐｈｙｓ．３１−２（１２Ｂ）Ｌ１７７５，１９９２、および、Ｓｃｉｅｎｃｅ，２６８，１４６６，１９９５には、ポーラスアルマイトにレジストを埋め込みネガパターンを形成した後、酸化物、白金（Ｐｔ）などのレプリカを形成して、このレプリカからマスクを形成する方法が開示されている。
【００９３】
Ｓｃｉｅｎｃｅ，２６８，１４６６，１９９５に開示されている方法においては、レプリカの材料として、酸化物、白金以外にさらにＳｉＣ、ＳｉＯ₂ 、ａ−Ｃ：ＨなどのＣＶＤ成長材料を用いることができる。そのため、前述のポーラスアルマイト自体をマスク化する場合に比べて、マスクの耐エッチング性、機械強度を向上させることができる。
【００９４】
なお、このようにレプリカからマスクを作製するときには、ポーラスアルマイトのパターンからそのままマスクを作製しても良いが、機械的保持のためにＣuなどの金属からなるメタルリングを用意し、メタルリングの開口部にポーラスアルマイトのハニカムパターンを配置したのちに、ポーラスアルマイトのパターンからマスクを作製しても良い。メタルリングを用いて作製すると、作製されたマスクの機械強度、ハンドリング性を著しく向上させることができる。
【００９５】
図４は、メタルリングの一例を示す概略平面図および概略断面図である。マスクはメタルリング１５の開口部１６に形成される。メタルリング１５を用いたマスクの作製は、例えばＳｃｉｅｎｃｅ，２６８，１４６６，９５に開示されているレプリカ法を修正した方法によって行うことができる。
【００９６】
（Ｂ）酸化物微小球のガス中蒸着法を用いてマスクを製造する方法
本方法は、以下の工程を含んでいる。
【００９７】
（ａ）１０ｎｍオーダの微小球を形成するＴｉＯ₂ 等の酸化物を、例えば電子ビーム蒸着装置の原料ボートに入れて真空排気後、電子ビームをボートに照射してＴｉＯ₂ を蒸発させる。
【００９８】
（ｂ）蒸発物質を、蒸着室内に設けた隔壁の通過孔からガス圧力の高い別室に導く。この別室においては、蒸発物質の過冷却により、気相中で１０ｎｍオーダのＴｉＯ₂ の微小球が形成される。
【００９９】
（ｃ）形成された微小球をプラズマ中に通過させる、または微小球にオゾナイザーを吹きかけるなどして帯電させてから、帯電した微小球をマスク基板に堆積させる。堆積した微小球は、基板上で互いにクーロン力によって反発しながら規則的に配列する。配列の結果、粒径１０ｎｍオーダのＴｉＯ₂ 球の規則的な自己組織化パターンが形成される。
【０１００】
（ｄ）形成されたパターンからマスクを作製する。マスクの作製は、例えば以下のようにして行う。形成されたパターンに、例えばレジストを埋め込み、規則的に配列した凹部を有するレジストのネガパターンを作製する。ネガパターンを転写プロセスに供することによって、自己組織化パターンと同じパターンを有するマスクを形成することができる。
【０１０１】
次に、本発明に係る磁気記録媒体の製造方法について説明する。
まず、上述のようにして作製したマスクを用いて製造する方法について説明する。次に、マスクを用いずに磁気記録媒体を製造する方法について説明する。
【０１０２】
＜マスクを用いて本発明に係る磁気記録媒体を製造する方法＞
上述のようにして作製したマスクのうち、特にポーラスアルマイトから作製したマスクを用いて本発明に係る規則的磁性粒子媒体、および規則的非磁性ポア媒体を製造する方法について説明する。
【０１０３】
（Ａ）規則的磁性粒子媒体の製造方法
まず、通常のパターンを有する規則的磁性粒子媒体の製造方法について説明する。そして、次に、サーボパターンを有する規則的磁性粒子媒体の製造方法について説明する。
【０１０４】
（Ａ−１）通常のパターンの規則的磁性粒子媒体の製造方法
図１の構成の規則的磁性粒子媒体は、例えば、多室マグネトロンスパッタリング装置などの成膜装置内に装着した基板上に、スパッタリングによって、シード層、磁性層、保護層を順次成膜することによって、作製することができる。
【０１０５】
本方法には、基本的に２通りのプロセス、第１のプロセスおよび第２のプロセスが適用できる。両方のプロセス共に、図１に示した規則的磁性粒子媒体の作製に用いる事ができる。第１のプロセスは、第２のプロセスに比較してプロセス数が多くＰＥＰ工程も必要となるが、自己組織化マスクがプロセス中に何ら変質を受けないために繰り返して何回でも使用できるという利点がある。
【０１０６】
図５に、これらのプロセスフローを示す。
【０１０７】
（１）第１のプロセス
（ａ）基板上に磁性層を形成する。前述したように、シード層、保護層は形成してもしなくても良い。
（ｂ）磁性層の上にレジストをコートする。
（ｃ）前述のようにして作製した自己組織化マスクの直下に、基板を配置する。
【０１０８】
（ｄ）マスクの上から光照射、もしくは電子ビーム一括照射を行って、レジストを露光する。露光したのちレジストを現像する。ポジ型レジストを用いれば、現像処理によって露光部のみが磁性層の上にパターンとして残る。このレジストパターンは、前記の自己組織化マスクの開口部のハニカム状パターンと一致する。
【０１０９】
（ｅ）イオンミリング法もしくはＲＩＥ法などにより、レジストパターンを磁性層に転写する。イオンミリング法は、磁性層の形成された基板（ＨＤＤ応用の場合にはディスク基板）よりも大口径のイオン源を用いて一括ミリングするか、小口径のイオン源の下部で基板を回転するなどして行う。レジスト、磁性層、シード層、保護層のミリングレートをあらかじめ調査しておく。調査したレートを参照してミリング時間を設定すれば、レジストがミリングオフされる前に磁性層のみを規則的な柱状磁性粒子にパターニングできる。シード層は磁性粒子の下部にそのまま残るので良好な磁気特性が保持される。磁性粒子間のシード層は、ミリングされても構わない。
【０１１０】
（ｆ）磁性層をパターニングしたのち、必要に応じてレジスト残渣を除去（アッシング、ディッピング等を利用）する。
【０１１１】
以上の（ａ）〜（ｆ）の工程によって、本発明に係る規則的磁性粒子媒体が製造される。
【０１１２】
（ｇ）媒体の機械強度、耐食性を向上する上で、上述のようにして製造された磁性粒子の間に、さらにマトリクス材料を埋め込む。
【０１１３】
埋め込みは、ＣＶＤ、スパッタ、蒸着等の成膜方法によって行うことができる。磁性粒子間へのマトリクス材料の埋め込み性の点からは、コリメーションスパッタ等の異方性成膜法が好ましいが、埋め込み深さ（磁性粒子の厚みと同等程度の深さ）が１０ｎｍ程度と非常に小さいので、どのような手法を用いても比較的良好な埋め込みを行うことができる。
【０１１４】
（ｈ）マトリクスの埋め込み後は媒体の表面は凹凸面をなしているので、必要に応じて、媒体表面に表面平坦プロセスを施す。表面平坦プロセスの方法としては、例えば、ワッフルバニッシュ、テープバニッシュ、ＣＭＰ、イオンポリッシング、またはこれらの組合せなどが挙げられる。
【０１１５】
例えば、マトリクスとしてＣＶＤ−Ｃ、表面平坦化にテープバニッシュとイオンポリッシングを組合せたときには、表面粗さとしてＲａ＜１ｎｍを実現することが可能である。
【０１１６】
（ｉ）平坦化プロセス後、マトリクス材料が磁性粒子の上部を覆っている状態であれば、そのまま規則的磁性粒子媒体として使用可能である。マトリクス材料が磁性粒子の上部を覆わず磁性粒子の上部が露出しているときには、平坦化プロセスの後に媒体の表面に保護膜をコートするのが好ましい。
【０１１７】
（ｊ）図５には図示していないが、最後に、通常の磁気媒体と同様に、潤滑層を媒体の表面にコートする。潤滑層は保護膜の代わりに用いることができるので、上述のように磁性粒子が露出しているときに、潤滑層を媒体の表面にコートしても良い。
【０１１８】
（２）第２のプロセス
（ａ）基板上にマトリクスとなる材料を連続膜として形成する。前述したように、シード層、保護層は形成してもしなくても良い。
（ｂ）基板を、自己組織化マスクの直下に配置する。
（ｃ）イオンミリング法もしくはＲＩＥ法などにより、自己組織化マスクに対応して、マトリクス材料をパターニングする。パターニングにより、マトリクス材料に規則的に配列された複数の孔が形成される。
【０１１９】
（ｄ）マトリクス材料に形成された孔に磁性粒子材料を埋め込む。埋め込みはコリメーションスパッタ等の異方性成膜法を適用するのが、孔側壁近傍の磁気特性を良好に維持する上で好ましいが、埋め込み厚さは厚くても５０ｎｍ程度なので、通常の等方性成膜を用いても磁気特性の劣化は微々たるものであり実用上は問題がない。
【０１２０】
（ｅ）磁性粒子埋め込み後は、バニッシュ、ＣＭＰ、イオンポリッシングなどの第１のプロセスと同様の方法で表面の平坦化を行う。
【０１２１】
第１のプロセスでは下側に磁性体、上側に通常は磁性体よりも硬質のマトリクス材料が配されるので平坦化プロセスのエンドポイントの管理は厳密に行う必要があるが、このプロセス（Ｂ）では下側に硬質のマトリクス材料、上側に磁性材料が配されるので、いずれの平坦化プロセスにおいてもエンドポイントの管理は比較的平易である。平坦化後のプロセスは第１のプロセスに準じて実施可能である。
【０１２２】
上述した第１のプロセス、第２のプロセスの両方において、媒体の磁気特性の調整は、磁性体形成温度の調整、磁性粒子形成後のアニールの実施などによっても行うことが可能である。
【０１２３】
そして、上述の第１のプロセス、第２のプロセスの両方において、本発明に係る、連続非磁性膜中に規則的に配列する複数の磁性粒子を備え、最小磁気記録セル内に含まれる磁性粒子について、トラックの長さ方向に配列する粒子数が少なくとも４個であり、最近接粒子間の距離の分布の全半値幅が最近接粒子間の平均距離の±４０％以下であり、粒径分布の全半値幅が平均粒径の±２０％以下である磁気記録媒体を製造することが可能である。
【０１２４】
（Ａ−２）サーボパターンを有する規則的磁性粒子媒体の製造方法
次に、サーボパターンを有する規則的磁性粒子媒体の製造方法について述べる。
図６は磁気ディスクのサーボパターンの一例を示す概略図であり、図６（ａ）は配置例、図６（ｂ）はサーボパターンの形態である。本発明をサーボパターンを有する磁性媒体に適用する場合、以下の３つの態様が考えられる。すなわち、（ｉ）サーボパターンを形成したのちに磁性粒子部を形成する態様、（ｉｉ）サーボパターンと磁性粒子部とを同時に形成する態様、（ｉｉｉ）磁性粒子部を形成したのちにサーボパターンを形成する態様、である。
【０１２５】
以下、各態様について、説明する。
（ｉ）サーボパターンを形成したのちに磁性粒子部を形成する態様は、例えば日本応用磁気学会第１０３回研究会資料ｐ．７５に開示されているように、以下の一連の工程を適用することが可能である。
【０１２６】
（ａ）基板上にレジストでサーボパターンを形成する
（ｂ）レジストをマスクとして基板表面にパターンを転写する
（ｃ）基板にサーボ用の磁性膜を埋め込む
（ｄ）レジストをリフトオフする
（ｅ）表面を平坦化する
埋め込みサーボを形成した後は、前述のようにして規則的磁性粒子媒体を形成すれば良い。
【０１２７】
（ｉｉ）サーボパターンと規則的磁性粒子部とを同時に形成する態様は、あらかじめ自己組織化マスクの一部にサーボパターンを設けることによって、行うことができる。
【０１２８】
具体的には、例えばポーラスアルマイトからマスクを形成する転写プロセスにおいて、レジストのネガの一部をサーボパターンに従って露光・現像すれば良い。
【０１２９】
（ｉｉｉ）規則的磁性粒子部を作製したのちにサーボパターンを形成する態様においては、規則的に配列する磁性粒子上にレジストをパターニングし、複数の磁性粒子を含むデータ部はそのまま保存して、サーボ部のみを必要に応じてエッチングし、サーボ用磁性膜を埋め込む等すれば良い。
【０１３０】
（Ｂ）規則的非磁性ポア媒体の製造方法
まず、通常のパターンを有する規則的非磁性ポア媒体の製造方法について説明する。そして、次に、サーボパターンを有する規則的非磁性ポア媒体の製造方法について説明する。
【０１３１】
（Ｂ−１）通常のパターンの規則的非磁性ポア媒体の製造方法
図２に示した規則的非磁性ポア媒体は、例えば、図５に示した規則的磁性粒子媒体の製造方法に準じて行うことができる。すなわち、図５の規則的磁性粒子媒体のプロセスフローにおいて、磁性層とマトリクス層、磁性粒子とマトリクスを逆にすれば良い。本方法においても、図５に図示したような第１のプロセスおよび第２のプロセスが適用できる。
【０１３２】
（１）第１のプロセス
（ａ）基板上に非磁性マトリクス層を形成する。シード層、保護層は形成してもしなくても良い。
（ｂ）非磁性マトリクス層の上にレジストをコートする。
（ｃ）前述のようにして作製した自己組織化マスクの直下に、基板を配置する。
【０１３３】
（ｄ）マスクの上から光照射、もしくは電子ビーム一括照射を行って、レジストを露光する。露光したのちレジストを現像する。ポジ型レジストを用いれば、現像処理によって露光部のみが磁性層の上にパターンとして残る。このレジストのパターンは、前記の自己組織化マスクの開口部のハニカム状パターンと一致する。
【０１３４】
（ｅ）イオンミリング法もしくはＲＩＥ法などにより、レジストパターンを非磁性マトリクスに転写する。イオンミリング法は、マトリクス層の形成された基板（ＨＤＤ応用の場合にはディスク基板）よりも大口径のイオン源を用いて一括ミリングするか、小口径のイオン源の下部で基板を回転するなどして行う。レジスト、非磁性層、シード層、保護層のミリングレートをあらかじめ調査しておく。調査したレートを参照してミリング時間を設定すれば、レジストがミリングオフされる前にマトリクス層のみを規則的な柱状非磁性粒子にパターニングできる。シード層は非磁性粒子の下部にそのまま残る。非磁性粒子間のシード層は、ミリングされても構わない。
【０１３５】
（ｆ）このようにして非磁性層をパターニングしたのち、必要に応じてレジスト酸渣を除去（アッシング、ディッピング等を利用）する。
【０１３６】
（ｇ）非磁性粒子の間に、磁性材料を埋め込む。埋め込みは、ＣＶＤ、スパッタ、蒸着等の成膜方法によって行うことができる。非磁性粒子間への磁性材料の埋め込み性の点からは、コリメーションスパッタ等の異方性成膜法が好ましいが、埋め込み深さ（非磁性粒子の厚みと同等程度の深さ）が１０ｎｍ程度と非常に小さいので、どのような手法を用いても比較的良好な埋め込みを行うことができる。
【０１３７】
（ｈ）磁性材料の埋め込み後は媒体の表面は凹凸面をなしているので、必要に応じて、媒体表面に表面平坦プロセスを施す。表面平坦プロセスの方法としては、例えば、ワッフルバニッシュ、テープバニッシュ、ＣＭＰ、イオンポリッシング、、またはこれらの組合せなどが挙げられる。
【０１３８】
（ｉ）平坦化プロセス後、媒体の表面に保護膜をコートする。
（ｊ）図５には図示していないが、最後に、通常の磁気媒体と同様に、ルブのような潤滑層を媒体の表面にコートする。潤滑層を保護膜の代わりに媒体の表面にコートしても良い。
【０１３９】
（２）第２のプロセス
（ａ）基板上に磁性層となる材料を連続膜として形成する。前述したように、シード層、保護層は形成してもしなくても良い。
（ｂ）基板を、自己組織化マスクの直下に配置する。
（ｃ）イオンミリング法もしくはＲＩＥ法などにより、自己組織化マスクに対応して、磁性材料をパターニングする。パターニングにより、磁性材料に規則的に配列された複数の孔が形成される。
【０１４０】
（ｄ）磁性材料に形成された孔に非磁性粒子材料を埋め込む。埋め込みはコリメーションスパッタ等の異方性成膜法を適用するのが好ましいが、埋め込み厚さは厚くても５０ｎｍ程度なので、通常の等方性成膜を用いても実用上は問題がない。
【０１４１】
（ｅ）非磁性粒子の埋め込み後は、バニッシュ、ＣＭＰ、イオンポリッシングなどの第１のプロセスと同様の方法で表面の平坦化を行う。
【０１４２】
第２のプロセスでは下側に軟質の磁性材料、上側に通常は磁性材料よりも硬質な非磁性マトリクス材料が配されるので、平坦化エンドポイントの管理は厳密に行う必要があるが、第１のプロセスでは下側に非磁性マトリクス材料、上側に磁性材料が配されるので、いづれの平坦化プロセスにおいてもエンドポイントの管理は比較的平易である。平坦化後のプロセスは第１のプロセスに準じて実施可能である。
【０１４３】
上述した第１のプロセス、第２のプロセスの両方において、本発明に係る、続磁性膜中に規則的に配列する複数の非磁性ポアを備え、磁性膜中の磁化転移部が非磁性ポアを連結する磁壁からなり、非磁性ポアの平均粒径が磁壁の平均幅の０．５ないし３倍である磁気記録媒体、およびこれらの特性に加えて最小磁気記録セル内の最近接ポア間の距離の分布の全半値幅が、最近接ポア間の平均距離の±４０％以下である磁気記録媒体を製造することが可能である。
【０１４４】
また、上述した第１のプロセス、第２のプロセスの両方において、媒体の磁気特性の調整は、磁性体形成温度の調整、磁性粒子形成後のアニールの実施などによっても行うことが可能である。
【０１４５】
（Ｂ−２）サーボパターンを有する規則的非磁性ポア媒体の作製
次に、サーボパターンを有する規則的非磁性ポア媒体の製造方法について述べる。サーボパターンとしては、規則的磁性粒子媒体と同様に、例えば図６のパターンを用いる事ができる。
【０１４６】
本発明をサーボパターンを有する媒体に適用する場合に、以下の３つの態様が考えられる。すなわち、（ｉ）サーボパターンを形成したのちに非磁性ポア部を形成する態様、（ｉｉ）サーボパターンと非磁性ポア部とを同時に形成する態様、（ｉｉｉ）非磁性ポア部を形成したのちにサーボパターンを形成する態様、である。
【０１４７】
以下、各態様について、説明する。
（ｉ）サーボパターンを形成したのちに非磁性ポア部を形成する態様は、例えば日本応用磁気学会第１０３回研究会資料ｐ．７５に開示されているように、以下の一連の工程を適用することが可能である。
【０１４８】
（ａ）基板上にレジストでサーボパターンを形成する
（ｂ）レジストをマスクとして基板表面にパターンを転写する
（ｃ）基板にサーボ用の磁性膜を埋め込む
（ｄ）レジストをリフトオフする
（ｅ）表面を平坦化する
埋め込みサーボを形成した後は、前述のようにして規則的非磁性ポア媒体を形成すれば良い。
【０１４９】
（ｉｉ）サーボパターンと非磁性ポア部とを同時に形成する態様は、あらかじめ自己組織化マスクの一部にサーボパターンを設けることによって、行うことができる。
【０１５０】
具体的には、例えばポーラスアルマイトからマスクを形成する転写プロセスにおいて、レジストのネガの一部をサーボパターンに従って露光・現像すれば良い。
【０１５１】
（ｉｉｉ）非磁性ポア部を形成したのちにサーボパターンを形成する態様においては、規則的に配列するポア上にレジストをパターニングし、複数の非磁性ポアを含むデータ部はそのまま保持して、サーボ部のみを必要に応じてエッチングし、サーボ用磁性膜を埋め込む等すれば良い。
【０１５２】
＜マスクを用いないで本発明に係る磁気記録媒体を製造する方法＞
次に、上述した自己組織化マスクのようなマスクを用いないで本発明に係る磁気記録媒体を製造する方法について説明する。一例として、マスクを用いないで本発明に係る規則的磁性粒子媒体を製造する方法について説明する。
【０１５３】
図７は、マスクを用いないで規則的磁性粒子媒体を製造するための装置の一例を示す概略図である。
【０１５４】
図７に示す装置は、ガス導入系を排気系を連通する真空容器２０を備えている。
【０１５５】
真空容器２０の床部には、誘導加熱型蒸発源２１が配置されている。蒸発源２１は、ヒーター２２が周囲に巻かれたルツボ２３、ルツボ２３の上部に配置されたシャッター２４からなる。ヒーター２２は、容器２０の外部に配置されたＲＦ電源２５と接続されている。ルツボ２３の中に、蒸発させるための蒸発試料２６が充填される。
【０１５６】
真空容器２０の天井部には、超伝導体部２７が配置されている。超伝導体部２７は、天井から吊下げられたコールドヘッド２８、コールドヘッド２８の下面に取付けられた超伝導体２９、超伝導体２９の下面に取付けられた磁気ディスク基板３０、これらの部材の側方部に配置された磁界印加用コイル３１からなる。コイル３１も天井から吊下げられている。
【０１５７】
図７の装置を用いて、以下の手順により、規則的磁性粒子媒体を製造することができる。
（ａ）真空容器２０内容を１０−４Ｐａ以下に排気したのち、コールドヘッド２８を動作して超伝導体２９を超伝導状態が発現する温度まで冷却する。
（ｂ）磁界印加用コイル３１を通電して、超伝導体２９に垂直な方向の磁界を印加する。
【０１５８】
超伝導状態にある超伝導体２９に磁界が印加されると、超伝導体２９内部に規則的に配列する三角格子状の渦電流が流れる。それぞれの渦電流の中心部から超伝導体２９の表面と垂直な磁界３２が発生し、渦電流中心部以外では磁界３２は発生しない。すなわち、超伝導体２９表面には、三角格子状に規則的に配列する表面に垂直な磁束を有する磁界３２のパターンが形成される。
【０１５９】
磁界３２のパターンの間隔は、超伝導体２９の種類との印加する磁界強度に依存する。例えば超伝導体２９に酸化物高温超伝導体であるＹＢＣＯを用いて、印加磁界を１Ｔとした場合には、磁界３２のパターンの間隔は５０ｎｍ弱となり、本発明の実施の好適な値を示す。磁界３２のパターンの間隔は印加磁界強度の平方根に逆比例するので、磁界強度を高めればパターン間隔は狭くする事ができる。例えば、超伝導体２９としてＹＢＣＯを用いたときには、磁界３２のパターン間隔は２５〜５０ｎｍである。
【０１６０】
（ｃ）超伝導体２９表面に自己組織的に形成された磁界３２のパターン上に磁性体微粒子（図示せず）を蒸着する。
磁性体微粒子の蒸着には、ガス中蒸着法などを適用する事ができる。例えば、ＣｏＰｔなどの磁性体を原料として蒸発試料２６に混合しておき、誘導加熱により磁性体を蒸発させる。具体的にはシャッター２４を閉じた状態でＲＦ電源２５を動作して誘導加熱コイル２２を通電すると、磁性体の加熱と蒸発が起こる。
【０１６１】
（ｄ）真空容器２０中に不活性ガスを数１０〜数１００Ｐａ程度導入する。導入により、蒸発した磁性体が気相中で過冷却状態になり、例えば直径サブｎｍ〜１０数ｎｍ程度の磁性クラスターが形成される。
【０１６２】
（ｅ）磁性クラスターが形成された状態でシャッター２４を開き、クラスターを規則的磁界パターンを形成している基板３０上に導く。
【０１６３】
磁性クラスターはほとんど運動エネルギーを持たないので、基板３０付近まではランダムに基板３０に向かって飛来するが、基板３０の近傍では規則的に配列する磁界３２のパターンに従って基板上に規則的に配列する。こうして、基板３０上に規則的磁性粒子を作製することができる。
（ｆ）規則的磁性粒子を得たのちの媒体の形成プロセスは、前述の規則的磁性粒子媒体の形成プロセスと同様にして実施可能である。また、この様な手法で得られた規則的磁性粒子媒体の特性も、前述の自己組成化マスクを用いて形成した規則的磁性粒子媒体の特性と同様である。
【０１６４】
以上、詳述したように、本発明を用いれば、特にヘッド、サーボ、信号処理装置などの磁気記録媒体以外の要素技術に特に負担をかけることなく、大幅な記録密度の向上が図れる。
【０１６５】
なお、本発明に係る媒体は、高記録密度化への他の手法と組合せることが容易なので、組合わせの例をいくつか例示しておく。
【０１６６】
＜本発明と他の技術との組み合わせの例示＞
本発明に係る媒体と垂直記録方式との組合せは、すでに本明細書中に記載済みである。本発明の媒体を垂直記録に適した単磁極ヘッドと組合せて実施すれば、さらに高記録密度化できる可能性がある。
【０１６７】
本発明に係る媒体と熱アシスト記録方式との組合せも容易である。熱アシスト記録方式は、室温において磁気異方性が非常に大きい媒体を採用して熱擾乱耐性を向上させ、さらなる微粒子化を可能にするものである。しかし、磁気異方性の高い記録媒体を使用すると磁気記録を行うためには大きな磁界を必要とするので、ヘッドにかかる負担が大きくなりすぎて実用的ではない。そこで熱アシスト記録方式では、記録する部分のみをレーザビーム等を用いて加熱し、記録する瞬間のみ異方性すなわち記録磁界を低下させる。この様な手法を適用すれば多粒子ランダム媒体でも粒径をさらに微細化できるので高密度化可能となる。本発明の規則的磁性粒子媒体においても、高磁気異方性の磁性粒子材料を採用すること、および磁気記録時に光熱アシストを行うことが可能である。従って、本発明に係る媒体と熱アシスト記録方式とを組合せることによって、やはり格段の高記録密度化が期待できる。
【０１６８】
上記の他に、ＩＥＥＥ−Ｔｒａｎｓ．Ｍａｇｎ．３４（４）１５５２および１５５５，１９９８に開示されているキーパー層を用いた媒体、軟磁性下引きの代りに半硬磁性下引きを用いてバーストノイズを低減しようとする垂直媒体との組合せ等、本発明の主旨を逸脱しない範囲で他の技術との組合せが可能である。
【０１６９】
【実施例】
＜ポーラスアルマイトの形成＞
（実施例１）
前述した高純度Ａｌの陽極酸化によるマスクの製造方法に従って、ポーラスアルマイトを作製した。下表２に陽極酸化条件と、作製したポーラスアルマイトのポア径Ｐ、酸化Ａｌ壁の厚みＷの測定結果を示す。
【０１７０】
【表２】

【０１７１】
Ｐ、Ｗは、図３に示すポーラスアルマイトの表面をＳＥＭ観察して画像処理を行ったのち、処理した画像から各ポアについて測定したＰ、Ｗの値を平均したものである。なお、陽極酸化速度は、印加電圧を調整して１０±１ｎｍ／分に調整した。
【０１７２】
上表２から、数〜数１０ｎｍの径の孔と、単位印加電圧当りサブｎｍ〜１ｎｍの厚さの壁が形成できていることが判る。
【０１７３】
次に、Ａｌの純度、陽極酸化前の処理方法、陽極酸化の回数を変えて、微小孔の孔径分布と孔間隔分布を変える実験を行った。下表３に実験結果を示す。
【０１７４】
【表３】

【０１７５】
孔径分布のＦＷＨＭ（Ｐσ）および孔間隔分布のＦＷＨＭ（Ｃσ）は、作製したポーラスアルマイトをＳＥＭ観察した像を画像処理することによって導出した。なお、Ｐσ、Ｃσは表２に示した平均孔径、平均孔間隔に対する分散量であり、例えばＰσ：２０％は±１０％に相当する。陽極酸化前の処理条件は、バフ研磨した高純度Ａｌの化学研磨条件を変えることによって変えた。陽極酸化速度は、印加電圧を調整して１０±１ｎｍ／分に調整した。
【０１７６】
上表中、最も孔径、孔間隔の分散の少ないｂ８の試料は、孔のイグナイターとしての欠陥部をあらかじめ規則的に配列したものである。
【０１７７】
欠陥の配列は以下のようにして行った。
まず、平坦・平滑な表面を有するＳｉＣ基板をＥＢ描画装置に設置した。そして、ＳｉＣ基板表面に電子ビームをラスタースキャンさせて、ＳｉＣ表面に格子状に配列した高さサブｎｍの複数の突起を形成した。次に、突起が形成されたＳｉＣ基板をＥＢ描画装置から取り出し、このＳｉＣ基板を高純度Ａｌ板に押し当ててＡｌ表面に格子状に配列した複数の凹部を形成した。次に、凹部が形成されたＡｌ板を、表３に示した条件の陽極酸化処理に供した。
【０１７８】
ｂ８の試料においては、陽極酸化処理の前にＥＢ描画パターンに従って形成したＳｉＣ基板上の凹部が、Ａｌ板の孔のイグナイターとして作用している。そのため、孔の配列はＥＢ描画パターン従っており、孔径、孔間隔共、分散は極めて少ない。
【０１７９】
表２、３の条件の組合せと陽極酸化電圧制御により、平均孔径：８〜４０ｎｍ、孔径分布のＦＷＨＭ：８〜１２０％（１２０％は±６０％を意味する）、平均孔間隔：１２〜６０ｎｍ、孔間隔分布ＦＷＨＭ：１５〜２００％の範囲でポーラスアルマイトを作製した。
【０１８０】
なお、陽極酸化速度を数〜３０ｎｍ／分程度までの範囲で変化させても、Ｐσ、Ｃσはほぼ表２に示した値を示した。陽極酸化速度が３０ｎｍ／分以上では、表２中のｂ８の試料以外の試料については、酸化速度を１０ｎｍ／分だけ増加させるとＰσ，Ｃσはほぼ５％の割合で増加した。ｂ８の試料については、成長速度を３０ｎｍ／分以上に増加させてもＰσ，Ｃσの増加は特に見られなかった。
【０１８１】
＜メタルリングを用いたマスクの形成＞
（実施例２）
前述したＳｃｉｅｎｃｅ，２６８，１４６６，１９９５に開示されているレプリカ法を修正した方法を用いて、メタルリングを用いてマスクを形成した。
【０１８２】
まず、Ｃｕリングを用意した。次に、ポーラスアルマイトのパターンが写し取られたレジストをＣｕリングの開口部に配置した。次に、Ｃｕリング上には連続的にＰｔを成長させ、リングの開口部にはレジストパターン通りにＰｔを成長させた。こうして、ポーラスアルマイトのハニカム状のパターンを有するＰｔからなるレプリカを形成した。形成したレプリカからマスクを形成した。
【０１８３】
以上の様にして形成したマスクの開口形状は、ポーラスアルマイトの有するパターンと１ｎｍ以内の誤差で一致した。
【０１８４】
図８に試作したマスクを上部から見込んだＳＥＭ像を示す。図８において、黒い円が貫通孔部、白がＰｔ壁部に相当する。図８に示したマスクは、平均孔径が２０ｎｍ、平均孔間隔が３０ｎｍ、孔径分布ＦＷＨＭが３０％、孔間隔分布ＦＷＨＭが４０％に、それぞれ調整されている。
【０１８５】
孔の深さは転写前のポーラスアルマイトの厚み以外にレプリカ形成時のＰｔ成長時間で調整可能であり、本例では磁気媒体プロセスへの適用性を考慮して５００ｎｍとした。メタルリングの開口部の面積にもよるが、メタルリングの内径が数ｃｍあれば、メタルリングによる機械的保持の効果のために、Ｐｔの厚さが５００ｎｍ程度に薄くても、レプリカの取り扱いに注意すれば破壊を防止できる。
【０１８６】
＜規則的磁性粒子媒体の作製＞
（実施例３）
前述した規則的磁性粒子媒体の製造方法に従って、実施例２で作製したマスクを用いて本発明に係る規則的磁性粒子媒体を作製した。
【０１８７】
磁性粒子上の保護膜厚は、従来媒体との比較のために、従来媒体に用いた膜厚と同じ１０ｎｍとした。保護膜材料は第１のプロセスではマトリクス材料もしくはＣ膜、第２のプロセスではＣ膜とした。また、全ての試料の最表面にはフルオロカーボン系の潤滑層を２〜３ｎｍ程度塗布した。
【０１８８】
図９は実際に試作した規則的磁性粒子媒体を上部からＳＥＭ観察した像である。図９において、白い部分が非磁性マトリクス４に、黒い円が磁性粒子５に相当する。
【０１８９】
実施例２で作製した各種の自己組織化マスクを使用して、平均粒径：７〜４２ｎｍ、粒径分布ＦＷＨＭ：８〜１５０％（１５０％は±７５％を意味する）、平均粒間隔：１２〜６０ｎｍ、粒間隔分布ＦＷＨＭ：１５〜２５０％の範囲で規則的磁性粒子媒体を作製した。
【０１９０】
＜規則的磁性粒子媒体の評価＞
実施例３で作製した規則的磁性粒子媒体を、以下のようにして評価した。
ＶＳＭを用いて、容易軸の向き、容易軸方向の残留磁化（Ｍｒ）と磁性粒子厚さ（ｔ）の積、保磁力（Ｈｃ）、保磁力角形比（Ｓ^* ）を求めた。揺らぎ場測定により活性化磁気モーメントを求めた。磁性粒子体積比および飽和磁化の測定値から、磁性粒子の活性化サイズ（Ｄａ）を求めた。Ｄａは磁性粒子の最小反転サイズに反応し、粒子間の交換相互作用がない場合には物理的な粒子１つのサイズと一致する。
【０１９１】
また、ＴＥＭおよびＳＥＭ観察と観察像の画像処理から、磁性粒子の平均粒径（Ｄ）、磁性粒子間の平均距離（Ｃ）、粒径の分布のＦＷＨＭ（Ｄσ）、磁性粒子間距離の分布のＦＷＨＭ（Ｃσ）を求めた。
【０１９２】
磁性粒子の平均粒径（Ｄ）は自己組織化マスクの平均孔径Ｐに対応するが、マスクからの転写プロセスによりＤとＰは若干異なる値を示した。粒径分布のＦＷＨＭ（Ｄσ）は自己組織化マスクの孔径分散Ｐσに対応するが、Ｄσは転写プロセスでの分散がＰσに重畳されて若干大きな値を示した。磁性粒子間の平均距離（Ｃ）は観察の結果、自己組織化マスクの孔間平均距離（Ｃ）と有意差が無かったので同じ符号Ｃで示す。粒子間距離の分布（Ｃ’σ）と自己組織化マスクの孔間隔の分散（Ｃσ）は、粒径分散Ｄσと孔径分散Ｐσの違いを反映して完全には一致せず若干の差異を示した。
【０１９３】
以上の平均値と分布を調べた媒体上の対象領域は２μｍ角であり、これは本発明を適用する最小記録セルサイズよりも十分に大きい範囲である。従って、対象領域の２μｍ角内での分布が例えば２０％以下であれば、当然のことながら最小記録セル中の分布も２０％以下である。
【０１９４】
また、最終的な評価として、ディスク状に形成した媒体試料をスピンスタンド上に装着したのち、ＭＲヘッドを用いて、媒体ノイズ特性を中心とした録音再生特性を調べた。以下に評価結果を順次述べていく事にする。
【０１９５】
（実施例４）
図１０は、磁性粒子間の平均距離（Ｃ）と、残留磁化と膜厚の積（Ｍｒｔ）との間の関係を測定した結果を示す図である。
【０１９６】
面内に磁化容易軸を有する試料（長手記録媒体）は、面内方向のメジャーループ測定でＭｒｔを求めた。また、垂直方向に磁化容易軸を有する試料は、垂直方向のメジャーループ測定でＭｒｔを求めた。また、図１０は、複数の試料の中から、平均粒径Ｄが９〜１１ｎｍ、粒径分散Ｄσが３０％（±１５％）以下、粒間分散Ｃσが６０％（±３０％）以下の規則的磁性粒子媒体を選んで調べた結果である。また、測定は、磁性粒子の厚みが１０ｎｍの媒体について行った。
【０１９７】
図１０において、Ａは磁性粒子材料がＣｏ−Ｆｅの本発明の媒体についての測定結果、Ｂは磁性粒子がＣｏ−Ｐｔの本発明の媒体の測定結果、Ｃは比較のための従来媒体の測定結果である。従来媒体Ｃは、基板上にＣｒ（１００ｎｍ）／ＣｏＣｒＴａＰｔ（１０ｎｍ）／Ｃ（１０ｎｍ）／潤滑剤（３ｎｍ）を形成した多粒子系のランダム配列の構造をなしている。従来媒体は、磁性層をスパッタリング成膜する時の温度を変えて磁性粒子径を異ならせた２つの試料を用意した。
【０１９８】
膜厚と粒径が一定の場合、磁性体が特に劣化していない場合には、ＭｒｔはＣ^-2に比例する。図１０のＡ、Ｂの測定結果においては、この理論通りにＭｒｔがＣ^-2に比例している。しかし、従来媒体の測定結果においては、理論通りになっていない。
【０１９９】
また、同じＣに対するＭｒｔの値は磁性粒子に占める磁性元素の量で決まる。本発明のＣｏ−Ｐｔの媒体と従来のＣｏＣｒＴａＰｔの媒体とでは、磁性元素濃度がほぼ同じであるにも拘わらず、従来媒体のＭｒｔの方が本発明の媒体のそれよりも低い。この結果は、従来媒体では粒径分布の幅が広いために熱擾乱によって超常磁性化している粒子が存在しＭｒｔを低めているが、本発明の規則的磁性粒子媒体では粒径分散が小さいために超常磁性化している粒子が殆どないことを示している。
【０２００】
Ｍｒｔは、磁気記録特性上は信号出力と磁化転移幅に関係する量であり、Ｍｒｔが大きいほど信号出力は大きいが、保磁力が同じ場合にはＭｒｔが大きいほど磁化転移幅が広くなり高密度記録が難しくなる。従って、Ｍｒｔは、媒体の他の磁気特性、ノイズ特性、ヘッドなどの記録再生系の特性に合わせて適切に調整すべき量である。本実施例によって示されるように、本発明の媒体においては、磁性粒子間の平均距離Ｃの調整によってＭｒｔを適切に調整できることが分かる。
【０２０１】
（実施例５）
図１１は、磁性粒子の平均粒径Ｄと保磁力Ｈｃとの間の関係を測定した結果を示す図である。Ｈｃは各試料の磁化容易軸方向での測定値である。図１１のＢは、Ｃｏ−Ｐｔ磁性粒子を用いた本発明の媒体の測定結果、Ｃは実施例４で用いた従来媒体についての測定結果である。Ｂの測定結果は、粒径分散Ｄσが３０％（±１５％）以下、粒子間距離の平均値が平均粒径Ｄ＋（１〜２ｎｍ）、粒子間距離の分散が６０％（±３０％）以下である本発明の規則的磁性粒子媒体についての測定結果である。
【０２０２】
保磁力Ｈｃの測定は、室温で１０数分の時間をかけたＶＳＭメジャーループの測定により行った。磁性粒子の粒径が小さいほど、室温熱擾乱の影響でＨｃは低くなる。熱擾乱の影響は粒子の磁気異方性と粒子体積から見積もることができる。
【０２０３】
図１１中の実線は、本発明の媒体のＣｏ−Ｐｔ磁性粒子の理論的なＨｃの曲線であり、磁性粒子の粒径が十分に大きいとしたときのＨｃでフィッティングしたものである。また、図１１中の破線は、従来媒体のＣｏＣｒＴａＰｔ磁性粒子の理論的なＨｃの曲である。測定結果の曲線と理論的な曲線とを比較すると、粒径分散の少ない本発明の媒体では両曲線が一致しているが、分散の大きい従来媒体では測定結果が理論曲線を下回っている。このように下回るのは、実施例３でのＭｒｔの測定結果について説明した内容と同様に、従来媒体は超常磁性的な粒子を含んでいるためと考えられる。
【０２０４】
Ｈｃは、磁気記録特性上は磁化転移幅と記録感度に関係する量である。Ｍｒｔが同じ場合には、Ｈｃが大きいほど磁化転移幅は狭くなり高密度記録に適する。しかし、保磁力角形比Ｓ^* が同じ場合には、Ｈｃが増加すると記録感度は低下する。従って、Ｈｃも記録再生系に合わせて適切に調整すべき量である。本実施例によって示されるように、本発明の媒体においては、磁性粒子の平均粒径の調整によってＨｃを適切に調整できることが分かる。
【０２０５】
（実施例６）
図１２は、粒子間距離の分散Ｃσ’（ＦＷＨＭの１／２で記載してある）と、磁性粒子の活性化サイズＤａと磁性粒子の平均粒径Ｄとの比であるＤａ／Ｄとの間の関係を測定した結果を示す図である。
【０２０６】
図１２において、Ａは磁性粒子材料がＣｏ−Ｆｅの本発明の媒体についての測定結果、Ｂは磁性粒子がＣｏ−Ｐｔである本発明の媒体の測定結果、Ｃは実施例４で用いた従来媒体についての測定結果である。本発明の媒体についての測定は、粒径分散ＤσがＦＷＨＭで３０％以内に調整されている媒体試料について行った。
【０２０７】
本発明の媒体についての測定結果より、粒子間距離の分散が±４０％（ＦＷＨＭ：８０％）以下に調整されている媒体においては、Ｄａ／Ｄが１となることが分かる。Ｄａは最小磁化反転単位であり、磁性粒子間の交換相互作用が分離されている場合には物理的な粒系Ｄと一致する。また、分散が８０％以上の領域において分散とともにＤａ／Ｄが増加しているのは、以下のように解釈できる。すなわち、自己組織化マスクの完成度が低いか規則的磁気媒体の作製プロセスに不備があるために粒子間距離の分散Ｃ’σが大きいときには、粒子と粒子とが局所的に接触して大きな粒子となりＤａ／Ｄが大きくなっていると考えられる。
【０２０８】
従来媒体においては、粒子間距離の分散が±５０％（ＦＷＨＭ：１００％）以上の値を示し、また粒子と粒子が局所的に接触していることを反映してＤａ／Ｄが１よりも大きい値を示すとともに、同じ粒子間距離の分散量において本発明の媒体と比べてＤａ／Ｄが大きい。これは、従来媒体においては粒子間距離の分散Ｃ’σだけではなく粒径分散Ｄσも大きいために、粒子と粒子との間の局所的な接触が本発明の媒体よりも多いためであると考えられる。
【０２０９】
Ｄａ／Ｄは、磁気記録特性的には磁性粒子間の交換相互作用に起因するノイズに関連する量であり、２以下とするのが良い。本実施例より、本発明の規則的磁性粒子媒体においても、Ｄａ／Ｄを２以下とするために粒子間距離の分散を±６５％（ＦＷＨＭ：１３０％）以下に抑えるのが好ましく、最も好ましくはＤａ／Ｄがほぼ１を示す様に分散±４０％（ＦＷＨＭ：８０％）以下とするのが良いことが分かる。
【０２１０】
（実施例７）
図１３は、粒径分散Ｄσ（ＦＷＨＭの１／２で記載してある）と、保磁力角形比Ｓ^* との関係を測定した結果を示す図である。Ｓ^* は、長手媒体に対してはＶＳＭメジャーループ測定結果から導き出し、垂直媒体に対しては飽和磁化の測定値に反磁界補正を行って導出した。図１３中、Ａ、Ｂ、Ｃの符号は、実施例５で用いた符号と同様である。
【０２１１】
本発明の媒体についての測定は、平均粒径Ｄが１２〜１３ｎｍ、粒子間距離の分散Ｃσが±３０％（ＦＷＨＭ：６０％）以下である媒体試料について行った。
【０２１２】
保磁力角形比Ｓ^* は、磁性粒子のＨｃの分散に対応する量である。保磁力角形比Ｓ^* は、粒径が十分大きい範囲では粒子の磁気特性の分散（例えば結晶磁気異方性の分散）を反映するが、粒径自体には依存しない。また、粒径が小さくなって室温熱擾乱によるＨｃ低下が発生する場合には、Ｓ^* は粒径依存性を示す。
【０２１３】
図１３に示されているように、本発明の媒体においては、平均粒径Ｄが１２〜１３ｎｍと小さくても、粒径分散が±２０％（ＦＷＨＭ：４０％）に調整されている場合にはＳ^* は大きな値を示す。このことより、逆に粒径分散が±２０％よりも大きくなると本発明においてもＨｃの小さい磁性粒子成分が発生して、Ｓ^* を低下させることがわかる。
【０２１４】
従来媒体においては、粒径分散は±２５％以上あり、熱擾乱でＨｃが低下している粒子がかなり含まれるていることが分かる。また、従来媒体においては、同じ粒径分散においてＳ^* が本発明の媒体のそれよりも小さい値を示している。これは、従来媒体では粒径分散だけではなく粒子間距離の分散も大きく、粒子と粒子とが接触してＨｃが見掛け上大きくなっている成分も含むために、Ｈｃの分散がより大きくなったことによると考えられる。
【０２１５】
Ｓ^* は、磁気記録特性上は記録感度に関連する量である。Ｈｃが同じ場合にはＳ^* が大きいほど記録感度とオーバライト消去比が向上するため、ヘッドの記録能力にもよるが、Ｓ^* は０．５以上であるのが良い。従って、図８の結果より、本発明の規則的粒子媒体においても粒径分散は±３５％以下（ＦＷＨＭで７０％以下）とすることが好ましく、さらに好ましくはＳ^* が高い一定値を示す±２０％以下（ＦＷＨＭで４０％以下）とするのが良いことが分かる。
【０２１６】
（実施例８）
ＭＲヘッドを用いて、本発明に係る媒体の記録再生特性を評価した。
用いたＭＲヘッドは、記録トラック幅：１．３μｍ、再生トラック幅：１．０μｍ、再生ギャップ：０．１μｍのＡＭＲ再生部を有する試作品である。このヘッドは、トラック間のガードバンド幅を０．１５μｍとしたときに、４．３Ｇｂ／ｉｎ² の面密度まで記録再生能力を有する。また、このヘッドは基本的には長手記録用に設計されたヘッドだが、垂直媒体の記録再生にも使用可能であることは言うまでもない。垂直媒体、特に磁性体の下側にＮｉＦｅ軟磁性膜、ＮｉＦｅＣｏ半硬磁性膜を有する構造の本発明の垂直媒体に対しては、単磁極ヘッドで記録するのが好ましい。しかし、本発明の媒体ノイズ特性の評価においては長手用のリングタイプヘッドを使用することもできるので、本発明の垂直媒体に対してもこのヘッドを用いることとした。
【０２１７】
このヘッドで記録可能な最小記録セルサイズは１．３μｍ×０．１μｍであり、すなわち、最小記録セルは１．３×１０Ｅ５（ｎｍ^２ ）の面積を有する。本発明の規則的磁性粒子媒体においては、磁性粒子間隔が１２〜６０ｎｍであるため、最小記録セル中に含まれる磁性粒子数は３６〜９０２となる。
【０２１８】
記録再生特性の測定条件は、ディスク回転数：１８００ｒｐｍ、記録半径位置：２２ｍｍ、ヘッド浮上量２５ｎｍである。記録は記録周波数を変えて行い、各周波数における規格化媒体ノイズを調べた。記録電流は、カーバライト消去比が−４０ｄＢ以上（マイナス側に）になる飽和記録電流とした。規格化媒体ノイズは、全周波数帯域に渡って積分した媒体ノイズ（Ｎｍ）の値を低域の信号出力（Ｓ０）で除した値であり、再生トラック幅単位長（１μｍ）当りに規格化した値である。
【０２１９】
図１４は、媒体の空間記録周波数ＬＤと規格化媒体ノイズとの関係を測定した結果の一例を示す図である。図１４中、Ａ、Ｂ、Ｃの符号は、図１０で用いた符号と同様である。
【０２２０】
本実施例において測定された発明の媒体は、磁性粒子の平均粒径が１５ｎｍ、粒径分散がＦＷＨＭ：２５％、粒子間の平均距離が１８ｎｍ、粒子間距離の分布の分散がＦＷＨＭ：５０％に調整されているものである。
【０２２１】
図１４より、従来媒体に比べて本発明の媒体は格段に低ノイズであることが分かる。これは、本発明の媒体は、従来媒体に比べて、粒径分散、粒子間距離の分散が抑制され、磁性粒子が規則的に配列しているためである。
【０２２２】
図１４に示されているように、本発明の媒体においては、ＣｏＦｅ粒子を用いた媒体（曲線Ａ）およびＣｏＰｔ粒子を用いた媒体（曲線Ｂ）の両方についてノイズが極めて低いが、ＣｏＰｔ粒子を用いた媒体（曲線Ｂ）の方がＣｏＦｅ粒子を用いた媒体（曲線Ａ）よりもより低ノイズである。これは、図１０に示されているように、ＣｏＰｔ粒子媒体（図１０の曲線Ｂ）の方がＣｏＦｅ粒子媒体（図１０の曲線Ａ）よりもＭｒｔが小さく、従って、ＣｏＰｔ粒子媒体においてより磁化転移幅が狭く、またよりシャープな磁化転移が形成されているためと考えられる。
【０２２３】
（実施例９）
図１５は、本発明に係る磁気媒体を２５０ｋｆｃｉの空間記録周波数で記録したときの、規格化媒体ノイズと平均粒径Ｄとの関係を調べた結果を示す図である。
【０２２４】
本発明の媒体についての測定は、粒径分散がＦＷＨＭで２５％以下、粒子間距離の平均値が平均粒径Ｄ＋（１〜３ｎｍ）、粒子間距離の分散がＦＷＨＭで５０％以下に調整されている媒体について行った。
【０２２５】
図１５より、空間周波数が２５０ｋｆｃｉである場合、すなわち記録セル長がほぼ０．１μｍの場合には、平均粒径が２５ｎｍ程度以下においてノイズレベルは極めて低いが、２５ｎｍ以上ではノイズレベルは急激に高くなることが分かる。
【０２２６】
規格化媒体ノイズと空間記録周波数との関係を測定したところ（測定結果は図示せず）、本発明の規則的磁性粒子媒体においても、磁性粒子径が記録セル長の１／４よりも大きくなるとノイズレベルが増加した。この結果より、本発明の媒体において低ノイズ効果が顕著に現れるためには、磁性粒子の粒径が記録セル長の１／４以下であることが良いことが分かる。トラック幅方向に並ぶ磁性粒子の粒子数は、記録するときのトラック幅が最短記録セル長よりも短くならない限り、なんら制限は受けない。従って、最小記録セル中のトラック幅方向の磁性粒子数の下限は４個であることが分かる。実際には、数１０個以上の磁性粒子が最小記録セルのトラック幅方向に並ぶ。
【０２２７】
（実施例１０）
図１６は、磁性粒子の粒径分散Ｄσ、粒子間距離の分散Ｃ’σ、および媒体ノイズの間の関係を測定した結果を示す図である。測定は、粒径が記録セル長の１／４以下、粒子間距離が粒径＋（１〜３ｎｍ）に調整された本発明の媒体と空間記録周波数を選んで行った。
【０２２８】
図１６において、実線は本発明の規則的磁性粒子媒体についての測定結果を規格化媒体ノイズの等高線としてまとめたものである。また、図１６プロットは、従来媒体のうち低ノイズだった媒体についての測定結果である。
【０２２９】
図１６の結果より、本発明の媒体において低ノイズ効果が明確に現れるためには、粒径の分散が±２０％以下（ＦＷＨＭで４０％以下）、粒子間距離の分散が±４０％以下（ＦＷＨＭで８０％以下）であることが好ましいことが分かる。なお、より好ましくは、粒径の分散が±１０％以下（ＦＷＨＭで２０％以下）、粒子間距離の分散が±２０％以下（ＦＷＨＭで４０％以下）であり、最も好ましくは、粒径の分散が±５％以下（ＦＷＨＭで１０％以下）、粒子間距離の分散が±１０％以下（ＦＷＨＭで２０％以下）であることも分かる。
【０２３０】
また、図１６において、従来媒体についてのノイズは、同程度の分散量を有する本発明の媒体よりも高い。これは、本発明が磁性粒子の規則的配列を基本とし、分散は規則的配列位置からのズレ量を示しているのに対して、従来媒体は基本的に不規則配列を有するためであると考えられる。
【０２３１】
なお、図１６に示す結果は、現時点で試作可能な磁気ヘッドを用いて測定した結果である。従って、将来、より狭いヘッドギャップを有し再生分解能がより向上している磁気ヘッドを用いて測定した場合には、図１６の規格化媒体ノイズの等高線はより大きな値にシフトすると考えられる。従って、このようなヘッドを用いて記録する場合には、粒径と粒子間距離の分布がより狭く設定された磁気媒体を用いるべきである。
【０２３２】
＜規則的非磁性ポアの作製＞
（実施例１１）
前述の規則的非磁性ポア媒体の製造方法に従って、規則的非磁性ポアを作製した。磁性材料としてはＣｏＰｔとＴｂＣｏを用いた。ＣｏＰｔの場合には、規則的磁性粒子媒体の場合と同様に、シード層材料、シード層の膜厚、磁性層の厚さ、磁性層の成膜条件で磁化容易軸を設定した。ＴｂＣｏを用いた場合は特にシード層は設けずに垂直磁化膜を形成した。
【０２３３】
＜規則的非磁性ポアの評価＞
作製した規則的非磁性ポア媒体の試料の評価を、規則的磁性粒子媒体の評価に準じて行った。規則的非磁性ポア媒体の微細構造の評価は、平均ポア径（Ｐ’）、ポア径分布のＦＷＨＭ（Ｐ′σ）、平均ポア間隔（Ｃ）、ポア間隔分布のＦＷＨＭ（Ｃ’σ）を用いて行った。これらのパラメーターの値は、実施例１で求めた自己組織化マスクの有する各パラメーター、すなわち、平均孔径、孔径分布のＦＷＨＭ、平均孔間隔、孔間隔分布のＦＷＨＭに、プロセス変動による値を加味した値となる。本実施例におけるＰ′、Ｐ′σ、Ｃ、Ｃ′σの範囲は、実施例３で求めた規則的磁性粒子媒体の平均粒径Ｄ、粒径分布のＦＷＨＭＤσ、磁性粒子間の平均距離Ｃ、磁性粒子間距離の分布のＦＷＨＭＣ′σの範囲とほぼ同等であった。
【０２３４】
（実施例１２）
まず、磁壁の評価のためにＭＦＭ観察を行った。ＭＦＭ観察の結果、ＴｂＣｏを磁性体に用いた場合には、磁壁の幅は、組成比、膜厚に依存するが、補償組成となる組成比の極く近傍を除いて、１０〜２０ｎｍであった。また、ＣｏＰｔを磁性体に用いた場合には、磁壁の幅は７〜１３ｎｍであった。磁壁の幅は異方性エネルギーが大きいほど狭く、例えばＣｏＰｔでもＣｏ：５０ａｔ％の組成の場合には磁壁幅は５〜１０ｎｍとなり、また磁気異方性の大きいＳｍＣｏを用いた場合には、磁壁の幅は３〜６ｎｍとなると推定される。このように、本発明における非磁性ポア径は、用いる磁性体の種類によって様々に調整できることが分かる。
【０２３５】
（実施例１３）
非磁性ポア間の平均間隔Ｃ’と、残留磁化と膜厚の積（Ｍｒｔ）との間の関係を測定した。測定結果は、図１０に示した規則的磁性粒子媒体についてのＣとＭｒｔとの間の相関と逆の相関を示した。すなわち、Ｃ’が大きいほど磁性体の占有比率が増加するため、Ｍｒｔは増加した。ＭｒｔとＣ’との関係は、計算から予測される通りとなり、規則的非磁性ポア媒体においてもＭｒｔの適切な調整が容易であることが分かった。
【０２３６】
（実施例１４）
非磁性ポアの平均ポア径Ｐ’と保磁力Ｈｃとの間の関係を測定した。測定結果は、図１１で示した規則的磁性粒子媒体についての平均粒径Ｄと保磁力Ｈｃとの間の関係と同様の関係を示した。すなわちＰ’が磁壁幅の１／２以下において、Ｈｃは低下した。これは、非磁性ポア径が磁壁幅の１／２以上のときには、非磁性ポアが磁壁のピンニングサイトとして作用するため大きなＨｃを発現するが、ポア径が磁壁幅の１／２未満では、磁壁がポアでピンニングされずに自由に動いてしまうために、Ｈｃは低下することによるものである。
【０２３７】
（実施例１５）
非磁性ポア間隔の分散Ｃ’σと、非磁性ポアの活性化サイズＤａと平均ポア径Ｐ’との比Ｄａ／Ｐ’との間の関係を測定した。測定結果は、図１２に示すＤａと比べて極めて大きな値のＤａを示した。これは、磁性母材が膜面全域においで連結しているためにＤａの値が非常に大きいからである。測定結果より、本発明の規則的非磁性ポア媒体においては、多粒子系もしくは規則的磁性粒子媒体とは異なり、熱擾乱の影響が全くないことが明らかとなった。
【０２３８】
（実施例１６）
非磁性ポア間隔の分散Ｃ’σと、保磁力角形比Ｓ^*との間の関係を測定した。測定結果は、平均ポア径Ｐ’が小さいときには、図１３で示した規則的磁性粒子媒体についての結果と同様に、ポア径分散Ｐ’σが大きくなるにつれてＳ^*が低下した。これは、ポア径分散Ｐ’σが大きくなるにつれて、磁壁幅の１／２未満のポア径が出現することに起因するものである。しかし、平均ポア径Ｐ’が比較的大きい場合、またはポア径分散Ｐ’σが十分小さい場合には、Ｓ^* は１に近い値を示した。
【０２３９】
（実施例１７）
規則的磁性粒子媒体の評価に使用したＭＲヘッドを用いて、非磁性ポア媒体の空間記録周波数ＬＤと規格化媒体ノイズとの関係を測定した。測定結果は、ポア径が磁壁幅の１／２〜３倍の間に調整され、かつポア間間隔の分散がＣ’σが±４０％（ＦＷＨＭで８０％）以下に調整されている場合には、図１４の規則的磁性粒子媒体についての測定結果と同様に、低ノイズ性能を示した。
【０２４０】
（実施例１８）
図１７は、非磁性ポア媒体について、２５０ｋｆｃｉでの規格化媒体ノイズと、平均ポア径Ｐ’と磁壁幅δとの間の比Ｐ’／δとの関係を示す測定結果である。測定は、ポア間隔分布のＦＷＨＭ（Ｃ’σ）が８０％以下に調整されている媒体について行った。
【０２４１】
図１７から、Ｐ’／δが１／２〜３の範囲においては、本発明に係る非磁性ポア媒体は良好な低ノイズ性能を示すことが分かる。Ｐ’／δが１／２未満においてノイズが上昇するのは、磁壁がポアによってピンニングされずに動いてしまうため、磁壁の位置が定まらずに磁化転移部が乱れるためである。また、Ｐ’／δが３よりも大きい場合にノイズが上昇するのは、磁壁はポアにピンニングされていて磁壁部の磁化転移部の形状は良好であるが、ポア径が大きすぎるために非磁性ポア自体がノイズ源となるからである。
【０２４２】
（実施例１９）
図１８は、非磁性ポア媒体について、２５０ｋｆｃｉにおける規格化媒体ノイズとのポア間隔分布のＦＷＨＭ（Ｃ’σ）との間の関係を示す測定結果である。測定は、Ｐ’／δが１／２〜３の範囲に調整されている非磁性媒体について行った。
【０２４３】
図１８に示されているように、Ｃ’σが８０％以下においてはＣ’σの増加に伴ってノイズは緩やかに増加し、Ｃ’σが８０％を上回るとノイズは急激に増加する。
【０２４４】
ＳＥＭ観察とＭＦＭ観察の結果、Ｃ’σが８０％を上回ると、ポア径にも依存するが、ポアが互いに連結するために実質的なポア径が過大となってポア自体がノイズ源となること、および磁化転移に沿って配列するポア以外のポア間において磁壁が互いに連結するために磁化転移の形状が乱れることが分かった。
【０２４５】
【発明の効果】
以上、詳述したように、本発明によれば、Ｓ／Ｎを向上し高密度化を実現することが可能な磁気記録媒体およびその製造方法が提供される。その結果、磁性粒子を過度に微細化することなく、磁性粒子の異方性エネルギーを過度に増加させることなく、メモリ動作温度内での実用的な熱擾乱耐性とシステムの要求する媒体Ｓ／Ｎを両立することが可能となる。
【図面の簡単な説明】
【図１】本発明に係る規則的磁性粒子媒体の一例を示す概略図。
【図２】本発明に係る規則的非磁性ポア媒体の一例を示す概略図。
【図３】本発明に係る陽極酸化バリア層およびポーラスアルマイトの一例を示す概略断面図。
【図４】本発明に係るメタルリングを示す概略図。
【図５】本発明に係る製造方法の一例を示すプロセスフロー図。
【図６】本発明に係る磁気ディスクのサーボパターンの一例を示す概略図。
【図７】本発明に係る規則的磁性粒子媒体を製造するための装置の一例を示す概略図。
【図８】本発明の実施例において試作したマスクのＳＥＭ像を示す図。
【図９】本発明の実施例において試作した規則的磁性粒子媒体のＳＥＭ像を示す図。
【図１０】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１１】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１２】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１３】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１４】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１５】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１６】本発明の実施例において規則的磁性粒子媒体を評価した結果を示す図。
【図１７】本発明の実施例において規則的非磁性ポア媒体を評価した結果を示す図。
【図１８】本発明の実施例において規則的非磁性ポア媒体を評価した結果を示す図。
【符号の説明】
１…基板
２…シード層
３…磁気記録層
４…非磁性マトリックス
５…磁性粒子
６…保護層
７…最小記録セル
８…連続状磁性膜
９…非磁性ポア
１０…磁壁
１１…Ａｌ板
１２…バリア層部
１３…微小孔
１４…ポーラスアルマイト部
１５…メタルリング
１６…開口部
２０…真空容器
２１…誘導加熱型蒸発源
２２…ヒーター
２３…ルツボ
２４…シャッター
２５…ＲＦ電源
２６…蒸発試料
２７…超伝導体部
２８…コールドヘッド
２９…超伝導体
３０…磁気ディスク基板
３１…磁界印加用コイル
３２…磁界[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium for magnetically recording / reproducing information and a method for manufacturing the same.
[0002]
[Prior art]
Magnetic recording media are widely used for personal data files, communication servers, large computer files, etc., mainly as fixed magnetic disk devices, and are mainly used as magnetic tape devices for personal and broadcast station image and audio files. Etc. are widely used. This is because the magnetization reversal speed of the magnetic recording medium, which is an aggregate of magnetic crystal grains, that is, the recording data transfer speed is remarkably fast, several hundred Mbps or more, and several tens Gb / in.²This is because a high recording density can be achieved. High recording density is realized by the isolation of the particles and the miniaturization of the magnetic particles by reducing the exchange interaction between the magnetic particles. As the amount of information continues to increase dramatically toward the multimedia era, magnetic recording media are expected to have higher transfer speeds and higher densities.
[0003]
Among the magnetic recording media, the surface recording density of fixed magnetic disk devices (HDDs) whose recording density is increasing has been improved by an average annual rate of 60% or more over the past 5 years or more, and is currently several Gb / s. in²Has reached. The improvement of the surface density is achieved by adopting magnetoresistive effect reproduction method, increasing the saturation magnetic flux density of the recording magnetic pole material, improving the narrow track head processing technology, narrowing the magnetic head gap, miniaturizing the slider and increasing the accuracy. This is due to the reform and improvement of various elemental technologies such as machining, higher servo accuracy, and the introduction of new modulation / demodulation technologies such as PRML. As for the magnetic recording medium itself, the flying height of the head is reduced by smoothing the surface and flattening, the magnetic transition width is shortened by increasing the coercive force and thinning of the magnetic layer, the exchange interaction between magnetic particles is reduced, and the fineness of the magnetic particles is reduced. Advances in elemental technologies, such as media noise reduction, due to the progress of computerization.
[0004]
In the conventional so-called multi-particle magnetic media as described above, it has been found that if the magnetic particles of the medium are isolated and miniaturized to reduce noise, the recording density limit will be reached due to thermal disturbance. ing.
[0005]
The thermal disturbance will be outlined below.
If the recording density is improved, the size of the recording cell formed on the medium is reduced, and the strength of the signal magnetic field generated from the medium is reduced. In order to satisfy the S / N ratio required by the system, the noise must be reduced by the reduced signal amount. The medium noise is mainly caused by the fluctuation of the magnetization transition part, and the fluctuation amount of the magnetization transition part is proportional to the size of the magnetization reversal unit of the magnetic particles. Therefore, in order to reduce the medium noise, the exchange interaction between the magnetic particles is interrupted to isolate the magnetic particles (the fluctuation of the magnetization transition portion is reduced to the order of the size of one magnetic particle), and the magnetic properties are reduced. It is necessary to refine the particles.
[0006]
The magnetic energy of one isolated magnetic particle is given by the product of the magnetic anisotropy energy density of the particle and the volume of the particle. Thinning the medium to reduce the magnetization transition width and miniaturizing the magnetic particles to meet the requirements for low noise lead to a significant decrease in the magnetic particle volume and the magnetic energy of the particles. Is significantly reduced. If the magnetic energy of the particles is several hundred times the thermal energy at the operating temperature (at least room temperature) as a magnetic memory, it is considered that the resistance to thermal disturbance is sufficient. However, when the magnetic energy of the particles is less than 100 times the thermal energy, the magnetization direction of the magnetic particles changes due to thermal disturbance, and the recorded information may be lost. This is a thermal disturbance problem, and the surface density of the HDD is 40 to 50 Gb / in.²That is why it is said that the limit will be reached.
[0007]
Several methods have been proposed to overcome the thermal disturbance problem.
[0008]
One is to use a material having high magnetic anisotropy as the magnetic particle material. However, when the magnetic anisotropy is increased, the recording saturation magnetic field required by the medium increases, and it becomes necessary to further increase the saturation magnetic flux density of the recording head magnetic pole material. This cannot be a practical method as long as available soft magnetic film materials including the research level are considered.
[0009]
The other is photothermal assist recording. In this method, recording is performed with an available recording head by using a material having high magnetic anisotropy to heat the recording portion by light irradiation during recording, and reducing the anisotropy of magnetic particles and the recording saturation magnetic field. . However, this method is not practical because it is necessary to provide a light irradiation system in an HDD that has almost no extra space in the drive including between disks. In addition, this method is accompanied by an increase in power consumption and an accompanying increase in the amount of heat generated.
[0010]
As another method for solving the thermal disturbance problem, a near-field recording method using SIL or evanescent light has been proposed as a technical seed for overcoming the recording density limit of HDD. However, in optical recording, it is impossible to realize a transfer rate as high as magnetic recording as long as the heat mode process is adopted. In addition, a method using a photon-mode ultrahigh-speed / high-density material has also been proposed, but this method is still in the research stage and is not yet complete as a technology.
[0011]
The above method cannot provide an appropriate solution for the problem of the thermal disturbance of the medium that physically hinders high density magnetic recording.
[0012]
It is considered that the most effective method for solving the thermal disturbance problem is a magnetic recording medium (hereinafter referred to as a regular magnetic particle medium) having magnetic particles regularly arranged in a non-magnetic matrix. And a magnetic recording medium having non-magnetic particles (pores) regularly arranged in a continuous magnetic body (hereinafter referred to as a regular non-magnetic pore medium). .
[0013]
First, the regular magnetic particle medium will be described.
A conventional multi-particle magnetic medium such as a CoCr system has a structure in which a Cr-rich nonmagnetic grain boundary is mainly precipitated between magnetic particles in order to reduce exchange coupling between the magnetic particles. However, since the dispersion of the particle size and the distance between the particles is large, and the particles are irregularly arranged, even if the exchange interaction between the particles is broken and the particles are isolated, the medium noise is sufficient. However, the recording density did not decrease and became an impediment to improving the recording density.
[0014]
Specifically, when the particle size variation is expressed by the full width at half maximum (FWHM) of the particle size distribution, it is ± 50% for a typical medium, and even for a medium in which variation is suppressed by devising low-speed sputtering or the like ± A value of 25% or more is shown. For example, a medium having an average particle diameter of 20 nm typically has a large number of particles between 10 nm and 30 nm, and there are a considerable number of particles having a particle diameter of less than 10 nm that are strongly affected by thermal disturbance. means.
[0015]
Inter-particle variation is more conspicuous, with a typical example being ± 70% for FWHM and a well-adjusted example being ± 45% or more. That is, a medium having an average interparticle distance of 2 nm typically has a large number of particles having an interparticle distance of 0.6 nm to 3.4 nm, and there are a considerable number of particles connected to each other in an exchange coupling state. Means. Further, the particle arrangement is random without any regularity.
[0016]
Examples of the magnetic recording medium having regularly arranged magnetic particles include, for example, J. Org. Appl. Phys. 76 (10) 6673, 1994. This is because a sample coated with an Au plating seed layer and a resist on a Si wafer is exposed by electron beam (EB) direct drawing, and Ni is plated and grown in a plurality of micro holes formed by EB direct drawing after development. Ni pillar arrays having a diameter of 35 nm are regularly formed at intervals of 100 nm.
[0017]
The medium described in the above-mentioned document has been studied with application to a magnetic recording medium in mind, but it is not disclosed how to use it specifically. In this document, the medium simply has a pattern with 100 nm spacing, so 65 Gb / in²This suggests the possibility of realizing a high recording density. That is, in this document, one magnetic particle is regarded as a minimum recording unit, and one magnetic particle is present in the minimum recording cell. However, a magnetic for performing recording / reproduction using such a small recording unit is used. There is no description of devices such as heads and servo systems.
[0018]
In addition to the above, an example of producing regularly arranged magnetic particles using the EB direct drawing method is described in J. Org. Vac. Sci. Technol. B13 (6) 2850, 1995 and J. Org. Vac. Sci. Technol. B12 (6) 3196, 1994 can be mentioned. Although these are slightly different in the production method other than the EB direct drawing process of the regularly arranged magnetic particle group, they coincide with each other in that one particle is a minimum recording unit. Further, these documents do not describe magnetic particle size distribution, intergranular distribution, and the like.
[0019]
However, EB direct drawing has no problem when used to produce one sample at the laboratory level, but it is inappropriate from the viewpoint of cost and productivity when used in the process of manufacturing magnetic media industrially. Needless to say.
[0020]
In addition, the method of using one magnetic particle as the minimum recording unit places a significant burden on factors other than the medium, such as a much narrower track of the recording / reproducing head, a greatly improved reproducing head sensitivity, and a much improved servo accuracy. Forcing. Even if a high-resolution head is made, since one particle constitutes one recording cell, medium noise is high and sufficient S / N cannot be obtained.
[0021]
Further, in the conventional magnetic medium, the address pattern or servo pattern is formed by magnetic recording by the manufacturer of the magnetic disk device (servo write). J. et al. Appl. Phys. 69 (8) 4724, 1991 proposes to implement an address pattern and a servo pattern by patterning a thin film. However, the medium used in this document is not one in which magnetic particles are regularly arranged.
[0022]
For a method of manufacturing a magnetic medium, see Jpn. J. et al. Appl. Phys. 30 (2) 282, 1991, and J. Am. Electrochem. Soc. 122 (1) 32, 1975 discloses a method in which a magnetic material is plated and grown in porous alumite. In this method, a Co—Cr based alloy is preferably used as the medium, and the exchange interaction between crystal grains is reduced by precipitating a Cr-rich non-magnetic material at the grain boundaries to reduce noise. Yes. However, the matrix is Al₂O_ThreeThe magnetic material is also limited to Co, Co—Cr, Co—Ni, Fe—Cu, Fe—P and the like that can be plated.
[0023]
Next, the regular nonmagnetic pore medium will be described.
When recording is performed on the magnetic continuous film, the shape of the domain wall is greatly disturbed, so the medium noise is extremely large. Therefore, a magnetic continuous film is not used for magnetic recording, and a multi-particle magnetic medium is used instead. By regularly arranging the non-magnetic pores in the magnetic continuous film, disorder of the domain wall shape can be prevented.
[0024]
The above-described thermal disturbance is caused by a decrease in the volume of the magnetic particles as the density increases. When the magnetic material itself is a continuous form like a regular non-magnetic pore medium, the volume of the magnetic material can be regarded as infinite. Therefore, in a regular nonmagnetic pore medium, there is no problem of thermal disturbance even if the nonmagnetic pore is miniaturized and densified.
[0025]
An example in which non-magnetic pores are arranged in a magnetic continuous film is described in IEEE-Trans. Magn. 34 (4), 1609, 1998 6 is disclosed as a network medium. This document is related to noise simulation of a virtual medium in which non-magnetic pores are regularly arranged in a multi-particle magnetic film. In this document, the nonmagnetic pore size, the distribution of the distance between pores, the address pattern, and the servo pattern are not mentioned at all.
[0026]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic recording medium capable of improving S / N and realizing high density and a method for manufacturing the same.
[0028]
[Means for Solving the Problems]
  According to the present invention, a plurality of nonmagnetic pores arranged in a continuous magnetic film are provided, the magnetization transition portion in the magnetic film is formed of a domain wall connecting the nonmagnetic pores, and the average particle size of the nonmagnetic pores is that of the domain wall. There is provided a magnetic recording medium characterized by being 0.5 to 3 times the average width.
[0029]
In the present invention, it is preferable that the full width at half maximum of the distance distribution between the nearest pores in the minimum magnetic recording cell is ± 40% or less of the average distance between the nearest pores.
[0031]
According to the present invention, (a) a step of disposing a photosensitive layer on the continuous magnetic film, (b) a step of disposing a mask having openings arranged by self-assembly on the photosensitive layer, and (c) A step of exposing the photosensitive layer by irradiating light or electrons from above the mask and developing the photosensitive layer to form a mask pattern in which a portion corresponding to the opening remains, and (d) the mask pattern. According to the present invention, there is provided a method for manufacturing a magnetic recording medium, comprising: forming a plurality of magnetic particles arranged in a continuous magnetic film; and (e) filling a nonmagnetic material between the magnetic particles. Is done.
[0032]
In the present invention, each step includes a plurality of magnetic particles arranged in a continuous nonmagnetic film, and the magnetic particles contained in the minimum magnetic recording cell have at least the number of particles arranged in the track length direction. 4 and the full width at half maximum of the distribution of the distance between the nearest particles is ± 40% or less of the average distance between the nearest particles, and the full width at half maximum of the particle size distribution is ± 20% or less of the average particle diameter. It is preferable to manufacture a magnetic recording medium.
[0033]
Further, according to the present invention, (a) a step of arranging a mask having openings arranged by self-organization on the continuous magnetic film, and (b) irradiation of an ion beam from above the mask in the continuous magnetic film. A method of manufacturing a magnetic recording medium, comprising: forming a plurality of holes arranged in a plurality of holes; and (c) forming a nonmagnetic pore by filling the holes with a nonmagnetic material. Is done.
[0034]
In the present invention, each step includes a plurality of nonmagnetic pores arranged in a continuous magnetic film, and the magnetization transition portion in the magnetic film is formed of a domain wall connecting the nonmagnetic pores. It is preferable to manufacture a magnetic recording medium having a particle size of 0.5 to 3 times the average width of the domain wall.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a magnetic recording medium of a regular magnetic particle medium and a regular non-magnetic pore medium, and a method for producing them.
[0036]
Both the regular magnetic particle medium and the regular nonmagnetic pore medium have a form in which magnetic particles or nonmagnetic pores having a size of several tens of nm or less are regularly arranged.
[0037]
Hereinafter, the present invention will be described in detail with reference to the drawings.
<Configuration of Magnetic Recording Medium According to the Present Invention>
(A) Regular magnetic particle medium
1A and 1B are schematic views showing an example of a regular magnetic particle medium according to the present invention. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view.
[0038]
In the regular magnetic particle medium shown in FIG. 1, a seed layer 2 is formed on a substrate 1, and a magnetic recording layer 3 is formed on the seed layer 2. The magnetic recording layer 3 is composed of a plurality of magnetic particles 5 regularly arranged in a nonmagnetic matrix 4. A protective layer 6 is formed on the magnetic recording layer 3. Here, the regular arrangement means that the full width at half maximum of the distance distribution between the nearest magnetic particles is ± 40% or less of the average distance between the nearest magnetic particles.
[0039]
Examples of the material for forming the substrate 1 include glass, Si, and materials similar to those used for ordinary magnetic media, such as NiP-coated material.
[0040]
The seed layer 2 is a layer for controlling the crystallinity of the magnetic layer 3, but may not be present. Examples of the seed layer 2 include Cr, a Cr alloy system, Cr, and NiFe.
[0041]
The film thickness of the seed layer 2 is preferably 0 to 200 nm (0 nm is a form without the seed layer 2), more preferably 0 to 100 nm.
[0042]
The meaning of the seed layer is mainly for controlling the crystallinity of the recording layer in the case of longitudinal recording, and when the main component of the recording layer is Co, the lattice constant mismatching with Co hcp crystal is relatively small. A Cr-based or V-based alloy can be used as a seed layer. The seed layer grows in the shape of a cone or a column on the substrate surface. However, when the film thickness is too thin, the seed layer itself has insufficient crystallinity and the effect as the seed layer is insufficient. The crystallinity in the thin film region of the seed layer also depends on the film forming method, and when the ultra-high vacuum sputtering method is applied, sufficiently good crystallinity is exhibited even at a film thickness of 50 nm or less, for example, 20 nm. Therefore, the lower limit of the thickness of the seed layer in terms of controlling the crystallinity of the recording layer can be said to be 20 nm or less. However, in the magnetic medium of the present invention, the matrix material can have the function of the seed layer. Therefore, a seed layer having no seed layer (0 nm) and a seed layer having a thickness of 0 to 20 nm which can be used to promote the crystallinity control effect of the magnetic particles by the matrix although the crystallinity is still insufficient are also applied to the present invention. Can be made. When an amorphous magnetic material such as RE-TM is used as the magnetic particle material, it is not necessary to select a seed layer in terms of crystallinity control and a matrix material in terms of crystallinity control. In the form without the seed layer, the recording layer may be formed directly on the substrate, or may be formed on some underlying layer other than the seed layer. When the seed layer is too thick, the crystal grain size on the surface of the seed layer becomes excessive, and the grain size refinement of the recording layer formed thereon is impaired. Therefore, the upper limit of the film thickness of the seed layer is preferably 200 nm, more preferably 100 nm, and still more preferably 50 nm.
[0043]
The film thickness of the magnetic recording layer 3 is preferably 5 to 50 nm, more preferably 10 to 25 nm. Since the lower limit of the film thickness is determined by the resistance to thermal disturbance, it varies depending on the magnetic material used. For example, since Co—Cr based magnetic materials cannot secure sufficient thermal disturbance resistance below 10 nm, the lower limit of the film thickness is 10 nm. Sufficient thermal disturbance resistance is exhibited up to a film thickness of about 7 nm. Further, in the case of a highly anisotropic Sm—Co based magnetic material, sufficient thermal disturbance resistance is exhibited even at 5 nm. The upper limit is determined by the resolution. Since the resolution index is Mrt / Hc for the longitudinal medium, the thickness t of the recording layer can be increased when Hc is high. The upper limit of the recording layer thickness depends on the linear recording density (required value of resolution) and Hc, but is 50 nm at most, more preferably 25 nm.
[0044]
As the nonmagnetic matrix 4, C (carbon), Si-O, Si-N, Si-C, Ti-N, Ti-C, Al-N, Ta-O, Ta-N, Al-O, ITO, A wide selection can be made from oxides, nitrides, carbides, borides, and organics such as In-N, In-O, B-N, Zr-N, Zr-O, and PTFE.
[0045]
The material for forming the magnetic particles 5 can be selected from a wide variety of materials such as Co-based alloys, rare earth / transition metal alloys (RE-TM) (RE: rare earth, TM: transition metal), and magnetic oxides. is there. Examples of Co-based alloys include Co—Cr, Co—Pt, Co—Fe, Co—Cr—Ta, Co—Cr—Pt, Co—Cr—Pt—Ta, Co, Fe, Tb—Fe, Tb—Co, Tb—Fe—Co, Gd—Tb—Fe—Co, Gd—Dy—Fe—Co, Nd—Fe—Co, Nd—Tb—Fe—Co, PtMnSb, Co ferrite, Ba ferrite, etc. .
[0046]
Of the magnetic particle materials described above, materials that are particularly suitable in the present invention are magnetic materials with little segregation, such as Co—Pt-based alloys, Co—Tb, Co, Co—Fe, and rare earth / transition metal alloys.
[0047]
The magnetic recording medium of the present invention is preferably manufactured by a dry process using an ion beam or the like. Since it is a dry process, the selection range of the magnetic material and the matrix material is wide and desired magnetic characteristics are easily obtained.
[0048]
Examples of the protective layer 6 include C, but the protective layer 6 may be omitted.
[0049]
The thickness of the protective layer 6 is preferably 0 to 20 nm (0 nm is a form without the protective layer 6), more preferably 0 to 10 nm. The lower limit is defined by the protective function of the recording layer. In the case of a multi-particle random metal medium having a fine structure in which conventional magnetic particles are surrounded by grain boundaries, the mechanical and chemical stability itself is insufficient. The coating was essential, and a protective film of about 10 nm was required at the minimum. In the present invention, since the protective function of the magnetic particles can be assigned to the matrix material, the protective film may be omitted (0 nm). In addition, it is more effective to provide a protective film in the range of 0 to 10 nm in order to promote the protective function by the matrix. The upper limit of the protective film thickness is defined by the spacing loss. As the protective film thickness increases, the steepness of the recording magnetic field from the head is impaired, and the spatial steepness of the signal magnetic field generated from the medium is also impaired. The upper limit of the protective film thickness depends on the linear density, the head structure, the head flying height, etc., but is 20 nm at most, preferably 10 nm.
[0050]
The crystal magnetic anisotropy and magnetic properties of the magnetic layer 3 are adjusted by adjusting the crystallinity of the seed layer 2 material, the film thickness of the seed layer 2, the material of the magnetic layer 3, and the film thickness of the magnetic layer 3. can do.
[0051]
For example, when relatively thick Cr is used for the seed layer 2 and relatively thin Co—Pt and Co—Fe are used for the magnetic layer 3, the magnetic layer 3 has in-plane magnetic anisotropy. Show. For example, when a relatively thin Cr is used for the seed layer 2, the magnetic layer 3 exhibits three-dimensional random magnetic isotropy. Further, for example, when NiFe is used for the seed layer 2 and relatively thick Co—Pt, Co—Fe is used for the magnetic layer 3, the magnetic layer 3 is magnetically anisotropic in a direction perpendicular to the film surface. Showing gender.
[0052]
The magnetocrystalline anisotropy and magnetic characteristics of the magnetic layer 3 can also be adjusted by adjusting the film formation conditions of the seed layer 2 and the magnetic layer 3. In the present invention, the anisotropy and magnetic properties after the regular magnetic particles 5 are formed from the magnetic material are more important than the magnetic anisotropy of the continuous film made of the magnetic material.
[0053]
The inventors performed simulation of magnetic recording medium noise prior to the implementation of the present invention. As a result of the simulation, it was found that when the magnetic particles 5 are regularly arranged, the medium noise is greatly reduced and the S / N is improved. Further, it has been found that the reduction effect is remarkable when the variation in the distance between the particles is 40% or less, and more remarkable when the variation in the particle diameter is 20% or less in FWHM.
[0054]
In the regular magnetic particle medium of the present invention, one magnetic particle 5 is not the minimum recording unit. That is, the minimum recording cell 7 shown in FIG. 1 is not composed of one magnetic particle 5, but is composed of at least four magnetic particles 5 in the track length direction. The minimum recording cell is a recording cell corresponding to the shortest cell length.
[0055]
If the minimum recording cell 7 is composed of a plurality of magnetic particles 5 according to the present invention, it is possible to design a magnetic recording medium in accordance with the track width, gap length, servo accuracy, etc. of the head and sufficiently reduce the medium noise. S / N can be improved. The number of magnetic particles 5 in the minimum recording cell 7 depends on the recording density and the aspect ratio of the recording cell.
[0056]
In the present invention, since the nonmagnetic material 4 is basically used between the particles 5, it is not necessary to segregate Cr or the like.
[0057]
(B) Regular non-magnetic pore medium
FIG. 2 is a schematic view showing an example of a regular non-magnetic pore medium according to the present invention. FIG. 2A is a plan view of a minimum recording cell, and FIG. In the regular nonmagnetic pore medium shown in FIG. 2, a seed layer 2 is formed on a substrate 1, and a magnetic recording layer 3 is formed on the seed layer 2. The magnetic recording layer 3 is composed of a plurality of nonmagnetic pores 9 regularly arranged in the continuous magnetic film 8. A protective layer 6 is formed on the magnetic recording layer 3. Note that the regular arrangement means that the full width at half maximum of the distribution of the distance between the nearest nonmagnetic pores is ± 40% or less of the average distance between the nearest nonmagnetic pores.
[0058]
The material for forming the substrate 1, the seed layer 2, and the protective layer 6 should be the same material as the material for forming the regular magnetic particle medium substrate 1, seed layer 2, and protective layer 6 shown in FIG. 1. Can do.
[0059]
The film thickness of the magnetic recording layer 3 in FIG. 2 is the same as the film thickness of the magnetic recording layer 3 of the regular magnetic particle medium in FIG.
The magnetic material forming the continuous magnetic film 8 can be selected from the same magnetic particle materials as those in the regular magnetic particle medium, and can be selected widely from polycrystalline magnetic materials and amorphous magnetic materials. Particularly preferred materials are Co—Pt-based alloys, Co—Tb, Co, Co—Fe, rare earth / transition metal alloys (RE-TM), which are easy to form a continuous magnetic material and have few domain wall pinning sites. It is a magnetic material such as (RE: rare earth, TM: transition metal).
[0060]
Co-Tb is a material belonging to the RE-TM system and is a material for magneto-optical recording rather than for magnetic recording. However, since it is an amorphous continuous magnetic film, it is free of grain boundaries and has good workability. In addition, Co-Tb has a relatively large saturation magnetization (Ms) in the RE-TM system, a high signal output, a high Curie point, excellent operating temperature characteristics, good corrosion resistance, and CSS resistance. It has advantages such as being easy.
[0061]
The nonmagnetic material for forming the nonmagnetic pore 9 can be selected from the same materials as those for forming the nonmagnetic matrix 4 in the regular magnetic particle medium.
[0062]
The nonmagnetic pores 9 are connected by a domain wall 10. The domain wall 10 is a part of the continuous magnetic film 8. In the domain wall 10, for example, when the magnetizations of two adjacent recording cells have opposite directions, the domain wall 10 positioned between the two cells has a magnetization in the middle of the two directions. Various types can be applied to the domain wall 10 in the present invention depending on the type of the magnetic film 8, and there is no particular limitation. For example, the type of the domain wall 10 includes a Bloch domain wall or a Neel domain wall.
[0063]
In the regular nonmagnetic pore medium of the present invention, the regularly arranged nonmagnetic pores 9 act as pinning sites of the domain wall 10, and therefore the shape of the domain wall 10 follows the regularity of the pore 9. Therefore, although the magnetic film 8 is continuous, the medium has extremely low noise and the S / N is improved. In order for the pore 9 to act effectively as a pinning site of the domain wall 10, the pore size is preferably 0.5 or more of the width of the domain wall 10. In order to obtain low noise characteristics, the pore size is three times the width of the domain wall 10. The following is preferable.
[0064]
Normally, when a regular nonmagnetic pore medium is formed, if a method such as film formation in a magnetic field is not performed, the continuous magnetic film portion 8 shows a magnetization state having a domain wall 10 immediately after the formation. In general, the pattern of the domain wall 10 appearing in the continuous magnetic film 8 immediately after the film formation is a random maize pattern. However, when the nonmagnetic pore diameter is between 0.5 and 3 times the domain wall width as in the present invention, the domain wall 10 is not maize-like, and for example, a nonmagnetic pore 9 as shown in FIG. 13 is connected. Shows a regular array.
[0065]
Whether the domain wall 10 connects the nonmagnetic pore 9 depends on a comparison between the domain wall energy and the demagnetizing field energy. That is, when the domain wall energy is larger than the demagnetizing field energy, the domain wall 10 connects the nonmagnetic pores 9 because the domain wall 10 is more stable in terms of energy when the nonmagnetic pores 9 are continuous. However, in the opposite case, the domain wall 10 is rather energetically stable if the domain wall 10 is formed in a portion other than the nonmagnetic pore 9 without connecting the nonmagnetic pore 9. Do not concatenate.
[0066]
The present inventors have found that it is preferable to select a magnetic material and a nonmagnetic pore arrangement so that the domain wall energy becomes higher than the demagnetizing field energy in order to reduce medium noise and improve S / N.
[0067]
That is, the FWHM of the distance distribution between the nearest pores of the nonmagnetic pores constituting the minimum recording cell is adjusted to be ± 40% or less of the average distance between the nearest pores to reduce the magnetization transition noise. Preferred above.
[0068]
Table 1 below shows the recording density assumed to be applied to the present invention and the magnetic particle diameter, magnetic particle spacing, pore diameter, and pore spacing required when the present invention is applied.
[0069]
[Table 1]

[0070]
Table 1 shows that the aspect ratio of the recording cell is about 20 in the conventional magnetic medium, but the aspect ratio is expected to become smaller in the future, that is, the direction in which the track becomes narrower will develop more rapidly than the narrower bit pitch. Therefore, the case where the aspect is 10 and the case where the aspect is 1 (proposed as a so-called square bit) are shown. Although the relationship between the bit density and the shortest cell length depends on the signal processing method, in Table 1, a converted value when the 1/7 modulation method is adopted is used.
[0071]
As described above, in the case of the regular magnetic particle medium, the minimum recording cell is composed of at least four magnetic particles. Therefore, the most preferable particle diameter for realizing low noise performance is 1/4 of the minimum recording cell length. It is as follows. For this reason, in Table 1, the particle diameter is 1/4 of the cell length.
[0072]
The density of the magnetic particles was set to 50% or more for obtaining a sufficiently large medium signal output, and the particle spacing was set to particle size + 1 nm so that the exchange interaction between particles could be completely divided. In Table 1, the number of magnetic particles contained in the minimum recording cell is represented by a value obtained by dividing the product of the track width and the shortest recording cell length by the particle interval.
[0073]
In the regular non-magnetic pore medium, the pore density was set to 50% or less in order to obtain a sufficiently large medium signal output. In addition, the pore width can be practically used as long as it is equal to or smaller than the track width. However, in Table 1, the magnetic domain wall (magnetization transition) connecting the pores has a sufficient stability and the track width is 0.2.
[0074]
From Table 1, it is clear that both the regular magnetic particle medium and the regular non-magnetic pore medium of the present invention are useful as candidates for ultra-high density magnetic recording media.
[0075]
<Manufacturing Method of Mask According to the Present Invention>
Both the regular magnetic particle medium and the regular non-magnetic pore medium according to the present invention can be manufactured using a mask having openings that are regularly arranged. Therefore, first, a method for manufacturing a process mask having regularly arranged openings will be described.
[0076]
A mask for producing a plurality of magnetic particles regularly arranged from a magnetic layer or a plurality of nonmagnetic pores arranged regularly from a nonmagnetic matrix layer is manufactured using, for example, a self-assembly process. can do.
[0077]
Examples of the self-organization process include the following.
(A) J.A. Electrochem. Soc. 100, 411, 1953, anodizing method of high purity Al.
(B) Dispersion precipitation method of oxide microspheres.
(C) In-gas deposition method of oxide microspheres.
(D) Ge or Bi deposition on stearic acid as disclosed in Applied Physics Vol. 52, No. 8, 712, 1983.
(E) Heteroepitaxial growth of Cu phthalocyanine on graphite.
(F) Appl. Phys. Lett. 64 (2) 196, 1994, InAs dot formation on GaAs.
(G) Appl. Phys. Lett. 64 (4) 422, 1994, Au dot formation on a composite organic material.
In the present invention, any method of the above-described self-organization process can be applied, and other methods that do not use the self-organization process are also applicable.
[0078]
As an example of a method for manufacturing a mask using a self-assembly process, the mask is manufactured using the above-described (a) high-purity Al anodic oxidation method and (c) oxide microsphere vapor deposition method. A method will be described.
[0079]
(A) Method for producing a mask by anodizing high purity Al
The production of a self-assembled mask by anodizing of Al comprises (1) a step of forming porous anodized and (2) a step of producing a mask from porous anodized.
[0080]
Hereinafter, each step will be described sequentially.
(1) Stage of forming porous anodized
This stage includes the following steps (a) to (c).
(A) A 4N or 5N grade high-purity Al plate is mirror-polished.
(B) The mirror-polished Al plate is neutralized after perchloric acid chemical polishing or alkali polishing in a sodium hydroxide solution.
(C) After neutralization, the Al plate is immersed in an anodic oxidation solution of several percent to several tens percent, and a positive voltage is applied to the Al plate with Pt, C, etc. as the negative electrode, and anodization is performed for a predetermined time. To do.
[0081]
As an anodic oxidation solution, an aqueous solution of oxalic acid, phosphoric acid, sulfuric acid, chromic acid and mixed acids thereof is used. Continuous anodic Al on the surface of the Al plate by anodic oxidation₂O_ThreeA barrier layer is formed, and porous anodized (Al₂O_Three) Is formed. Porous alumite has a plurality of unpenetrated micropores regularly arranged. The formation of such a porous anodized is called self-organization.
[0082]
FIG. 3 is a schematic cross-sectional view showing a barrier layer formed by anodization and porous alumite. As shown in FIG. 3, an anodized Al initial growth barrier layer portion 12 is formed on a high-purity Al plate 11 by anodizing treatment, and anodized Al porous anodized metal having a plurality of micro holes 13 thereon. Part 14 is formed. In FIG. 3, C represents the unit cell size of porous anodized (corresponding to the interval between the micropores), P represents the micropore size, and W represents the thickness of the anodized wall surrounding the micropores.
[0083]
The formation mechanism of such self-organized porous alumite 14 is such that Al and oxidized Al (Al₂O_Three) Both due to dissolution. That is, when a raw material Al is immersed in an oxidizing solution and a voltage is applied, an anodized Al layer is formed while the Al surface is dissolved, and a part of the formed Al oxide is dissolved in the solution. On the Al oxide surface after the Al oxide is dissolved and flows out into the solution, the electric field concentrates and the current density increases. As the current density increases, the dissolution of Al oxide is promoted, so that the micropores 13 are formed. At the same time, dissolved excess Al or Al oxide is supplied around the micropores 13 to promote the growth of Al oxide walls.
[0084]
The partial dissolution of Al oxide as described above, that is, local dissolution occurs selectively in Al itself or in a defect portion of naturally oxidized Al remaining on the Al surface. As described above, after the local dissolution occurs, the electric field is weakened when the micropores 13 are formed and the Al oxide wall grows. When the electric field is weakened, in order to maintain the total electric field strength on the surface of the oxidized Al, a portion having a strong electric field is formed again next to the oxidized Al wall, and the microhole 13 is formed.
[0085]
In the initial stage of anodization, the formation of the micropores 13 is started from randomly distributed defect portions. However, as described above, since a periodic and regular electric field spatial distribution is generated around the formed micropores 13, it is considered that the micropores 13 form a regular array in a self-organizing manner.
[0086]
As shown in FIG. 3, at the interface between the Al plate 11 and the Al oxide barrier layer 12, a concave surface is formed for each unit cell. When the member on which the porous alumite 14 has grown is immersed in a relatively high concentration phosphoric acid or chromic acid solution to remove the porous alumite 14, the Al plate 11 having regularly arranged concave surfaces is obtained. When the above-described anodization is performed again on the Al plate 11, the protrusions located between the concave surfaces on the Al plate 11 serve as the defect portions described above, and are more regular than the first anodization. Porous alumite 14 having a good self-organization pattern can be obtained.
[0087]
The growth rate of the porous alumite 14 depends on the anodizing conditions, mainly the anodizing voltage, but is typically several to 100 nm / min. Further, the depth of the microhole 13 can be adjusted by the anodic oxidation time.
[0088]
In the trial production of a magnetic medium to be described later, the size of the micropores 13 formed as described above corresponds to the magnetic particle size or the nonmagnetic pore size, and the interval between the micropores 13 corresponds to the magnetic particle interval or the nonmagnetic pore interval. . Further, the depth of the microhole 13 is related to the characteristics of the magnetic film processing. The size of the micropores 13 and the interval between the micropores 13 depend on the type of acid used for anodization, the anodizing voltage, and the anodizing bath temperature.
[0089]
As described above, when the pore interval is C, the pore diameter is P, the thickness of the Al oxide wall formed around the hole is W, and the voltage applied to Al is E, the following relationship is experimentally established. .
C = 2WE + P ……………………… (1)
The pore diameter P and the Al oxide wall thickness W depend on the type, concentration, and bath temperature of the anodizing solution. The diameter of the micropores 13 can be adjusted by the acid type, concentration, and bath temperature, and the interval between the micropores 13 can be widely adjusted by the acid type, concentration, bath temperature, and applied voltage. The regularity of the arrangement of the micropores 13, that is, the pore size distribution and the pore spacing distribution depend on the purity of Al, the amount of additive such as Mg in Al, the treatment method before anodization, the anodization rate, and the number of anodizations. Dependent.
[0090]
(2) Stage of making a mask from porous anodized
A method for forming a mask from porous alumite 14 formed on Al is disclosed in, for example, Jpn. J. et al. Appl. Phys. 35-2 (1B) L126, 1996.
[0091]
This method includes the following steps (a) to (e).
(A) An organic resin mold such as a resist is formed on the surface of the porous alumite 14 shown in FIG.
(B) The Al plate 11 is removed by etching.
(C) The Al oxide barrier layer 12 is removed.
(D) Fill a resin mold with a metal such as platinum.
(E) The resin mold is removed.
Through the series of steps described above, a metal mask such as platinum having a through hole is produced.
[0092]
Jpn. J. et al. Appl. Phys. In 31-2 (12B) L1775, 1992, and Science, 268, 1466, 1995, a resist is embedded in porous alumite to form a negative pattern, and then a replica of oxide, platinum (Pt), etc. is formed. A method of forming a mask from this replica is disclosed.
[0093]
In the method disclosed in Science, 268, 1466, 1995, in addition to oxide and platinum, SiC, SiO, and other materials can be used as replica materials.₂CVD growth materials such as aC: H can be used. Therefore, the etching resistance and mechanical strength of the mask can be improved as compared with the case where the porous anodized itself is masked.
[0094]
When the mask is manufactured from the replica in this way, the mask may be manufactured as it is from the porous alumite pattern, but a metal ring made of metal such as Cu is prepared for mechanical holding, and the opening of the metal ring is prepared. After the porous alumite honeycomb pattern is disposed in the part, a mask may be produced from the porous alumite pattern. When manufactured using a metal ring, the mechanical strength and handling of the manufactured mask can be significantly improved.
[0095]
FIG. 4 is a schematic plan view and a schematic cross-sectional view showing an example of a metal ring. The mask is formed in the opening 16 of the metal ring 15. Fabrication of a mask using the metal ring 15 can be performed by a method obtained by modifying the replica method disclosed in, for example, Science, 268, 1466, 95.
[0096]
(B) Method of manufacturing a mask by using an oxide microsphere vapor deposition method in a gas
The method includes the following steps.
[0097]
(A) TiO that forms microspheres on the order of 10 nm₂An oxide such as, for example, is put into a raw material boat of an electron beam vapor deposition apparatus, evacuated, and then irradiated with an electron beam to the boat to produce TiO 2.₂Evaporate.
[0098]
(B) The evaporating substance is led from the passage hole of the partition wall provided in the vapor deposition chamber to another chamber having a high gas pressure. In this separate chamber, TiO of the order of 10 nm in the gas phase is obtained by supercooling the evaporated substance.₂Microspheres are formed.
[0099]
(C) The formed microsphere is passed through plasma or charged by spraying an ozonizer on the microsphere, and then the charged microsphere is deposited on the mask substrate. The deposited microspheres are regularly arranged on the substrate while repelling each other by Coulomb force. As a result of the arrangement, TiO with a particle size of the order of 10 nm₂A regular self-organized pattern of spheres is formed.
[0100]
(D) A mask is produced from the formed pattern. For example, the mask is manufactured as follows. For example, a resist negative pattern is formed by embedding a resist in the formed pattern and having concave portions regularly arranged. By subjecting the negative pattern to a transfer process, a mask having the same pattern as the self-assembled pattern can be formed.
[0101]
Next, a method for manufacturing a magnetic recording medium according to the present invention will be described.
First, a manufacturing method using the mask manufactured as described above will be described. Next, a method for manufacturing a magnetic recording medium without using a mask will be described.
[0102]
<Method for Manufacturing Magnetic Recording Medium According to the Present Invention Using a Mask>
Of the masks produced as described above, a method for producing a regular magnetic particle medium and a regular nonmagnetic pore medium according to the present invention using a mask produced from porous alumite will be described.
[0103]
(A) Method for producing regular magnetic particle medium
First, a method for producing a regular magnetic particle medium having a normal pattern will be described. Next, a method for producing a regular magnetic particle medium having a servo pattern will be described.
[0104]
(A-1) Method for producing regular magnetic particle medium having normal pattern
The regular magnetic particle medium having the configuration shown in FIG. 1 is formed by sequentially forming a seed layer, a magnetic layer, and a protective layer by sputtering on a substrate mounted in a film forming apparatus such as a multi-chamber magnetron sputtering apparatus. Can be produced.
[0105]
Basically, two processes, a first process and a second process can be applied to this method. Both processes can be used to make the ordered magnetic particle media shown in FIG. The first process has a larger number of processes than the second process and requires a PEP process. However, the self-assembled mask can be used any number of times because it does not undergo any alteration during the process. There is.
[0106]
FIG. 5 shows these process flows.
[0107]
(1) First process
(A) A magnetic layer is formed on a substrate. As described above, the seed layer and the protective layer may or may not be formed.
(B) A resist is coated on the magnetic layer.
(C) A substrate is placed directly under the self-assembled mask produced as described above.
[0108]
(D) Light exposure or electron beam batch irradiation is performed from above the mask to expose the resist. After exposure, the resist is developed. If a positive resist is used, only the exposed portion remains as a pattern on the magnetic layer by the development process. This resist pattern matches the honeycomb pattern in the opening of the self-organizing mask.
[0109]
(E) The resist pattern is transferred to the magnetic layer by ion milling or RIE. In the ion milling method, batch milling is performed using an ion source having a larger diameter than the substrate on which the magnetic layer is formed (disk substrate in the case of HDD application), or the substrate is rotated under the small-diameter ion source. And do it. The milling rate of the resist, magnetic layer, seed layer, and protective layer is previously investigated. If the milling time is set with reference to the investigated rate, only the magnetic layer can be patterned into regular columnar magnetic particles before the resist is milled off. Since the seed layer remains as it is under the magnetic particles, good magnetic properties are maintained. The seed layer between the magnetic particles may be milled.
[0110]
(F) After patterning the magnetic layer, the resist residue is removed (using ashing, dipping, etc.) as necessary.
[0111]
The regular magnetic particle medium according to the present invention is manufactured by the steps (a) to (f).
[0112]
(G) In order to improve the mechanical strength and corrosion resistance of the medium, a matrix material is further embedded between the magnetic particles produced as described above.
[0113]
The embedding can be performed by a film forming method such as CVD, sputtering, or vapor deposition. From the viewpoint of embedding of the matrix material between the magnetic particles, an anisotropic film formation method such as collimation sputtering is preferable, but the embedding depth (a depth equivalent to the thickness of the magnetic particles) is as small as about 10 nm. Any method can be used for relatively good embedding.
[0114]
(H) Since the surface of the medium has an uneven surface after the matrix is embedded, the surface of the medium is subjected to a surface flattening process as necessary. Examples of the surface flattening process include a waffle burnish, a tape burnish, CMP, ion polishing, or a combination thereof.
[0115]
For example, when CVD-C is used as a matrix and tape vanishing and ion polishing are combined with surface flattening, it is possible to realize Ra <1 nm as surface roughness.
[0116]
(I) If the matrix material covers the top of the magnetic particles after the planarization process, it can be used as a regular magnetic particle medium as it is. When the matrix material does not cover the top of the magnetic particles and the top of the magnetic particles is exposed, it is preferable to coat a protective film on the surface of the medium after the planarization process.
[0117]
(J) Although not shown in FIG. 5, finally, a lubricant layer is coated on the surface of the medium in the same manner as a normal magnetic medium. Since the lubricating layer can be used instead of the protective film, the lubricating layer may be coated on the surface of the medium when the magnetic particles are exposed as described above.
[0118]
(2) Second process
(A) A matrix material is formed on the substrate as a continuous film. As described above, the seed layer and the protective layer may or may not be formed.
(B) The substrate is placed directly under the self-organizing mask.
(C) The matrix material is patterned corresponding to the self-organizing mask by ion milling or RIE. By patterning, a plurality of holes regularly arranged in the matrix material are formed.
[0119]
(D) A magnetic particle material is embedded in the holes formed in the matrix material. For embedding, it is preferable to apply an anisotropic film formation method such as collimation sputtering in order to maintain good magnetic properties in the vicinity of the hole side wall. However, the deterioration of the magnetic characteristics is slight and there is no problem in practical use.
[0120]
(E) After embedding the magnetic particles, the surface is flattened by the same method as the first process such as varnish, CMP, ion polishing and the like.
[0121]
In the first process, a magnetic material is disposed on the lower side, and a matrix material that is usually harder than the magnetic material is disposed on the upper side. Therefore, it is necessary to strictly manage the end point of the planarization process. This process (B) Then, since the hard matrix material is disposed on the lower side and the magnetic material is disposed on the upper side, the management of the end point is relatively easy in any planarization process. The process after planarization can be performed in accordance with the first process.
[0122]
In both the first process and the second process described above, the magnetic characteristics of the medium can also be adjusted by adjusting the magnetic material formation temperature, performing annealing after forming the magnetic particles, or the like.
[0123]
In both the first process and the second process described above, the magnetic particles according to the present invention are provided with a plurality of magnetic particles regularly arranged in the continuous nonmagnetic film, and are included in the minimum magnetic recording cell. The number of particles arranged in the track length direction is at least 4, and the full width at half maximum of the distribution of the distance between the closest particles is not more than ± 40% of the average distance between the closest particles. It is possible to manufacture a magnetic recording medium whose full width at half maximum is ± 20% or less of the average particle diameter.
[0124]
(A-2) Method for producing regular magnetic particle medium having servo pattern
Next, a method for producing a regular magnetic particle medium having a servo pattern will be described.
FIG. 6 is a schematic diagram showing an example of a servo pattern of a magnetic disk. FIG. 6A shows an arrangement example, and FIG. 6B shows a servo pattern form. When the present invention is applied to a magnetic medium having a servo pattern, the following three modes are conceivable. That is, (i) an aspect in which the magnetic particle part is formed after forming the servo pattern, (ii) an aspect in which the servo pattern and the magnetic particle part are formed simultaneously, and (iii) the servo pattern after forming the magnetic particle part. It is an aspect to form.
[0125]
Hereinafter, each aspect will be described.
(I) A mode in which the magnetic particle part is formed after forming the servo pattern is described in, for example, p. As disclosed in 75, the following sequence of steps can be applied.
[0126]
(A) A servo pattern is formed on a substrate with a resist.
(B) The pattern is transferred to the substrate surface using the resist as a mask.
(C) Embedding a servo magnetic film in the substrate
(D) Lift off resist
(E) Flatten the surface
After the embedded servo is formed, the regular magnetic particle medium may be formed as described above.
[0127]
(Ii) A mode in which the servo pattern and the regular magnetic particle portion are simultaneously formed can be performed by providing the servo pattern in a part of the self-organizing mask in advance.
[0128]
Specifically, for example, in a transfer process of forming a mask from porous alumite, a part of the resist negative may be exposed and developed according to a servo pattern.
[0129]
(Iii) In an aspect in which the servo pattern is formed after the regular magnetic particle portion is formed, the resist is patterned on the regularly arranged magnetic particles, and the data portion including a plurality of magnetic particles is stored as it is, It is only necessary to etch only the servo portion as necessary and embed a magnetic film for servo.
[0130]
(B) Method for producing regular nonmagnetic pore medium
First, a method for producing a regular nonmagnetic pore medium having a normal pattern will be described. Next, a method for manufacturing a regular nonmagnetic pore medium having a servo pattern will be described.
[0131]
(B-1) Manufacturing method of regular non-magnetic pore medium having normal pattern
The regular nonmagnetic pore medium shown in FIG. 2 can be performed, for example, according to the method for producing the regular magnetic particle medium shown in FIG. That is, in the process flow of the regular magnetic particle medium in FIG. 5, the magnetic layer and the matrix layer, and the magnetic particles and the matrix may be reversed. Also in this method, the first process and the second process as illustrated in FIG. 5 can be applied.
[0132]
(1) First process
(A) A nonmagnetic matrix layer is formed on a substrate. The seed layer and the protective layer may or may not be formed.
(B) A resist is coated on the nonmagnetic matrix layer.
(C) A substrate is placed directly under the self-assembled mask produced as described above.
[0133]
(D) Light exposure or electron beam batch irradiation is performed from above the mask to expose the resist. After exposure, the resist is developed. If a positive resist is used, only the exposed portion remains as a pattern on the magnetic layer by the development process. This resist pattern matches the honeycomb pattern of the opening of the self-organizing mask.
[0134]
(E) The resist pattern is transferred to the nonmagnetic matrix by ion milling or RIE. In the ion milling method, batch milling is performed using an ion source having a larger diameter than the substrate on which the matrix layer is formed (disk substrate in the case of HDD application), or the substrate is rotated under the small-diameter ion source. And do it. The milling rate of the resist, nonmagnetic layer, seed layer, and protective layer is previously investigated. If the milling time is set with reference to the investigated rate, only the matrix layer can be patterned into regular columnar nonmagnetic particles before the resist is milled off. The seed layer remains as it is under the nonmagnetic particles. The seed layer between nonmagnetic particles may be milled.
[0135]
(F) After patterning the nonmagnetic layer in this way, the resist residue is removed (using ashing, dipping, etc.) as necessary.
[0136]
(G) A magnetic material is embedded between nonmagnetic particles. The embedding can be performed by a film forming method such as CVD, sputtering, or vapor deposition. From the viewpoint of embedding of the magnetic material between the nonmagnetic particles, an anisotropic film forming method such as collimation sputtering is preferable, but the embedding depth (a depth equivalent to the thickness of the nonmagnetic particles) is as large as about 10 nm. Since it is small, relatively good embedding can be performed using any method.
[0137]
(H) Since the surface of the medium is uneven after embedding the magnetic material, a surface flattening process is performed on the medium surface as necessary. Examples of the surface flattening process include waffle burnish, tape burnish, CMP, ion polishing, or a combination thereof.
[0138]
(I) After the planarization process, a protective film is coated on the surface of the medium.
(J) Although not shown in FIG. 5, finally, a lubricant layer such as a lub is coated on the surface of the medium in the same manner as a normal magnetic medium. A lubricating layer may be coated on the surface of the medium instead of the protective film.
[0139]
(2) Second process
(A) A material to be a magnetic layer is formed on the substrate as a continuous film. As described above, the seed layer and the protective layer may or may not be formed.
(B) The substrate is placed directly under the self-organizing mask.
(C) The magnetic material is patterned corresponding to the self-organized mask by ion milling or RIE. By patterning, a plurality of holes regularly arranged in the magnetic material are formed.
[0140]
(D) A nonmagnetic particle material is embedded in the holes formed in the magnetic material. For embedding, it is preferable to apply an anisotropic film formation method such as collimation sputtering. However, since the embedding thickness is about 50 nm even if it is thick, there is no problem in practical use even if ordinary isotropic film formation is used.
[0141]
(E) After embedding the nonmagnetic particles, the surface is flattened by the same method as the first process such as varnish, CMP, ion polishing and the like.
[0142]
In the second process, a soft magnetic material is disposed on the lower side and a nonmagnetic matrix material that is usually harder than the magnetic material is disposed on the upper side. Therefore, it is necessary to strictly manage the planarization endpoint. In this process, since the non-magnetic matrix material is disposed on the lower side and the magnetic material is disposed on the upper side, the management of the end point is relatively easy in any planarization process. The process after planarization can be performed in accordance with the first process.
[0143]
In both the first process and the second process described above, a plurality of nonmagnetic pores regularly arranged in the secondary magnetic film according to the present invention are provided, and the magnetization transition portion in the magnetic film has a nonmagnetic pore. Magnetic recording medium consisting of connecting domain walls, in which the average grain size of nonmagnetic pores is 0.5 to 3 times the average width of domain walls, and the distance between nearest pores in the minimum magnetic recording cell in addition to these characteristics It is possible to manufacture a magnetic recording medium having a full width at half maximum of ± 40% or less of the average distance between nearest pores.
[0144]
Further, in both the first process and the second process described above, the magnetic properties of the medium can be adjusted by adjusting the magnetic material formation temperature, performing annealing after forming the magnetic particles, or the like.
[0145]
(B-2) Preparation of regular nonmagnetic pore medium having servo pattern
Next, a method for manufacturing a regular nonmagnetic pore medium having a servo pattern will be described. As the servo pattern, for example, the pattern shown in FIG. 6 can be used as in the regular magnetic particle medium.
[0146]
When the present invention is applied to a medium having a servo pattern, the following three modes can be considered. That is, (i) a mode in which a nonmagnetic pore portion is formed after forming a servo pattern, (ii) a mode in which a servo pattern and a nonmagnetic pore portion are formed simultaneously, (iii) after a nonmagnetic pore portion is formed This is an aspect of forming a servo pattern.
[0147]
Hereinafter, each aspect will be described.
(I) A mode in which the nonmagnetic pore portion is formed after forming the servo pattern is described in, for example, p. As disclosed in 75, the following sequence of steps can be applied.
[0148]
(A) A servo pattern is formed on a substrate with a resist.
(B) The pattern is transferred to the substrate surface using the resist as a mask.
(C) Embedding a servo magnetic film in the substrate
(D) Lift off resist
(E) Flatten the surface
After the embedded servo is formed, a regular nonmagnetic pore medium may be formed as described above.
[0149]
(Ii) A mode in which the servo pattern and the nonmagnetic pore portion are simultaneously formed can be performed by providing the servo pattern in a part of the self-organizing mask in advance.
[0150]
Specifically, for example, in a transfer process of forming a mask from porous alumite, a part of the resist negative may be exposed and developed according to a servo pattern.
[0151]
(Iii) In a mode in which the servo pattern is formed after forming the non-magnetic pore portion, the resist is patterned on the regularly arranged pores, and the data portion including a plurality of non-magnetic pores is held as it is, and the servo pattern is formed. Only the portion may be etched as necessary, and the servo magnetic film may be embedded.
[0152]
<Method for Producing Magnetic Recording Medium According to the Present Invention without Using a Mask>
Next, a method for manufacturing a magnetic recording medium according to the present invention without using a mask such as the self-organizing mask described above will be described. As an example, a method for producing a regular magnetic particle medium according to the present invention without using a mask will be described.
[0153]
FIG. 7 is a schematic view showing an example of an apparatus for producing a regular magnetic particle medium without using a mask.
[0154]
The apparatus shown in FIG. 7 includes a vacuum vessel 20 that communicates a gas introduction system with an exhaust system.
[0155]
An induction heating type evaporation source 21 is disposed on the floor of the vacuum vessel 20. The evaporation source 21 includes a crucible 23 around which a heater 22 is wound, and a shutter 24 disposed above the crucible 23. The heater 22 is connected to an RF power source 25 disposed outside the container 20. The crucible 23 is filled with an evaporation sample 26 for evaporation.
[0156]
A superconductor portion 27 is disposed on the ceiling portion of the vacuum container 20. The superconductor portion 27 includes a cold head 28 suspended from the ceiling, a superconductor 29 attached to the lower surface of the cold head 28, a magnetic disk substrate 30 attached to the lower surface of the superconductor 29, and the components. It consists of a magnetic field application coil 31 arranged in the side part. The coil 31 is also suspended from the ceiling.
[0157]
A regular magnetic particle medium can be manufactured by the following procedure using the apparatus of FIG.
(A) After evacuating the content of the vacuum vessel 20 to 10 −4 Pa or less, the cold head 28 is operated to cool the superconductor 29 to a temperature at which a superconducting state is developed.
(B) Energize the magnetic field application coil 31 to apply a magnetic field in a direction perpendicular to the superconductor 29.
[0158]
When a magnetic field is applied to the superconductor 29 in the superconducting state, triangular lattice eddy currents regularly arranged inside the superconductor 29 flow. A magnetic field 32 perpendicular to the surface of the superconductor 29 is generated from the center of each eddy current, and no magnetic field 32 is generated except in the eddy current center. That is, a pattern of a magnetic field 32 having a magnetic flux perpendicular to the surface regularly arranged in a triangular lattice pattern is formed on the surface of the superconductor 29.
[0159]
The pattern interval of the magnetic field 32 depends on the applied magnetic field strength with the type of superconductor 29. For example, when YBCO, which is an oxide high-temperature superconductor, is used as the superconductor 29 and the applied magnetic field is 1 T, the pattern spacing of the magnetic field 32 is less than 50 nm, which is a suitable value for implementing the present invention. . Since the pattern spacing of the magnetic field 32 is inversely proportional to the square root of the applied magnetic field strength, the pattern spacing can be narrowed by increasing the magnetic field strength. For example, when YBCO is used as the superconductor 29, the pattern interval of the magnetic field 32 is 25 to 50 nm.
[0160]
(C) Magnetic fine particles (not shown) are deposited on the pattern of the magnetic field 32 formed in a self-organized manner on the surface of the superconductor 29.
For vapor deposition of magnetic fine particles, an in-gas deposition method or the like can be applied. For example, a magnetic material such as CoPt is mixed with the evaporation sample 26 as a raw material, and the magnetic material is evaporated by induction heating. Specifically, when the RF power source 25 is operated with the shutter 24 closed and the induction heating coil 22 is energized, the magnetic material is heated and evaporated.
[0161]
(D) An inert gas is introduced into the vacuum vessel 20 by several tens to several hundreds Pa. As a result of the introduction, the evaporated magnetic material becomes supercooled in the gas phase, and, for example, a magnetic cluster having a diameter of about sub nm to several tens nm is formed.
[0162]
(E) The shutter 24 is opened with the magnetic clusters formed, and the clusters are guided onto the substrate 30 on which the regular magnetic field pattern is formed.
[0163]
Since the magnetic clusters have almost no kinetic energy, they fly randomly toward the substrate 30 up to the vicinity of the substrate 30, but are regularly arranged on the substrate according to the pattern of the magnetic field 32 regularly arranged in the vicinity of the substrate 30. . Thus, regular magnetic particles can be produced on the substrate 30.
(F) The process for forming the medium after obtaining the regular magnetic particles can be carried out in the same manner as the process for forming the regular magnetic particle medium described above. Further, the characteristics of the regular magnetic particle medium obtained by such a method are the same as the characteristics of the regular magnetic particle medium formed using the above-mentioned self-composing mask.
[0164]
As described above in detail, when the present invention is used, the recording density can be greatly improved without particularly burdening elemental technologies other than the magnetic recording medium such as the head, servo, and signal processing device.
[0165]
Since the medium according to the present invention can be easily combined with other methods for increasing the recording density, some examples of combinations are illustrated.
[0166]
<Examples of combinations of the present invention and other technologies>
The combination of the medium and the perpendicular recording system according to the present invention has already been described in this specification. If the medium of the present invention is combined with a single pole head suitable for perpendicular recording, there is a possibility that the recording density can be further increased.
[0167]
A combination of the medium according to the present invention and the heat-assisted recording method is also easy. The heat-assisted recording method employs a medium having a very large magnetic anisotropy at room temperature to improve the resistance to thermal disturbance and enable further finer particles. However, if a recording medium with high magnetic anisotropy is used, a large magnetic field is required to perform magnetic recording, so that the burden on the head becomes too large to be practical. Therefore, in the heat-assisted recording method, only the portion to be recorded is heated using a laser beam or the like, and the anisotropy, that is, the recording magnetic field is reduced only at the moment of recording. If such a method is applied, the particle size can be further reduced even in a multi-particle random medium, so that the density can be increased. Also in the regular magnetic particle medium of the present invention, it is possible to employ a magnetic particle material having high magnetic anisotropy and to perform photothermal assist during magnetic recording. Therefore, by combining the medium according to the present invention and the heat-assisted recording method, a markedly higher recording density can be expected.
[0168]
In addition to the above, IEEE-Trans. Magn. 34 (4) 1552 and 1555, 1998, a medium using a keeper layer, a combination with a vertical medium that attempts to reduce burst noise by using a semi-hard magnetic undercoat instead of a soft magnetic undercoat, etc. Combinations with other techniques are possible without departing from the spirit of the present invention.
[0169]
【Example】
<Formation of porous anodized>
Example 1
Porous alumite was prepared according to the above-described mask manufacturing method by high-purity Al anodic oxidation. Table 2 below shows the measurement results of the anodizing conditions, the pore diameter P of the produced porous alumite, and the thickness W of the oxidized Al wall.
[0170]
[Table 2]

[0171]
P and W are values obtained by averaging the values of P and W measured for each pore from the processed image after SEM observation of the surface of the porous alumite shown in FIG. 3 and image processing. The anodic oxidation rate was adjusted to 10 ± 1 nm / min by adjusting the applied voltage.
[0172]
From Table 2 above, it can be seen that holes having a diameter of several to several tens of nm and walls having a thickness of sub nm to 1 nm per unit applied voltage can be formed.
[0173]
Next, experiments were conducted to change the pore size distribution and the pore spacing distribution of the micropores by changing the purity of Al, the pre-anodizing treatment method, and the number of times of anodizing. The experimental results are shown in Table 3 below.
[0174]
[Table 3]

[0175]
The FWHM (Pσ) of the pore size distribution and the FWHM (Cσ) of the pore spacing distribution were derived by performing image processing on an image obtained by SEM observation of the produced porous alumite. Pσ and Cσ are dispersion amounts with respect to the average pore diameter and the average pore interval shown in Table 2, for example, Pσ: 20% corresponds to ± 10%. The treatment conditions before the anodization were changed by changing the chemical polishing conditions for buffed high purity Al. The anodic oxidation rate was adjusted to 10 ± 1 nm / min by adjusting the applied voltage.
[0176]
In the above table, the sample of b8 with the smallest dispersion of the hole diameter and the hole interval is one in which the defect portions as the igniters of the holes are regularly arranged in advance.
[0177]
Defects were arranged as follows.
First, a SiC substrate having a flat and smooth surface was set in an EB drawing apparatus. Then, an electron beam was raster-scanned on the surface of the SiC substrate to form a plurality of sub-nm high protrusions arranged in a lattice pattern on the SiC surface. Next, the SiC substrate on which the protrusions were formed was taken out from the EB drawing apparatus, and this SiC substrate was pressed against a high-purity Al plate to form a plurality of recesses arranged in a lattice pattern on the Al surface. Next, the Al plate in which the recesses were formed was subjected to anodizing treatment under the conditions shown in Table 3.
[0178]
In the sample of b8, the recess on the SiC substrate formed according to the EB drawing pattern before the anodizing treatment acts as an igniter for the hole in the Al plate. Therefore, the arrangement of the holes follows the EB drawing pattern, and the dispersion is extremely small for both the hole diameter and the hole interval.
[0179]
By combining the conditions in Tables 2 and 3 and controlling the anodic oxidation voltage, the average pore size: 8 to 40 nm, FWHM of the pore size distribution: 8 to 120% (120% means ± 60%), average pore spacing: 12 to 60 nm Porous alumite was produced in a pore spacing distribution FWHM of 15 to 200%.
[0180]
Even when the anodic oxidation rate was changed in the range of about several to 30 nm / min, Pσ and Cσ substantially showed the values shown in Table 2. When the anodic oxidation rate was 30 nm / min or more, for samples other than the sample b8 in Table 2, when the oxidation rate was increased by 10 nm / min, Pσ and Cσ increased at a rate of approximately 5%. For the b8 sample, there was no particular increase in Pσ and Cσ even when the growth rate was increased to 30 nm / min or more.
[0181]
<Formation of mask using metal ring>
(Example 2)
A mask was formed using a metal ring by using a method modified from the replica method disclosed in the above-mentioned Science, 268, 1466, 1995.
[0182]
First, a Cu ring was prepared. Next, the resist in which the porous alumite pattern was copied was placed in the opening of the Cu ring. Next, Pt was continuously grown on the Cu ring, and Pt was grown according to the resist pattern in the opening of the ring. Thus, a replica made of Pt having a honeycomb-like pattern of porous anodized was formed. A mask was formed from the formed replica.
[0183]
The opening shape of the mask formed as described above coincided with the pattern of porous anodized with an error within 1 nm.
[0184]
FIG. 8 shows an SEM image in which the prototype mask is viewed from above. In FIG. 8, black circles correspond to through-hole portions, and white corresponds to Pt wall portions. The mask shown in FIG. 8 is adjusted such that the average pore diameter is 20 nm, the average pore spacing is 30 nm, the pore diameter distribution FWHM is 30%, and the pore spacing distribution FWHM is 40%.
[0185]
The depth of the hole can be adjusted by the Pt growth time at the time of replica formation in addition to the thickness of the porous alumite before transfer. In this example, the thickness is set to 500 nm in consideration of applicability to the magnetic medium process. Although it depends on the area of the opening of the metal ring, if the inner diameter of the metal ring is several centimeters, the replica can be handled even if the Pt thickness is as thin as about 500 nm due to the mechanical holding effect of the metal ring. If you are careful, you can prevent destruction.
[0186]
<Preparation of regular magnetic particle medium>
(Example 3)
A regular magnetic particle medium according to the present invention was produced using the mask produced in Example 2 in accordance with the method for producing a regular magnetic particle medium described above.
[0187]
The protective film thickness on the magnetic particles was set to 10 nm, which is the same as the film thickness used for the conventional medium, for comparison with the conventional medium. The protective film material was a matrix material or C film in the first process, and a C film in the second process. In addition, a fluorocarbon-based lubricating layer was applied to the outermost surface of all samples by about 2 to 3 nm.
[0188]
FIG. 9 is an image obtained by SEM observation of a regular magnetic particle medium actually produced from the top. In FIG. 9, white portions correspond to the nonmagnetic matrix 4 and black circles correspond to the magnetic particles 5.
[0189]
Using various self-assembled masks produced in Example 2, average particle size: 7 to 42 nm, particle size distribution FWHM: 8 to 150% (150% means ± 75%), average particle spacing: Regular magnetic particle media were prepared in the range of 12 to 60 nm, grain spacing distribution FWHM: 15 to 250%.
[0190]
<Evaluation of regular magnetic particle media>
The regular magnetic particle medium produced in Example 3 was evaluated as follows.
Using VSM, easy axis direction, product of remanent magnetization (Mr) and magnetic particle thickness (t) in easy axis direction, coercive force (Hc), coercive force squareness ratio (S^*) The activation magnetic moment was obtained by fluctuation field measurement. The activation size (Da) of the magnetic particles was determined from the measured values of the magnetic particle volume ratio and saturation magnetization. Da reacts to the minimum reversal size of the magnetic particles and matches the size of one physical particle when there is no exchange interaction between the particles.
[0191]
Also, from TEM and SEM observations and image processing of observed images, the average particle size (D) of magnetic particles, the average distance between magnetic particles (C), the FWHM of particle size distribution (Dσ), and the distribution of distances between magnetic particles The FWHM (Cσ) of was determined.
[0192]
The average particle diameter (D) of the magnetic particles corresponds to the average pore diameter P of the self-assembled mask, but D and P showed slightly different values depending on the transfer process from the mask. The FWHM (Dσ) of the particle size distribution corresponds to the pore size dispersion Pσ of the self-organizing mask, but Dσ shows a slightly large value because the dispersion in the transfer process is superimposed on Pσ. As a result of observation, the average distance (C) between the magnetic particles is not significantly different from the average distance (C) between the holes of the self-assembled mask, and is therefore indicated by the same symbol C. The distribution of the interparticle distance (C′σ) and the dispersion of the pore spacing of the self-organizing mask (Cσ) reflect the difference between the particle diameter dispersion Dσ and the hole diameter dispersion Pσ, and are not completely the same. It was.
[0193]
The target area on the medium for which the above average value and distribution were examined is a 2 μm square, which is a range sufficiently larger than the minimum recording cell size to which the present invention is applied. Therefore, if the distribution in the 2 μm square of the target area is 20% or less, for example, the distribution in the minimum recording cell is naturally 20% or less.
[0194]
As a final evaluation, a medium sample formed in a disk shape was mounted on a spin stand, and then the recording / reproduction characteristics centered on the medium noise characteristics were examined using an MR head. The evaluation results will be described sequentially below.
[0195]
Example 4
FIG. 10 is a diagram showing the results of measuring the relationship between the average distance (C) between magnetic particles and the product of residual magnetization and film thickness (Mrt).
[0196]
For a sample having a magnetization easy axis in the plane (longitudinal recording medium), Mrt was determined by measuring a major loop in the in-plane direction. Further, Mrt was obtained by measuring the vertical direction of the sample having the easy magnetization axis in the vertical direction. FIG. 10 shows that among a plurality of samples, the average particle diameter D is 9 to 11 nm, the particle diameter dispersion Dσ is 30% (± 15%) or less, and the intergranular dispersion Cσ is 60% (± 30%) or less. It is the result of selecting and investigating a regular magnetic particle medium. The measurement was performed on a medium having a magnetic particle thickness of 10 nm.
[0197]
In FIG. 10, A is the measurement result of the medium of the present invention in which the magnetic particle material is Co—Fe, B is the measurement result of the medium of the present invention in which the magnetic particle is Co—Pt, and C is the measurement of the conventional medium for comparison. It is a result. The conventional medium C has a multi-particle random array structure in which Cr (100 nm) / CoCrTaPt (10 nm) / C (10 nm) / lubricant (3 nm) is formed on a substrate. As the conventional medium, two samples having different magnetic particle diameters by changing the temperature when the magnetic layer was formed by sputtering were prepared.
[0198]
If the film thickness and particle size are constant, and Mrt is C^-2Is proportional to In the measurement results of A and B in FIG. 10, Mrt is C according to this theory.^-2It is proportional to However, the measurement results of conventional media are not as theoretical.
[0199]
Further, the value of Mrt for the same C is determined by the amount of magnetic element in the magnetic particles. Although the Co—Pt medium of the present invention and the conventional CoCrTaPt medium have substantially the same magnetic element concentration, the Mrt of the conventional medium is lower than that of the medium of the present invention. As a result, in the conventional medium, since the particle size distribution is wide, there are particles that are superparamagnetic due to thermal disturbance and the Mrt is lowered. However, in the regular magnetic particle medium of the present invention, the particle size dispersion is small. Shows that there are almost no superparamagnetic particles.
[0200]
Mrt is an amount related to the signal output and the magnetization transition width in terms of magnetic recording characteristics. The larger the Mrt, the larger the signal output, but when the coercive force is the same, the larger the Mrt, the wider the magnetization transition width and the higher the density. Recording becomes difficult. Therefore, Mrt is an amount that should be appropriately adjusted in accordance with other magnetic characteristics of the medium, noise characteristics, and characteristics of the recording / reproducing system such as the head. As shown by this example, it can be seen that in the medium of the present invention, Mrt can be adjusted appropriately by adjusting the average distance C between the magnetic particles.
[0201]
(Example 5)
FIG. 11 is a diagram showing the results of measuring the relationship between the average particle diameter D of magnetic particles and the coercive force Hc. Hc is a measured value in the easy axis direction of each sample. B of FIG. 11 is a measurement result of the medium of the present invention using Co—Pt magnetic particles, and C is a measurement result of the conventional medium used in Example 4. The measurement result of B is that the particle size dispersion Dσ is 30% (± 15%) or less, the average value of the interparticle distance is the average particle size D + (1 to 2 nm), and the dispersion of the interparticle distance is 60% (± 30%). It is the measurement result about the regular magnetic particle | grain medium of this invention which is the following.
[0202]
The coercive force Hc was measured by measuring a VSM major loop which took 10 minutes at room temperature. The smaller the particle size of the magnetic particles, the lower the Hc due to the influence of room temperature thermal disturbance. The influence of thermal disturbance can be estimated from the magnetic anisotropy and particle volume of the particles.
[0203]
The solid line in FIG. 11 is a theoretical Hc curve of the Co—Pt magnetic particles of the medium of the present invention, which is fitted with Hc when the particle size of the magnetic particles is sufficiently large. Moreover, the broken line in FIG. 11 is the theoretical Hc curve of the CoCrTaPt magnetic particle of the conventional medium. When the curve of the measurement result is compared with the theoretical curve, the two curves agree with each other in the medium of the present invention having a small particle size dispersion, but the measurement result is lower than the theoretical curve in the conventional medium having a large dispersion. The reason for this decrease is considered to be because the conventional medium contains superparamagnetic particles as in the case of the contents described for the Mrt measurement result in Example 3.
[0204]
Hc is an amount related to the magnetization transition width and the recording sensitivity in terms of magnetic recording characteristics. When Mrt is the same, the larger the Hc, the narrower the magnetization transition width, which is suitable for high density recording. However, coercivity squareness ratio S^*Are the same, the recording sensitivity decreases as Hc increases. Therefore, Hc is also an amount that should be adjusted appropriately according to the recording / reproducing system. As shown by this example, it can be seen that in the medium of the present invention, Hc can be appropriately adjusted by adjusting the average particle diameter of the magnetic particles.
[0205]
(Example 6)
FIG. 12 shows the dispersion Cσ ′ of the interparticle distance (described as 1/2 of FWHM) and Da / D which is the ratio of the activation size Da of the magnetic particles to the average particle diameter D of the magnetic particles. It is a figure which shows the result of having measured the relationship between.
[0206]
In FIG. 12, A is the measurement result of the medium of the present invention in which the magnetic particle material is Co—Fe, B is the measurement result of the medium of the present invention in which the magnetic particle is Co—Pt, and C is the conventional result used in Example 4. It is a measurement result about a medium. The measurement of the medium of the present invention was performed on a medium sample in which the particle size dispersion Dσ was adjusted to within 30% by FWHM.
[0207]
From the measurement results of the medium of the present invention, it can be seen that Da / D is 1 in the medium in which the dispersion of the interparticle distance is adjusted to ± 40% (FWHM: 80%) or less. Da is the minimum magnetization reversal unit, and coincides with the physical grain system D when the exchange interaction between the magnetic particles is separated. Moreover, it can be interpreted as follows that Da / D increases with dispersion in the region where dispersion is 80% or more. That is, when the dispersion C′σ of the interparticle distance is large due to the low degree of perfection of the self-organizing mask or the lack of a regular magnetic medium production process, the particles and the particles are locally contacted to form large particles. It is considered that Da / D is increased.
[0208]
In the conventional medium, the dispersion of the inter-particle distance shows a value of ± 50% (FWHM: 100%) or more, and Da / D is more than 1 reflecting that the particles are in local contact with each other. While showing a large value, Da / D is large compared with the medium of this invention in the dispersion amount of the same interparticle distance. This is because, in the conventional medium, not only the dispersion C′σ of the interparticle distance but also the particle size dispersion Dσ is large, so that the local contact between the particles is larger than that of the medium of the present invention. Conceivable.
[0209]
Da / D is an amount related to noise caused by exchange interaction between magnetic particles in terms of magnetic recording characteristics, and is preferably 2 or less. From this example, also in the regular magnetic particle medium of the present invention, it is preferable to suppress the dispersion of the interparticle distance to ± 65% (FWHM: 130%) or less in order to make Da / D 2 or less, most preferably. It can be seen that the dispersion is preferably within ± 40% (FWHM: 80%) or less so that Da / D is approximately 1.
[0210]
(Example 7)
FIG. 13 shows the particle size dispersion Dσ (described as 1/2 of FWHM) and the coercive force squareness ratio S.^*It is a figure which shows the result of having measured the relationship. S^*Is derived from the VSM major loop measurement results for the longitudinal medium, and is derived by performing demagnetizing field correction on the measured value of the saturation magnetization for the perpendicular medium. In FIG. 13, the symbols A, B, and C are the same as those used in the fifth embodiment.
[0211]
The measurement of the medium of the present invention was performed on a medium sample having an average particle diameter D of 12 to 13 nm and a dispersion Cσ of interparticle distance of ± 30% (FWHM: 60%) or less.
[0212]
Coercivity squareness ratio S^*Is an amount corresponding to the dispersion of Hc in the magnetic particles. Coercivity squareness ratio S^*Reflects the dispersion of the magnetic properties of the particles (for example, dispersion of magnetocrystalline anisotropy) within a sufficiently large range, but does not depend on the particle size itself. In addition, when the particle size becomes small and Hc lowering due to thermal disturbance at room temperature occurs, S^*Indicates particle size dependence.
[0213]
As shown in FIG. 13, in the medium of the present invention, even when the average particle diameter D is as small as 12 to 13 nm, the particle diameter dispersion is adjusted to ± 20% (FWHM: 40%). Is S^*Indicates a large value. On the contrary, when the particle size dispersion is larger than ± 20%, a magnetic particle component having a small Hc is generated in the present invention, and S^*It turns out that it reduces.
[0214]
In the conventional medium, the particle size dispersion is ± 25% or more, and it can be seen that there are considerably contained particles whose Hc is lowered due to thermal disturbance. Moreover, in the conventional medium, S is the same in the same particle size dispersion.^*Indicates a smaller value than that of the medium of the present invention. This is because not only the dispersion of the particle diameter but also the dispersion of the inter-particle distance is large in the conventional medium, and the dispersion of Hc is further increased because the particles are in contact with each other and the component in which Hc is apparently increased is included. It is thought that.
[0215]
S^*Is an amount related to recording sensitivity in terms of magnetic recording characteristics. S if Hc is the same^*The larger the value, the higher the recording sensitivity and overwrite erasure ratio.^*Is preferably 0.5 or more. Therefore, from the results of FIG. 8, it is preferable that the particle size dispersion is ± 35% or less (70% or less by FWHM) in the regular particle medium of the present invention, and more preferably, S^*It can be seen that it is good to be ± 20% or less (40% or less by FWHM) showing a high constant value.
[0216]
(Example 8)
The recording / reproducing characteristics of the medium according to the present invention were evaluated using an MR head.
The MR head used is a prototype having an AMR reproducing section with a recording track width: 1.3 μm, a reproducing track width: 1.0 μm, and a reproducing gap: 0.1 μm. This head has 4.3 Gb / in when the guard band width between tracks is 0.15 μm.²Recording / reproducing ability up to the surface density. Further, this head is basically designed for longitudinal recording, but it goes without saying that it can also be used for recording and reproduction of perpendicular media. For a perpendicular medium, particularly a perpendicular medium of the present invention having a structure having a NiFe soft magnetic film and a NiFeCo semi-hard magnetic film under the magnetic material, recording with a single pole head is preferred. However, since the longitudinal ring type head can be used in the evaluation of the medium noise characteristics of the present invention, this head is also used for the vertical medium of the present invention.
[0217]
The minimum recording cell size that can be recorded by this head is 1.3 μm × 0.1 μm, that is, the minimum recording cell is 1.3 × 10E5 (nm² ). In the regular magnetic particle medium of the present invention, since the magnetic particle interval is 12 to 60 nm, the number of magnetic particles contained in the minimum recording cell is 36 to 902.
[0218]
The recording / reproduction characteristics were measured under the following conditions: disk rotation speed: 1800 rpm, recording radius position: 22 mm, and head flying height of 25 nm. Recording was performed by changing the recording frequency, and the normalized medium noise at each frequency was examined. The recording current was a saturation recording current at which the carbalite erasure ratio was −40 dB or more (minus side). The normalized medium noise is a value obtained by dividing the value of the medium noise (Nm) integrated over the entire frequency band by the low-frequency signal output (S0), and is normalized per unit reproduction track width (1 μm). Value.
[0219]
FIG. 14 is a diagram illustrating an example of the result of measuring the relationship between the spatial recording frequency LD of the medium and the normalized medium noise. In FIG. 14, the symbols A, B, and C are the same as those used in FIG.
[0220]
In the medium of the invention measured in this example, the average particle size of the magnetic particles is 15 nm, the particle size dispersion is FWHM: 25%, the average distance between the particles is 18 nm, and the distribution of the interparticle distance distribution is FWHM: 50%. It has been adjusted to.
[0221]
FIG. 14 shows that the medium of the present invention has much lower noise than the conventional medium. This is because in the medium of the present invention, the dispersion of the particle diameter and the distance between the particles are suppressed and the magnetic particles are regularly arranged as compared with the conventional medium.
[0222]
As shown in FIG. 14, in the medium of the present invention, the noise is extremely low for both the medium using CoFe particles (curve A) and the medium using CoPt particles (curve B). The medium used (curve B) has lower noise than the medium (curve A) using CoFe particles. This is because, as shown in FIG. 10, the CoPt particle medium (curve B in FIG. 10) has a lower Mrt than the CoFe particle medium (curve A in FIG. 10), and is therefore more magnetized in the CoPt particle medium. This is probably because the transition width is narrow and sharper magnetization transition is formed.
[0223]
Example 9
FIG. 15 is a diagram showing the results of examining the relationship between the normalized medium noise and the average particle diameter D when the magnetic medium according to the present invention is recorded at a spatial recording frequency of 250 kfci.
[0224]
In the measurement of the medium of the present invention, the particle size dispersion is adjusted to 25% or less by FWHM, the average value of the interparticle distance is adjusted to the average particle size D + (1 to 3 nm), and the dispersion of the interparticle distance is adjusted to 50% or less by FWHM. I went about the media.
[0225]
From FIG. 15, when the spatial frequency is 250 kfci, that is, when the recording cell length is approximately 0.1 μm, the noise level is extremely low when the average particle size is about 25 nm or less, but at 25 nm or more, the noise level increases rapidly. I understand that
[0226]
When the relationship between the normalized medium noise and the spatial recording frequency was measured (measurement results are not shown), even in the regular magnetic particle medium of the present invention, the magnetic particle diameter is larger than ¼ of the recording cell length. The noise level has increased. From this result, it can be seen that the magnetic particle diameter is preferably ¼ or less of the recording cell length in order for the low noise effect to be remarkably exhibited in the medium of the present invention. The number of magnetic particles arranged in the track width direction is not limited at all unless the track width during recording is shorter than the shortest recording cell length. Therefore, it can be seen that the lower limit of the number of magnetic particles in the track width direction in the minimum recording cell is four. Actually, several tens or more of magnetic particles are arranged in the track width direction of the smallest recording cell.
[0227]
(Example 10)
FIG. 16 is a diagram showing the results of measuring the relationship among the particle size dispersion Dσ, the interparticle distance dispersion C′σ, and the medium noise of the magnetic particles. The measurement was performed by selecting the medium of the present invention in which the particle diameter was adjusted to 1/4 or less of the recording cell length and the interparticle distance was adjusted to the particle diameter + (1 to 3 nm) and the spatial recording frequency.
[0228]
In FIG. 16, the solid line is a summary of the measurement results for the regular magnetic particle medium of the present invention as contour lines of normalized medium noise. Also, the plot of FIG. 16 is a measurement result for a medium that has low noise among conventional media.
[0229]
From the results of FIG. 16, in order for the low noise effect to clearly appear in the medium of the present invention, the dispersion of the particle diameter is ± 20% or less (40% or less by FWHM), and the dispersion of the interparticle distance is ± 40% or less ( It can be seen that it is preferably 80% or less by FWHM. More preferably, the dispersion of the particle size is ± 10% or less (20% or less by FWHM), the dispersion of the distance between particles is ± 20% or less (40% or less by FWHM), and most preferably It can also be seen that the dispersion is ± 5% or less (10% or less by FWHM) and the dispersion of the interparticle distance is ± 10% or less (20% or less by FWHM).
[0230]
In FIG. 16, the noise of the conventional medium is higher than that of the medium of the present invention having the same amount of dispersion. This is because the present invention is based on the regular arrangement of magnetic particles and the dispersion shows the amount of deviation from the regular arrangement position, whereas the conventional medium basically has an irregular arrangement. Conceivable.
[0231]
The results shown in FIG. 16 are the results of measurement using a magnetic head that can be prototyped at the present time. Therefore, in the future, when measurement is performed using a magnetic head having a narrower head gap and a higher reproduction resolution, it is considered that the contour line of the normalized medium noise in FIG. 16 shifts to a larger value. Therefore, when recording using such a head, a magnetic medium in which the distribution of the particle diameter and the distance between the particles is set narrower should be used.
[0232]
<Preparation of regular nonmagnetic pores>
(Example 11)
Regular nonmagnetic pores were produced according to the above-described method for producing regular nonmagnetic pore media. CoPt and TbCo were used as magnetic materials. In the case of CoPt, the easy axis of magnetization was set according to the seed layer material, the seed layer thickness, the magnetic layer thickness, and the magnetic layer deposition conditions, as in the regular magnetic particle medium. When TbCo was used, a perpendicular magnetization film was formed without providing a seed layer.
[0233]
<Evaluation of regular non-magnetic pores>
Evaluation of the sample of the produced regular nonmagnetic pore medium was performed according to the evaluation of the regular magnetic particle medium. Evaluation of the microstructure of the regular non-magnetic pore medium is carried out by using the average pore diameter (P ′), the pore diameter distribution FWHM (P′σ), the average pore spacing (C), and the pore spacing distribution FWHM (C′σ). Used. The values of these parameters are obtained by adding the values due to process variation to the parameters of the self-organized mask obtained in Example 1, that is, the average pore diameter, the FWHM of the pore diameter distribution, the average pore spacing, and the FWHM of the pore spacing distribution. Value. The ranges of P ′, P′σ, C, and C′σ in this example are the average particle diameter D of the regular magnetic particle medium obtained in Example 3, the FWHMDσ of the particle size distribution, and the average distance C between the magnetic particles. It was almost the same as the range of FWHMC′σ in the distribution of the distance between magnetic particles.
[0234]
(Example 12)
First, MFM observation was performed for the evaluation of the domain wall. As a result of MFM observation, when TbCo is used for the magnetic material, the domain wall width depends on the composition ratio and the film thickness, but it is 10 to 20 nm except for the very vicinity of the composition ratio to be the compensation composition. It was. When CoPt was used for the magnetic material, the domain wall width was 7 to 13 nm. The width of the domain wall is narrower as the anisotropy energy is larger. For example, even CoPt has a domain wall width of 5 to 10 nm in the case of Co: 50 at%, and when SmCo having a large magnetic anisotropy is used, the domain wall is used. Is estimated to be 3-6 nm. Thus, it can be seen that the non-magnetic pore diameter in the present invention can be variously adjusted depending on the type of magnetic material used.
[0235]
(Example 13)
The relationship between the average spacing C 'between nonmagnetic pores and the product of residual magnetization and film thickness (Mrt) was measured. The measurement results showed an inverse correlation with the correlation between C and Mrt for the regular magnetic particle medium shown in FIG. That is, since the occupation ratio of the magnetic material increases as C ′ increases, Mrt increases. The relationship between Mrt and C ′ is as predicted from the calculation, and it has been found that appropriate adjustment of Mrt is easy even in a regular nonmagnetic pore medium.
[0236]
(Example 14)
The relationship between the average pore diameter P ′ of the nonmagnetic pores and the coercive force Hc was measured. The measurement results showed the same relationship as the relationship between the average particle diameter D and the coercive force Hc for the regular magnetic particle medium shown in FIG. That is, Hc decreased when P ′ was ½ or less of the domain wall width. This is because when the non-magnetic pore diameter is ½ or more of the domain wall width, the non-magnetic pore acts as a pinning site of the domain wall, so that large Hc is expressed. However, when the pore diameter is less than ½ of the domain wall width, This is because Hc is lowered because it moves freely without being pinned at the pore.
[0237]
(Example 15)
The relationship between the dispersion C′σ of the nonmagnetic pore interval and the ratio Da / P ′ of the activation size Da of the nonmagnetic pore and the average pore diameter P ′ was measured. As a result of the measurement, Da was very large compared to Da shown in FIG. This is because the value of Da is very large because the magnetic base material is connected across the entire film surface. From the measurement results, it has been clarified that the regular nonmagnetic pore medium of the present invention has no influence of thermal disturbance unlike the multi-particle or regular magnetic particle medium.
[0238]
(Example 16)
Nonmagnetic pore spacing dispersion C′σ and coercivity squareness ratio S^*The relationship between was measured. The measurement result shows that when the average pore diameter P ′ is small, as the pore diameter dispersion P′σ increases, as in the case of the regular magnetic particle medium shown in FIG.^*Decreased. This is because the pore diameter less than 1/2 of the domain wall width appears as the pore diameter dispersion P′σ increases. However, when the average pore diameter P ′ is relatively large, or when the pore diameter dispersion P′σ is sufficiently small, S^*Showed a value close to 1.
[0239]
(Example 17)
The relationship between the spatial recording frequency LD of the nonmagnetic pore medium and the normalized medium noise was measured using the MR head used for the evaluation of the regular magnetic particle medium. The measurement results are obtained when the pore diameter is adjusted to be 1/2 to 3 times the domain wall width, and the dispersion of the inter-pore spacing is adjusted to C′σ of ± 40% (80% in FWHM) or less. Shows low noise performance, similar to the measurement results for the regular magnetic particle medium of FIG.
[0240]
(Example 18)
FIG. 17 is a measurement result showing the relationship between the normalized medium noise at 250 kfci and the ratio P ′ / δ between the average pore diameter P ′ and the domain wall width δ for the nonmagnetic pore medium. The measurement was performed on a medium in which the pore spacing distribution FWHM (C′σ) was adjusted to 80% or less.
[0241]
From FIG. 17, it can be seen that when P ′ / δ is in the range of 1/2 to 3, the nonmagnetic pore medium according to the present invention exhibits good low noise performance. The reason why the noise rises when P ′ / δ is less than ½ is that the domain wall moves without being pinned by the pores, so that the position of the domain wall is not fixed and the magnetization transition portion is disturbed. Further, when P ′ / δ is larger than 3, the noise rises because the domain wall is pinned to the pore and the shape of the magnetization transition portion of the domain wall is good, but the pore diameter is too large, and therefore the noise rises. This is because the magnetic pore itself becomes a noise source.
[0242]
(Example 19)
FIG. 18 is a measurement result showing the relationship between the non-magnetic pore medium and the FWHM (C′σ) of the pore interval distribution with the normalized medium noise at 250 kfci. The measurement was performed on a non-magnetic medium in which P ′ / δ was adjusted to a range of 1/2 to 3.
[0243]
As shown in FIG. 18, when C′σ is 80% or less, the noise gradually increases as C′σ increases, and when C′σ exceeds 80%, the noise increases rapidly.
[0244]
As a result of SEM observation and MFM observation, when C′σ exceeds 80%, it depends on the pore diameter, but since the pores are connected to each other, the substantial pore diameter becomes excessive and the pore itself becomes a noise source. It was also found that the shape of the magnetization transition is disturbed because the domain walls are connected to each other between pores other than the pores arranged along the magnetization transition.
[0245]
【The invention's effect】
As described above in detail, according to the present invention, a magnetic recording medium capable of improving S / N and realizing high density and a manufacturing method thereof are provided. As a result, practical thermal disturbance resistance within the memory operating temperature and medium S / N required by the system without excessively miniaturizing the magnetic particles and without excessively increasing the anisotropic energy of the magnetic particles. It is possible to achieve both.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a regular magnetic particle medium according to the present invention.
FIG. 2 is a schematic view showing an example of a regular nonmagnetic pore medium according to the present invention.
FIG. 3 is a schematic cross-sectional view showing an example of an anodized barrier layer and porous alumite according to the present invention.
FIG. 4 is a schematic view showing a metal ring according to the present invention.
FIG. 5 is a process flow diagram showing an example of a manufacturing method according to the present invention.
FIG. 6 is a schematic diagram showing an example of a servo pattern of a magnetic disk according to the present invention.
FIG. 7 is a schematic view showing an example of an apparatus for producing a regular magnetic particle medium according to the present invention.
FIG. 8 is a view showing an SEM image of a prototype mask produced in an example of the present invention.
FIG. 9 is a view showing an SEM image of a regular magnetic particle medium experimentally produced in an example of the present invention.
FIG. 10 is a view showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 11 is a diagram showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 12 is a view showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 13 is a view showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 14 is a diagram showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 15 is a view showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 16 is a view showing a result of evaluating a regular magnetic particle medium in an example of the present invention.
FIG. 17 is a diagram showing a result of evaluating a regular nonmagnetic pore medium in an example of the present invention.
FIG. 18 is a diagram showing a result of evaluating a regular nonmagnetic pore medium in an example of the present invention.
[Explanation of symbols]
1 ... Board
2 ... Seed layer
3 ... Magnetic recording layer
4. Non-magnetic matrix
5. Magnetic particles
6 ... Protective layer
7 ... Minimum recording cell
8: Continuous magnetic film
9 ... Nonmagnetic pore
10 ... domain wall
11 ... Al plate
12 ... Barrier layer
13 ... Micropore
14 ... Porous anodized club
15 ... Metal ring
16 ... opening
20 ... Vacuum container
21 ... Induction heating type evaporation source
22 ... Heater
23 ... crucible
24 ... Shutter
25 ... RF power supply
26 ... Evaporated sample
27 ... Superconductor part
28 ... Cold head
29 ... Superconductor
30 ... Magnetic disk substrate
31 ... Magnetic field application coil
32 ... Magnetic field

Claims (6)

  A plurality of nonmagnetic pores arranged in a continuous magnetic film are provided, and a magnetization transition portion in the magnetic film is made up of domain walls connecting the nonmagnetic pores, and the average particle diameter of the nonmagnetic pores is 0.5 of the average width of the domain walls. A magnetic recording medium characterized in that it is three times as much. 2. The magnetic recording medium according to claim 1 , wherein the full width at half maximum of the distance distribution between the nearest pores in the smallest magnetic recording cell is ± 40% or less of the average distance between the nearest pores. (A) disposing a photosensitive layer on the continuous magnetic film;
(B) disposing a mask having openings arranged by self-assembly on the photosensitive layer;
(C) exposing the photosensitive layer by irradiating light or electrons from above the mask, developing the photosensitive layer, and forming a mask pattern in which a portion corresponding to the opening is left;
(D) forming a plurality of magnetic particles arranged in a continuous magnetic film according to the mask pattern;
And (e) a step of filling a nonmagnetic material between the magnetic particles. Each of the above steps includes a plurality of magnetic particles arranged in a continuous nonmagnetic film, and the number of particles arranged in the track length direction is at least four for the magnetic particles contained in the minimum magnetic recording cell, A magnetic recording medium in which the full width at half maximum of the distance distribution between the closest particles is ± 40% or less of the average distance between the closest particles, and the full width at half maximum of the particle size distribution is ± 20% or less of the average particle diameter. 4. The method of manufacturing a magnetic recording medium according to claim 3 , wherein the magnetic recording medium is manufactured. (A) disposing a mask having openings arranged by self-assembly on the continuous magnetic film;
(B) irradiating an ion beam from above the mask to form a plurality of holes arranged in the continuous magnetic film;
(C) filling the hole with a nonmagnetic material to form a nonmagnetic pore, and a method for manufacturing a magnetic recording medium. Each of the above steps includes a plurality of nonmagnetic pores arranged in a continuous magnetic film, and the magnetization transition portion in the magnetic film is made up of domain walls that connect the nonmagnetic pores. 6. The method according to claim 5 , wherein a magnetic recording medium having a width of 0.5 to 3 times is manufactured.

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