JP2004272957A

JP2004272957A - Perpendicular magnetic recording medium and its manufacturing method

Info

Publication number: JP2004272957A
Application number: JP2003059101A
Authority: JP
Inventors: Shunji Takenoiri; 俊司竹野入; Yasushi Sakai; 泰志酒井
Original assignee: Fuji Electric Device Technology Co Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 2003-03-05
Filing date: 2003-03-05
Publication date: 2004-09-30

Abstract

<P>PROBLEM TO BE SOLVED: To suppress magnetic domain walls in a soft magnetic backing layer against an external magnetic field which is larger than before. <P>SOLUTION: At least the following layers are formed in this order on a non-magnetic substrate 1: an anti-ferromagnetic pinned layer 2, a soft magnetic backing underlayer 3, a non-magnetic metal layer 4, a soft magnetic backing upper layer 5, a non-magnetic underlayer 6, a magnetic recording layer 7, and a protective film 8. Further, a liquid lubricant layer 9 is formed on them. The soft magnetic backing underlayers 3, the non-magnetic metal layer 4, and the soft magnetic backing upper layer 5 are laminated together to form a soft magnetic backing layer 10. The magnetizing direction of the soft magnetic backing underlayer 3 and the soft magnetic backing upper layer 5 having the non-magnetic metal layer 4 in-between is parallel with the film surface, and these layers 3 and 5 are ferromagnetically coupled together with 180° angle differences between them. By introducing an artificial AFC in addition to the conventional anti-ferromagnetic pinned layer, magnetic domain wall formation can be suppressed in the soft magnetic lining layer against the external magnetic field larger than before. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、垂直磁気記録媒体及びその製造方法に関し、より詳細には、各種磁気記録装置に搭載される垂直磁気記録媒体及びその製造方法に関する。
【０００２】
【従来の技術】
近年、磁気記録の高密度化を実現する技術として、従来の長手磁気記録方式に代えて、垂直磁気記録方式が注目されつつある。
【０００３】
垂直磁気記録媒体は、硬質磁性材料の磁気記録層と、この磁気記録層への記録に用いられる、磁気ヘッドが発生する磁束を集中させる役割を担う軟磁性材料の裏打ち層から構成されている。このような構造の垂直磁気記録媒体において問題となるノイズのひとつであるスパイクノイズは、裏打ち層である軟磁性層に形成された磁壁によるものであることが知られている。磁壁形成およびノイズ発生のメカニズムは以下の通りである。
【０００４】
すなわち、基体上に軟磁性層を形成すると、異方性が小さいため、軟磁性層内外周端部において静磁エネルギーを減少させるために還流磁区が発生する。実用程度の軟磁性層の膜厚では磁壁はブロッホ型となっていることから、磁壁内でスピンは膜厚方向に回転しているため磁壁上下端に垂直方向の磁極が現れることとなり、これがノイズの原因となる。そのため、垂直磁気記録媒体の低ノイズ化のためには、軟磁性層内外周端部における磁壁形成を阻止する必要がある。
【０００５】
従来、この軟磁性裏打ち層の磁壁の制御については、軟磁性層を非磁性層で分断して多層にする方法が提案されている（例えば、特許文献１，２参照）。しかしながら、この方法で軟磁性裏打ち層の特性を損なわずにスパイクノイズを完全に抑制するためには、軟磁性裏打ち層と非磁性層を交互に数層以上積層する必要があり、生産性に問題があった。
【０００６】
また他の方法として、軟磁性裏打ち層の上層や下層に反強磁性薄膜を形成し、交換結合を利用して磁化をピン止めする方法が提案されている。しかしながら、十分な交換結合磁界（Ｈｅｘ）を得るためには、成膜後に数分から数時間を要する熱処理をする必要があったり、また、熱処理無しでも比較的大きなＨｅｘが得られるＦｅＭｎやＩｒＭｎ等の不規則合金系反強磁性材料を使用した場合でも、軟磁性裏打ち層膜厚が厚いために十分な大きさの交換結合磁界が得られないなど、実用上解決すべき問題点が多くあるというのが現状であった。
【０００７】
【特許文献１】
特開平１−１２８２２６号公報
【０００８】
【特許文献２】
特開平７−８５４４２号公報
【０００９】
【非特許文献１】
Ｋ．Ｗ．Ｗｉｅｒｍａｎ，ｅｔａｌ．，ＩＥＥＥＴｒａｎｓ．Ｍａｇｎ．，ｖｏｌ．３７，Ｎｏ．６，ｐｐ．３９５６−３９５９，２００１
【００１０】
【発明が解決しようとする課題】
反強磁性膜を用いて軟磁性裏打ち層との交換結合により磁壁の制御を行なう方法は、交換結合が十分に得られた場合、軟磁性裏打ち層の磁壁形成を阻止することができ非常に効果的である。しかしながら、ブロッキング温度が高く、大きな交換結合磁界が得られるＰｔＭｎやＮｉＭｎなどの規則合金系反強磁性材料では、十分なＨｅｘを得るために成膜後に数分から数時間を要する加熱処理をする必要があり、大量生産を行なう場合に非常に不利であった。また、軟磁性裏打ち層の膜厚は、数十〜数百ｎｍ程度必要であると言われているが、Ｈｅｘが
【００１１】
【数１】

【００１２】
で決る（ここで、Ｊｅｘは交換結合エネルギー、Ｍｓは軟磁性層の飽和磁化、ｔは軟磁性層の膜厚）ことから、厚い軟磁性裏打ち層に対して大きなＨｅｘを得ることは難しい。そのため、熱処理を必要としないプロセスによってある程度大きなＨｅｘを確保するためには、軟磁性層と反強磁性層を何層も積層するなど、複雑かつコスト高な方法を使わざるを得なかった（例えば、非特許文献１参照）。
【００１３】
本発明は、このような問題に鑑みてなされたもので、その目的とするところは、従来のものよりも大きな外部磁場に対して軟磁性裏打ち層の磁壁形成の抑止を行なうことのできる垂直磁気記録媒体及びその製造方法を提供することにある。
【００１４】
【課題を解決するための手段】
本発明は、このような目的を達成するために、請求項１に記載の発明は、非磁性基体上に、少なくとも反強磁性ピン層と軟磁性裏打ち層と非磁性下地層と磁気記録層と保護膜とが順次積層されてなる垂直磁気記録媒体において、前記軟磁性裏打ち層が、軟磁性裏打ち下層と非磁性金属層と軟磁性裏打ち上層とが積層された構造をなしており、かつ、前記非磁性金属層を挟んだ前記軟磁性裏打ち下層及び前記軟磁性裏打ち上層の磁化の向きが、膜面に平行で互いに１８０°異なる向きを向いて反強磁性的に結合していることを特徴とする。
【００１５】
また、請求項２に記載の発明は、請求項１に記載の発明において、前記軟磁性裏打ち層が、膜厚１０ｎｍ以上、５００ｎｍ以下の軟磁性裏打ち下層と、膜厚０．１ｎｍ以上、５ｎｍ以下の非磁性金属層と、膜厚１０ｎｍ以上、５００ｎｍ以下の軟磁性裏打ち上層が積層された構造をなしていることを特徴とする。
【００１６】
また、請求項３に記載の発明は、請求項１又は２に記載の発明において、前記非磁性金属層を挟んだ前記軟磁性裏打ち下層の磁化が、反強磁性ピン層により一方向に固定されていることを特徴とする。
【００１７】
また、請求項４に記載の発明は、請求項１，２又は３に記載の発明において、前記非磁性金属層を挟んだ前記軟磁性裏打ち下層の膜厚及び飽和磁化をｔ_１及びＭ_１、前記軟磁性裏打ち上層の膜厚及び飽和磁化をｔ_２及びＭ_２とした時、ｔ_１×Ｍ_１＞ｔ_２×Ｍ_２を満たすように前記軟磁性裏打ち下層及び前記軟磁性裏打ち上層の膜厚及び飽和磁化が調整されていることを特徴とする。
【００１８】
また、請求項５に記載の発明は、請求項１乃至４いずれかに記載の発明において、前記非磁性金属層が、Ｃｕ，Ｒｕ，Ｒｈ，Ｐｄ，Ｒｅのいずれかの金属またはそれらの合金を主体とする材料からなることを特徴とする。
【００１９】
また、請求項６に記載の発明は、非磁性基体上に、少なくとも反強磁性ピン層と軟磁性裏打ち層と非磁性下地層と磁気記録層と保護膜とが順次積層されてなる垂直磁気記録媒体の製造方法において、前記軟磁性裏打ち層が、軟磁性裏打ち下層と非磁性金属層と軟磁性裏打ち上層とで積層されており、かつ、前記非磁性金属層を挟んだ前記軟磁性裏打ち下層及び前記軟磁性裏打ち上層の磁化の向きが、膜面に平行で互いに１８０°異なる向きを向いて反強磁性的に結合するように形成することを特徴とする。
【００２０】
また、請求項７に記載の発明は、請求項６に記載の発明において、前記軟磁性裏打ち層が、膜厚１０ｎｍ以上、５００ｎｍ以下の軟磁性裏打ち下層と、膜厚０．１ｎｍ以上、５ｎｍ以下の非磁性金属層と、膜厚１０ｎｍ以上、５００ｎｍ以下の軟磁性裏打ち上層とで積層することを特徴とする。
【００２１】
また、請求項８に記載の発明は、請求項６又は７に記載の発明において、前記非磁性金属層を挟んだ前記軟磁性裏打ち下層の磁化が、反強磁性ピン層により一方向に固定することを特徴とする。
【００２２】
また、請求項９に記載の発明は、請求項６，７又は８に記載の発明において、前記非磁性金属層を挟んだ前記軟磁性裏打ち下層の膜厚及び飽和磁化をｔ_１及びＭ_１、前記軟磁性裏打ち上層の膜厚及び飽和磁化をｔ_２及びＭ_２とした時、ｔ_１×Ｍ_１＞ｔ_２×Ｍ_２を満たすように前記軟磁性裏打ち下層及び前記軟磁性裏打ち上層の膜厚及び飽和磁化を調整することを特徴とする。
【００２３】
また、請求項１０に記載の発明は、請求項６乃至９いずれかに記載の発明において、前記非磁性金属層が、Ｃｕ，Ｒｕ，Ｒｈ，Ｐｄ，Ｒｅのいずれかの金属またはそれらの合金を主体とする材料からなることを特徴とする。
【００２４】
また、請求項１１に記載の発明は、請求項６乃至１０いずれかに記載の発明において、前記磁気記録層の成膜直後に磁場中急冷することを特徴とする。
【００２５】
また、請求項１２に記載の発明は、請求項６乃至１０いずれかに記載の発明において、前記磁気記録層の成膜直後に急加熱した後、磁場中急冷することを特徴とする。
【００２６】
また、請求項１３に記載の発明は、請求項１１又は１２に記載の発明において、前記磁場中急冷時に、基板の半径方向に平行に、少なくとも軟磁性裏打ち層の保磁力以上の数十〜千数百Ｇａｕｓｓの磁場を印加することを特徴とする。
【００２７】
また、請求項１４に記載の発明は、請求項１２に記載の発明において、前記磁気記録層の成膜直後の急加熱において、加熱温度を少なくとも反強磁性ピン層のブロッキング温度程度とすることを特徴とする。
【００２８】
このような構成により、極薄い非磁性金属層を軟磁性層中に設けることにより人工的に作り出す反強磁性的な結合（Ａｎｔｉｆｅｒｒｏｍａｇｎｅｔｉｃｃｏｕｐｌｉｎｇ；ＡＦＣ）と反強磁性膜を併用することで大きなＨｅｘを確保し、軟磁性裏打ち層の磁壁ノイズを抑制することができた。この時、
（１）軟磁性裏打ち層の磁化は膜面内にあり、磁化容易軸の向きが非磁性金属層を挟んでお互いに反平行になるように非磁性金属層の膜厚を調整する。非磁性金属層の膜厚の最適値は用いる材料により異なるが、概ね０．１ｎｍ以上、５ｎｍ以下であることが、結合力および生産性の観点から望ましい。
（２）（１）の非磁性金属層には、Ｃｕ，Ｒｕ，Ｒｈ，Ｐｄ，Ｒｅのいずれかの金属またはそれらの合金を主体とする材料を用いる。
（３）非磁性金属層を挟む軟磁性裏打ち層のうち、反強磁性層と結合している方を軟磁性裏打ち下層とし、その膜厚および飽和磁化（以下Ｍｓ）をｔ_１およびＭ_１と記述し、他方を軟磁性裏打ち上層としてその膜厚およびＭｓをｔ_２およびＭ_２と記述すると、軟磁性裏打ち下層及び軟磁性裏打ち上層は、
ｔ_１×Ｍ_１＞ｔ_２×Ｍ_２
なる関係を満たすように、膜厚、Ｍｓを選ぶことが望ましい。
【００２９】
【発明の実施の形態】
以下、図面を参照して本発明の実施形態について説明する。
図１は、本発明の垂直磁気記録媒体を説明するための断面模式図で、図中符号１は非磁性基体、２は反強磁性ピン層、３は軟磁性裏打ち下層、４は非磁性金属層、５は軟磁性裏打ち上層、６は非磁性下地層、７は磁気記録層、８は保護膜、９は液体潤滑材層、１０は軟磁性裏打ち層を示している。
【００３０】
本発明の垂直磁気記録媒体は、非磁性基体１上に、少なくとも反強磁性ピン層２と、軟磁性裏打ち下層３と、非磁性金属層４と、軟磁性裏打ち上層５と、非磁性下地層６と、磁気記録層７と、保護膜８とが順に形成された構造を有しており、さらにその上に液体潤滑材層９が形成されている。そして、軟磁性裏打ち層１０が、軟磁性裏打ち下層３と非磁性金属層４と軟磁性裏打ち上層５とが積層された構造をなしている。
【００３１】
非磁性基体１としては、通常の磁気記録媒体用に用いられる、ＮｉＰメッキを施したＡｌ合金や強化ガラス、結晶化ガラスなどを用いることができる。磁気記録層７は、少なくともＣｏとＣｒを含む合金の強磁性材料が好適に用いられ、その六方最密充填構造のｃ軸が膜面に垂直方向に配向していることが垂直磁気記録媒体として用いるために必要である。
【００３２】
軟磁性裏打ち上層５と磁気記録層７の間に、磁気記録層７の結晶配向性や結晶粒径を好ましく制御するために、例えば、ＴｉやＴｉＣｒ合金からなる非磁性下地層６を用いることもできる。保護膜８は、例えば、カーボンを主体とする薄膜が用いられる。また、液体潤滑材層９は、例えば、パーフルオロポリエーテル系の潤滑剤を用いることができる。
【００３３】
反強磁性ピン層２としては、ＰｔＭｎ，ＮｉＭｎ等の規則合金材料、ＦｅＭｎ，ＩｒＭｎ等の不規則合金材料、また、ＮｉＯ等の酸化物材料などを用いることができる。この反強磁性ピン層２の膜厚は、使用する材料や軟磁性層との組合せにより変化するが、おおむね１ｎｍ以上、１００ｎｍ以下程度あることが、生産性との兼ね合いから望ましい。
【００３４】
軟磁性裏打ち下層３及び軟磁性裏打ち上層５としては、結晶のＮｉＦｅ合金、センダスト（ＦｅＳｉＡｌ）合金など、また、非晶質のＣｏ合金であるＣｏＺｒＮｂなどを用いることができる。この軟磁性裏打ち下層３及び軟磁性裏打ち上層５の膜厚は、記録に使用する磁気ヘッドの構造や特性によって最適値が変化するが、その膜厚はそれぞれ１０ｎｍ以上、５００ｎｍ以下であることが、生産性との兼ね合いから望ましい。
【００３５】
軟磁性裏打ち下層３及び軟磁性裏打ち上層５の磁化容易軸は、基板面と平行で互いに１８０°異なる向きに結合している必要があるが、その理由は、非磁性金属層４を挟んだ軟磁性裏打ち下層３及び軟磁性裏打ち上層５同士の磁化が反平行に反強磁性的に結合している場合、その結合強度以下の外部磁界を印加しても磁化の向きが変化しない、すなわち、軟磁性層中に磁壁を生じず、スパイクノイズの発生を抑制できるからである。またこの時、軟磁性裏打ち下層３の膜厚及びＭｓをｔ_１，Ｍ_１とし、軟磁性裏打ち上層５の膜厚及びＭｓをｔ_２，Ｍ_２とすると、ｔ_１×Ｍ_１＞ｔ_２×Ｍ_２の関係を満たすようにｔ_１，Ｍ_１，ｔ_２，Ｍ_２を調整する。これは、ｔ_１×Ｍ_１＜ｔ_２×Ｍ_２とした場合、Ｈｅｘよりも小さい磁界でも軟磁性裏打ち層１０の磁化反転が起こり、スパイクノイズが発生するためである。ｔ_１×Ｍ_１＞ｔ_２×Ｍ_２とした場合には、Ｈｅｘよりも小さい外部磁場に対してスパイクノイズの発生を完全に抑制できる。
【００３６】
非磁性金属層４としては、Ｃｕ，Ｒｕ，Ｒｈ，Ｐｄ，Ｒｅのいずれかの金属またはそれらの合金を主体とする材料を用いることができる。この非磁性金属層４の膜厚は、軟磁性裏打ち下層３及び軟磁性裏打ち上層５の磁化容易軸が基板面と平行で互いに１８０°異なる方向を向きかつ強い結合強度が得られるよう適切に選ぶ必要があるが、強い外部磁場耐性を導くためには、少なくともその膜厚を０．１ｎｍ以上、５ｎｍ以下とする必要がある。理由は以下の通りである。
【００３７】
非磁性金属層４の膜厚を０ｎｍから次第に厚くしていくと、軟磁性裏打ち下層３及び軟磁性裏打ち上層５の磁化容易軸が基板面と平行で互いに同じ方向を向く結合（強磁性的な結合）と基板面と平行で互いに１８０°異なる方向を向く結合（反強磁性的な結合）が交互に現れる。例えば、非磁性金属層４としてＲｕを用いた場合、Ｒｕ膜厚が０〜０．３ｎｍの範囲では、軟磁性裏打ち下層３と軟磁性裏打ち上層５は強磁性的に結合し、０．３〜１．２ｎｍでは反強磁性的に結合する。更に膜厚を増加させると、１．２ｎｍ〜１．８ｎｍでは強磁性的に結合し、１．８〜３ｎｍでは反強磁性的に結合する。
【００３８】
このように、非磁性金属層４の膜厚増加に伴い強磁性的結合と反強磁性的結合が周期的に現れるため、適切な膜厚を選べば軟磁性裏打ち下層３及び軟磁性裏打ち上層５を反強磁性的に結合させることが可能であるが、その結合強度は非磁性金属層４の膜厚が増加するに従い減少する。結合強度が強いほど外部磁場に対する耐性が強くなることから、強い外部磁場耐性を得るためには適切な膜厚を選ぶ必要がある（適切な膜厚は非磁性金属層４に用いる材料により異なるが、ハードディスクドライブ中の浮揚磁場に対して十分な耐性を確保するためには、少なくともその膜厚を０．１ｎｍ以上、５ｎｍ以下とすることが必要となる。
【００３９】
軟磁性裏打ち下層３及び軟磁性裏打ち上層５の磁化容易軸は基体に対して半径方向に向いていることが望ましいが、このような磁化容易軸の配向は、反強磁性ピン層２、軟磁性裏打ち下層３及び軟磁性裏打ち上層５の成膜時に磁界を印加すること、あるいは形成後に反強磁性ピン層２のブロッキング温度（反強磁性ピン層２と軟磁性裏打ち下層３の結合が消失する温度）付近まで加熱した後磁場中で急冷することで制御可能である。磁場印加用マグネットには、ＮｄＦｅＢ，ＳｍＣｏ，アルニコ（ＦｅＮｉＡｌＣｏ），ＦｅＣｒＣｏなどの強磁性体が使用されることが望ましく、その発生磁場は、基板位置において軟磁性裏打ち層の保磁力以上であることが最低限必要であり、おおむね数十〜千数百Ｇａｕｓｓ程度であることが好ましい。
【００４０】
非磁性基体１の上に積層される各層は、垂直磁気記録媒体の分野で通常用いられる様々な成膜技術によって形成することが可能である。液体潤滑材層９を除く各層の形成には、例えば、ＤＣマグネトロンスパッタリング法、ＲＦマグネトロンスパッタリング法、真空蒸着法を用いることが出来る。また、液体潤滑材層９の形成には、例えば、ディップ法、スピンコート法を用いることができる。しかしながら、これらに限定されるものではない。
【００４１】
以下に本発明の垂直磁気記録媒体の具体的な実施例について説明する。
【００４２】
［実施例１］
非磁性基体１として表面が平滑な化学強化ガラス基板（例えば、ＨＯＹＡ社製Ｎ−１０ガラス基板）を用い、これを洗浄後にスパッタ装置内に導入し、反強磁性ピン層２を配向させるための下地層としてＮｉ_７８Ｆｅ_２２ターゲットを用いてＮｉＦｅ軟磁性下地層を５ｎｍ成膜した。次に、Ｉｒ_５０Ｍｎ_５０ターゲットを用いてＩｒＭｎ反強磁性ピン層２を１０ｎｍ成膜した。
【００４３】
引き続いて、Ｃｏ_８５Ｚｒ_１０Ｎｂ_５ターゲットを用いてＣｏＺｒＮｂ非晶質軟磁性裏打ち下層３を１１０ｎｍ、Ｒｕターゲットを用いてＲｕ非磁性金属層４を０．８ｎｍ、Ｃｏ_８５Ｚｒ_１０Ｎｂ_５ターゲットを用いてＣｏＺｒＮｂ非晶質軟磁性裏打ち上層５を９０ｎｍ、順次成膜した。ＮｉＦｅ軟磁性下地層〜ＣｏＺｒＮｂ軟磁性裏打ち上層５の成膜時には、磁化を配向させるために基板面と平行で半径方向に数１０〜数１００Ｇａｕｓｓ程度の磁場を印加する必要があるが、これにはターゲットのマグネトロンからのもれ磁場（約１００Ｇａｕｓｓ）を利用した。
【００４４】
次に、マグネット付き冷却チャンバを用いて、基板の表面位置での半径方向外向きの平均磁場が８００Ｇａｕｓｓのような磁場を印加しながらチャンバ中にＨｅを導入し、４秒間２０Ｔｏｒｒにて冷却を行った。この時、基板の表面温度は、３００℃から１５０℃まで低下した。
【００４５】
最後に、カーボンターゲットを用いてカーボンからなる保護膜８を１０ｎｍ成膜後、真空装置から取り出した。ヒータ加熱及び磁場中冷却を除くこれらの成膜は、すべてＡｒガス圧５ｍＴｏｒｒ下でＤＣマグネトロンスパッタリング法により行なった。その後、パーフルオロポリエーテルからなる液体潤滑材層９を２ｎｍディップ法により形成し、軟磁性裏打ち層１０のみを有する（磁気記録層を有しない）垂直磁気記録媒体を作製した。
【００４６】
［比較例１］
非磁性基体として表面が平滑な化学強化ガラス基板（例えば、ＨＯＹＡ社製Ｎ−１０ガラス基板）を用い、これを洗浄後にスパッタ装置内に導入し、反強磁性ピン層を配向させるための下地層としてＮｉ_７８Ｆｅ_２２ターゲットを用いてＮｉＦｅ軟磁性下地層を５ｎｍ成膜した。次に、Ｉｒ_５０Ｍｎ_５０ターゲットを用いてＩｒＭｎ反強磁性ピン層を１０ｎｍ成膜した。引き続いて、Ｃｏ_８５Ｚｒ_１ _０Ｎｂ_５ターゲットを用いてＣｏＺｒＮｂ非晶質軟磁性裏打ち層を２００ｎｍ成膜した。
【００４７】
以下、実施例１と全く同様に液体潤滑材層まで成膜し、軟磁性裏打ち層のみを有する（磁気記録層を有しない）垂直磁気記録媒体を作製した。
【００４８】
実施例１及び比較例１の媒体のヒステリシスループを振動試料磁力計（ＶＳＭ）を用いて測定した結果を、図２及び図３にそれぞれ示す。ヒステリシスループの中心がＭ軸（Ｈ＝０）からシフトした量が交換結合磁界Ｈｅｘであり、Ｈｅｘの大きさまでは外部磁場がかかっても磁化は反転しない、つまり、磁壁は発生せずスパイクノイズは生じない。このことから、Ｈｅｘが大きいほど外部磁場に対する耐性が高く、安定性の高い媒体であると言える。
【００４９】
図３に示した比較例１のヒステリシスが従来の反強磁性ピン層のみの時のループであるが、これに対して、図２に示した実施例１の反強磁性ピン層に人工的なＡＦＣを加えたヒステリシスは、中央部にシフトを持つ特徴的なループとなる。それぞれの場合において、Ｈｅｘは図中に矢印で表された大きさになる。表１に実施例１および比較例１の媒体のＨｅｘを示す。
【００５０】
【表１】

【００５１】
表１から明らかなように、実施例１では比較例１に比べてＨｅｘが約１．６倍になっている。このように反強磁性ピン層と人工的ＡＦＣを併用することにより、熱処理のような量産性を損ねるプロセスを加えることなく外部磁場に対する耐性を高めることができた。
【００５２】
［実施例２］
非磁性基体１として表面が平滑な化学強化ガラス基板（例えば、ＨＯＹＡ社製Ｎ−１０ガラス基板）を用い、これを洗浄後にスパッタ装置内に導入し、反強磁性ピン層２を配向させるための下地層としてＮｉ_７８Ｆｅ_２２ターゲットを用いてＮｉＦｅ軟磁性下地層を５ｎｍ成膜した。次に、Ｉｒ_５０Ｍｎ_５０ターゲットを用いてＩｒＭｎ反強磁性ピン層２を１０ｎｍ成膜した。
【００５３】
引き続いて、Ｃｏ_５９Ｆｅ_２２Ｎｉ_１３Ｂ_６ターゲットを用いてＣｏＦｅＮｉＢ軟磁性裏打ち下層３を７０ｎｍ、Ｒｕターゲットを用いてＲｕ非磁性金属層４を０．８ｎｍ、Ｃｏ_８７Ｚｒ_８Ｎｂ_５ターゲットを用いてＣｏＺｒＮｂ非晶質軟磁性裏打ち上層５を９０ｎｍ、順次成膜した。ＮｉＦｅ軟磁性下地層〜ＣｏＺｒＮｂ軟磁性裏打ち上層５の成膜時には、磁化を配向させるために基板面と平行で半径方向に数１０〜数１００Ｇａｕｓｓ程度の磁場を印加する必要があるが、これにはターゲットのマグネトロンからのもれ磁場（約１００Ｇａｕｓｓ）を利用した。
【００５４】
引き続いて、ランプヒータを用いて基板の表面温度が３００℃になるように加熱を行なった後、Ｔｉターゲットを用いてＴｉ下地層６を１０ｎｍ、引き続き、Ｃｏ_７０Ｃｒ_２０Ｐｔ_１０ターゲットを用いてＣｏＣｒＰｔ磁気記録層７を３０ｎｍを成膜した。
【００５５】
次に、マグネット付き冷却チャンバを用いて、基板の表面位置での半径方向外向きの平均磁場が８００Ｇａｕｓｓになるような磁場を印加しながらチャンバ中にＨｅを導入し、４秒間２０Ｔｏｒｒにて冷却を行った。この時、基板の表面温度は３００℃から１５０℃まで低下した。
【００５６】
最後に、カーボンターゲットを用いてカーボンからなる保護膜８を１０ｎｍを成膜後、真空装置から取り出した。ヒータ加熱および磁場中冷却を除くこれらの成膜は、すべてＡｒガス圧５ｍＴｏｒｒ下でＤＣマグネトロンスパッタリング法により行なった。その後、パーフルオロポリエーテルからなる液体潤滑材層９を２ｎｍディップ法により形成して垂直磁気記録媒体とした。
【００５７】
Ｃｏ_５９Ｆｅ_２２Ｎｉ_１３Ｂ_６のＭｓは１．６［Ｔ］であり、Ｃｏ_８７Ｚｒ_８Ｎｂ_５のＭｓは１．０［Ｔ］である。Ｃｏ_５９Ｆｅ_２２Ｎｉ_１３Ｂ_６軟磁性裏打ち下層のＭｓ及び膜厚をＭ_１，ｔ_１，Ｃｏ_８７Ｚｒ_８Ｎｂ_５軟磁性裏打ち上層のＭｓ及び膜厚をＭ_２，ｔ_２と記述すると、ｔ_１×Ｍ_１＝１１２［Ｔ・ｎｍ］、ｔ_２×Ｍ_２＝９０［Ｔ・ｎｍ］となり、ｔ_１×Ｍ_１＞ｔ_２×Ｍ_２の関係を満たしている。
【００５８】
［比較例２］
非磁性基体として表面が平滑な化学強化ガラス基板（例えば、ＨＯＹＡ社製Ｎ−１０ガラス基板）を用い、これを洗浄後にスパッタ装置内に導入し、反強磁性ピン層を配向させるための下地層としてＮｉ_７８Ｆｅ_２２ターゲットを用いてＮｉＦｅ軟磁性下地層を５ｎｍ成膜した。次に、Ｉｒ_５０Ｍｎ_５０ターゲットを用いてＩｒＭｎ反強磁性ピン層を１０ｍ成膜した。
【００５９】
引き続いて、Ｃｏ_５９Ｆｅ_２２Ｎｉ_１３Ｂ_６ターゲットを用いてＣｏＦｅＮｉＢ軟磁性裏打ち下層を７０ｎｍ、Ｃｏ_８５Ｚｒ_１０Ｎｂ_５ターゲットを用いてＣｏＺｒＮｂ非晶質軟磁性裏打ち層を９０ｎｍ成膜した。ＮｉＦｅ軟磁性下地層〜ＣｏＺｒＮｂ軟磁性裏打ち上層の成膜時には、磁化を配向させるために基板面と平行で半径方向に数１０〜数１００Ｇａｕｓｓ程度の磁場を印加する必要があるが、これには実施例１と同様にターゲットのマグネトロンからのもれ磁場（約１００Ｇａｕｓｓ）を利用した。以下、実施例１と全く同様に液体潤滑材層まで成膜して垂直磁気記録媒体とした。
【００６０】
表２に実施例２及び比較例２の媒体のＨｅｘをＶＳＭにより測定した結果を示す。
【００６１】
【表２】

【００６２】
表２から分かるように、実施例２では比較例２よりもＨｅｘが大きくなっており、外部磁場に対する耐性を高くすることができている。
【００６３】
次に、実施例２及び比較例２の垂直磁気記録媒体の軟磁性裏打ち層に形成される磁壁の有無を確認するために、スピンスタンドテスターを用いて、ＤＣイレーズした媒体の再生波形を観察することで、スパイクノイズの有無を調べた。なお、外部磁場に対する耐性を比較するため、ディスク下部に永久磁石を近付け、ディスク内周部付近に約３０［Ｏｅ］の磁場がかかるようにして測定している。
【００６４】
図４及び図５に、上述した方法により測定した、実施例２及び比較例２のスパイクノイズマップを示す。図中で白く見える点がスパイクノイズによる出力があることを示している。図４と図５を比較すると明らかであるが、図４に示す実施例２の垂直磁気記録媒体からはスパイクノイズが検出されなかったのに対し、図５に示す比較例２の垂直磁気記録媒体からは媒体全面に渡ってスパイクノイズが検出された。これは、約３０［Ｏｅ］の外部磁場に対し、実施例２の垂直磁気記録媒体では軟磁性裏打ち層の磁区形成による磁壁ノイズが発生していないのに対し、比較例２の垂直磁気記録媒体では磁区が形成し磁壁ノイズが発生していることを示している。
【００６５】
以上のように、本発明の垂直磁気記録媒体では、従来の垂直磁気記録媒体に比較して外部磁場耐性が向上していることが確認された。
【００６６】
【発明の効果】
以上説明したように本発明によれば、従来の反強磁性ピン層に加えて人工的な反強磁性的な結合（ＡＦＣ）を導入することで、従来よりも大きな外部磁場に対して軟磁性裏打ち層の磁壁形成の抑止を行なうことができる。また、成膜後に数分から数時間を要する加熱処理をする必要がなく、また、層構成も５ｎｍ以下の膜が１層増えるだけであるので、コストの増大もほとんどなく、かつ大量生産にも非常に適したものである。
【図面の簡単な説明】
【図１】本発明の垂直磁気記録媒体を説明するための断面模式図である。
【図２】実施例１の垂直磁気記録媒体のヒステリシスループを示す図である。
【図３】比較例１の垂直磁気記録媒体のヒステリシスループを示す図である。
【図４】実施例２の垂直磁気記録媒体のスパイクノイズマップを示す図である。
【図５】比較例２の垂直磁気記録媒体のスパイクノイズマップを示す図である。
【符号の説明】
１非磁性基体
２反強磁性ピン層
３軟磁性裏打ち下層
４非磁性金属層
５軟磁性裏打ち上層
６非磁性下地層
７磁気記録層
８保護膜
９液体潤滑材層
１０軟磁性裏打ち層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a perpendicular magnetic recording medium and a method for manufacturing the same, and more particularly, to a perpendicular magnetic recording medium mounted on various magnetic recording devices and a method for manufacturing the same.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a perpendicular magnetic recording method has been attracting attention as a technique for realizing high density magnetic recording, in place of the conventional longitudinal magnetic recording method.
[0003]
The perpendicular magnetic recording medium includes a magnetic recording layer made of a hard magnetic material and a backing layer made of a soft magnetic material used for recording on the magnetic recording layer and having a role of concentrating a magnetic flux generated by a magnetic head. It is known that spike noise, which is one of the problems in the perpendicular magnetic recording medium having such a structure, is caused by domain walls formed in a soft magnetic layer serving as a backing layer. The mechanism of domain wall formation and noise generation is as follows.
[0004]
That is, when the soft magnetic layer is formed on the substrate, since the anisotropy is small, return magnetic domains are generated at the inner and outer peripheral edge portions of the soft magnetic layer to reduce the magnetostatic energy. When the soft magnetic layer has a practical thickness, the domain wall is of a Bloch type, and the spins rotate in the direction of the film thickness in the domain wall, so that vertical magnetic poles appear at the upper and lower ends of the domain wall. Cause. Therefore, in order to reduce noise of the perpendicular magnetic recording medium, it is necessary to prevent domain walls from being formed at the inner and outer peripheral edges of the soft magnetic layer.
[0005]
Conventionally, for controlling the domain wall of the soft magnetic underlayer, a method has been proposed in which the soft magnetic layer is divided into non-magnetic layers to form a multilayer (for example, see Patent Documents 1 and 2). However, in order to completely suppress spike noise without impairing the characteristics of the soft magnetic backing layer in this method, it is necessary to alternately laminate several layers of the soft magnetic backing layer and the nonmagnetic layer, which is a problem in productivity. was there.
[0006]
As another method, a method has been proposed in which an antiferromagnetic thin film is formed on an upper layer or a lower layer of a soft magnetic underlayer, and magnetization is pinned using exchange coupling. However, in order to obtain a sufficient exchange coupling magnetic field (Hex), it is necessary to perform a heat treatment requiring several minutes to several hours after film formation, or to obtain a relatively large Hex without heat treatment, such as FeMn or IrMn. Even when an irregular alloy-based antiferromagnetic material is used, there are many problems that need to be solved in practice, such as not being able to obtain a sufficiently large exchange coupling magnetic field due to the large thickness of the soft magnetic backing layer. Was the current situation.
[0007]
[Patent Document 1]
JP-A-1-128226
[0008]
[Patent Document 2]
JP-A-7-85442
[0009]
[Non-patent document 1]
K. W. Wierman, et al. , IEEE Trans. Magn. , Vol. 37, no. 6, pp. 3956-3959, 2001
[0010]
[Problems to be solved by the invention]
The method of controlling the domain wall by exchange coupling with the soft magnetic backing layer using an antiferromagnetic film is very effective because when the exchange coupling is sufficiently obtained, the domain wall formation of the soft magnetic backing layer can be prevented. It is a target. However, in an ordered alloy-based antiferromagnetic material such as PtMn or NiMn having a high blocking temperature and a large exchange coupling magnetic field, it is necessary to perform a heat treatment requiring several minutes to several hours after film formation in order to obtain sufficient Hex. Yes, it is very disadvantageous for mass production. It is said that the thickness of the soft magnetic underlayer is required to be about several tens to several hundreds of nm.
[0011]
(Equation 1)

[0012]
(Where Jex is the exchange coupling energy, Ms is the saturation magnetization of the soft magnetic layer, and t is the thickness of the soft magnetic layer), it is difficult to obtain a large Hex for a thick soft magnetic underlayer. Therefore, in order to secure Hex to a certain degree by a process that does not require heat treatment, a complicated and expensive method has to be used, such as laminating a number of soft magnetic layers and antiferromagnetic layers (for example, , Non-Patent Document 1).
[0013]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a perpendicular magnetic field capable of suppressing the formation of a domain wall of a soft magnetic underlayer against an external magnetic field larger than that of the related art. It is to provide a recording medium and a manufacturing method thereof.
[0014]
[Means for Solving the Problems]
In order to achieve such an object, the present invention provides a method according to claim 1, wherein at least an antiferromagnetic pinned layer, a soft magnetic underlayer, a nonmagnetic underlayer, and a magnetic recording layer are formed on a nonmagnetic substrate. In a perpendicular magnetic recording medium in which a protective film is sequentially laminated, the soft magnetic underlayer has a structure in which a soft magnetic underlayer, a non-magnetic metal layer, and a soft magnetic underlayer are laminated, and The soft magnetic backing lower layer and the soft magnetic backing upper layer sandwiching the non-magnetic metal layer are antiferromagnetically coupled with each other in directions of magnetization parallel to the film surface and oriented in directions different from each other by 180 °. I do.
[0015]
The invention according to claim 2 is the invention according to claim 1, wherein the soft magnetic underlayer is a soft magnetic underlayer having a thickness of 10 nm or more and 500 nm or less, and a thickness of 0.1 nm or more and 5 nm or less. And a soft magnetic backing upper layer having a film thickness of 10 nm or more and 500 nm or less.
[0016]
According to a third aspect of the present invention, in the first or second aspect, the magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer is fixed in one direction by an antiferromagnetic pinned layer. It is characterized by having.
[0017]
According to a fourth aspect of the present invention, in the first, second, or third aspect, the thickness and saturation magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer are set to t.₁And M₁The thickness and saturation magnetization of the soft magnetic underlayer are represented by t₂And M₂And t₁× M₁> T₂× M₂The thickness and saturation magnetization of the lower soft magnetic underlayer and the upper soft magnetic underlayer are adjusted to satisfy the following conditions.
[0018]
According to a fifth aspect of the present invention, in the first aspect of the invention, the nonmagnetic metal layer is made of any one of Cu, Ru, Rh, Pd, and Re or an alloy thereof. It is characterized by being composed of a main material.
[0019]
According to a sixth aspect of the present invention, there is provided a perpendicular magnetic recording apparatus comprising at least an antiferromagnetic pinned layer, a soft magnetic underlayer, a nonmagnetic underlayer, a magnetic recording layer, and a protective film sequentially laminated on a nonmagnetic substrate. In the method for manufacturing a medium, the soft magnetic underlayer is laminated with a soft magnetic underlayer, a nonmagnetic metal layer, and a soft magnetic underlayer, and the soft magnetic underlayer sandwiching the nonmagnetic metal layer; The soft magnetic backing upper layer is formed so that the magnetization directions thereof are parallel to the film surface and are different from each other by 180 ° and are antiferromagnetically coupled.
[0020]
The invention according to claim 7 is the invention according to claim 6, wherein the soft magnetic underlayer has a soft magnetic underlayer having a thickness of 10 nm or more and 500 nm or less, and a thickness of 0.1 nm or more and 5 nm or less. And a soft magnetic backing upper layer having a film thickness of 10 nm or more and 500 nm or less.
[0021]
The invention according to claim 8 is the invention according to claim 6 or 7, wherein the magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer is fixed in one direction by an antiferromagnetic pinned layer. It is characterized by the following.
[0022]
According to a ninth aspect of the present invention, in the invention of the sixth, seventh or eighth aspect, the thickness and saturation magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer are set to t.₁And M₁The thickness and saturation magnetization of the soft magnetic underlayer are represented by t₂And M₂And t₁× M₁> T₂× M₂The thickness and saturation magnetization of the soft magnetic underlayer and the soft magnetic underlayer are adjusted so as to satisfy the following.
[0023]
The invention according to claim 10 is the invention according to any one of claims 6 to 9, wherein the nonmagnetic metal layer is made of any one of Cu, Ru, Rh, Pd, and Re or an alloy thereof. It is characterized by being composed of a main material.
[0024]
The invention according to claim 11 is characterized in that, in the invention according to any one of claims 6 to 10, the magnetic recording layer is rapidly cooled in a magnetic field immediately after the formation of the magnetic recording layer.
[0025]
According to a twelfth aspect of the present invention, in the invention according to any one of the sixth to tenth aspects, the magnetic recording layer is rapidly heated immediately after being formed, and then rapidly cooled in a magnetic field.
[0026]
The invention according to claim 13 is the invention according to claim 11 or 12, wherein, during the rapid cooling in the magnetic field, at least several tens to 1,000 of the coercive force of the soft magnetic backing layer or more in parallel to the radial direction of the substrate. It is characterized by applying a magnetic field of several hundred Gauss.
[0027]
According to a fourteenth aspect, in the twelfth aspect, in the rapid heating immediately after the formation of the magnetic recording layer, the heating temperature is at least about the blocking temperature of the antiferromagnetic pinned layer. Features.
[0028]
With such a configuration, a large Hex is obtained by using an antiferromagnetic coupling (AFC) artificially created by providing an extremely thin nonmagnetic metal layer in the soft magnetic layer and an antiferromagnetic film. As a result, the domain wall noise of the soft magnetic underlayer could be suppressed. At this time,
(1) The thickness of the nonmagnetic metal layer is adjusted so that the magnetization of the soft magnetic backing layer is in the film plane and the direction of the axis of easy magnetization is antiparallel to each other across the nonmagnetic metal layer. Although the optimum value of the film thickness of the nonmagnetic metal layer varies depending on the material used, it is preferably about 0.1 nm or more and 5 nm or less from the viewpoint of bonding force and productivity.
(2) For the non-magnetic metal layer of (1), a material mainly composed of any one of Cu, Ru, Rh, Pd, and Re or an alloy thereof is used.
(3) Among the soft magnetic underlayers sandwiching the nonmagnetic metal layer, the one that is coupled to the antiferromagnetic layer is defined as the soft magnetic underlayer, and its thickness and saturation magnetization (hereinafter Ms) are represented by t.₁And M₁And the thickness and Ms are t₂And M₂When described, the soft magnetic backing lower layer and the soft magnetic backing upper layer are:
t₁× M₁> T₂× M₂
It is desirable to select the film thickness and Ms so as to satisfy the following relationship.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view for explaining a perpendicular magnetic recording medium of the present invention. In the drawing, reference numeral 1 denotes a nonmagnetic substrate, 2 denotes an antiferromagnetic pinned layer, 3 denotes a soft magnetic underlayer, and 4 denotes a nonmagnetic metal. Reference numeral 5 denotes a soft magnetic underlayer, 6 denotes a nonmagnetic underlayer, 7 denotes a magnetic recording layer, 8 denotes a protective film, 9 denotes a liquid lubricant layer, and 10 denotes a soft magnetic underlayer.
[0030]
The perpendicular magnetic recording medium according to the present invention comprises, on a nonmagnetic substrate 1, at least an antiferromagnetic pinned layer 2, a soft magnetic backing lower layer 3, a nonmagnetic metal layer 4, a soft magnetic backing upper layer 5, and a nonmagnetic underlayer. 6, a magnetic recording layer 7, and a protective film 8 are formed in this order, and a liquid lubricant layer 9 is further formed thereon. The soft magnetic backing layer 10 has a structure in which a soft magnetic backing lower layer 3, a non-magnetic metal layer 4, and a soft magnetic backing upper layer 5 are laminated.
[0031]
As the nonmagnetic substrate 1, a NiP-plated Al alloy, tempered glass, crystallized glass, or the like, which is used for a normal magnetic recording medium, can be used. For the magnetic recording layer 7, a ferromagnetic material of an alloy containing at least Co and Cr is preferably used, and the c-axis of the hexagonal close-packed structure is oriented perpendicular to the film surface as a perpendicular magnetic recording medium. Needed to use.
[0032]
In order to preferably control the crystal orientation and crystal grain size of the magnetic recording layer 7, for example, a nonmagnetic underlayer 6 made of a Ti or TiCr alloy may be used between the soft magnetic underlayer 5 and the magnetic recording layer 7. it can. As the protective film 8, for example, a thin film mainly composed of carbon is used. Further, for the liquid lubricant layer 9, for example, a perfluoropolyether-based lubricant can be used.
[0033]
As the antiferromagnetic pinned layer 2, an ordered alloy material such as PtMn or NiMn, an irregular alloy material such as FeMn or IrMn, or an oxide material such as NiO can be used. The thickness of the antiferromagnetic pinned layer 2 varies depending on the material to be used and the combination with the soft magnetic layer. However, it is preferable that the thickness be approximately 1 nm or more and 100 nm or less from the viewpoint of productivity.
[0034]
As the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5, a crystalline NiFe alloy, a sendust (FeSiAl) alloy, or the like, or an amorphous Co alloy, CoZrNb, or the like can be used. The film thickness of the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5 varies optimally according to the structure and characteristics of the magnetic head used for recording, but the film thickness is preferably 10 nm or more and 500 nm or less. Desirable from the viewpoint of productivity.
[0035]
The axes of easy magnetization of the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5 need to be parallel to the substrate surface and bonded in directions different from each other by 180 ° because the soft magnetic backing layer 3 and the soft magnetic backing layer When the magnetizations of the magnetic underlayer 3 and the soft magnetic underlayer 5 are antiparallel and antiferromagnetically coupled, the direction of the magnetization does not change even when an external magnetic field less than the coupling strength is applied. This is because a magnetic domain wall is not generated in the magnetic layer, and generation of spike noise can be suppressed. At this time, the thickness and Ms of the soft magnetic underlayer 3 are set to t.₁, M₁And the thickness and Ms of the soft magnetic underlayer 5 are t₂, M₂Then t₁× M₁> T₂× M₂T to satisfy the relationship₁, M₁, T₂, M₂To adjust. This is t₁× M₁<T₂× M₂In this case, the magnetization reversal of the soft magnetic underlayer 10 occurs even with a magnetic field smaller than Hex, and spike noise occurs. t₁× M₁> T₂× M₂In this case, the generation of spike noise can be completely suppressed for an external magnetic field smaller than Hex.
[0036]
As the non-magnetic metal layer 4, a material mainly composed of any one of Cu, Ru, Rh, Pd, and Re or an alloy thereof can be used. The thickness of the non-magnetic metal layer 4 is appropriately selected such that the easy axes of magnetization of the soft magnetic underlayer 3 and the soft magnetic underlayer 5 are parallel to the substrate surface, are oriented in directions different from each other by 180 °, and a strong coupling strength is obtained. However, in order to induce strong external magnetic field resistance, it is necessary that the film thickness is at least 0.1 nm or more and 5 nm or less. The reason is as follows.
[0037]
When the thickness of the nonmagnetic metal layer 4 is gradually increased from 0 nm, coupling in which the axes of easy magnetization of the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5 are parallel to the substrate surface and are oriented in the same direction (ferromagnetic (Coupling) and coupling (antiferromagnetic coupling) parallel to the substrate surface and oriented in directions different from each other by 180 ° appear alternately. For example, when Ru is used as the nonmagnetic metal layer 4, when the Ru film thickness is in the range of 0 to 0.3 nm, the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5 are ferromagnetically coupled to each other. At 1.2 nm, coupling is antiferromagnetic. When the film thickness is further increased, the ferromagnetic coupling takes place between 1.2 nm and 1.8 nm, and the antiferromagnetic coupling takes place between 1.8 nm and 3 nm.
[0038]
As described above, since the ferromagnetic coupling and the antiferromagnetic coupling appear periodically as the thickness of the nonmagnetic metal layer 4 increases, if the appropriate film thickness is selected, the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5 can be selected. Can be antiferromagnetically coupled, but the coupling strength decreases as the thickness of the nonmagnetic metal layer 4 increases. The stronger the coupling strength, the stronger the resistance to the external magnetic field. Therefore, it is necessary to select an appropriate film thickness in order to obtain a strong external magnetic field resistance. In order to ensure sufficient resistance to a levitation magnetic field in a hard disk drive, it is necessary that the film thickness be at least 0.1 nm or more and 5 nm or less.
[0039]
It is desirable that the axes of easy magnetization of the soft magnetic backing lower layer 3 and the soft magnetic backing upper layer 5 be oriented in the radial direction with respect to the substrate. Applying a magnetic field during the formation of the backing lower layer 3 and the soft magnetic backing upper layer 5, or blocking temperature of the antiferromagnetic pinned layer 2 after formation (temperature at which the coupling between the antiferromagnetic pinned layer 2 and the soft magnetic backing lower layer 3 is lost) ) It can be controlled by heating to near and then rapidly cooling in a magnetic field. It is desirable that a ferromagnetic material such as NdFeB, SmCo, alnico (FeNiAlCo), or FeCrCo be used for the magnet for applying a magnetic field, and the generated magnetic field be greater than the coercive force of the soft magnetic underlayer at the substrate position. The minimum is necessary, and it is preferably about several tens to several hundreds Gauss.
[0040]
Each layer laminated on the non-magnetic substrate 1 can be formed by various film forming techniques usually used in the field of a perpendicular magnetic recording medium. The layers other than the liquid lubricant layer 9 can be formed by, for example, a DC magnetron sputtering method, an RF magnetron sputtering method, or a vacuum evaporation method. For forming the liquid lubricant layer 9, for example, a dipping method or a spin coating method can be used. However, it is not limited to these.
[0041]
Hereinafter, specific examples of the perpendicular magnetic recording medium of the present invention will be described.
[0042]
[Example 1]
A chemically strengthened glass substrate (for example, N-10 glass substrate manufactured by HOYA) having a smooth surface is used as the nonmagnetic substrate 1, introduced into a sputtering apparatus after cleaning, and used to orient the antiferromagnetic pin layer 2. Ni as base layer₇₈Fe₂₂A NiFe soft magnetic underlayer was formed to a thickness of 5 nm using a target. Next, Ir₅₀Mn₅₀An IrMn antiferromagnetic pinned layer 2 was formed to a thickness of 10 nm using a target.
[0043]
Subsequently, Co₈₅Zr₁₀Nb₅Using a target, the CoZrNb amorphous soft magnetic underlayer 3 was 110 nm, the Ru nonmagnetic metal layer 4 was 0.8 nm using a Ru target,₈₅Zr₁₀Nb₅Using a target, a CoZrNb amorphous soft magnetic backing upper layer 5 was sequentially formed to a thickness of 90 nm. When forming the NiFe soft magnetic underlayer to the CoZrNb soft magnetic underlayer 5, it is necessary to apply a magnetic field of about several tens to several hundreds Gauss in the radial direction in parallel with the substrate surface in order to orient the magnetization. The leakage magnetic field (about 100 Gauss) from the target magnetron was used.
[0044]
Next, using a cooling chamber with a magnet, He is introduced into the chamber while applying a magnetic field such as 800 Gauss in the radially outward average magnetic field at the surface position of the substrate, and cooling is performed at 20 Torr for 4 seconds. Was. At this time, the surface temperature of the substrate dropped from 300 ° C. to 150 ° C.
[0045]
Finally, a protective film 8 made of carbon was formed to a thickness of 10 nm using a carbon target and then taken out of the vacuum apparatus. All of these film formations except for the heater heating and the cooling in the magnetic field were performed by a DC magnetron sputtering method under an Ar gas pressure of 5 mTorr. Thereafter, a liquid lubricant layer 9 made of perfluoropolyether was formed by a 2 nm dipping method, and a perpendicular magnetic recording medium having only a soft magnetic underlayer 10 (having no magnetic recording layer) was manufactured.
[0046]
[Comparative Example 1]
A chemically strengthened glass substrate (for example, N-10 glass substrate manufactured by HOYA) having a smooth surface is used as the non-magnetic substrate, and after washing, introduced into a sputtering apparatus to orient an antiferromagnetic pin layer. As Ni₇₈Fe₂₂A NiFe soft magnetic underlayer was formed to a thickness of 5 nm using a target. Next, Ir₅₀Mn₅₀An IrMn antiferromagnetic pin layer was formed to a thickness of 10 nm using a target. Subsequently, Co₈₅Zr₁ ₀Nb₅Using a target, a CoZrNb amorphous soft magnetic underlayer was formed to a thickness of 200 nm.
[0047]
Thereafter, a liquid lubricant layer was formed in exactly the same manner as in Example 1 to produce a perpendicular magnetic recording medium having only a soft magnetic underlayer (not having a magnetic recording layer).
[0048]
The results of measuring the hysteresis loop of the media of Example 1 and Comparative Example 1 using a vibrating sample magnetometer (VSM) are shown in FIGS. 2 and 3, respectively. The amount by which the center of the hysteresis loop is shifted from the M axis (H = 0) is the exchange coupling magnetic field Hex, and the magnitude of Hex does not reverse the magnetization even when an external magnetic field is applied. That is, no domain wall is generated and spike noise is generated. Does not occur. From this, it can be said that the larger the Hex, the higher the resistance to an external magnetic field and the higher the stability of the medium.
[0049]
The hysteresis of Comparative Example 1 shown in FIG. 3 is a loop when only the conventional antiferromagnetic pinned layer is used. On the other hand, the antiferromagnetic pinned layer of Example 1 shown in FIG. The hysteresis with the addition of AFC results in a characteristic loop with a shift in the center. In each case, Hex has the size indicated by the arrow in the figure. Table 1 shows Hex of the media of Example 1 and Comparative Example 1.
[0050]
[Table 1]

[0051]
As is clear from Table 1, Hex is about 1.6 times greater in Example 1 than in Comparative Example 1. As described above, by using the antiferromagnetic pinned layer and the artificial AFC together, it was possible to increase the resistance to an external magnetic field without adding a process such as heat treatment that would impair mass productivity.
[0052]
[Example 2]
A chemically strengthened glass substrate (for example, N-10 glass substrate manufactured by HOYA) having a smooth surface is used as the nonmagnetic substrate 1, introduced into a sputtering apparatus after cleaning, and used to orient the antiferromagnetic pin layer 2. Ni as base layer₇₈Fe₂₂A NiFe soft magnetic underlayer was formed to a thickness of 5 nm using a target. Next, Ir₅₀Mn₅₀An IrMn antiferromagnetic pinned layer 2 was formed to a thickness of 10 nm using a target.
[0053]
Subsequently, Co₅₉Fe₂₂Ni_ThirteenB₆Using a target, the CoFeNiB soft magnetic underlayer 3 is 70 nm, a Ru nonmagnetic metal layer 4 is 0.8 nm using a Ru target,₈₇Zr₈Nb₅Using a target, a CoZrNb amorphous soft magnetic backing upper layer 5 was sequentially formed to a thickness of 90 nm. When forming the NiFe soft magnetic underlayer to the CoZrNb soft magnetic underlayer 5, it is necessary to apply a magnetic field of about several tens to several hundreds Gauss in the radial direction in parallel with the substrate surface in order to orient the magnetization. The leakage magnetic field (about 100 Gauss) from the target magnetron was used.
[0054]
Subsequently, after heating was performed using a lamp heater so that the surface temperature of the substrate was 300 ° C., the Ti underlayer 6 was formed to 10 nm using a Ti target,₇₀Cr₂₀Pt₁₀A CoCrPt magnetic recording layer 7 was formed to a thickness of 30 nm using a target.
[0055]
Next, using a cooling chamber with a magnet, He was introduced into the chamber while applying a magnetic field such that the average magnetic field outward in the radial direction at the surface of the substrate became 800 Gauss, and cooling was performed at 20 Torr for 4 seconds. went. At this time, the surface temperature of the substrate dropped from 300 ° C. to 150 ° C.
[0056]
Finally, a protective film 8 made of carbon was formed to a thickness of 10 nm using a carbon target, and then taken out of the vacuum apparatus. All of these film formations except for the heating of the heater and the cooling in the magnetic field were performed by a DC magnetron sputtering method under an Ar gas pressure of 5 mTorr. Thereafter, a liquid lubricant layer 9 made of perfluoropolyether was formed by a 2 nm dipping method to obtain a perpendicular magnetic recording medium.
[0057]
Co₅₉Fe₂₂Ni_ThirteenB₆Is 1.6 [T] and Cos₈₇Zr₈Nb₅Is 1.0 [T]. Co₅₉Fe₂₂Ni_ThirteenB₆Ms and thickness of the soft magnetic underlayer₁, T₁, Co₈₇Zr₈Nb₅Ms and thickness of the soft magnetic underlayer₂, T₂Is written as t₁× M₁= 112 [T · nm], t₂× M₂= 90 [T · nm], and t₁× M₁> T₂× M₂Meet the relationship.
[0058]
[Comparative Example 2]
A chemically strengthened glass substrate (for example, N-10 glass substrate manufactured by HOYA) having a smooth surface is used as the non-magnetic substrate, and after washing, introduced into a sputtering apparatus to orient the antiferromagnetic pin layer. As Ni₇₈Fe₂₂A NiFe soft magnetic underlayer was formed to a thickness of 5 nm using a target. Next, Ir₅₀Mn₅₀Using a target, an IrMn antiferromagnetic pinned layer was formed to a thickness of 10 m.
[0059]
Subsequently, Co₅₉Fe₂₂Ni_ThirteenB₆Using a target, the CoFeNiB soft magnetic underlayer was₈₅Zr₁₀Nb₅A 90 nm CoZrNb amorphous soft magnetic underlayer was formed using a target. When forming the NiFe soft magnetic underlayer to the CoZrNb soft magnetic backing upper layer, it is necessary to apply a magnetic field of about several tens to several hundreds Gauss in the radial direction in parallel with the substrate surface in order to orient the magnetization. As in Example 1, a leakage magnetic field (about 100 Gauss) from the target magnetron was used. Hereinafter, a film up to the liquid lubricant layer was formed in the same manner as in Example 1 to obtain a perpendicular magnetic recording medium.
[0060]
Table 2 shows the results of measuring Hex of the media of Example 2 and Comparative Example 2 by VSM.
[0061]
[Table 2]

[0062]
As can be seen from Table 2, Hex is higher in Example 2 than in Comparative Example 2, and resistance to an external magnetic field can be increased.
[0063]
Next, in order to confirm the presence or absence of a magnetic domain wall formed in the soft magnetic underlayer of the perpendicular magnetic recording media of Example 2 and Comparative Example 2, a reproduction waveform of the DC-erased medium is observed using a spin stand tester. In this way, the presence or absence of spike noise was examined. In order to compare the resistance to an external magnetic field, a permanent magnet was approached to the lower part of the disk, and the measurement was performed so that a magnetic field of about 30 [Oe] was applied near the inner peripheral part of the disk.
[0064]
FIGS. 4 and 5 show spike noise maps of Example 2 and Comparative Example 2 measured by the above-described method. A point that looks white in the figure indicates that there is an output due to spike noise. 4 and FIG. 5, it is clear that no spike noise was detected from the perpendicular magnetic recording medium of Example 2 shown in FIG. 4, whereas the perpendicular magnetic recording medium of Comparative Example 2 shown in FIG. From this, spike noise was detected over the entire surface of the medium. This is because the perpendicular magnetic recording medium of Example 2 did not generate domain wall noise due to the formation of magnetic domains in the soft magnetic underlayer with respect to an external magnetic field of about 30 [Oe], whereas the perpendicular magnetic recording medium of Comparative Example 2 did not. Indicates that a magnetic domain is formed and domain wall noise is generated.
[0065]
As described above, it has been confirmed that the perpendicular magnetic recording medium of the present invention has improved external magnetic field resistance as compared with the conventional perpendicular magnetic recording medium.
[0066]
【The invention's effect】
As described above, according to the present invention, by introducing an artificial antiferromagnetic coupling (AFC) in addition to the conventional antiferromagnetic pinned layer, the soft magnetic property against an external magnetic field larger than the conventional one can be improved. The formation of the domain wall of the backing layer can be suppressed. In addition, there is no need to perform a heat treatment requiring several minutes to several hours after the film formation, and the layer configuration has only one layer of 5 nm or less, so that there is almost no increase in cost and very large-scale production. It is suitable for
[Brief description of the drawings]
FIG. 1 is a schematic sectional view for explaining a perpendicular magnetic recording medium of the present invention.
FIG. 2 is a diagram illustrating a hysteresis loop of the perpendicular magnetic recording medium according to the first embodiment.
FIG. 3 is a diagram showing a hysteresis loop of the perpendicular magnetic recording medium of Comparative Example 1.
FIG. 4 is a diagram showing a spike noise map of the perpendicular magnetic recording medium of Example 2.
FIG. 5 is a diagram showing a spike noise map of the perpendicular magnetic recording medium of Comparative Example 2.
[Explanation of symbols]
1 Non-magnetic substrate
2 Antiferromagnetic pinned layer
3 Soft magnetic underlayer
4 Non-magnetic metal layer
5 Upper layer of soft magnetic backing
6 Non-magnetic underlayer
7 Magnetic recording layer
8 Protective film
9 Liquid lubricant layer
10 Soft magnetic underlayer

Claims

In a perpendicular magnetic recording medium in which at least an antiferromagnetic pinned layer, a soft magnetic underlayer, a nonmagnetic underlayer, a magnetic recording layer, and a protective film are sequentially laminated on a nonmagnetic substrate, the soft magnetic underlayer is A magnetic underlayer, a nonmagnetic metal layer, and a soft magnetic underlayer have a laminated structure, and the magnetization directions of the soft magnetic underlayer and the soft magnetic underlayer sandwiching the nonmagnetic metal layer are different. A perpendicular magnetic recording medium which is antiferromagnetically coupled to the film surface in directions different from each other by 180 °.

The soft magnetic underlayer has a soft magnetic underlayer having a thickness of 10 nm or more and 500 nm or less, a nonmagnetic metal layer having a thickness of 0.1 nm or more and 5 nm or less, and a soft magnetic underlayer having a thickness of 10 nm or more and 500 nm or less. 2. The perpendicular magnetic recording medium according to claim 1, wherein the perpendicular magnetic recording medium has a laminated structure.

3. The perpendicular magnetic recording medium according to claim 1, wherein the magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer is fixed in one direction by an antiferromagnetic pinned layer.

When the thickness and saturation magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer are t ₁ and M ₁ , and the thickness and saturation magnetization of the soft magnetic underlayer are t ₂ and M ₂ , t ₁ × 4. The perpendicular magnetic recording medium according to claim 1, wherein the thickness and saturation magnetization of the soft magnetic underlayer and the soft magnetic underlayer are adjusted so as to satisfy M ₁ > t ₂ × M _{2. 5.} Magnetic recording medium.

5. The perpendicular magnetic recording according to claim 1, wherein the nonmagnetic metal layer is made of a material mainly composed of any one of Cu, Ru, Rh, Pd, and Re or an alloy thereof. Medium.

The method of manufacturing a perpendicular magnetic recording medium, comprising a non-magnetic substrate and at least an antiferromagnetic pinned layer, a soft magnetic backing layer, a non-magnetic underlayer, a magnetic recording layer, and a protective film laminated in this order. Is laminated with a soft magnetic backing lower layer, a non-magnetic metal layer and a soft magnetic backing upper layer, and the direction of magnetization of the soft magnetic backing lower layer and the soft magnetic backing upper layer sandwiching the nonmagnetic metal layer, A method for manufacturing a perpendicular magnetic recording medium, wherein the perpendicular magnetic recording medium is formed so as to be antiferromagnetically coupled in directions different from each other by 180 ° parallel to a film surface.

The soft magnetic underlayer has a soft magnetic underlayer with a thickness of 10 nm or more and 500 nm or less, a nonmagnetic metal layer with a thickness of 0.1 nm or more and 5 nm or less, and a soft magnetic underlayer with a thickness of 10 nm or more and 500 nm or less. 7. The method for manufacturing a perpendicular magnetic recording medium according to claim 6, wherein the layers are laminated.

8. The method according to claim 6, wherein the magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer is fixed in one direction by an antiferromagnetic pinned layer.

When the thickness and saturation magnetization of the soft magnetic underlayer sandwiching the nonmagnetic metal layer are t ₁ and M ₁ , and the thickness and saturation magnetization of the soft magnetic underlayer are t ₂ and M ₂ , t ₁ × M _1> t ₂ × perpendicular magnetic recording according to claim 6, 7 or 8, characterized in that adjusting the soft magnetic backing layer and the said soft magnetic backing layer of the film thickness and the saturation magnetization so as to satisfy the M ₂ The method of manufacturing the medium.

10. The perpendicular magnetic recording according to claim 6, wherein the nonmagnetic metal layer is made of a material mainly composed of any one of Cu, Ru, Rh, Pd, and Re or an alloy thereof. The method of manufacturing the medium.

The method for manufacturing a perpendicular magnetic recording medium according to claim 6, wherein the magnetic recording layer is rapidly cooled in a magnetic field immediately after the formation of the magnetic recording layer.

The method for manufacturing a perpendicular magnetic recording medium according to claim 6, wherein the magnetic recording layer is rapidly heated immediately after being formed, and then rapidly cooled in a magnetic field.

The quenching in the magnetic field according to claim 11 or 12, wherein a magnetic field of several tens to several hundreds of Gauss at least equal to or higher than the coercive force of the soft magnetic underlayer is applied in parallel to the radial direction of the substrate. A method for manufacturing a magnetic recording medium.

13. The method for manufacturing a perpendicular magnetic recording medium according to claim 12, wherein in the rapid heating immediately after the formation of the magnetic recording layer, the heating temperature is at least about the blocking temperature of the antiferromagnetic pinned layer.