JP4034485B2 - Magnetic recording medium - Google Patents
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- JP4034485B2 JP4034485B2 JP34048599A JP34048599A JP4034485B2 JP 4034485 B2 JP4034485 B2 JP 4034485B2 JP 34048599 A JP34048599 A JP 34048599A JP 34048599 A JP34048599 A JP 34048599A JP 4034485 B2 JP4034485 B2 JP 4034485B2
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Description
【0001】
【発明の属する技術分野】
本発明は、磁気記録装置に使用される磁気記録媒体に関する。
【0002】
【従来の技術】
従来、高透磁率な軟磁性裏打ち層上に基板面に対して垂直異方性を有する磁気記録層を積層した垂直二層媒体において、軟磁性裏打ち層は、磁気記録層を磁化した磁気ヘッドからの記録磁界を水平方向に通して磁気ヘッド側へ還流させる磁気ヘッドの機能の一部を担っており、記録再生効率を向上させる役目を果たしている。
【0003】
しかしながら、磁気ディスク装置内では、主にスピンドルモータやボイスコイルモータから漏洩する浮遊磁界が発生しており、磁気ヘッドによる記録磁界と比較して極めて微弱ではあるものの、浮遊磁界が磁気ディスク内の軟磁性裏打ち層に吸収されて、磁気ヘッドの主磁極先端に集中することなどにより、垂直記録層の記録磁化を減磁あるいは消磁してしまうという問題があった。
【0004】
このような垂直二層媒体における減磁や消磁を防止するために、媒体外部からの浮遊磁界の影響を受けにくいような軟磁性裏打ち層の透磁率や膜厚などの条件が提案されている。
【0005】
また、垂直二層媒体の再生出力波形の均一性を改善する目的で、軟磁性裏打ち層の磁化容易軸を半径方向もしくは円周方向などに揃えるために、硬磁性層や反強磁性層を軟磁性裏打ち層の下部に設けた場合や多層構造の中間層として用いた場合には、磁壁の移動に制限が加わることから減磁や消磁を抑制する効果もあることが考えられる。
【0006】
しかしながら、軟磁性裏打ち層の透磁率や膜厚などの条件を限定することは、記録再生特性をも制限することになるという問題があり、しかも、そのような条件は材料や成膜条件に大きく依存し易いことから、実用上扱いにくいことが考えられる。また、軟磁性裏打ち層の磁化容易軸を揃えた場合でも、磁化容易方向では軟磁性層の透磁率が高いために、僅かな外部磁界で磁化状態が変動し、減磁や消磁を抑制する効果に関しては十分ではないという問題があった。
【0007】
【発明が解決しようとする課題】
本発明は、上記事情に鑑みてなされたもので、外部浮遊磁界による磁気記録層の記録磁化の減磁や消磁が抑制された磁気記録媒体を提供することを目的とする。
【0009】
【課題を解決するための手段】
本発明は、非磁性基板上に、軟磁性裏打ち層、及び該非磁性基板の面に対し垂直異方性を有する磁気記録層を積層した磁気記録媒体において、前記軟磁性裏打ち層は、二層の軟磁性層間に各々非磁性中間層を配置した構造をなし、外部磁界一定の大きさ以下のとき該非磁性中間層を介して隣接する軟磁性層が互いに反強磁性的に結合し、一定の大きさ以上の外部磁界を印加したとき該非磁性中間層を介して隣接する軟磁性層の磁化の向きが平行になることを特徴とする磁気記録媒体を提供する。
【0010】
【発明の実施の形態】
第1の発明に係る磁気記録媒体は、非磁性基板上に、軟磁性裏打ち層、及び該非磁性基板の面に対し垂直異方性を有する磁気記録層の積層を有し、この軟磁性裏打ち層は、膜面内方向に磁界を印加し、飽和磁化状態から逆向きの飽和状態に磁化を反転させたときの磁化曲線の微分値が2つのピークを有するという特性を有する。
【0011】
また、第2の発明に係る磁気記録媒体は、第1の発明に係る磁気記録媒体の構成の一例を示すもので、非磁性基板上に、軟磁性裏打ち層、及び該非磁性基板の面に対し垂直異方性を有する磁気記録層の積層を有し、軟磁性裏打ち層は、複数の軟磁性層間に各々非磁性中間層を配置した多層構造をなし、一定の大きさ以下の外部磁界では該非磁性中間層を介して隣接する軟磁性層が互いに反強磁性的に結合し、一定の大きさ以上の外部磁界では隣接する軟磁性層の磁化の向きが平行になるという特性を有する。
【0012】
第1の発明によれば、その磁化を反転させたときの磁化曲線の微分値が2つのピークを持つような軟磁性裏打ち層を用いることにより、本来、透磁率が高く僅かな浮遊磁界に対しても磁化状態が大きく変動しやすい裏打ち層において、2つのピーク間の外部磁界が0となる近傍のみの磁界に対する磁化状態の変化を小さく抑えることができる。これにより、外部浮遊磁界による垂直記録層の記録磁化の減磁や消磁を防止することができる。
【0013】
好ましくは、この2つのピークが現れる範囲を記録磁界未満とすることにより、記録磁界を印加したとき、裏打ち層が磁気ヘッドからの磁束を還流させることが可能となる。また、好ましくは、この2つのピークが現れる範囲をおおよそ浮遊磁界程度の外部磁界になるよう調整することにより、軟磁性層の磁化状態の変化を抑制して外部浮遊磁界による垂直記録層の記録磁化の減磁や消磁を防止することができる。
【0014】
また、第2の発明によれば、軟磁性裏打ち層を非磁性中間層との多層構造として一定の大きさ以下の外部磁界では隣接する軟磁性層を互いに反強磁性的に結合させることにより、その飽和磁化状態から逆向きの飽和状態にさせたときの磁化曲線の微分値が2つのピークを持つような軟磁性裏打ち層が得られる。これにより、外部浮遊磁界による垂直記録層の記録磁化の減磁や消磁を防止することができる。
【0015】
また、この2つのピークが現れる範囲を記録磁界未満であり、おおよそ浮遊磁界程度の外部磁界になるよう調整すると、隣接する軟磁性層を、記録磁界を印加した場合には、互いに磁化の向きが平行になり、記録磁界未満の浮遊磁界程度では、反強磁的に結合させることができるので、記録に支障なく、外部浮遊磁界による影響を防ぐことができる。このように軟磁性裏打ち層の磁化状態の変化を抑制することにより外部浮遊磁界による垂直記録層の記録磁化の減磁や消磁を防止することができる。
【0016】
第2の発明において、各軟磁性層の磁気モーメントはほぼ同一であることが好ましく、軟磁性層の磁気モーメントが異なると、磁化曲線の対称性が崩れ、残留磁化の値が大きくなり、軟磁性裏打ち層全体としての漏れ磁束が生じやすくなる。
【0017】
図1に、第1の発明に係る磁気記録媒体の一例の構成を表す図を示す。
【0018】
図示するように、この記録媒体は、非磁性ガラス基板1上に、軟磁性裏打ち層2及び磁気記録層3を積層した構造を有する。
【0019】
また、図2に、第2の発明に係る磁気記録媒体の一例の構成を表す図を示す。
【0020】
図示するように、この記録媒体は、非磁性ガラス基板1上に、第1の軟磁性層12、非磁性中間層13、及び第2の軟磁性層14、磁気記録層15を積層した構造を有する。
【0021】
第2の発明に係る磁気記録媒体のように、強磁性遷移金属と非磁性金属を多層化した薄膜においては、非磁性層の厚さに対して強磁性層間の強磁性、反強磁性的結合が周期的に現れることが見出されており、多くの多層膜((Fe,Co)/(V,Cr,Cu,Mo,Ru,Rh,Re))において、隣接する強磁性層が互いに反強磁性的(または強磁性的)に結合する周期は約1nmであることが知られている( A. Heinlich and J. A. C. Bland, Ultrathin Magnetic Structures II, Springer-Verlag(1994) )。また、このような反強磁性的結合すなわち隣接する強磁性層の磁化が反平行となる状態が最初に現れる非磁性層厚は、おおよそ1nm以下付近であり、その後、約1nm間隔での非磁性層厚の増加に伴って、反強磁性的結合は弱くなっていくことから、非磁性層を適当な厚さにすることで結合の強さを選ぶことができる。したがって、ヘッドから印加する記録磁界程度の外部磁界に対しては磁化が平行となるように結合強度を、すなわち非磁性層厚を選ぶことにより、記録時にヘッドから磁界を印加した場合には、優れた軟磁性裏打ち層として機能する一方で、記録時以外の浮遊磁界に対しては、磁化状態の変化が抑制されることから、記録に支障なく外部浮遊磁界による磁気記録層の記録磁化の減磁や消磁を防止することができる。非磁性中間層厚は0.5nm以上1.5nm未満が好ましい。
【0023】
本発明の磁気記録媒体においては、軟磁性裏打ち層の磁化容易軸を円周方向または半径方向に揃えるため、非磁性基板と軟磁性裏打ち層の間にFeMnなどの反強磁性層やCoSmなどの硬磁性層を形成しても良い。
【0024】
軟磁性裏打ち層と垂直記録層との間には、Ru、Ti、非磁性CoCr合金などの非磁性下地層を形成しても良い。
【0025】
軟磁性層の材料には、センダストの他、FeSi合金、FeCo合金や、パーマロイなどのNiFe合金、CoZrNbなどのCoZr合金などの高透磁率を有する軟磁性合金を使用することができる。なお、軟磁性裏打ち層を多層化する上では、軟磁性層の材料は、非磁性中間層と結晶構造が類似しており、格子定数も近いものや、非晶質材料が好ましいと考えられる。
【0026】
非磁性中間層としては、V,Cr,Cu,Mo,Ru,Rh,及びReを使用することが好ましく、さらに好ましくはRuである。
【0027】
軟磁性層と非磁性中間層との組み合わせとしては、センダストやFeSi及びFeCo合金に対しては、V,Cr,Mo,及びNiFe合金に対してはCu,Ru,Rh,及びReが好ましいと考えられ、CoZrNb等の非晶質材料は、どのような非磁性中間層材料に対しても好ましいと考えられる。
【0028】
垂直異方性を有する磁気記録層に使用される磁性材料としては、CoCrPt、CoCrTaなどのCoCr合金の他、CoPtOやCoPtBなどのCoPt合金などがあげられる。
【0029】
本発明の磁気記録媒体では、上述のような軟磁性裏打ち層上に、直接または非磁性下地層を介して基板に対して垂直異方性を有する磁気記録層が積層される。
【0030】
【実施例】
まず、本発明に係る軟磁性裏打ち層の磁気特性について調べた。
【0031】
非磁性基板には、2.5インチ磁気ディスクの標準仕様を満たすガラス基板を用い、各層の作製はすべてDCマグネトロンスパッタリングにより行った。
【0032】
はじめに、非磁性基板上に、第1軟磁性層として厚さ27nm程度のセンダストを形成した。
【0033】
次に、非磁性中間層として厚さ1nm程度のRu層を形成した。
【0034】
その上に、再び第2軟磁性層として厚さ27nm程度のセンダストを積層した。この3層構造の軟磁性裏打ち層上に、保護層として10nmのCを形成した。
【0035】
また、比較例として、非磁性中間層であるRu層の厚さを1.5nm程度とした以外は同様にして積層を行った。
【0036】
得られた軟磁性裏打ち層について、振動試料型磁力計(VSM)による膜面内方向に磁界を印加したときの磁化曲線と、磁化曲線を磁界について微分した結果を表すグラフ図をそれぞれ図3および図4に示す。また、図5および図6はそれぞれRu層の厚さを1.5nm程度とした場合の磁化曲線と微分値である。なお、図4及び図6中、実線は印加磁界を負から正へ、点線は磁界を正から負へ変化させた場合に対応している。
【0037】
図3に示すように、本発明に用いられる軟磁性裏打ち層の磁化曲線は、非磁性中間層を適当な厚さに設定することにより上下軟磁性層が反強磁性的に結合することを示しており、磁界0近傍において上下軟磁性層の磁化が共に磁界と同じ向きに揃おうとする変化が抑制されることから、主に磁界0近傍のみの磁界に対する磁化の変化が小さく抑えられていることが分かる。
【0038】
ここで、印加磁界が0近傍における磁化の値が小さく抑えられ、磁化曲線がおおよそ原点について対称となっているのは、非磁性中間層上下の磁気モーメントが等しいためであり、上下の軟磁性層の磁気モーメントが異なると、磁化曲線の対称性が崩れ、残留磁化の値が大きくなり、軟磁性裏打ち層全体としての漏れ磁束が生じやすくなることから、上下軟磁性層の磁気モーメントはほぼ同一であることが望ましい。
【0039】
これに対し、比較例では、図5に示すように、Ru層の厚さを1.5nm程度とした場合の軟磁性裏打ち層の磁化曲線は、非磁性中間層厚が上下の軟磁性層を反強磁性的に結合させるのに適当な厚さではないために、基本的には一般的な軟磁性層のそれと同様であり、透磁率が高いことから20Oe程度の外部磁界を印加しただけでも磁化状態が大きく変動することが分かる。
【0040】
図5の磁化曲線から、Ru層の厚さを1.5nmとした場合には、非磁性中間層上下の軟磁性層は強磁性的に結合しているものと考えられる。このRu層厚よりも薄いときに強磁性的に結合する層厚は、その周期性から0.5nm未満と予想され、反強磁性的な結合が現れるRu層厚は0.5nm以上1.5nm未満の範囲内であり、外部浮遊磁界に対する磁化状態の変化を最も効果的に抑制できるRu中間層厚はこの範囲内にあると考えられる。
【0041】
図3と図5におけるこのような磁化曲線の変化の違いは、微分後の曲線においてはピークの数の違いとして見ることができる。すなわち、印加磁界を負から正または正から負へと変化させて磁化を反転させたとき、比較例においては図6に示すようにピークは一つであるのに対し、実施例においては図4に示すように二つのピークを見ることができる。ピークの位置は実線と点線では20Oe程度異なっているが、おおよそこれらのピークをとる磁界の大きさを閾値とすると、実施例においては磁界が0から閾値までの間に磁化状態の変化を抑制した領域が存在するのに対し、比較例においてはそのような領域は存在していないことが分かる。
【0042】
上述の軟磁性裏打ち層上に、DCマグネトロンスパッタリング法により、非磁性下地層として厚さ20nmのRu層を形成した。
【0043】
次に、非磁性下地層上にCoPtCrO磁性層を形成した。
【0044】
その後、保護層として、10nmのC層を形成した。
【0045】
得られた磁気記録媒体について、ヘルムホルツコイルにより発生させた外部磁界中で磁気抵抗効果を利用したヘッドにより再生信号出力の安定性の評価を行った。
【0046】
その結果、20Oeの外部磁界を印加した場合に、比較例においては再生出力の減少や再生波形の変動が観察されたのに対し、実施例においては、そのような変化は観察されなかった。このような20Oeの外部磁界に対する変化の違いは上述の磁化曲線と良く対応している。
【0047】
本発明に関わる垂直磁気記録媒体は、実施例として挙げたような軟磁性裏打ち層上に、直接または非磁性下地層を介して垂直記録層を積層した構成を有する。
【0048】
この磁気記録媒体における軟磁性裏打ち層は、上述の閥値を磁気ヘッドによる記録磁界より小さく、かつ磁気ディスク装置内の浮遊磁界程度に設定することにより、記録磁界を磁気ヘッド側へ還流させる機能を果たしながら、浮遊磁界に対して磁化状態の変動を十分に抑制したものとなる。また、軟磁性裏打ち層を実施例のような多層構造とすることにより、透磁率や膜厚などの設計の自由度を損ねることなく、外部浮遊磁界による垂直記録層の記録磁化の減磁や消磁を十分に防止した垂直磁気記録媒体を得ることができる。
【0049】
なお、上記実施例では、いずれも非磁性基板としてガラス基板を用いているが、Al系の合金基板あるいは表面が酸化したSi単結晶基板、セラミックス、プラスチックなども使用することができる。さらに、それら非磁性基板表面にNiP合金などのメッキが施されている場合でも同様の効果が期待される。また、軟磁性裏打ち層の成膜法としてスパッタリング法のみを取り上げたが、真空蒸着法などでも同様の効果を得ることができる。
【0050】
【発明の効果】
本発明の磁気記録媒体によれば、外部浮遊磁界による影響を受けにくいため、磁気記録層の記録磁化の減磁や消磁を防止することができる。
【図面の簡単な説明】
【図1】 第1の発明に係る磁気記録媒体の一例を表す概略図
【図2】 第2の発明に係る磁気記録媒体の一例を表す概略図
【図3】 本発明に用いられる軟磁性裏打ち層の一例の磁化曲線を表すグラフ図
【図4】 図3の微分値を表すグラフ図
【図5】 比較のための軟磁性裏打ち層の磁化曲線を表すグラフ図
【図6】 図5の微分値を表すグラフ図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium used in a magnetic recording apparatus.
[0002]
[Prior art]
Conventionally, in a perpendicular two-layer medium in which a magnetic recording layer having perpendicular anisotropy with respect to a substrate surface is laminated on a soft magnetic backing layer having a high magnetic permeability, the soft magnetic backing layer is formed from a magnetic head that has magnetized the magnetic recording layer. It plays a part of the function of the magnetic head that causes the recording magnetic field to flow back to the magnetic head side in the horizontal direction, and plays the role of improving the recording and reproducing efficiency.
[0003]
However, a stray magnetic field that leaks mainly from the spindle motor and voice coil motor is generated in the magnetic disk device, and the stray magnetic field is soft compared with the recording magnetic field by the magnetic head, but the stray magnetic field is soft in the magnetic disk. There is a problem that the recording magnetization of the perpendicular recording layer is demagnetized or demagnetized by being absorbed by the magnetic backing layer and concentrating on the tip of the main pole of the magnetic head.
[0004]
In order to prevent such demagnetization and demagnetization in the perpendicular double-layer medium, conditions such as the permeability and film thickness of the soft magnetic underlayer that are not easily affected by the stray magnetic field from the outside of the medium have been proposed.
[0005]
In addition, in order to improve the uniformity of the reproduced output waveform of the perpendicular double-layer medium, the hard magnetic layer and the antiferromagnetic layer are softened so that the easy axis of magnetization of the soft magnetic underlayer is aligned in the radial direction or the circumferential direction. When it is provided under the magnetic backing layer or used as an intermediate layer having a multilayer structure, it is considered that there is an effect of suppressing demagnetization and demagnetization because the movement of the domain wall is restricted.
[0006]
However, limiting the conditions such as the magnetic permeability and film thickness of the soft magnetic underlayer has the problem of limiting the recording / reproducing characteristics, and such conditions largely depend on the material and film forming conditions. Because it is easy to depend on, it can be difficult to handle practically. In addition, even when the easy magnetization axis of the soft magnetic underlayer is aligned, the magnetic state of the soft magnetic layer is high in the easy magnetization direction, so that the magnetization state fluctuates with a slight external magnetic field, thereby suppressing demagnetization and demagnetization. There was a problem that was not enough.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic recording medium in which demagnetization and demagnetization of recording magnetization of a magnetic recording layer due to an external stray magnetic field is suppressed.
[0009]
[Means for Solving the Problems]
The present invention provides a magnetic recording medium in which a soft magnetic backing layer and a magnetic recording layer having perpendicular anisotropy with respect to the surface of the nonmagnetic substrate are laminated on a nonmagnetic substrate, wherein the soft magnetic backing layer comprises two layers . It has a structure in which nonmagnetic intermediate layers are arranged between soft magnetic layers. When the external magnetic field is below a certain level, adjacent soft magnetic layers are antiferromagnetically coupled to each other through the nonmagnetic intermediate layer, and have a certain size. Provided is a magnetic recording medium characterized in that the magnetization directions of adjacent soft magnetic layers are parallel to each other through the nonmagnetic intermediate layer when an external magnetic field of more than 10 mm is applied.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
A magnetic recording medium according to a first aspect of the present invention has a soft magnetic backing layer and a magnetic recording layer having a perpendicular anisotropy with respect to the surface of the nonmagnetic substrate on a nonmagnetic substrate, and the soft magnetic backing layer Has a characteristic that the differential value of the magnetization curve when the magnetic field is applied in the in-plane direction and the magnetization is reversed from the saturated magnetization state to the opposite saturation state has two peaks.
[0011]
The magnetic recording medium according to the second invention is an example of the configuration of the magnetic recording medium according to the first invention. The soft magnetic backing layer and the surface of the nonmagnetic substrate on the nonmagnetic substrate. The soft magnetic backing layer has a multilayer structure in which a nonmagnetic intermediate layer is arranged between a plurality of soft magnetic layers, and the nonmagnetic intermediate layer has a perpendicular magnetic anisotropy layer. Adjacent soft magnetic layers are antiferromagnetically coupled to each other through the magnetic intermediate layer, and the magnetization direction of the adjacent soft magnetic layers becomes parallel in an external magnetic field of a certain magnitude or more.
[0012]
According to the first invention, by using the soft magnetic underlayer having a differential value of the magnetization curve when the magnetization is reversed with two peaks, the magnetic permeability is originally high with respect to a slight stray magnetic field. However, in the backing layer in which the magnetization state is likely to fluctuate greatly, the change in the magnetization state with respect to the magnetic field only in the vicinity where the external magnetic field between the two peaks becomes zero can be suppressed to a small level. Thereby, demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer due to the external stray magnetic field can be prevented.
[0013]
Preferably, by the extent to which the two peaks appear lower than the recording magnetic field, upon application of a recording magnetic field, the backing layer is that Do allow Rukoto refluxed magnetic flux from the magnetic head. Preferably, by adjusting the range in which these two peaks appear to be an external magnetic field of approximately the stray magnetic field, the change in the magnetization state of the soft magnetic layer is suppressed and the recording magnetization of the perpendicular recording layer by the external stray magnetic field is suppressed. Can be prevented from demagnetizing and demagnetizing.
[0014]
Further, according to the second invention, the soft magnetic backing layer is formed into a multilayer structure with the nonmagnetic intermediate layer, and the adjacent soft magnetic layers are antiferromagnetically coupled to each other in an external magnetic field of a certain size or less. A soft magnetic underlayer is obtained in which the differential value of the magnetization curve when the saturated magnetization state is reversed to the opposite saturation state has two peaks. Thereby, demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer due to the external stray magnetic field can be prevented.
[0015]
Further, when the range in which these two peaks appear is less than the recording magnetic field and is adjusted to be an external magnetic field of approximately the stray magnetic field, when the recording magnetic field is applied to the adjacent soft magnetic layers, the directions of magnetization are mutually different. When the stray magnetic field is parallel and less than the recording magnetic field, the magnetic field can be coupled antiferromagnetically, so that recording can be prevented and the influence of the external stray magnetic field can be prevented. By suppressing the change in the magnetization state of the soft magnetic underlayer in this way, it is possible to prevent demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer due to the external stray magnetic field.
[0016]
In the second invention, the magnetic moment of each soft magnetic layer is preferably approximately the same, the magnetic moment of the soft magnetic layers are different, collapses symmetry of the magnetization curve, the value of the residual magnetization increases, soft Leakage magnetic flux as the entire magnetic backing layer is likely to occur.
[0017]
FIG. 1 is a diagram showing the configuration of an example of a magnetic recording medium according to the first invention.
[0018]
As shown in the figure, this recording medium has a structure in which a soft
[0019]
FIG. 2 is a diagram showing the configuration of an example of the magnetic recording medium according to the second invention.
[0020]
As shown in the figure, this recording medium has a structure in which a first soft
[0021]
In a thin film in which a ferromagnetic transition metal and a nonmagnetic metal are multilayered as in the magnetic recording medium according to the second aspect of the invention, the ferromagnetic and antiferromagnetic coupling between the ferromagnetic layers with respect to the thickness of the nonmagnetic layer Appearing periodically, in many multilayer films ((Fe, Co) / (V, Cr, Cu, Mo, Ru, Rh, Re)), adjacent ferromagnetic layers are opposite to each other. It is known that the period of ferromagnetic coupling (or ferromagnetic coupling) is about 1 nm ( A. Heinlich and JAC Bland, Ultrathin Magnetic Structures II, Springer-Verlag (1994) ). In addition, the thickness of the nonmagnetic layer in which the antiferromagnetic coupling, that is, the state in which the magnetization of the adjacent ferromagnetic layer is antiparallel, first appears is approximately 1 nm or less, and thereafter, the nonmagnetic layer is spaced at approximately 1 nm intervals. As the layer thickness increases, the antiferromagnetic coupling becomes weaker. Therefore, the coupling strength can be selected by setting the nonmagnetic layer to an appropriate thickness. Therefore, when the magnetic field is applied from the head during recording by selecting the coupling strength, that is, the nonmagnetic layer thickness, so that the magnetization is parallel to the external magnetic field of the recording magnetic field applied from the head, it is excellent. While it functions as a soft magnetic underlayer, the change in the magnetization state is suppressed for stray magnetic fields other than during recording, so the recording magnetization of the magnetic recording layer can be demagnetized by an external stray magnetic field without hindering recording. And demagnetization can be prevented. The nonmagnetic intermediate layer thickness is preferably 0.5 nm or more and less than 1.5 nm.
[0023]
In the magnetic recording medium of the present invention, since the easy axis of magnetization of the soft magnetic backing layer is aligned in the circumferential direction or the radial direction, an antiferromagnetic layer such as FeMn or CoSm is provided between the nonmagnetic substrate and the soft magnetic backing layer. A hard magnetic layer may be formed.
[0024]
A nonmagnetic underlayer such as Ru, Ti or a nonmagnetic CoCr alloy may be formed between the soft magnetic underlayer and the perpendicular recording layer.
[0025]
As a material for the soft magnetic layer, a soft magnetic alloy having a high magnetic permeability such as FeSi alloy, FeCo alloy, NiFe alloy such as permalloy, and CoZr alloy such as CoZrNb can be used in addition to Sendust. In order to make the soft magnetic underlayer multi-layered, it is considered that the soft magnetic layer is preferably a material having a crystal structure similar to that of the nonmagnetic intermediate layer and having a close lattice constant or an amorphous material.
[0026]
As the nonmagnetic intermediate layer, V, Cr, Cu, Mo, Ru, Rh, and Re are preferably used, and Ru is more preferable.
[0027]
As a combination of the soft magnetic layer and the nonmagnetic intermediate layer, Cu, Ru, Rh, and Re are considered preferable for V, Cr, Mo, and NiFe alloys for Sendust, FeSi, and FeCo alloys. Therefore, an amorphous material such as CoZrNb is considered preferable for any nonmagnetic interlayer material.
[0028]
Examples of the magnetic material used for the magnetic recording layer having perpendicular anisotropy include CoPt alloys such as CoPtO and CoPtB in addition to CoCr alloys such as CoCrPt and CoCrTa.
[0029]
In the magnetic recording medium of the present invention, a magnetic recording layer having perpendicular anisotropy with respect to the substrate is laminated directly or via a nonmagnetic underlayer on the soft magnetic underlayer as described above.
[0030]
【Example】
First, the magnetic properties of the soft magnetic underlayer according to the present invention were examined.
[0031]
As the non-magnetic substrate, a glass substrate satisfying the standard specification of a 2.5 inch magnetic disk was used, and all layers were produced by DC magnetron sputtering.
[0032]
First, Sendust having a thickness of about 27 nm was formed as a first soft magnetic layer on a nonmagnetic substrate.
[0033]
Next, a Ru layer having a thickness of about 1 nm was formed as a nonmagnetic intermediate layer.
[0034]
On top of that, Sendust having a thickness of about 27 nm was again laminated as the second soft magnetic layer. 10 nm of C was formed as a protective layer on the soft magnetic backing layer having the three-layer structure.
[0035]
Further, as a comparative example, lamination was performed in the same manner except that the thickness of the Ru layer as the nonmagnetic intermediate layer was set to about 1.5 nm.
[0036]
With respect to the obtained soft magnetic backing layer, a magnetization curve when a magnetic field is applied in the in-plane direction by a vibrating sample magnetometer (VSM) and a graph showing the result of differentiating the magnetization curve with respect to the magnetic field are shown in FIG. As shown in FIG. FIG. 5 and FIG. 6 show the magnetization curve and differential value when the thickness of the Ru layer is about 1.5 nm, respectively. 4 and 6, the solid line corresponds to the case where the applied magnetic field is changed from negative to positive, and the dotted line corresponds to the case where the magnetic field is changed from positive to negative.
[0037]
As shown in FIG. 3, the magnetization curve of the soft magnetic underlayer used in the present invention shows that the upper and lower soft magnetic layers are antiferromagnetically coupled by setting the nonmagnetic intermediate layer to an appropriate thickness. Since the change in which the magnetizations of the upper and lower soft magnetic layers are aligned in the same direction as the magnetic field in the vicinity of the
[0038]
Here, the applied magnetic field is suppressed small values of magnetization in the vicinity of 0, the magnetization curve is in the approximate origin for symmetry is because the magnetic moments of the upper and lower non-magnetic intermediate layer is equal to, the upper and lower soft When the magnetic moments of the layers is different, collapses symmetry of the magnetization curve, the value of the residual magnetization increases, since the leakage flux of the entire soft magnetic backing layer is likely to occur, the magnetic moments of the upper and lower soft magnetic layer is approximately It is desirable that they are the same.
[0039]
On the other hand, in the comparative example, as shown in FIG. 5, the magnetization curve of the soft magnetic backing layer when the thickness of the Ru layer is about 1.5 nm indicates that the nonmagnetic intermediate layer thickness is the upper and lower soft magnetic layers. Since the thickness is not suitable for antiferromagnetic coupling, it is basically the same as that of a general soft magnetic layer, and since the magnetic permeability is high, even when an external magnetic field of about 20 Oe is applied. It can be seen that the magnetization state varies greatly.
[0040]
From the magnetization curve of FIG. 5, when the thickness of the Ru layer is 1.5 nm, it is considered that the soft magnetic layers above and below the nonmagnetic intermediate layer are ferromagnetically coupled. When the thickness is less than this Ru layer thickness, the thickness of the ferromagnetically coupled layer is expected to be less than 0.5 nm due to its periodicity, and the Ru layer thickness at which antiferromagnetic coupling appears is 0.5 nm to 1.5 nm. It is considered that the Ru intermediate layer thickness that can most effectively suppress the change in the magnetization state with respect to the external stray magnetic field is within this range.
[0041]
3 and 5 can be seen as a difference in the number of peaks in the differentiated curve. That is, when the magnetization is reversed by changing the applied magnetic field from negative to positive or from positive to negative, the comparative example has one peak as shown in FIG. Two peaks can be seen as shown in FIG. Although the peak position differs by about 20 Oe between the solid line and the dotted line, if the magnitude of the magnetic field that takes these peaks is set as a threshold value, in the embodiment, the change in the magnetization state is suppressed between the magnetic field from 0 to the threshold value. It can be seen that such a region does not exist in the comparative example while the region exists.
[0042]
On the soft magnetic underlayer, a Ru layer having a thickness of 20 nm was formed as a nonmagnetic underlayer by a DC magnetron sputtering method.
[0043]
Next, a CoPtCrO magnetic layer was formed on the nonmagnetic underlayer.
[0044]
Thereafter, a 10 nm C layer was formed as a protective layer.
[0045]
The obtained magnetic recording medium was evaluated stability of the reproduced signal output by the head utilizing the magnetoresistance effect in an external magnetic field in which is generated by the Helmholtz coils.
[0046]
As a result, when an external magnetic field of 20 Oe was applied, a decrease in reproduction output and a change in reproduction waveform were observed in the comparative example, whereas such a change was not observed in the example. The difference in change with respect to the external magnetic field of 20 Oe corresponds well with the above-described magnetization curve.
[0047]
The perpendicular magnetic recording medium according to the present invention has a structure in which a perpendicular recording layer is laminated directly or via a nonmagnetic underlayer on a soft magnetic underlayer as mentioned in the examples.
[0048]
The soft magnetic backing layer in this magnetic recording medium has a function of returning the recording magnetic field to the magnetic head side by setting the above threshold value to be smaller than the recording magnetic field by the magnetic head and about the stray magnetic field in the magnetic disk device. However, the fluctuation of the magnetization state is sufficiently suppressed with respect to the stray magnetic field. In addition, since the soft magnetic underlayer has a multilayer structure as in the embodiment, demagnetization and demagnetization of the recording magnetization of the perpendicular recording layer by an external stray magnetic field without impairing the freedom of design such as permeability and film thickness. Can be obtained.
[0049]
In each of the above embodiments, a glass substrate is used as the nonmagnetic substrate. However, an Al-based alloy substrate, a Si single crystal substrate whose surface is oxidized, ceramics, plastic, or the like can also be used. Furthermore, the same effect is expected even when the surfaces of these nonmagnetic substrates are plated with NiP alloy or the like. Further, although only the sputtering method has been taken up as the film formation method of the soft magnetic backing layer, the same effect can be obtained by a vacuum evaporation method or the like.
[0050]
【The invention's effect】
According to the magnetic recording medium of the present invention, demagnetization and demagnetization of the recording magnetization of the magnetic recording layer can be prevented because the magnetic recording medium is hardly affected by the external stray magnetic field.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a magnetic recording medium according to the first invention. FIG. 2 is a schematic diagram illustrating an example of a magnetic recording medium according to the second invention. FIG. 3 is a soft magnetic backing used in the present invention. derivative of the graph [6] Figure 5 represents the magnetization curve of the soft magnetic underlayer for graph Figure 5 comparison representing a differential value of the graph [4] FIG. 3 represents an example magnetization curves of the layers Graph diagram showing values
Claims (5)
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JP3350512B2 (en) | 2000-05-23 | 2002-11-25 | 株式会社日立製作所 | Perpendicular magnetic recording medium and magnetic recording / reproducing device |
JP2002358618A (en) * | 2000-12-28 | 2002-12-13 | Showa Denko Kk | Magnetic recording medium, manufacturing method therefor, and magnetic recording and reproducing device |
US7166375B2 (en) | 2000-12-28 | 2007-01-23 | Showa Denko K.K. | Magnetic recording medium utilizing a multi-layered soft magnetic underlayer, method of producing the same and magnetic recording and reproducing device |
JP2003045015A (en) * | 2001-07-27 | 2003-02-14 | Anelva Corp | Perpendicular magnetic recording medium and its manufacturing method |
WO2004019322A1 (en) | 2002-08-26 | 2004-03-04 | Fujitsu Limited | Lining magnetic film |
JP2004348777A (en) | 2003-05-20 | 2004-12-09 | Hitachi Ltd | Vertical magnetic recording medium and magnetic recording device |
JP2006018876A (en) | 2004-06-30 | 2006-01-19 | Toshiba Corp | Perpendicular magnetic recording apparatus |
JP2006114162A (en) | 2004-10-15 | 2006-04-27 | Hitachi Global Storage Technologies Netherlands Bv | Perpendicular magnetic recording medium and magnetic recording apparatus using the same |
US20060147758A1 (en) * | 2005-01-06 | 2006-07-06 | Hong-Sik Jung | Perpendicular magnetic recording medium with magnetically resetable single domain soft magnetic underlayer |
JP4902210B2 (en) | 2005-02-01 | 2012-03-21 | 国立大学法人東北大学 | Perpendicular magnetic recording medium, method for manufacturing the same, and perpendicular magnetic recording / reproducing apparatus |
WO2006106628A1 (en) * | 2005-03-31 | 2006-10-12 | Hoya Corporation | Magnetic recording medium-use substrate and vertical magnetic recording medium |
US7910159B2 (en) | 2005-06-03 | 2011-03-22 | Wd Media, Inc. | Radial magnetic field reset system for producing single domain soft magnetic underlayer on perpendicular magnetic recording medium |
KR100773541B1 (en) * | 2005-06-30 | 2007-11-07 | 삼성전자주식회사 | Perpendicular magnetic recording media with soft magnetic underlayer |
JP4527645B2 (en) * | 2005-10-17 | 2010-08-18 | ヒタチグローバルストレージテクノロジーズネザーランドビーブイ | Perpendicular magnetic recording medium |
KR100738108B1 (en) | 2006-02-22 | 2007-07-12 | 삼성전자주식회사 | Perpendicular magnetic recording media |
JP4771222B2 (en) | 2006-09-13 | 2011-09-14 | 富士電機デバイステクノロジー株式会社 | Perpendicular magnetic recording medium |
JP2008123602A (en) | 2006-11-10 | 2008-05-29 | Hitachi Global Storage Technologies Netherlands Bv | Perpendicular magnetic recording medium |
JP2008140528A (en) | 2006-12-05 | 2008-06-19 | Hitachi Global Storage Technologies Netherlands Bv | Perpendicular magnetic recording medium |
JP5064145B2 (en) * | 2007-08-29 | 2012-10-31 | 昭和電工株式会社 | Magnetic recording medium and magnetic recording apparatus |
JP5213470B2 (en) | 2008-02-01 | 2013-06-19 | 昭和電工株式会社 | Perpendicular magnetic recording medium and magnetic storage device |
JP2009289360A (en) | 2008-05-30 | 2009-12-10 | Fujitsu Ltd | Perpendicular magnetic recording medium and device |
JP4922995B2 (en) | 2008-05-30 | 2012-04-25 | 昭和電工株式会社 | Perpendicular magnetic recording medium and magnetic storage device |
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