JPH04366417A - Magnetic recording medium and its manufacture - Google Patents
Magnetic recording medium and its manufactureInfo
- Publication number
- JPH04366417A JPH04366417A JP14182891A JP14182891A JPH04366417A JP H04366417 A JPH04366417 A JP H04366417A JP 14182891 A JP14182891 A JP 14182891A JP 14182891 A JP14182891 A JP 14182891A JP H04366417 A JPH04366417 A JP H04366417A
- Authority
- JP
- Japan
- Prior art keywords
- magnetic
- thin film
- alloy
- substrate
- ferromagnetic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 230000005291 magnetic effect Effects 0.000 title claims abstract description 72
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 6
- 239000000758 substrate Substances 0.000 claims abstract description 60
- 239000010409 thin film Substances 0.000 claims abstract description 55
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 47
- 239000000956 alloy Substances 0.000 claims abstract description 47
- 230000005294 ferromagnetic effect Effects 0.000 claims abstract description 27
- 238000005204 segregation Methods 0.000 claims abstract description 6
- 238000004544 sputter deposition Methods 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 5
- 239000000203 mixture Substances 0.000 abstract description 8
- 238000000926 separation method Methods 0.000 abstract description 8
- 229910018104 Ni-P Inorganic materials 0.000 abstract description 7
- 229910018536 Ni—P Inorganic materials 0.000 abstract description 7
- 229910001004 magnetic alloy Inorganic materials 0.000 abstract description 3
- 238000007772 electroless plating Methods 0.000 abstract description 2
- 239000000470 constituent Substances 0.000 abstract 2
- 238000005299 abrasion Methods 0.000 abstract 1
- 238000003754 machining Methods 0.000 abstract 1
- 239000010408 film Substances 0.000 description 15
- 239000013078 crystal Substances 0.000 description 12
- 229910001362 Ta alloys Inorganic materials 0.000 description 8
- 239000010410 layer Substances 0.000 description 8
- 229910000838 Al alloy Inorganic materials 0.000 description 7
- 239000004642 Polyimide Substances 0.000 description 7
- 239000010419 fine particle Substances 0.000 description 7
- 230000005415 magnetization Effects 0.000 description 7
- 229920001721 polyimide Polymers 0.000 description 7
- 238000001556 precipitation Methods 0.000 description 7
- 238000001228 spectrum Methods 0.000 description 7
- 238000000655 nuclear magnetic resonance spectrum Methods 0.000 description 6
- 229910052804 chromium Inorganic materials 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 238000001225 nuclear magnetic resonance method Methods 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- 229910052715 tantalum Inorganic materials 0.000 description 5
- 238000005481 NMR spectroscopy Methods 0.000 description 4
- 238000003917 TEM image Methods 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 238000007796 conventional method Methods 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 229910052697 platinum Inorganic materials 0.000 description 4
- 229910001260 Pt alloy Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 238000000265 homogenisation Methods 0.000 description 3
- 238000009413 insulation Methods 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000011241 protective layer Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 229910000599 Cr alloy Inorganic materials 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- QZPSXPBJTPJTSZ-UHFFFAOYSA-N aqua regia Chemical compound Cl.O[N+]([O-])=O QZPSXPBJTPJTSZ-UHFFFAOYSA-N 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000001755 magnetron sputter deposition Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000001376 precipitating effect Effects 0.000 description 2
- 239000013598 vector Substances 0.000 description 2
- 229910000846 In alloy Inorganic materials 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000003486 chemical etching Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 229910000701 elgiloys (Co-Cr-Ni Alloy) Inorganic materials 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 230000005389 magnetism Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000002250 progressing effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 238000007738 vacuum evaporation Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Abstract
Description
【０００１】0001
【産業上の利用分野】本発明は、情報の記録再生時に媒
体ノイズが小さく、かつＳ／Ｎの高い磁性薄膜媒体およ
びその製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic thin film medium with low medium noise and high S/N ratio during recording and reproduction of information, and a method of manufacturing the same.
【０００２】0002
【従来の技術】近年、情報化社会の高度化にともない、
固定磁気ディスク装置などの磁気記憶装置の高記録密度
化、大容量化が強く要望されてきている。この高密度記
録化のために、合金薄膜磁性媒体の研究開発が活発にな
されてきている。スパッタリングや真空蒸着法などで製
造される磁気記録用合金磁性薄膜媒体の高記録密度化に
おいては、記録ビットサイズが小さくなるにしたがい、
対向する記録ビットの磁化ベクトルの反発力によりビッ
ト間の領域に存在する磁壁はジグザグ形状となり、ノイ
ズの発生原因となる。そのジグザグ磁壁の発生を抑制す
るためは非磁性介在物により交換相互作用を切断し、強
磁性領域を磁気的に孤立化させ、微粒子化することが有
効であり、その強磁性微粒子のサイズは小さい方が好ま
しいといわれている。このように従来の磁壁移動により
磁化反転が生ずる「磁壁移動型」薄膜に対し、強磁性領
域が磁気的に孤立された「微粒子型」膜構造を持つ薄膜
の開発が、高記録密度化には必須である。[Background Art] In recent years, with the advancement of information society,
There is a strong demand for higher recording density and larger capacity of magnetic storage devices such as fixed magnetic disk devices. To achieve this high-density recording, research and development of alloy thin film magnetic media has been actively conducted. In order to increase the recording density of alloy magnetic thin film media for magnetic recording manufactured by sputtering or vacuum evaporation, as the recording bit size becomes smaller,
Due to the repulsive force of the magnetization vectors of the opposing recording bits, the domain walls existing in the area between the bits have a zigzag shape, which causes noise generation. In order to suppress the generation of zigzag domain walls, it is effective to break the exchange interaction with non-magnetic inclusions, magnetically isolate the ferromagnetic region, and make it into fine particles, and the size of the ferromagnetic fine particles is small. It is said that it is preferable. In contrast to the conventional "domain wall displacement type" thin film in which magnetization reversal occurs due to domain wall motion, the development of a thin film with a "fine grain type" film structure in which the ferromagnetic region is magnetically isolated has made it possible to achieve higher recording density. Required.
【０００３】従来、強磁性領域を微粒子化するために薄
膜成長時の堆積原子の移動度を低下させ、「島状構造」
を形成することがノイズ低減に有効であることが提案さ
れている［Ｔ．Ｙｏｇｉ，Ｔ．Ａ．Ｎｇｕｙｅｎ，Ｓ．
Ｅ．Ｌａｍｂｅｒｔ，Ｇ．Ｌ．Ｇｏｒｍａｎ ａｎｄ
Ｇ．Ｃａｓｔｉｌｌｏ：ＩＥＥＥ Ｔｒａｎｓ．
Ｍａｇｎ．ｖｏｌ．２６ （１９９０）ｐ．１５７８
−ｐ．１５８０．）。これは、スパッタリング法を用い
て製造される合金薄膜磁性媒体において、スパッタリン
グ用アルゴンガス圧力を通常の場合の数ｍＴｏｒｒより
２４ｍＴｏｒｒに高め、さらに膜形成時の基板温度を、
通常の場合の１００℃よりも低い２５℃とすることによ
り、強磁性領域を微粒子化させた「島状構造」を形成し
、媒体ノイズの低減を図るものである。Conventionally, in order to make the ferromagnetic region finer, the mobility of deposited atoms during thin film growth was reduced, resulting in an "island structure".
It has been proposed that forming a Yogi, T. A. Nguyen, S.
E. Lambert, G. L. Gorman and
G. Castillo: IEEE Trans.
Magn. vol. 26 (1990) p. 1578
-p. 1580. ). In alloy thin film magnetic media manufactured using the sputtering method, the argon gas pressure for sputtering is increased from the usual several mTorr to 24 mTorr, and the substrate temperature during film formation is increased.
By setting the temperature to 25° C., which is lower than the normal 100° C., an “island structure” in which the ferromagnetic region is made into fine particles is formed, thereby reducing medium noise.
【０００４】0004
【発明が解決しようとする課題】しかし、従来行なわれ
てきた堆積原子の移動度を低下させる手法においては、
次のような問題点が存在する。島状構造の薄膜は、空間
で隔てられた不連続構造となるために媒体の機械的強度
が低下し、記録媒体としての長期使用に対しては、磁気
ヘッドの接触などにより媒体破損が生じる恐れがあり、
信頼性が著しく低下する問題点がある。また、長手磁気
記録（面内磁気記録）用媒体の製造においては、非磁性
基板上に非磁性Ｃｒ下地層を形成し、このＣｒ下地上に
Ｃｏ基合金磁性薄膜をエピタキシャル成長させ、Ｃｏ基
合金薄膜の結晶磁気異方性軸を膜面内に配向させること
により、膜面内方向の保磁力，角型比などの磁気特性を
向上させる手法が用いられている。従来の手法による堆
積原子の移動度の低下は、Ｃｒ下地層へのＣｏ基合金薄
膜のエピタキシャル成長を阻害する問題点がある。さら
に、島状構造は通常複数の結晶粒からなっているため微
細化には限界があり、たとえ、移動度を極端に低下させ
微粒子化を行なっても、結晶欠陥が発生し、磁気特性は
著しく劣化する問題点が生ずる。[Problem to be solved by the invention] However, in the conventional method of reducing the mobility of deposited atoms,
The following problems exist. A thin film with an island-like structure has a discontinuous structure separated by spaces, which reduces the mechanical strength of the medium, and when used for a long time as a recording medium, there is a risk of damage to the medium due to contact with a magnetic head, etc. There is,
There is a problem that reliability is significantly reduced. In addition, in the production of longitudinal magnetic recording (in-plane magnetic recording) media, a nonmagnetic Cr underlayer is formed on a nonmagnetic substrate, a Co-based alloy magnetic thin film is epitaxially grown on this Cr underlayer, and a Co-based alloy thin film is formed on the Cr underlayer. A method has been used to improve magnetic properties such as coercive force and squareness ratio in the film in-plane direction by orienting the magnetocrystalline anisotropy axis of the film in the film plane. The reduction in the mobility of deposited atoms by conventional methods has the problem of inhibiting the epitaxial growth of a Co-based alloy thin film on a Cr underlayer. Furthermore, since island-like structures usually consist of multiple crystal grains, there is a limit to their miniaturization. Even if the mobility is extremely reduced and the particles are made finer, crystal defects will occur and the magnetic properties will significantly deteriorate. The problem of deterioration arises.
【０００５】本発明は、記録再生時に媒体ノイズが小さ
く、かつ高いＳ／Ｎを持つ磁気記録媒体を提供すること
を目的とする。SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium with low medium noise and high S/N during recording and reproduction.
【０００６】[0006]
【課題を解決するための手段】上述した目的を達成する
ために、本発明による磁気記録媒体は、非磁性基板と、
該基板上に形成されたＣｏ−Ｃｒ−Ｔａ強磁性合金薄膜
からなる磁性層を有し、該磁性層中に薄膜中の平均Ｃｏ
濃度より高いＣｏ濃度の強磁性成分が組成分離して析出
していることを特徴とする。[Means for Solving the Problems] In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention includes a non-magnetic substrate,
A magnetic layer made of a Co-Cr-Ta ferromagnetic alloy thin film is formed on the substrate, and the average Co in the thin film is contained in the magnetic layer.
It is characterized in that a ferromagnetic component with a Co concentration higher than the Co concentration is separated and precipitated.
【０００７】本発明による製造方法は、非磁性基板を１
５０℃〜２８０℃に加熱しながら、スパッタリングによ
ってＣｏ−Ｃｒ−Ｔａ合金からなる強磁性薄膜を前記基
板上に形成する工程を含むことを特徴とする。[0007] In the manufacturing method according to the present invention, a non-magnetic substrate is
The method is characterized by including a step of forming a ferromagnetic thin film made of a Co-Cr-Ta alloy on the substrate by sputtering while heating at 50°C to 280°C.
【０００８】[0008]
【作用】Ｃｏ−Ｃｒ−Ｍ（ＭはＴａ，Ｐｔ，Ｎｉのうち
少なくとも一つからなる）強磁性合金薄膜において、Ｃ
ｏ濃度が膜平均値よりも高い強磁性成分が組成分離して
析出し、さらには結晶粒界がＣｒ偏析をした組成的不均
一構造を持つ強磁性合金薄膜を用いることにより上述し
た従来の問題は解決される。[Operation] In a Co-Cr-M (M is at least one of Ta, Pt, and Ni) ferromagnetic alloy thin film, C
The above-mentioned conventional problems can be solved by using a ferromagnetic alloy thin film that has a compositionally non-uniform structure in which a ferromagnetic component whose concentration is higher than the average value of the film separates and precipitates, and furthermore, the grain boundaries have Cr segregation. is resolved.
【０００９】従来においては、Ｃｏ−Ｃｒ−Ｔａ，Ｃｏ
−Ｃｒ−Ｐｔ，Ｃｏ−Ｃｒ−Ｎｉ系の強磁性合金薄膜の
研究がなされてきているが、先に述べたように、堆積原
子の移動度を下げるためにスパッタリングガス圧力を高
め、基板温度を低下させることにより膜構造を島状構造
とし、それにより強磁性領域の微粒子化を図り、媒体ノ
イズを低減させることが有効と考えられていた。本発明
はそれとは逆に、スパッタリングガス圧力を上げず、基
板温度を高めることにより、高Ｃｏ濃度成分が組成分離
により結晶粒径よりもはるかに微細に析出する現象、さ
らには、結晶粒界はＣｒの偏析により磁気的に絶縁され
ている現象を初めて見出したことに基づいている。高Ｃ
ｏ濃度成分が組成分離して析出することは、本発明の実
施例に示されたように、核磁気共鳴法により初めて見い
だされたものであり、従来技術から本発明を類推するこ
とはきわめて困難である。本発明においては、連続薄膜
中に、高Ｃｏ濃度成分の組成分離析出を生じしめること
により、結晶粒径よりも微細な強磁性領域を有する微粒
子構造の形成を実現し、さらには結晶粒界をＣｒ偏析に
より磁気的に絶縁させることにより、媒体ノイズの低減
とＳ／Ｎの向上を図ることができる。Conventionally, Co-Cr-Ta, Co
Research has been carried out on -Cr-Pt and Co-Cr-Ni based ferromagnetic alloy thin films, but as mentioned earlier, sputtering gas pressure is increased to lower the mobility of deposited atoms, and the substrate temperature is lowered. It was thought that it would be effective to make the film structure into an island-like structure by lowering the magnetic field, thereby making the ferromagnetic region finer and reducing the medium noise. In the present invention, on the contrary, by increasing the substrate temperature without increasing the sputtering gas pressure, the high Co concentration component is precipitated much finer than the crystal grain size due to compositional separation, and furthermore, the crystal grain boundaries are This is based on the first discovery of the phenomenon of magnetic insulation due to segregation of Cr. High C
As shown in the examples of the present invention, the compositional separation and precipitation of o concentration components was first discovered by nuclear magnetic resonance, and it is extremely difficult to extrapolate the present invention from the prior art. It is. In the present invention, by causing compositional separation and precipitation of high Co concentration components in a continuous thin film, it is possible to form a fine grain structure with ferromagnetic regions that are finer than the crystal grain size, and furthermore, to form grain boundaries. By magnetically insulating through Cr segregation, it is possible to reduce media noise and improve S/N.
【００１０】0010
【実施例】図１は、本発明に係る媒体の一実施例を示す
模式的断面図である。図１（ａ）の１は５０μｍ厚のポ
リイミド基板、２は非磁性Ｃｒ下地層、３は強磁性合金
薄膜層、図１（ｂ）の４は、内外径加工および面切削を
施したＡｌ合金からなるディスク状基板、５は基板４の
表面に無電解メッキで形成されたＮｉ−Ｐ合金からなる
非磁性合金層であり、その表面は超精密平面研磨したあ
と同心円状にテクスチャー加工（アルミナなどの微粒子
によって、円周方向にごく微細な傷をつける加工）を施
して、中心線平均粗さＲａで約６ｎｍを有する表面形状
を有する基板、２は非磁性金属下地層、３は強磁性合金
薄膜層、６は保護層である。DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic cross-sectional view showing an embodiment of a medium according to the present invention. 1 in Fig. 1(a) is a polyimide substrate with a thickness of 50 μm, 2 is a nonmagnetic Cr underlayer, 3 is a ferromagnetic alloy thin film layer, and 4 in Fig. 1(b) is an Al alloy with internal and external diameter processing and surface cutting. 5 is a non-magnetic alloy layer made of Ni-P alloy formed on the surface of the substrate 4 by electroless plating, and the surface is subjected to ultra-precision plane polishing and then concentrically textured (with alumina, etc.). 2 is a non-magnetic metal underlayer, 3 is a ferromagnetic alloy. The thin film layer 6 is a protective layer.
【００１１】図１（ａ）に示したポリイミド基板１、あ
るいは図１（ｂ）に示したＮｉ−Ｐ／Ａｌ合金ディスク
状基板４を精密洗浄ホルダーにセットして、インライン
方式のＤＣマグネトロンスパッタ装置の仕込み室へ送り
込み、５×１０−６Ｔｏｒｒ以下の真空に排気し、基板
温度を２５℃から３００℃の範囲内の所定の温度に加熱
保持する。続いてホルダーを成膜室へ搬送し、５ｍＴｏ
ｒｒのＡｒガス雰囲気中で、ＤＣマグネトロンスパッタ
法を用いて、Ｃｒからなり膜厚が２００ｎｍの非磁性金
属下地層を形成し、ついで所定の組成の合金をターゲッ
トとして５０ｎｍの強磁性合金薄膜を順次成膜形成する
。
テクスチャー処理がなされたＮｉ−Ｐ／Ａｌ合金基板を
用いた場合は、さらにアモルファス・カーボンからなり
膜厚２０ｎｍの保護層を成膜し、磁気記録媒体とする。The polyimide substrate 1 shown in FIG. 1(a) or the Ni-P/Al alloy disk-shaped substrate 4 shown in FIG. 1(b) is set in a precision cleaning holder, and an in-line type DC magnetron sputtering apparatus is used. The substrate is sent to a preparation chamber, evacuated to a vacuum of 5×10 −6 Torr or less, and the substrate temperature is maintained at a predetermined temperature within the range of 25° C. to 300° C. Next, the holder was transported to the film forming chamber, and 5mTo
A non-magnetic metal underlayer made of Cr and having a thickness of 200 nm is formed using DC magnetron sputtering in an Ar gas atmosphere of RR, and then a ferromagnetic alloy thin film of 50 nm is sequentially formed using an alloy of a predetermined composition as a target. Form a film. When a textured Ni-P/Al alloy substrate is used, a protective layer made of amorphous carbon and having a thickness of 20 nm is further formed to form a magnetic recording medium.
【００１２】実施例１
図２は、ポリイミド基板を用いて作製したＣｏ−１２原
子％Ｃｒ−２原子％Ｔａ合金磁性薄膜の磁気特性の、ス
パッタ時の基板温度による変化を示したものである。基
板温度が２５℃では、保磁力Ｈｃは約７００Ｏｅと低い
が、基板温度を１５０℃以上に高めると、保磁力は１０
００Ｏｅ以上となり、基板温度が１８０℃〜２８０℃で
は約１２００Ｏｅとなる。飽和磁化Ｍｓは基板温度２５
℃から２８０℃でほとんど変化しないが、基板温度が３
００℃になると保磁力，飽和磁化ともに低下する。高密
度磁気記録媒体に適した１０００Ｏｅ以上の保磁力と高
い飽和磁化をもつ合金磁性薄膜を作製できる基板温度範
囲は１５０℃〜２８０℃であることがわかる。Ｎｉ−Ｐ
／Ａｌ合金非磁性基板を用いた場合も、ポリイミド基板
を用いた場合とほぼ同様な磁気特性が得られた。Example 1 FIG. 2 shows the change in magnetic properties of a Co-12 atomic % Cr-2 atomic % Ta alloy magnetic thin film produced using a polyimide substrate depending on the substrate temperature during sputtering. When the substrate temperature is 25°C, the coercive force Hc is as low as about 700 Oe, but when the substrate temperature is increased to 150°C or higher, the coercive force decreases to 10
00 Oe or more, and at a substrate temperature of 180° C. to 280° C., it becomes about 1200 Oe. Saturation magnetization Ms is substrate temperature 25
There is almost no change from ℃ to 280℃, but when the substrate temperature is 3
When the temperature reaches 00°C, both coercive force and saturation magnetization decrease. It can be seen that the substrate temperature range in which an alloy magnetic thin film having a coercive force of 1000 Oe or more and high saturation magnetization suitable for high-density magnetic recording media can be produced is 150°C to 280°C. Ni-P
When the /Al alloy nonmagnetic substrate was used, almost the same magnetic properties were obtained as when the polyimide substrate was used.
【００１３】実施例２
図３は、５９Ｃｏのスピンエコー型核磁気共鳴法（ＮＭ
Ｒ）を用いて観測した共鳴スペクトルを示す。（ａ）は
組成均一化のための熱処理がなされたＣｏ−１２原子％
Ｃｒ−２原子％Ｔａバルク合金、（ｂ）から（ｄ）は、
実施例１において作製された基板温度Ｔｓが（ｂ）２５
℃、（ｃ）１５０℃、（ｄ）２５０℃のＣｏ−１２原子
％Ｃｒ−２原子％Ｔａ合金磁性薄膜、（ｅ）は均一化熱
処理がなされたＣｏ−５原子％Ｃｒバルク合金、の核磁
気共鳴スペクトルを示したものである。Example 2 FIG. 3 shows the spin echo nuclear magnetic resonance method (NM) of 59Co.
A resonance spectrum observed using R) is shown. (a) shows Co-12 atomic% that has been heat-treated to make the composition uniform.
Cr-2 atomic % Ta bulk alloys, (b) to (d) are
The substrate temperature Ts produced in Example 1 is (b) 25
℃, (c) 150℃, (d) Co-12 atomic% Cr-2 atomic% Ta alloy magnetic thin film, (e) Co-5 atomic% Cr bulk alloy subjected to homogenization heat treatment. This shows a magnetic resonance spectrum.
【００１４】純Ｃｏの核磁気共鳴スペクトルは、約２２
０ＭＨｚに１本の共鳴ピークを示す。磁性を弱めるＣｒ
などの非磁性元素の含有量が増えると、この共鳴周波数
は低周波数側に移行していくことが知られている（Ｋ．
Ｙｏｓｈｉｄａ，Ｈ．Ｋａｋｉｂａｙａｓｈｉ，Ｈ．Ｙ
ａｓｕｏｋａ，Ｊ．Ａｐｐｌ．Ｐｈｙｓ．，６８ （
１９９０）ｐ．７０５−ｐ．７１８）。組成的に均一な
Ｃｏ−１２原子％Ｃｒ−２原子％Ｔａバルク合金のスペ
クトルは、約１２０ＭＨｚにピークをもつブロードなス
ペクトルを示す。基板温度が２５℃の合金磁性薄膜のス
ペクトルは、バルク合金に類似したブロードなスペクト
ルを示すが、図中Ｍで記したように約２０６ＭＨｚに高
Ｃｏ濃度成分の析出を示す共鳴ピークがすでに現れ始め
ている。基板温度が１５０℃になると、この共鳴ピーク
Ｍは著しく強くなり共鳴ピークは２１６ＭＨｚの高周波
側にずれる。この共鳴周波数は図３（ｅ）に示したＣｏ
−５原子％Ｃｒバルク合金とほぼ同じであり、Ｃｏ濃度
が約９５原子％の強磁性成分が組成分離して析出してい
ることになる。さらに基板温度が２５０℃になると、こ
の共鳴周波数はさらに高くなり２１９ＭＨｚとなる。こ
れは、９７原子％Ｃｏ−３原子％Ｃｒバルク合金のスペ
クトルに相当するものである。The nuclear magnetic resonance spectrum of pure Co is approximately 22
One resonance peak is shown at 0 MHz. Cr weakens magnetism
It is known that as the content of non-magnetic elements such as K.
Yoshida, H. Kakibayashi, H. Y
asuoka, J. Appl. Phys. ,68 (
1990) p. 705-p. 718). The spectrum of a compositionally uniform Co-12 atomic % Cr-2 atomic % Ta bulk alloy shows a broad spectrum with a peak at about 120 MHz. The spectrum of the alloy magnetic thin film at a substrate temperature of 25°C shows a broad spectrum similar to that of a bulk alloy, but a resonance peak indicating the precipitation of a high Co concentration component has already begun to appear at about 206 MHz, as marked by M in the figure. There is. When the substrate temperature reaches 150° C., this resonance peak M becomes significantly stronger and shifts to the high frequency side of 216 MHz. This resonant frequency is shown in Fig. 3(e).
-5 atom% Cr bulk alloy, which means that the ferromagnetic component with a Co concentration of about 95 atom% is separated and precipitated. Furthermore, when the substrate temperature becomes 250° C., this resonance frequency becomes even higher to 219 MHz. This corresponds to the spectrum of a 97 atomic % Co-3 atomic % Cr bulk alloy.
【００１５】したがって、基板温度を１５０℃以上に高
めると、きわめてＣｏリッチな強磁性成分が組成分離し
て析出することを示しており、実施例１で示した保磁力
の増加は、大きな飽和磁化と高い結晶磁気異方性を持つ
高Ｃｏ濃度成分を持つ微粒子が組成分離して析出し、微
粒子型の膜構造を形成し、その結果保磁力が著しく向上
したと考えられる。[0015] This shows that when the substrate temperature is raised to 150°C or higher, a very Co-rich ferromagnetic component separates in composition and precipitates, and the increase in coercive force shown in Example 1 is due to the large saturation magnetization. It is considered that fine particles having a high Co concentration component with high magnetocrystalline anisotropy were separated in composition and precipitated, forming a fine particle type film structure, and as a result, the coercive force was significantly improved.
【００１６】実施例３
図４は、実施例１において、核磁気共鳴法で観測された
高Ｃｏ濃度成分の析出状態を示す透過型電子顕微鏡写真
の一例を模写したものである。磁性薄膜はポリイミド基
板を用いて基板温度１５０℃で作製されたＣｏ−１２原
子％Ｃｒ−２原子％Ｔａ合金磁性薄膜である。電子顕微
鏡による組成的構造観察のために、磁性合金薄膜は希王
水でＣｏリッチ領域を化学エッチングにより選択溶解処
理されたものであり、Ｃｏリッチ領域は薄くなっている
ために、図では白い領域に相当する。結晶粒界は化学エ
ッチングされずに残っており、Ｃｒ偏析が生じており（
図中、矢印Ａで示す）、結晶粒界は磁気的な絶縁が進ん
でいることが分かる。結晶粒内には、周期的に白と黒の
周期的構造が存在し（図中、矢印Ｂで示す）、高Ｃｏ濃
度成分は組成分離により各結晶粒内に微細に析出してい
ることが分かる。Example 3 FIG. 4 is a reproduction of an example of a transmission electron micrograph showing the precipitation state of the high Co concentration component observed by nuclear magnetic resonance method in Example 1. The magnetic thin film is a Co-12 atomic % Cr-2 atomic % Ta alloy magnetic thin film produced using a polyimide substrate at a substrate temperature of 150°C. In order to observe the compositional structure using an electron microscope, the magnetic alloy thin film was treated by selectively dissolving the Co-rich region by chemical etching with dilute aqua regia, and since the Co-rich region is thinner, it is shown as a white region in the figure. corresponds to The grain boundaries remain without being chemically etched, and Cr segregation occurs (
(indicated by arrow A in the figure), it can be seen that magnetic insulation is progressing at the grain boundaries. There is a periodic white and black structure within the crystal grains (indicated by arrow B in the figure), and the high Co concentration component is finely precipitated within each crystal grain due to compositional separation. I understand.
【００１７】本実施例は、核磁気共鳴法により観測され
た高Ｃｏ濃度成分は、粗大に析出するのではなく、各結
晶粒内に微細に析出することを示すものであり、本発明
は高記録密度用磁気記録媒体に非常に適した微粒子型の
膜構造を形成できることを示している。This example shows that the high Co concentration component observed by the nuclear magnetic resonance method does not precipitate coarsely but finely precipitates within each crystal grain. This shows that it is possible to form a fine grain type film structure that is highly suitable for high-density magnetic recording media.
【００１８】実施例４
図５は、テクスチャー処理が施されたＮｉ−Ｐ／Ａｌ合
金基板を用いて、基板温度１５０℃で作製されたＣｏ−
１２原子％Ｃｒ−２原子％Ｔａ合金磁性薄膜の透過型電
子顕微鏡写真を模写した図である。この薄膜試料も実施
例３と同様に、電子顕微鏡による組成的構造観察のため
に、磁性合金薄膜は希王水でＣｏリッチ領域を選択溶解
処理されたものである。結晶粒内には高Ｃｏ濃度成分が
微細に析出した構造が認められる。さらに、結晶粒がテ
クスチャー方向にならび、Ｃｒ偏析した結晶粒界がテク
スチャー方向に直線的に並んでいる（図中、矢印で示す
）。これは、テクスチャー方向と直角方向には磁気的に
絶縁されていることを示すものである。すなわち、テク
スチャー方向にそって記録される記録ビットが、テクス
チャー方向すなわちトラック方向に安定して記録される
ことを示しており、記録媒体としてきわめて好ましい微
粒子型膜構造が形成されている。Example 4 FIG. 5 shows a Co-P/Al alloy substrate fabricated at a substrate temperature of 150°C using a textured Ni-P/Al alloy substrate.
FIG. 2 is a reproduction of a transmission electron micrograph of a 12 at. % Cr-2 at. % Ta alloy magnetic thin film. As in Example 3, this thin film sample was also subjected to selective dissolution treatment of the Co-rich region with dilute aqua regia for compositional structure observation using an electron microscope. A structure in which high Co concentration components were finely precipitated within the crystal grains was observed. Furthermore, the crystal grains are aligned in the texture direction, and the crystal grain boundaries where Cr is segregated are aligned linearly in the texture direction (indicated by arrows in the figure). This indicates that there is magnetic insulation in the direction perpendicular to the texture direction. That is, it is shown that recording bits recorded along the texture direction are stably recorded in the texture direction, that is, in the track direction, and a fine grain type film structure is formed which is extremely preferable as a recording medium.
【００１９】本実施例は、テクスチャー処理された非磁
性基板を用いることにより、さらに高Ｃｏ濃度成分の組
成分離による効果の増大が図れる膜構造が形成できるこ
とを示している。This example shows that by using a textured nonmagnetic substrate, it is possible to form a film structure in which the effect of compositional separation of high Co concentration components can be further enhanced.
【００２０】実施例５
非磁性Ｎｉ−Ｐ／Ａｌ合金基板を用いて作製したＣｏ−
１２原子％Ｃｒ−２原子％Ｔａ合金磁性薄膜媒体におい
て、基板温度を２５℃から３００℃と変えて作製した媒
体に対し、ＭＩＧ型フェライイトリングヘッドを用いて
記録再生特性を調べた結果を図６に示す。なお、Ｓ／Ｎ
および媒体ノイズは記録密度が４０，０００ｆｌｕｘ
ｃｈａｎｇｅ／ｉｎｃｈの状態で測定されたものであ
る。基板温度が１５０℃〜２８０℃の範囲において、図
６（ａ）に示すように、Ｓ／Ｎが２０ｄＢ以上で、かつ
、図６（ｂ）に示すように媒体ノイズＮｗが４μＶ以下
の良好な記録再生が得られることが分かる。Example 5 Co-
The figure shows the results of investigating the recording and reproducing characteristics using a MIG type ferrite ring head for 12 at.% Cr-2 at. 6. In addition, S/N
And media noise is recording density 40,000 flux
It was measured in the state of change/inch. When the substrate temperature is in the range of 150°C to 280°C, the S/N is 20 dB or more as shown in Fig. 6(a), and the medium noise Nw is 4 μV or less as shown in Fig. 6(b). It can be seen that recording and reproduction can be obtained.
【００２１】本実施例は、高Ｃｏ濃度成分を組成分離析
出させ、微粒子型の膜構造とすることにより、媒体ノイ
ズの低減，Ｓ／Ｎの向上を図ることができることを示し
ている。This example shows that it is possible to reduce medium noise and improve S/N by separating and precipitating components with a high Co concentration and creating a fine particle type film structure.
【００２２】実施例６
図７はポリイミド基板を用いて作製したＣｏ−９原子％
Ｃｒ−１３原子％Ｐｔ合金薄膜の核磁気共鳴（ＮＭＲ）
スペクトルの変化を示す。（ａ）は均一化熱処理された
Ｃｏ−９原子％Ｃｒ−１３原子％Ｐｔバルク合金、（ｂ
），（ｃ）はそれぞれ基板温度Ｔｓが２５℃，１５０℃
のＣｏ−９原子％Ｃｒ−１３原子％Ｐｔ合金薄膜磁性媒
体、の核磁気共鳴スペクトルを示す。組成的に均一なＣ
ｏ−９原子％Ｃｒ−１３原子％Ｐｔバルク合金膜は約１
５０ＭＨｚを中心にブロードなスペクトルを示す。
基板温度が２５℃では、すでに高Ｃｏ濃度成分の析出を
示す２００〜２２０ＭＨｚの共鳴吸収が強くなっている
が、基板温度を１５０℃に高めると、２１０ＭＨｚに高
Ｃｏ濃度成分の析出を示す共鳴吸収ピークが著しく強く
なり、この共鳴周波数は９２原子％Ｃｏ−８原子％Ｃｒ
に相当する。Example 6 FIG. 7 shows Co-9 atomic % produced using a polyimide substrate.
Nuclear magnetic resonance (NMR) of Cr-13 atomic% Pt alloy thin film
Shows changes in spectrum. (a) Co-9 atomic% Cr-13 atomic% Pt bulk alloy subjected to homogenization heat treatment; (b)
) and (c), the substrate temperature Ts is 25℃ and 150℃, respectively.
2 shows a nuclear magnetic resonance spectrum of a Co-9 atomic % Cr-13 atomic % Pt alloy thin film magnetic medium. Compositionally uniform C
o-9 at% Cr-13 at% Pt bulk alloy film is approximately 1
It shows a broad spectrum centered around 50 MHz. At a substrate temperature of 25°C, resonance absorption at 200 to 220 MHz, which indicates the precipitation of a high Co concentration component, is already strong, but when the substrate temperature is increased to 150 °C, a resonance absorption at 210 MHz, which indicates the precipitation of a high Co concentration component, increases. The peak becomes significantly stronger, and this resonance frequency is 92 at.%Co-8 at.%Cr.
corresponds to
【００２３】実施例７
図８はポリイミド基板を用いて作製したＣｏ−７．５原
子％Ｃｒ−３０原子％Ｎｉ合金薄膜の核磁気共鳴（ＮＭ
Ｒ）スペクトルの変化を示す。（ａ）は、均一化熱処理
が施されたＣｏ−７．５原子％Ｃｒ−３０原子％Ｎｉバ
ルク合金、（ｂ）と（ｃ）はそれぞれ基板温度Ｔｓが２
５℃と１５０℃で作製されたＣｏ−７．５原子％Ｃｒ−
３０原子％Ｎｉ合金薄膜、の核磁気共鳴スペクトルを示
す。Ｃｏ−７．５原子％Ｃｒ−３０原子％Ｎｉバルク合
金は約１８０ＭＨｚにピークを持つブロードな共鳴吸収
スペクトルを持つ。基板温度が２５℃の場合、ほぼバル
ク合金に類似してブロードなスペクトルを示すが、基板
温度が１５０℃になると、約２００ＭＨｚに共鳴ピーク
が強く現れ、９０原子％Ｃｏ−１０原子％Ｃｒ相当の高
Ｃｏ濃度成分が組成分離して析出することを示している
。Example 7 FIG. 8 shows the nuclear magnetic resonance (NM
R) Shows a change in spectrum. (a) is a Co-7.5 atomic% Cr-30 atomic% Ni bulk alloy that has been subjected to homogenization heat treatment, and (b) and (c) are each a substrate temperature Ts of 2.
Co-7.5 at% Cr- prepared at 5°C and 150°C
The nuclear magnetic resonance spectrum of a 30 atomic % Ni alloy thin film is shown. The Co-7.5 at.% Cr-30 at.% Ni bulk alloy has a broad resonance absorption spectrum with a peak at about 180 MHz. When the substrate temperature is 25°C, it shows a broad spectrum similar to that of a bulk alloy, but when the substrate temperature reaches 150°C, a strong resonance peak appears at about 200 MHz, and a resonance peak corresponding to 90 atomic% Co-10 atomic% Cr appears. This shows that high Co concentration components are separated and precipitated.
【００２４】以上述べた、高Ｃｏ濃度成分が析出する現
象は、磁気記録層と通常使用されるＣｏ−Ｃｒ−Ｔａ合
金の組成の範囲、さらに合金磁性薄膜が８０原子％Ｃｏ
−１０原子％Ｃｒ−１０原子％Ｐｔ，８０原子％Ｃｏ−
１１原子％Ｃｒ−７原子％Ｐｔ−２原子％Ｔａ，８０原
子％Ｃｏ−１０原子％Ｃｒ−４原子％Ｐｔ−４原子％Ｎ
ｉ−２原子％Ｔａなどの場合にも認められ、いずれも記
録再生特性が向上するという結果が得られた。The above-mentioned phenomenon in which the high Co concentration component precipitates depends on the composition range of the Co--Cr--Ta alloy commonly used as the magnetic recording layer, and furthermore, when the alloy magnetic thin film contains 80 at.% Co.
-10 atom% Cr-10 atom% Pt, 80 atom% Co-
11 at.%Cr-7 at.%Pt-2 at.%Ta, 80 at.%Co-10 at.%Cr-4 at.%Pt-4 at.%N
This was also observed in the case of i-2 atomic % Ta, and the results showed that the recording and reproducing characteristics were improved in all cases.
【００２５】[0025]
【発明の効果】以上説明したように、Ｃｏ−Ｃｒ−Ｍ（
ＭはＴａ，Ｐｔ，Ｎｉのうち少なくとも一つを含む）合
金磁性薄膜を用いて、高Ｃｏ濃度成分を組成分離により
析出させることにより、結晶粒径よりも微細な強磁性微
粒子が析出した微粒子型の磁性薄膜を作製することが可
能となるのであるから、媒体ノイズの低減とＳ／Ｎの向
上が可能となる利点がある。さらには、テクスチャー処
理を施された非磁性基板を用いた場合には、テクスチャ
ー方向からはずれた方向へ磁化ベクトルが向くことを抑
制するものであり、磁気記録媒体として好ましい構造を
実現できる利点がある。また、従来の手法によっては避
けることができなかった不連続構造薄膜ではなく連続構
造薄膜となるために媒体強度は低下しない利点がある。
また、従来の手法による基板温度の低下やスパッタリン
グガス圧力を低下させた場合におけるＣｒ下地とのエピ
タキシャル成長の抑制や合金磁性薄膜の結晶性が低下す
るという問題点が発生しない利点がある。[Effect of the invention] As explained above, Co-Cr-M(
A fine grain type in which ferromagnetic fine particles finer than the crystal grain size are precipitated by precipitating a high Co concentration component by composition separation using an alloy magnetic thin film (M contains at least one of Ta, Pt, and Ni). Since it becomes possible to fabricate a magnetic thin film of 100 mL, there is an advantage that media noise can be reduced and S/N can be improved. Furthermore, when a textured non-magnetic substrate is used, it suppresses the magnetization vector from pointing in a direction away from the texture direction, which has the advantage of realizing a desirable structure as a magnetic recording medium. . Furthermore, since the thin film has a continuous structure instead of a discontinuous thin film that could not be avoided using conventional methods, there is an advantage that the strength of the medium does not decrease. Further, there is an advantage that problems such as suppression of epitaxial growth with a Cr undercoat and deterioration of crystallinity of the alloy magnetic thin film that occur when lowering the substrate temperature or sputtering gas pressure, which are caused by conventional methods, do not occur.
【図１】本発明の磁気記録媒体の模式的断面図である。FIG. 1 is a schematic cross-sectional view of a magnetic recording medium of the present invention.
【図２】Ｃｏ−Ｃｒ−Ｔａ／Ｃｒ合金磁性薄膜の磁気特
性の基板温度による変化を示す特性図である。FIG. 2 is a characteristic diagram showing changes in magnetic properties of a Co-Cr-Ta/Cr alloy magnetic thin film depending on substrate temperature.
【図３】Ｃｏ−Ｃｒ−Ｔａ合金におけるバルク合金と合
金薄膜、およびＣｏ−Ｃｒバルク合金のＮＭＲスペクト
ルである。FIG. 3 is an NMR spectrum of a bulk alloy in a Co-Cr-Ta alloy, an alloy thin film, and a Co-Cr bulk alloy.
【図４】高Ｃｏ濃度成分の析出状態を示す合金磁性薄膜
の透過型電子顕微鏡写真の一例を模写した図である。FIG. 4 is a reproduction of an example of a transmission electron micrograph of an alloy magnetic thin film showing the precipitation state of a high Co concentration component.
【図５】テクスチャー処理が施された非磁性基板を用い
た場合の、合金磁性薄膜の透過型電子顕微鏡写真の一例
を模写した図である。FIG. 5 is a reproduction of an example of a transmission electron micrograph of an alloy magnetic thin film when a textured nonmagnetic substrate is used.
【図６】Ｃｏ−Ｃｒ−Ｔａ／Ｃｒ媒体の記録再生特性図
である。FIG. 6 is a diagram showing recording and reproducing characteristics of a Co-Cr-Ta/Cr medium.
【図７】Ｃｏ−Ｃｒ−Ｐｔ合金におけるバルク合金と合
金薄膜のＮＭＲスペクトルである。FIG. 7 is an NMR spectrum of a bulk alloy and an alloy thin film in a Co-Cr-Pt alloy.
【図８】Ｃｏ−Ｃｒ−Ｎｉ／Ｃｒ合金におけるバルク合
金と合金薄膜のＮＭＲスペクトルである。FIG. 8 is an NMR spectrum of a bulk alloy and an alloy thin film in a Co-Cr-Ni/Cr alloy.
１ ポリイミド基板 ２ 非磁性金属下地層 ３ 合金磁性薄膜層 ４ Ａｌ合金非磁性基板 ５ 非磁性Ｎｉ−Ｐ層 ６ 保護層 1 Polyimide substrate 2 Non-magnetic metal underlayer 3 Alloy magnetic thin film layer 4 Al alloy nonmagnetic substrate 5 Nonmagnetic Ni-P layer 6 Protective layer
Claims (5)
Ｃｏ−Ｃｒ−Ｔａ強磁性合金薄膜からなる磁性層を有し
、該磁性層中に薄膜中の平均Ｃｏ濃度より高いＣｏ濃度
の強磁性成分が組成分離して析出していることを特徴と
する磁気記録媒体。1. A non-magnetic substrate and a magnetic layer formed on the substrate of a Co-Cr-Ta ferromagnetic alloy thin film, the magnetic layer having a Co concentration higher than the average Co concentration in the thin film. A magnetic recording medium characterized in that a ferromagnetic component is separated and precipitated.
偏析していることを特徴とする請求項１に記載の磁気記
録媒体。2. The grain boundaries of the ferromagnetic alloy thin film are Cr.
The magnetic recording medium according to claim 1, characterized in that the magnetic recording medium is segregated.
Ｃｒからなる下地層をさらに有することを特徴とする請
求項１または２のいずれかに記載の磁気記録媒体。3. The magnetic recording medium according to claim 1, further comprising an underlayer made of Cr between the nonmagnetic substrate and the magnetic layer.
れており、前記強磁性合金薄膜磁性層のＣｒ偏析が生じ
た結晶粒界がテクスチャー・ラインに沿って形成されて
いることを特徴とする請求項１ないし３のいずれかの項
に記載の磁気記録媒体。4. The nonmagnetic substrate is textured, and the grain boundaries where Cr segregation occurs in the ferromagnetic alloy thin film magnetic layer are formed along texture lines. The magnetic recording medium according to any one of items 1 to 3.
熱しながら、スパッタリングによってＣｏ−Ｃｒ−Ｔａ
合金からなる強磁性薄膜を前記基板上に形成する工程を
含むことを特徴とする磁気記録媒体の製造方法。5. While heating the nonmagnetic substrate to 150°C to 280°C, Co-Cr-Ta is formed by sputtering.
A method of manufacturing a magnetic recording medium, comprising the step of forming a ferromagnetic thin film made of an alloy on the substrate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14182891A JPH04366417A (en) | 1991-06-13 | 1991-06-13 | Magnetic recording medium and its manufacture |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14182891A JPH04366417A (en) | 1991-06-13 | 1991-06-13 | Magnetic recording medium and its manufacture |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH04366417A true JPH04366417A (en) | 1992-12-18 |
Family
ID=15301075
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP14182891A Pending JPH04366417A (en) | 1991-06-13 | 1991-06-13 | Magnetic recording medium and its manufacture |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH04366417A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1997018556A1 (en) * | 1995-11-16 | 1997-05-22 | Migaku Takahashi | Magnetic recording medium and production method thereof |
| US5774783A (en) * | 1995-03-17 | 1998-06-30 | Fujitsu Limited | Magnetic recording medium |
-
1991
- 1991-06-13 JP JP14182891A patent/JPH04366417A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5774783A (en) * | 1995-03-17 | 1998-06-30 | Fujitsu Limited | Magnetic recording medium |
| USRE38587E1 (en) | 1995-03-17 | 2004-09-14 | Fujitsu Limited | Magnetic recording medium |
| WO1997018556A1 (en) * | 1995-11-16 | 1997-05-22 | Migaku Takahashi | Magnetic recording medium and production method thereof |
| US6124020A (en) * | 1995-11-16 | 2000-09-26 | Takahashi; Migaku | Magnetic recording medium and production method thereof |
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