JP2004355784A - Magnetic recording media - Google Patents

Abstract

A high-density magnetic recording medium that can prevent magnetization deterioration due to storage and is suitable for use in a recording / reproducing system using an MR head or a linear system.
At least one magnetic layer formed on one surface of a non-magnetic support by a vacuum thin film forming technique and having a thickness per layer of 100 nm or less and a total laminated thickness of 150 nm or less. And 3b and at least one shield layer formed on one or both surfaces of at least one magnetic layer and containing at least one of aluminum and titanium and having a thickness of 1 nm or more and 30 nm or less. 2a to 2c.
[Selection diagram] Fig. 1

Description

【００８６】
（実施例２〜４および比較例２、３）
非磁性支持体と磁性層の間に形成されるシールド層の厚さを表１に示すように変更した以外は、実施例１と同様にサンプルテープを作製した。磁性層は単層で、厚さ２５ｎｍである。なお、図５のグラフは実施例１〜４および比較例２、３のサンプルテープの磁化劣化率と保磁力比をプロットしたものである。
【００８７】
（実施例５〜８および比較例４、５）
非磁性支持体と磁性層の間に形成されるシールド層を、表１に示す厚さのＡｌ層に変更した以外は、実施例１と同様にサンプルテープを作製した。磁性層は単層で、厚さ２５ｎｍである。シールド層のＡｌ層は、Ａｌターゲットを用いるスパッタにより形成した。なお、図６のグラフは実施例５〜８および比較例４、５のサンプルテープの磁化劣化率と保磁力比をプロットしたものである。
【００８８】
（実施例９〜１２および比較例６、７）
シールド層を非磁性支持体と磁性層の間に形成せず、磁性層と保護層の間に表１に示す厚さのシールド層を形成した以外は、実施例１と同様にサンプルテープを作製した。磁性層は単層で、厚さ２５ｎｍである。シールド層は、実施例１で非磁性支持体と磁性層の間にシールド層を形成する場合と同様の方法で形成した。
【００８９】
（実施例１３〜１６および比較例８、９）
シールド層を非磁性支持体と磁性層の間に形成せず、磁性層と保護層の間に表１に示す厚さのシールド層を形成し、シールド層をＡｌ層とした以外は、実施例１と同様にサンプルテープを作製した。磁性層は単層で、厚さ２５ｎｍである。シールド層は、実施例１で非磁性支持体と磁性層の間にシールド層を形成する場合と同様の方法で形成した。
【００９０】
（比較例１０〜１３）
シールド層を形成せず、単層の磁性層を表２に示す厚さに変更した以外は、実施例１と同様にサンプルテープを作製した。参考のため、磁性層の厚さが２５ｎｍである比較例１（表１参照）を表２にも示した。
【００９１】
【表２】

【００９２】
（実施例１７〜１９）
非磁性支持体と磁性層の間にシールド層として厚さ３０ｎｍのＴｉ層を形成し、単層の磁性層を表２に示す厚さに変更した以外は、実施例１と同様にサンプルテープを作製した。参考のため、磁性層の厚さが２５ｎｍである実施例４（表１参照）を表２にも示した。
【００９３】
（実施例２０〜２３）
非磁性支持体と磁性層の間にシールド層を形成せず、磁性層と保護層の間にシールド層として厚さ３０ｎｍのＴｉ層を形成し、単層の磁性層を表２に示す厚さに変更した以外は、実施例１と同様にサンプルテープを作製した。
【００９４】
（実施例２４〜２７）
非磁性支持体と磁性層の間にシールド層として厚さ３０ｎｍのＴｉ層を形成し、さらに、磁性層と保護層の間にもシールド層として厚さ３０ｎｍのＴｉ層を形成し、単層の磁性層を表２に示す厚さに変更した以外は、実施例１と同様にサンプルテープを作製した。
【００９５】
（実施例２８〜３０および比較例１４〜１６）
磁性層を２層として、磁性層の積層総厚が１５０ｎｍとなるように、上層の磁性層の厚さと下層の磁性層の厚さを表３に示す厚さにした。以下、磁性層を２層とした実施例および比較例において、上層の磁性層は上述した方法により、下層の磁性層と斜方柱状構造の傾きが逆向きとなるように形成した。実施例２８〜３０では、非磁性支持体と下層の磁性層の間にシールド層として厚さ５ｎｍのＴｉ層を形成した。比較例１４〜１６では、シールド層を形成しなかった。それ以外は、実施例１と同様にサンプルテープを作製した。
【００９６】
【表３】

【００９７】
（実施例３１〜３３）
非磁性支持体と下層の磁性層の間にシールド層を形成せず、下層の磁性層と上層の磁性層の間にシールド層を形成した以外は、実施例２８〜３０と同様にサンプルテープを作製した。シールド層は厚さ５ｎｍのＴｉ層である。
【００９８】
（実施例３４〜３６）
非磁性支持体と下層の磁性層の間にシールド層を形成せず、上層の磁性層と保護層の間にシールド層を形成した以外は、実施例２８〜３０と同様にサンプルテープを作製した。シールド層は厚さ５ｎｍのＴｉ層である。
【００９９】
（実施例３７〜４２および比較例１７、１８）
磁性層を２層として、磁性層の積層総厚が１００ｎｍとなるように、上層の磁性層の厚さと下層の磁性層の厚さを表４に示す厚さにした。実施例３７〜４２では、それぞれ表４に示す位置にシールド層として厚さ５ｎｍのＴｉ層を形成した。比較例１７、１８では、シールド層を形成しなかった。それ以外は、実施例１と同様にサンプルテープを作製した。
【０１００】
【表４】

【０１０１】
（実施例４３〜４８および比較例１９、２０）
磁性層を２層として、磁性層の積層総厚が７５ｎｍとなるように、上層の磁性層の厚さと下層の磁性層の厚さを表５に示す厚さにした。実施例４３〜４８では、それぞれ表５に示す位置にシールド層として厚さ５ｎｍのＴｉ層を形成した。比較例１９、２０では、シールド層を形成しなかった。それ以外は、実施例１と同様にサンプルテープを作製した。
【０１０２】
【表５】

【０１０３】
（実施例４９）
実施例４９〜５２では、表６に示すように磁性層を２層として、上層の磁性層の厚さを２５ｎｍ、下層の磁性層の厚さを５０ｎｍにした。非磁性支持体と下層の磁性層の間にシールド層として厚さ５ｎｍのＴｉ層を形成し、下層の磁性層と上層の磁性層の間にもシールド層として厚さ５ｎｍのＴｉ層を形成した。それ以外は、実施例１と同様にサンプルテープを作製した。
【０１０４】
【表６】

【０１０５】
（実施例５０）
磁性層を２層として、上層の磁性層の厚さを２５ｎｍ、下層の磁性層の厚さを５０ｎｍにした。下層の磁性層と上層の磁性層の間にシールド層として厚さ５ｎｍのＴｉ層を形成し、上層の磁性層と保護層の間にもシールド層として厚さ５ｎｍのＴｉ層を形成した。それ以外は、実施例１と同様にサンプルテープを作製した。
【０１０６】
（実施例５１）
磁性層を２層として、上層の磁性層の厚さを２５ｎｍ、下層の磁性層の厚さを５０ｎｍにした。非磁性支持体と下層の磁性層の間にシールド層として厚さ５ｎｍのＴｉ層を形成し、上層の磁性層と保護層の間にもシールド層として厚さ５ｎｍのＴｉ層を形成した。それ以外は、実施例１と同様にサンプルテープを作製した。
【０１０７】
（実施例５２）
磁性層を２層として、上層の磁性層の厚さを２５ｎｍ、下層の磁性層の厚さを５０ｎｍにした。下層の磁性層と上層の磁性層は、実施例１の単層の磁性層と同様の方法で形成した。非磁性支持体と下層の磁性層の間にシールド層として厚さ５ｎｍのＴｉ層を形成し、下層の磁性層と上層の磁性層の間にシールド層として厚さ５ｎｍのＴｉ層を形成し、上層の磁性層と保護層の間にもシールド層として厚さ５ｎｍのＴｉ層を形成した。それ以外は、実施例１と同様にサンプルテープを作製した。
【０１０８】
（実施例５３〜５６）
磁性層を厚さ２５ｎｍの単層とし、表１に示すように、実施例５３では実施例２のＴｉ層をＴｉ−Ｗ合金層に変更した。実施例５４では実施例１０のＴｉ層をＴｉ−Ｗ合金層に変更した。実施例５５では実施例６のＡｌ層をＡｌ−Ｍｇ合金層に変更した。実施例５６では実施例１４のＡｌ層をＡｌ−Ｍｇ合金層に変更した。
【０１０９】
表１は、磁性層を厚さ２５ｎｍの単層とし、シールド層の成膜位置や材料、厚さの効果を調べた結果を示す。シールド層が無い比較例１では、磁化劣化率が６２％と非常に大きい。これに比べ、ＴｉやＡｌのシールド層が１〜３０ｎｍの厚さで形成されている場合、磁化劣化量が非常に小さい。また、シールド層の厚さが１ｎｍ未満の場合、磁化劣化を抑制する効果が小さい。
【０１１０】
厚さ５０ｎｍのシールド層が非磁性支持体と磁性層の界面にある場合、磁化劣化量が１０％を超えてＮＧとなる。これは、シールド層が厚くなると表面の平滑性が悪くなり、その影響が磁性層や保護層にも及び、結果として保護層の欠陥が多くなるためであると考えられる。
【０１１１】
厚さ５０ｎｍのシールド層が磁性層と保護層の界面にある場合、磁化劣化率は許容されるが、記録再生でスペーシングロスが大きくなり、高記録密度化できないので、実用上使用されることは無いと考えられる。したがって、シールド層の厚さは１ｎｍ以上、３０ｎｍ以下と規定される。また、実施例５３〜５６は、シールド層がＴｉやＡｌを母材とした合金であるが、同様に磁化劣化を抑制する効果を示す。他の元素を含む場合でも同様の効果があることは明白である。
【０１１２】
表２は、磁性層が単層であり、シールド層として厚さ３０ｎｍのＴｉ層を形成した場合の効果について調べた結果を示す。この結果より、磁性層が薄くなると磁化劣化量が大きくなるが、シールド層があると、磁化劣化量が著しく小さくなることがわかる。磁性層の厚さが１２５ｎｍでは、シールド層が無くても磁化劣化率が１０％以下となる（比較例１０）。したがって、本発明では単層の磁性層の厚さを１００ｎｍ以下と規定するが、それ以上の厚さの場合でも、シールド層を設けることにより磁化劣化率を小さくできることは明白である。
【０１１３】
表３〜５は、磁性層が積層され、その総厚さを１５０ｎｍ以下とし、シールド層として厚さ３ｎｍのＴｉ層を形成した場合の効果について調べた結果を示す。各表の比較例より、磁性層が単層の場合と同様に、磁性層の総厚さが薄くなると磁化劣化量が大きくなる傾向があり、シールド層がある試料では著しく磁化劣化量が小さくなることがわかる。また、磁性層の総厚が１５０ｎｍの場合の表３と、磁性層の総厚が１００ｎｍの場合の表４より、磁性層の総厚や、磁性層の上層と下層の比率によらず、シールド層がある場合、磁化劣化率を非常に小さくできることがわかる。
【０１１４】
磁性層の総厚さが１５０ｎｍ以上でも同様の効果があることは明白であるが、総厚さが１５０ｎｍを超えると、例えばＧＭＲヘッドを用いた高密度磁気記録システムでは、ヘッドが飽和するため実用性が無い。したがって、本発明では、積層した磁性層の総厚を１５０ｎｍ以下と規定する。
【０１１５】
表５および表６は、磁性層が積層され、その総厚さが７５ｎｍであり、シールド層として厚さ３ｎｍのＴｉ層を形成した場合の効果について調べた結果を示す。この実験では、シールド層の成膜位置について、全ての組み合わせを検討した。その結果、シールド層は、最低でも１個所の界面にあれば、磁化劣化率を非常に小さくでき、シールド層を増やすと、より磁化劣化量を小さくできることがわかった。
【０１１６】
上記の本発明の実施形態の磁気記録媒体によれば、非磁性支持体側から各層を拡散、透過する酸素を各界面においてシールドすることができ、高温多湿環境下での保存特性が著しく向上する。また、磁性層と保護層の界面にシールド層を形成することにより、保護層を透過して磁性層に拡散する酸素をシールドでき、保護層側からの磁性層の磁化劣化をさらに効果的に抑制できる。本発明の実施形態の磁気記録媒体は、保存特性に優れ、高密度記録が可能であることから、特にデータストレージ用途に好適である。また、磁性層を薄くできるため、高感度ＭＲヘッドを用いる記録再生システムに適している。
【０１１７】
複数の磁性層が積層された場合、単層の磁性層が形成された場合に比較して、磁化劣化はより顕著となりやすいが、磁性層と接する少なくとも１層のシールド層を設けることにより、磁化劣化が効果的に防止される。例えば、斜方柱状構造の成長方向が異なる２層の磁性層が積層され、テープ走行の双方向での記録再生特性の差が低減された、リニア方式記録再生システムに好適な磁気記録媒体においても、保存による磁化劣化を防止できる。
【０１１８】
本発明は、上記の実施形態の説明に限定されない。例えば、シールド層材料をＴｉ−Ｗ系合金やＡｌ−Ｍｇ合金以外の合金としてもよい。また、斜方柱状構造の成長方向が同じ２層の磁性層が積層され、ヘリカルスキャン方式に好適である磁気記録媒体に上述したようなシールド層を設けてもよい。その他、本発明の要旨を逸脱しない範囲で、種々の変更が可能である。
【０１１９】
【発明の効果】
本発明によれば、保存性に優れ、高密度磁気記録が可能であり、ＭＲヘッドを用いる記録再生システムや、リニア方式システムに好適な磁気記録媒体が得られる。
【図面の簡単な説明】
【図１】図１は本発明の磁気記録媒体の一例を示す断面図である。
【図２】図２は本発明の磁気記録媒体のシールド層の形成に用いられるスパッタ装置の概略図である。
【図３】図３は本発明の磁気記録媒体の磁性層の形成に用いられる真空蒸着装置の概略図である。
【図４】図４は磁性層の厚さと磁化劣化率の関係を示す図である。
【図５】図５はＴｉシールド層の厚さに依存した磁化劣化率および保磁力の変化を示す図である。
【図６】図６はＡｌシールド層の厚さに依存した磁化劣化率および保磁力の変化を示す図である。
【図７】図７は従来の蒸着テープの断面図である。
【図８】図８は従来の蒸着テープの断面図である。
【符号の説明】
１…非磁性支持体、２ａ、２ｂ、２ｃ…シールド層、３…磁性層、３ａ…下層磁性薄膜、３ｂ…上層磁性薄膜、４…保護層、５…潤滑剤層、６…バックコート層、１０…磁気記録媒体、２０…マグネトロンスパッタ装置、２１…チャンバー、２２…真空ポンプ、２３…バルブ、２４…Ａｒガス導入管、２５…供給ロール、２６…冷却キャン、２７…巻き取りロール、２８…電極、２９…ターゲット、３０…真空蒸着装置、３１…真空室、３２…冷却キャン、３３…蒸着源、３４…供給ロール、３５…巻き取りロール、３６、３７…ガイドローラー、３８…電子銃、３９…電子ビーム、４０…第１のシャッタ、４１…第２のシャッタ、１０１…非磁性支持体、１０２…磁性層、１０２ａ、１０２ｂ…斜方蒸着膜。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high density magnetic recording medium.
[0002]
[Prior art]
Conventionally, as a magnetic recording medium, a powdered non-magnetic material such as an oxide magnetic powder or an alloy magnetic powder is coated on a non-magnetic support by an organic material such as a vinyl chloride-vinyl acetate copolymer, a polyester resin, a urethane resin, and a polyurethane resin. A coating type magnetic recording medium produced by applying and drying a magnetic coating material dispersed in a binder is widely used.
[0003]
On the other hand, with the increasing demand for high-density magnetic recording, metal magnetic materials such as Co-Ni-based alloys, Co-Cr-based alloys, and Co-O have been applied by plating and vacuum thin film forming techniques (vacuum evaporation and sputtering). A magnetic recording medium of a so-called metal magnetic thin film type, which is directly adhered to a non-magnetic support such as a polyester film, a polyamide, a polyimide film, or the like by a conventional method, an ion plating method, etc., has been proposed and attracts attention.
[0004]
This metal magnetic thin film type magnetic recording medium has excellent coercive force, squareness ratio, etc., not only excellent electromagnetic conversion characteristics at short wavelengths, but also extremely thin magnetic layer. The loss is extremely small. Further, since it is not necessary to mix a binder, which is a non-magnetic material, into the magnetic layer, the packing density of the magnetic material can be increased. The magnetic recording medium of the metal magnetic thin film type has such many advantages.
[0005]
Also, in order to improve the electromagnetic conversion characteristics of this type of magnetic recording medium and to obtain a larger output, when forming the magnetic layer of the magnetic recording medium, the magnetic layer is deposited obliquely, so-called obliquely. Evaporation has been proposed. A magnetic recording medium having a magnetic layer formed by this method has been put to practical use as a vapor deposition tape for high-band 8 mm video tape recorders and digital video tape recorders.
[0006]
This type of obliquely deposited magnetic tape is formed, for example, by running a long non-magnetic support in the longitudinal direction and depositing a magnetic material on one main surface of the non-magnetic support in a running state to form a magnetic layer. It is produced by the method of doing. According to this method, high productivity and excellent magnetic characteristics can be secured. Also, in order to obtain better electromagnetic conversion characteristics, a plurality of magnetic layers may be laminated.
[0007]
On the other hand, as the demand for a magnetic recording medium such as a magnetic tape as a data streamer increases, a further increase in the recording density of the magnetic recording medium is required. Further, as a magnetic head used for reproducing recorded information, a magnetoresistive magnetic head (MR head) or a giant magnetoresistive magnetic head (GMR head) has been applied instead of a conventional inductive head. Is coming. Since the MR head and the GMR head can detect minute leakage magnetic flux from the magnetic layer with high sensitivity, it is effective for improving the recording density.
[0008]
The MR head and the GMR head have a detection limit at which the sensitivity to the leakage magnetic flux is saturated, and cannot detect a leakage magnetic flux larger than a value permitted by the head design. Therefore, it is necessary to optimize the leakage magnetic flux of the magnetic layer by making the magnetic layer of the magnetic recording medium thin.
[0009]
As a system for recording / reproducing a magnetic tape for data streamer use, two types, a helical scan system and a linear system, have been put to practical use. The helical scan method is a method in which a magnetic head arranged on a rotating drum scans on a magnetic tape while rotating at high speed to perform recording and reproduction. According to the helical scan method, it is possible in principle to control not only to accurately record a recording track but also to accurately scan the recording track during reproduction. Therefore, it is possible to achieve a high recording density in a magnetic tape system. Such a helical scan system is widely used for home video recorders such as VHS, high-band 8 mm video tape recorders, and digital video tape recorders.
[0010]
On the other hand, the linear system is a system in which tracks are provided in the width direction of the magnetic tape and recording is performed in the longitudinal direction. According to the linear system, it is easy to run the tape at high speed, and at the same time, it is possible to improve the transfer rate of recording and reproduction by arranging many magnetic heads in parallel.
[0011]
In a magnetic recording tape system such as a camcorder application, a helical scan method capable of achieving a high recording density is advantageous. On the other hand, in data storage applications where the volume of the magnetic recording tape system is small, the linear system is widely used in practice, and products such as DLT (Digital Linear Tape) and LTO (Linear Tape-Open) have become mainstream in the market. ing.
[0012]
As such a magnetic tape medium for linear data storage, only a so-called coating type magnetic tape has been used, and a magnetic tape medium formed by oblique evaporation has not been used. This is because in the helical scan system, the relative movement between the magnetic tape and the magnetic head is in a fixed direction, whereas in the linear system, it moves in both directions.
[0013]
FIG. 7 is a schematic sectional view of a magnetic tape medium obtained by oblique evaporation. As shown in FIG. 7, a magnetic layer 102 is formed on a non-magnetic support 101. The magnetic tape medium formed by oblique deposition has a structure in which the axis of easy magnetization to which the recorded magnetic bits are directed rises not in the tape plane but in the plane.
[0014]
Therefore, when the head slides in the forward direction (the direction of arrow A in the figure) with respect to the columnar structure of the oblique deposition during recording / reproduction, good recording / reproducing characteristics are exhibited. On the other hand, when sliding in the opposite direction (the direction of arrow B in the figure), the characteristics such as the optimum recording current, phase characteristics, CN ratio, and output characteristics are inferior to those when sliding in the forward direction. There is a drawback that recording / reproducing characteristics cannot be obtained.
[0015]
For this reason, in the linear system in which recording and reproduction are performed bidirectionally, a magnetic tape medium using oblique evaporation has hardly been used. As a method of solving this problem, as shown in FIG. 8, a method of laminating two layers of obliquely deposited films 102a and 102b having different growth directions of columnar structures obtained by oblique deposition and forming a magnetic layer 102 is used. Has been proposed (see Patent Document 1). According to the magnetic recording medium described in Patent Literature 1, the difference between the recording and reproducing characteristics in both directions (the directions of arrows A and B in the figure) is reduced.
[0016]
[Patent Document 1]
JP-A-4-353622
[Patent Document 2]
JP-A-1-124115
[Patent Document 3]
JP-A-4-335206 (Japanese Patent No. 3093818)
[Patent Document 4]
JP-A-5-20662
[Non-patent document 1]
"Magnetoresistance head and spin valve head-basics and applications-2nd edition" (translated by Kazuhiko Hayashi, published in July 2002, Maruzen Co., Ltd.)
[0017]
[Problems to be solved by the invention]
In order to increase the areal density of recording / reproducing signals and make a magnetic recording medium compatible with an MR head or a GMR head, it is necessary to make the magnetic layer of the magnetic recording medium thin in order to prevent saturation of the head. However, the inventor of the present invention has found that when a magnetic recording medium having a thin magnetic layer is stored under high temperature and high humidity, the amount of magnetization is significantly reduced. Further, the inventors of the present invention have discovered that this phenomenon also occurs in a magnetic recording medium having magnetic layers stacked.
[0018]
In a magnetic recording medium having a single magnetic layer, when the thickness of the magnetic layer is 100 nm or less, the amount of magnetization is significantly reduced. In a magnetic recording medium in which a plurality of magnetic layers are stacked, if the total thickness of the plurality of magnetic layers (total thickness) is the same as the thickness of the magnetic layer of the magnetic recording medium having a single magnetic layer, the amount of magnetization can be reduced. The amount of reduction is greater than in the case of a single magnetic layer.
[0019]
Therefore, in a magnetic recording medium on which the magnetic layers are stacked, even if the total thickness of the stacked layers is about 150 nm, the reduction in the amount of magnetization under high temperature and high humidity becomes a practically problematic size. As a result of investigating the cause of such a phenomenon, a remarkable decrease in the amount of magnetization due to storage is a problem that is always encountered when the surface density of a recording / reproducing signal is increased and a magnetic recording medium is adapted to an MR head or a GMR head. It became clear that there was.
[0020]
As a method for preventing the corrosion of the magnetic layer due to moisture or corrosive gas, a 5-300 nm-thick aluminum (Al), chromium (Cr), titanium (Ti) or copper (Cu) layer is formed under the magnetic layer. A known method is known (see Patent Document 2). However, in Patent Document 2, the magnetic layer is as thick as 200 nm, for example, and the corrosive gas SO ₂ The corrosion resistance to gas has been evaluated.
[0021]
Patent Document 2 describes that forming a layer of Al, Ti, or the like on the underlayer of the magnetic layer improves the coercive force. When a thin metal layer having a thickness of 30 nm or less was formed, the coercive force decreased. However, when a thicker metal layer was formed under the magnetic layer, an increase in coercive force was also observed. That is, when the thickness ranges of the magnetic layer and the underlayer are different, the change in the magnetic properties depending on the thickness of the underlayer shows different behavior.
[0022]
In addition, the deterioration of the storage stability under high temperature and high humidity becomes apparent when the thickness of the magnetic layer becomes 100 nm or less, and SO 2 ₂ The mechanism (reaction) of magnetization deterioration differs from corrosion by gas. Actual experiments show that storage characteristics under high temperature and humidity and SO ₂ Of the corrosion resistance to gases, one is very good and the other is often problematic. That is, SO ₂ The method of improving the corrosion resistance to gas is not always effective in improving the storage characteristics under high temperature and high humidity.
[0023]
Patent Literature 3 describes that a layer of a metal and a metal oxide which is more base than Co is formed as a base layer of a magnetic layer to prevent corrosion of the magnetic layer. In the magnetic recording medium described in Patent Document 3, the thickness of the magnetic layer is preferably 120 to 300 nm, and in the example, 200 nm. The thickness of the underlayer is 50 to 200 nm.
[0024]
Patent Document 4 discloses that a metal layer having a thickness of 50 to 150 nm, preferably 80 to 120 nm is formed as a base layer of a magnetic layer to prevent corrosion of the magnetic layer. However, when the thickness of the magnetic layer is reduced to 100 nm or less and a thick underlayer as described in Patent Documents 3 and 4 is formed, the surface roughness of the underlayer increases, and the medium noise increases. Therefore, sufficient electromagnetic conversion characteristics cannot be obtained. This problem becomes more serious when a GMR head having higher sensitivity than the MR head is used as the reproducing head.
[0025]
The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent deterioration of magnetization due to storage and to use a magnetic recording medium suitable for high-density magnetic recording, in particular, a recording / reproducing system using an MR head, An object of the present invention is to provide a magnetic recording medium suitable for a linear system.
[0026]
[Means for Solving the Problems]
In order to achieve the above object, a magnetic recording medium of the present invention has a non-magnetic support, and is formed on one surface side of the non-magnetic support by a vacuum thin film forming technique, and has a thickness per layer of 100 nm or less. At least one magnetic layer, and a metal or alloy containing at least one of aluminum and titanium formed on one or both surfaces of the at least one magnetic layer, and having a thickness of 1 nm or more and 30 nm or less. And at least one shield layer. A plurality of magnetic layers may be stacked, in which case the total thickness of the plurality of magnetic layers is 150 nm or less.
[0027]
This makes it possible to prevent oxidation and magnetization deterioration of the magnetic layer caused by oxygen diffusing from the nonmagnetic support side into the magnetic layer. According to the magnetic recording medium of the present invention, even when the magnetic layer is formed as thin as 100 nm or less, the storage characteristics under high temperature and high humidity can be improved. The magnetic recording medium of the present invention has a thin magnetic layer and is suitable for a high-density recording / reproducing system using an MR head.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the magnetic recording medium of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an example of the magnetic recording medium according to the embodiment. As shown in FIG. 1, in a magnetic recording medium 10 of the present embodiment, at least one metal magnetic thin film made of a ferromagnetic metal material is formed as a magnetic layer 3 on one main surface of a nonmagnetic support 1, The protective layer 4 is formed on the upper layer, and the lubricant layer 5 is formed on the uppermost layer.
[0029]
FIG. 1 shows an example in which the magnetic layer 3 is composed of a lower magnetic thin film 3a and an upper magnetic thin film 3b, but the magnetic layer 3 may be a single layer or three or more magnetic thin films. A backcoat layer 6 is formed on the surface of the nonmagnetic support 1 opposite to the side on which the magnetic layer 3 is formed.
[0030]
In the magnetic recording medium according to the present invention, the shield layer 2a at the interface between the magnetic layer 3 and the non-magnetic support 1, the shield layer 2b between the magnetic layers (the interface between the lower magnetic thin film 3a and the upper magnetic thin film 3b), and the protection from the magnetic layer 3 It is characterized by having at least one of the shield layers 2c at the interface of the layer 4. These shield layers 2a, 2b, 2c are metals or alloys containing at least one of Al and Ti.
[0031]
Next, each layer of the magnetic recording medium 10 will be described. As the nonmagnetic support 1, any known material used in a conventional magnetic tape can be used. For example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate; and plastics such as polycarbonate, polyimide, polyamide and polyamide imide.
[0032]
Although not shown, an underlayer may be formed at the interface between the nonmagnetic support 1 and the magnetic layer 3. The underlayer is provided as necessary for the purpose of improving the durability and running property of the finally obtained magnetic recording medium 1 and the handling property when forming a magnetic tape. For example, a base layer may be formed with a paint containing a binder resin, a filler, a surfactant, and the like to add fine irregularities to the surface or to increase mechanical strength.
[0033]
Examples of the binder resin include an aqueous polyester resin, an aqueous acrylic resin, an aqueous polyurethane resin, and the like. Examples of the filler include particles made of a heat-resistant polymer, particles of silicon dioxide, calcium carbonate, and the like. The average particle size of the filler is, for example, 5 to 30 nm, and the density of surface projections formed by the filler is, for example, 500,000 to 30 million / mm. ² It is preferable to set the degree. Thereby, the running durability and the electromagnetic conversion characteristics of the magnetic recording medium 10 finally obtained can be improved.
[0034]
In addition to the method described above, a method of artificially forming irregularities on the nonmagnetic support 1 by lithography technology, or a method of forming an island-like structure by metal, inorganic compound, or organic polymer by plating or vacuum thin film forming technology is used. Alternatively, minute projections may be formed on the surface.
[0035]
The magnetic layer 3 is formed by directly applying a ferromagnetic metal material on the non-magnetic support 1, and has a two-layer structure of a lower magnetic thin film 3a and an upper magnetic thin film 3b. This metal magnetic material can be arbitrarily selected from those used for ordinary vapor deposition tapes. Examples of the metal magnetic material include ferromagnetic metals such as Fe, Co, and Ni, Fe—Co, Co—Ni, Fe—Co—Ni, Fe—Cu, Co—Cu, Co—Au, Co—Pt, and Mn—Bi. , Mn-Al, Fe-Cr, Co-Cr, Ni-Cr, ferromagnetic alloys such as Fe-Co-Cr, Co-Ni-Cr, and Fe-Co-Ni-Cr. In a magnetic tape for a linear system in which the tape runs in two directions (directions A and B in FIG. 1) with respect to the head, in order to reduce the difference in recording and reproduction characteristics in two directions, two magnetic layers are used. It is desirable to have a laminated structure of the above magnetic thin films. FIG. 1 illustrates a case where the magnetic layer has a two-layer structure.
[0036]
The magnetic recording medium 10 according to the present embodiment includes a magnetic layer 3 having a thickness of 100 nm or less composed of a single magnetic thin film, or a magnetic layer having a total thickness of 150 nm or less composed of a plurality of magnetic thin films having a thickness of 100 nm or less. Layer 3 is formed. At least one portion between the non-magnetic support 1 and the magnetic layer 3, between a plurality of magnetic thin films constituting the magnetic layer 3, and between the magnetic layer 3 and the protective layer 4, Al, Ti, or a metal thereof is used as a matrix. A shield layer made of an alloy is formed. Thereby, the storage characteristics of the magnetic recording medium are significantly improved.
[0037]
In the case where the magnetic layer 3 is, for example, a Co—CoO-based magnetic layer, the hydrogen standard electrode potential at 25 ° C. of Co, which bears the magnetism of the magnetic layer 3 at −25 ° C., is the hydrogen standard electrode potential of Al at 25 ° C. Is -1.662 V, and the hydrogen standard electrode potential of Ti at 25 ° C. is -1.628 V. Therefore, the shield layer is selectively oxidized with respect to the magnetic layer 3, and the deterioration of the magnetic layer 3 is effectively suppressed.
[0038]
The shield layers 2a to 2c are manufactured by a vacuum thin film forming technique. Examples of the vacuum thin film forming technique include physical vapor deposition (PVD) such as vacuum deposition, ion plating, and sputtering. According to the vacuum evaporation method, a metal material to be a material of a shield layer is heated and evaporated under vacuum, and adhered to a nonmagnetic support and / or a magnetic layer.
[0039]
According to the ion plating method, the metal material to be the material of the shield layer is evaporated during the discharge. According to the sputtering method, a glow discharge is caused in an atmosphere containing argon as a main component, and the generated argon ions strike out surface atoms of a target made of a material of a shield layer, and are deposited on a nonmagnetic support and / or a magnetic layer. Let it. According to these PVDs, the film formability of the shield layer can be improved.
[0040]
FIG. 2 is a diagram showing a configuration of a magnetron sputtering apparatus applicable to the formation of the shield layers 2a to 2c. The pressure inside the chamber 21 of the magnetron sputtering apparatus 20 shown in FIG. The evacuation speed from the chamber 21 to the vacuum pump 22 is adjusted by the angle of the valve 23. Ar gas is introduced into the chamber 21 from an argon (Ar) gas introduction pipe 24. The non-magnetic support 1 is unwound from the supply roll 25, travels on the peripheral surface of the cooling can 26, and is sequentially wound on the take-up roll 27. The cooling can 26 is cooled to, for example, −40 ° C., thereby preventing the nonmagnetic support 1 from being deformed by heat.
[0041]
An electrode 28 is arranged at a predetermined distance from the cooling can 26 so as to face the cooling can 26. When a predetermined voltage is applied between the cooling can 26 and the electrode 28, glow discharge generates argon ions. The atoms of the target 29 are beaten out by the argon ions, and are deposited on the nonmagnetic support 1. The magnetron sputtering apparatus 20 having the above-described configuration can be suitably used for forming the shield layers 2a to 2c of the magnetic recording medium of the present embodiment.
[0042]
Like the shield layers 2a to 2c, the magnetic thin films 3a and 3b constituting the magnetic layer 3 can be formed by PVD such as a vacuum evaporation method, an ion plating method, or a sputtering method. It is particularly preferable that the magnetic layer 3 is formed by a vacuum evaporation method in which oblique evaporation is performed. The oblique deposition method of forming a magnetic layer by running the long non-magnetic support 1 in the longitudinal direction and depositing magnetic fine particles on one main surface side of the running non-magnetic support 1 is a method of oblique evaporation. And has the advantage of high productivity.
[0043]
FIG. 3 is a diagram showing a configuration of a continuous winding vacuum evaporation apparatus applied to the formation of the magnetic layer 3. The vacuum evaporation apparatus 30 shown in FIG. 3 is configured for oblique evaporation, and a cooling can 32 and an evaporation source 33 for a ferromagnetic metal thin film are arranged in a vacuum chamber 31 so as to face each other. The inside of the vacuum chamber 31 is, for example, 1 × 10 ^-3 A vacuum of about Pa is applied. The cooling can 32 is cooled to, for example, about −20 ° C., and rotates in a direction indicated by an arrow A in the figure.
[0044]
A supply roll 34 and a take-up roll 35 are provided in the vacuum chamber 31. The non-magnetic support 1 is fed out from the supply roll 34 in the direction indicated by the arrow B in the figure, travels along the peripheral surface of the cooling can 32, and is wound up by the take-up roll 35. The underlayer and the shield layer may be formed on the non-magnetic support 1 supplied from the supply roll 34.
[0045]
In addition, guide rollers 36 and 37 are arranged between the supply roll 34 and the cooling can 32 and between the cooling can 32 and the take-up roll 35, respectively. The tension of the non-magnetic support 1 running according to the winding roll 35 is adjusted. Thereby, the non-magnetic support 1 runs smoothly.
[0046]
The evaporation source 33 is a container in which a ferromagnetic metal material such as Co is contained in a container such as a crucible. The vacuum evaporation device 30 is provided with an electron gun 38 for heating and evaporating the ferromagnetic metal material of the evaporation source 33. When an electron beam 39 is accelerated from the electron gun 38 onto the ferromagnetic metal material of the evaporation source 33, the ferromagnetic metal material of the evaporation source 33 is heated and evaporates as shown by an arrow C in the figure. The ferromagnetic metal material is deposited on the non-magnetic support 1 running along the peripheral surface of the cooling can 32 to form a ferromagnetic metal thin film.
[0047]
A first shutter 40 and a second shutter 41 are provided between the evaporation source 33 and the cooling can 32. The first shutter 40 is located on the front side of the traveling nonmagnetic support 1, and the second shutter 41 is located on the rear side of the traveling nonmagnetic support 1. The first shutter 40 and the second shutter 41 expose only a predetermined area of the non-magnetic support 1 running along the peripheral surface of the cooling can 32 to the outside.
[0048]
When depositing the ferromagnetic metal thin film, a predetermined amount of oxygen gas is supplied to the vicinity of the surface of the non-magnetic support 1 through an oxygen gas inlet (not shown), whereby the ferromagnetic metal thin film has magnetic properties, durability and weather resistance. It is preferable to improve the performance. In addition, in order to heat the vapor deposition source 33, in addition to the above-described heating means using an electron beam, known means such as a resistance heating means, a high frequency heating means, and a laser heating means can be used.
[0049]
In the vacuum vapor deposition device 30, the ferromagnetic metal material is evaporated from the vapor deposition source 33, and the non-magnetic support 1 is caused to run on the peripheral surface of the cooling can 32. The evaporated ferromagnetic metal material is deposited only between the first shutter 40 and the second shutter 41 on the portion where the nonmagnetic support 1 is exposed to the outside.
[0050]
Since the vacuum evaporation apparatus 30 causes the nonmagnetic support 1 to travel from the first shutter 40 side to the second shutter 41 side, the evaporated ferromagnetic metal material It is deposited on the support 1. Then, as the nonmagnetic support 1 travels from the first shutter 40 side to the second shutter 41 side, the evaporated ferromagnetic metal material is sequentially deposited. Therefore, the magnetic layer formed by limiting the incident angle of the magnetic fine particles by the above-described film forming method has a feature of having an oblique columnar structure.
[0051]
In the magnetic layer 3 of the oblique deposition tape suitable for the linear type magnetic recording tape system using the high-sensitivity MR head, the inclination of the oblique columnar structure of the lower magnetic thin film 3a and the inclination of the oblique columnar structure of the upper magnetic thin film 3b. Is reversed. In order to obtain the structure of the magnetic layer 3 described above, the lower magnetic thin film 3a is formed by performing oblique deposition while moving the roll-shaped non-magnetic support 1 in one direction, and then winding in a roll shape. . The wound roll is replaced with the supply roll 34, and oblique deposition is performed again as shown in FIG. Thereby, the magnetic layer 3 having a structure in which the inclination of the rhombic columnar structure of the two magnetic thin films is different from each other is obtained.
[0052]
In the magnetic layer 3 of the oblique deposition tape suitable for the helical scan method, the inclination of the oblique columnar structure of the lower magnetic thin film 3a and the inclination of the oblique columnar structure of the upper magnetic thin film 3b are the same. In order to obtain the structure of the magnetic layer 3 described above, the lower magnetic thin film 3a is formed by performing oblique deposition while moving the roll-shaped non-magnetic support 1 in one direction, and then winding in a roll shape. . The wound roll is newly rewound onto another roll and replaced with the supply roll 34, and oblique deposition is performed again as shown in FIG. Thereby, the magnetic layer 3 having a structure in which the inclination of the rhombic columnar structure of the two magnetic thin films is the same is obtained.
[0053]
As shown in FIG. 1, it is desirable to form a protective layer 4 on the magnetic layer 3. The protective layer 4 is provided to ensure good running durability and corrosion resistance, and is made of, for example, diamond-like carbon. The material of the protective layer 4 can be arbitrarily selected from those commonly used as ordinary protective films for metal magnetic thin films. ₂ , Al ₂ O ₃ , BN, Co oxide, MgO, SiO ₂ , Si ₃ N ₄ , SiN _x , SiC, SiN _x -SiO ₂ , ZrO ₂ , TiO ₂ , TiC and the like. The protective layer 4 may be a single-layer film or a multilayer film.
[0054]
The protective layer 4 can be formed by a CVD method using, for example, a plasma CVD (chemical vapor deposition) continuous film forming apparatus. As the CVD method, any of conventionally known methods such as a mesh electrode DC plasma method, an electron beam excited plasma source method, a cold cathode ion source method, an ionization vapor deposition method, and a catalytic CVD method can be used. As the carbon compound used in the CVD method, any of conventionally known materials such as a hydrocarbon compound, a ketone compound, and an alcohol compound can be used. At the time of plasma generation, Ar and H are used as gases for accelerating the decomposition of the carbon compound. ₂ Etc. may be introduced.
[0055]
A lubricant layer 5 is formed on the protective layer 4 as necessary to improve the running property of the magnetic recording medium. The lubricant layer 5 is formed, for example, by applying an arbitrary perfluoropolyether-based lubricant.
[0056]
A back coat layer 6 is formed on the surface of the nonmagnetic support 1 opposite to the surface on the side of the magnetic layer 3. The thickness of the back coat layer 6 is preferably about 0.2 to 0.7 μm. For the back coat layer 6, for example, solid particles such as inorganic pigments are dispersed in a binder, and kneaded with an organic solvent according to the type of the binder to prepare a coating for the back coat layer. Formed on the back side of the substrate. Further, it is desirable to apply a lubricant also to the surface of the back coat layer 6.
[0057]
Further, a support reinforcing layer may be provided between the back coat layer 6 and the non-magnetic support 1. The support reinforcement layer is a metal such as Mg, Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, W, or an alloy or oxide of these metals. Is preferred. The support reinforcement layer can be formed by a method such as a vapor deposition method, a sputtering method, and an ion plating method. The thickness of the support reinforcing layer is preferably about 20 nm to 500 nm.
[0058]
The magnetic recording medium 10 of the present embodiment manufactured as described above is particularly suitable as a magnetic recording medium for a magnetic recording tape system using an MR head. The MR head is a read-only magnetic head that detects a signal from a magnetic recording medium using a magnetoresistance effect. In general, an MR head is more suitable for a high-density magnetic recording medium because it has higher sensitivity and higher reproduction output than an induction type magnetic head that performs recording and reproduction using electromagnetic induction.
[0059]
The MR head includes a substantially rectangular MR element portion sandwiched between a pair of magnetic shields made of a soft magnetic material such as Ni-Zn polycrystalline ferrite via an insulator. A pair of terminals is led out from both ends of the MR element, and a sense current can be supplied to the MR element via these terminals. When reproducing a signal from a magnetic recording medium using an MR head, the MR element is slid on the magnetic recording medium. In this state, a sense current is supplied to the MR element via terminals connected to both ends of the MR element, and a voltage change of the sense current is detected.
[0060]
When a sense current is supplied to the MR element while the MR element is slid on the magnetic recording medium, the magnetization direction of the MR element changes according to the magnetic field from the magnetic recording medium and is supplied to the MR element. The relative angle between the sense current and the magnetization direction changes. Then, the resistance changes depending on the relative angle between the magnetization direction of the MR element and the direction of the sense current.
[0061]
For this reason, by making the value of the sense current supplied to the MR element unit constant, a voltage change occurs in the sense current. Therefore, by detecting the voltage change of the sense current, the signal magnetic field from the magnetic recording medium is detected, and the signal recorded on the magnetic recording medium is reproduced. As the reproducing magnetic head, a giant magnetoresistive magnetic head (GMR head) is also applicable.
[0062]
As a method of applying a bias magnetic field to the MR element, in addition to a SAL (soft adjustable layer) bias method, for example, a permanent magnet bias method, a shunt current bias method, a self-bias method, an exchange bias method, a barber pole method, a split element method, and a servo method. Various methods such as a bias method can be applied. The giant magnetoresistance effect element and various bias methods are described in detail in Non-Patent Document 1, for example.
[0063]
Next, the effect of the shield layer in the magnetic recording medium of the present embodiment will be described in detail. As described above, the inventor of the present invention has found that when the magnetic layer is thinned for the purpose of making a magnetic recording medium suitable for the MR head, the amount of magnetization of the magnetic layer is significantly reduced by storage. FIG. 4 shows the relationship between the thickness of the Co magnetic layer and the magnetization deterioration rate. The magnetization deterioration rate was calculated by using the following equation (1) by measuring the saturation magnetization Ms0 before leaving the magnetic recording medium in a high temperature and high humidity environment and measuring the saturation magnetization Ms1 after leaving the magnetic recording medium.
Magnetization degradation rate (%) = ((Ms0−Ms1) / Ms0) × 100 (1)
[0064]
As shown in FIG. 4, when the thickness of the magnetic layer becomes thinner than about 50 nm, the rate of magnetization deterioration sharply increases. In practice, the above-mentioned magnetization deterioration rate is preferably within 10%, and when the thickness of the magnetic layer is 50 nm or less, the magnetization deterioration rate is not allowed. When a magnetic recording medium is used for a GMR head having higher reproduction sensitivity than an MR head, the magnetic layer is thinner than a magnetic recording medium for an MR head. In a magnetic recording medium for a GMR head, the thickness of the magnetic layer is, for example, 50 nm or less, and preferably about 30 nm.
[0065]
When the thickness of the magnetic layer is reduced to 100 nm or less, the reproducing sensitivity is insufficient with the conventional inductive head, so that it is necessary to use an MR head or a GMR head for reproducing. That is, such an increase in the magnetization deterioration rate causes a problem when the areal density of the recording / reproducing signal is increased and the MR head or the GMR head is used for the reproduction. Although such a phenomenon has not been reported so far, the following mechanism can be considered.
[0066]
The magnetic layer is formed, for example, by depositing a magnetic metal such as Co, and the lower and upper portions of the magnetic layer are oxidized below the stoichiometric composition due to the reaction with oxygen introduced at that time and the atmosphere during the manufacturing process. It is in a state. The oxidized region exists at the interface between the magnetic layer and the nonmagnetic support, at the interface between the magnetic layer and the protective layer, and at the interface between the magnetic layer and the magnetic layer.
[0067]
Under a high-temperature and high-humidity environment, diffusion of oxygen contained in the magnetic layer and penetration of oxygen and moisture from the external environment are promoted. Thereby, the oxidized region at each interface is enlarged, and the oxygen ratio is increased. The enlargement speed of the oxidized region is reduced when the oxidized region has a certain thickness. This is because, when the oxide film is thick, the number of blocked portions of the diffusion path of oxygen and moisture increases, and it becomes difficult for oxygen to enter the inside of the magnetic layer. When the thickness of the magnetic layer is 100 nm or more, the decrease in the amount of magnetization at the center in the thickness direction of the magnetic layer is small.
[0068]
However, when the thickness of the magnetic layer is 100 nm or less, the entire magnetic layer is oxidized because the oxidized region extending from the upper and lower layers reaches the central region of the layer. Further, since the reaction does not stop until the entire magnetic layer has a stoichiometric composition of oxygen and Co, the amount of magnetization decreases rapidly.
[0069]
The remarkable decrease in the amount of magnetization can also be explained for the stacked magnetic layers for the same reason. However, when the magnetic layers are stacked, oxygen present at the interface between the magnetic layers is also diffused, so that the total thickness of the stacked magnetic layers is the same as the magnetic layer thickness in the magnetic recording medium having a single magnetic layer. For example, the amount of reduction in the amount of magnetization is greater when the magnetic layers are stacked.
[0070]
For example, if the thickness of a single magnetic layer is 150 nm, the deterioration of the amount of magnetization is hardly a problem. The reduction in the amount of magnetization has a size that poses a practical problem. When the total thickness exceeds 150 nm, the recording density becomes small, and thus, for example, there is no practical use in a high recording density magnetic recording system using a GMR head. Therefore, in the present invention, the total thickness of the laminated magnetic layers is specified to be 150 nm or less.
[0071]
FIG. 5 shows the magnetization deterioration rate and the coercive force ratio when a Ti shield layer is provided at the interface between the nonmagnetic support and the Co magnetic layer. FIG. 6 shows the magnetization deterioration rate and the coercive force ratio when an Al shield layer is provided at the interface between the nonmagnetic support and the Co magnetic layer. The thickness of the magnetic layer was set to a thickness (25 nm) at which the magnetization deterioration was largest in FIG. The magnetization deterioration rate was calculated using the above equation (1). FIGS. 5A and 6A show the magnetization degradation rate when the shield layer is not provided. The coercive force ratio was calculated from the coercive force before storage using the following equation (2).
Coercivity ratio = (Coercivity of sample) / (Coercivity without shield layer) (2)
[0072]
As shown in FIGS. 5 and 6, the magnetization deterioration rate is reduced when the Ti or Al shield layer is provided with a thickness of 0.5 nm and is provided with a thickness of 1 nm as compared with the case where no shield layer is provided. Significantly reduced when When the shield layer has a thickness of 5 to 10 nm, the magnetization deterioration rate becomes minimum, and when the shield layer is larger than 10 nm, the magnetization deterioration rate increases.
[0073]
When the standard allowable range of the magnetization deterioration rate in the magnetic recording medium for the GMR head is within 10% for practical use, if the thickness of the Ti shield layer or the Al shield layer exceeds 30 nm, the magnetization deterioration rate becomes unacceptable. In the above-mentioned conventional Patent Documents 2 to 4, since the underlayer is not formed in such a thickness range, the effect of a Ti layer or Al layer having a thickness of 30 nm or less on magnetic properties, the thickness of the Ti layer or Al layer, The behavior of the magnetic properties according to this is not studied.
[0074]
Regarding the coercive force ratio, as shown in FIGS. 5 and 6, by providing a shield layer of Ti or Al with a thickness of 0.5 to 50 nm, the coercive force is slightly reduced as compared with the case without the shield layer. . The coercive force ratio becomes minimal when the thickness of the shield layer is about 5 nm, but the coercive force ratio at this time is 0.8 or more, which is within a practically acceptable range.
[0075]
As described above, by forming the Ti or Al shield layer to have a thickness of 1 to 30 nm so as to be in contact with the magnetic layer, it is possible to effectively suppress a decrease in the amount of magnetization due to storage. Further, it was confirmed that even when the shield layer made of an alloy containing Ti or Al was formed with the same thickness, the decrease in the amount of magnetization due to storage could be similarly suppressed.
[0076]
【Example】
Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.
(Example 1 and Comparative Example 1)
As a non-magnetic support, a polyethylene terephthalate (PET) film having a thickness of 6.3 μm and a width of 150 mm was prepared. First, an underlayer having a thickness of 5 nm was formed on the surface of the nonmagnetic support on which the magnetic layer was to be formed. The underlayer was prepared by stirring silica particles having a diameter of 10 nm into a water-soluble latex containing acrylic ester as a main component, and having a density of 1 × 10 ⁷ Pieces / mm ² It was formed by coating so as to have the same degree.
[0077]
Next, in Example 1, a shield layer was formed on the underlayer by a sputtering method. Comparative Example 1 is the same as Example 1 except that this shield layer was not formed. The magnetron sputtering apparatus shown in FIG. 2 was used for forming the shield layer. In Example 1, Ti was used for the target 29. In the magnetron sputtering apparatus 20 shown in FIG. ^-4 The pressure was reduced to Pa. Thereafter, the exhaust speed was reduced by reducing the angle of the valve 23 for exhausting to the vacuum pump 22 side from the fully opened state to 10 degrees, and Ar gas was introduced from the Ar gas introducing pipe 24 to set the degree of vacuum to 0.8 Pa.
[0078]
Next, the raw PET film on which the underlayer is formed is set on the supply roll 25, and the PET film (non-magnetic support) 1 is caused to run along the peripheral surface of the cooling can 26 cooled to -40 ° C. The winding roll 27 can be sequentially wound up. The target 29 was arranged at a position 45 mm away from the cooling can 26 so as to face the cooling can 26. A voltage of 2000 V was applied between the cooling can 26 and the electrode 28, and a state in which a current of 1.4 A flowed was maintained. As a result, a Ti layer serving as the shield layer 2a (see FIG. 1) was formed on the nonmagnetic support unwound from the PET film source.
[0079]
The thickness of the shield layer is controlled by adjusting the film forming speed in the magnetron sputtering apparatus 20 shown in FIG. The film forming speed depends on the feed speed of the non-magnetic support from the supply roll 25 to the take-up roll 27 and the deposition speed of the target material on the non-magnetic support. The deposition rate of the target material on the non-magnetic support depends on the voltage applied between the cooling can 26 and the electrode 28 and the distance between the cooling can 26 and the target 29. By adjusting these, in Example 1, a Ti layer having a thickness of 1 nm was formed as a shield layer between the nonmagnetic support and the magnetic layer.
[0080]
Next, a magnetic layer was formed using the vacuum evaporation apparatus 30 shown in FIG. Co was used as a raw metal magnetic material (evaporation source 33). 6.0 × 10 oxygen in the vacuum chamber 31 ^-4 m ³ The deposition source 33 was heated by irradiating an electron beam 39 from an electron gun 38 and a Co—CoO-based magnetic layer was formed by reactive vacuum deposition. At this time, the minimum incident angle of the Co-deposited particles was adjusted to 45 ° and the maximum incident angle to 90 ° by the shutter. The thickness of the magnetic layer is set according to the film forming speed. In Example 1, the thickness of the magnetic layer was 25 nm.
[0081]
Next, a protective film made of diamond-like carbon was formed on the magnetic layer. The protective film made of diamond-like carbon was formed to have a thickness of 10 nm by a plasma CVD method. Next, perfluoropolyether was applied to a thickness of 2 nm on the protective film made of diamond-like carbon to form a lubricating layer.
[0082]
Further, in order to obtain running durability, a backcoat paint was applied to the surface (rear surface) of the nonmagnetic support opposite to the magnetic layer side to form a backcoat layer having a thickness of 0.5 μm. The back coat paint was prepared using carbon particles having an average particle size of 20 nm as an inorganic pigment and using a urethane resin as a binder. An application device by a direct gravure method was used for application of the coating material for the back coat. Finally, the material was cut into a width of 8 mm to obtain a sample tape.
[0083]
The storage characteristics of the prepared sample tapes were evaluated using the following method. The storage characteristics were estimated from the magnetization deterioration rate of the magnetic layer after the storage test in which the sample tape was stored for 6 days in an environment at a temperature of 65 ° C. and a relative humidity of 90%. The magnetization deterioration rate was calculated using the following equation (3) by measuring Ms0 (saturated magnetization) before leaving and Ms1 after leaving. For the Ms measurement, a vibrating sample magnetometer (VSM) was used.
Magnetization deterioration rate (%) = ((Ms0−Ms1) / Ms0) × 100 (3)
[0084]
Table 1 shows the magnetization deterioration rates of Example 1. Tables 1 to 6 summarize the magnetization degradation rates of other examples and comparative examples. Since the magnetization deterioration rate is set to be practically 10% or less as a standard, those having a magnetization deterioration rate exceeding 10% were judged as NG.
[0085]
[Table 1]

[0086]
(Examples 2 to 4 and Comparative Examples 2 and 3)
A sample tape was produced in the same manner as in Example 1, except that the thickness of the shield layer formed between the nonmagnetic support and the magnetic layer was changed as shown in Table 1. The magnetic layer is a single layer and has a thickness of 25 nm. In addition, the graph of FIG. 5 plots the magnetization deterioration rate and the coercive force ratio of the sample tapes of Examples 1 to 4 and Comparative Examples 2 and 3.
[0087]
(Examples 5 to 8 and Comparative Examples 4 and 5)
A sample tape was produced in the same manner as in Example 1, except that the shield layer formed between the nonmagnetic support and the magnetic layer was changed to an Al layer having a thickness shown in Table 1. The magnetic layer is a single layer and has a thickness of 25 nm. The Al layer of the shield layer was formed by sputtering using an Al target. In addition, the graph of FIG. 6 plots the magnetization deterioration rate and the coercive force ratio of the sample tapes of Examples 5 to 8 and Comparative Examples 4 and 5.
[0088]
(Examples 9 to 12 and Comparative Examples 6 and 7)
A sample tape was prepared in the same manner as in Example 1 except that the shield layer was not formed between the nonmagnetic support and the magnetic layer, and the shield layer having the thickness shown in Table 1 was formed between the magnetic layer and the protective layer. did. The magnetic layer is a single layer and has a thickness of 25 nm. The shield layer was formed by the same method as in the case of forming the shield layer between the nonmagnetic support and the magnetic layer in Example 1.
[0089]
(Examples 13 to 16 and Comparative Examples 8 and 9)
Example 1 except that the shield layer was not formed between the nonmagnetic support and the magnetic layer, the shield layer having the thickness shown in Table 1 was formed between the magnetic layer and the protective layer, and the shield layer was an Al layer. A sample tape was prepared in the same manner as in Example 1. The magnetic layer is a single layer and has a thickness of 25 nm. The shield layer was formed in the same manner as in Example 1, except that the shield layer was formed between the nonmagnetic support and the magnetic layer.
[0090]
(Comparative Examples 10 to 13)
A sample tape was produced in the same manner as in Example 1 except that the shield layer was not formed and the thickness of the single magnetic layer was changed to the thickness shown in Table 2. For reference, Table 2 also shows Comparative Example 1 (see Table 1) in which the thickness of the magnetic layer was 25 nm.
[0091]
[Table 2]

[0092]
(Examples 17 to 19)
A sample tape was prepared in the same manner as in Example 1 except that a 30-nm thick Ti layer was formed as a shield layer between the nonmagnetic support and the magnetic layer, and the thickness of the single magnetic layer was changed to the thickness shown in Table 2. Produced. For reference, Table 2 also shows Example 4 (see Table 1) in which the thickness of the magnetic layer was 25 nm.
[0093]
(Examples 20 to 23)
No shield layer was formed between the nonmagnetic support and the magnetic layer, a 30 nm thick Ti layer was formed as a shield layer between the magnetic layer and the protective layer, and the single magnetic layer was formed as shown in Table 2. A sample tape was produced in the same manner as in Example 1 except that the sample tape was changed to.
[0094]
(Examples 24 to 27)
A 30-nm thick Ti layer is formed as a shield layer between the nonmagnetic support and the magnetic layer, and a 30-nm thick Ti layer is formed as a shield layer between the magnetic layer and the protective layer. A sample tape was produced in the same manner as in Example 1 except that the thickness of the magnetic layer was changed to the thickness shown in Table 2.
[0095]
(Examples 28 to 30 and Comparative Examples 14 to 16)
With two magnetic layers, the thickness of the upper magnetic layer and the thickness of the lower magnetic layer were set to the thickness shown in Table 3 so that the total thickness of the magnetic layers was 150 nm. Hereinafter, in Examples and Comparative Examples in which two magnetic layers were used, the upper magnetic layer was formed by the above-described method such that the inclination of the lower magnetic layer and that of the rhombic columnar structure were reversed. In Examples 28 to 30, a 5 nm-thick Ti layer was formed as a shield layer between the nonmagnetic support and the lower magnetic layer. In Comparative Examples 14 to 16, no shield layer was formed. Otherwise, a sample tape was produced in the same manner as in Example 1.
[0096]
[Table 3]

[0097]
(Examples 31 to 33)
A sample tape was prepared in the same manner as in Examples 28 to 30, except that a shield layer was not formed between the nonmagnetic support and the lower magnetic layer, and a shield layer was formed between the lower magnetic layer and the upper magnetic layer. Produced. The shield layer is a 5 nm-thick Ti layer.
[0098]
(Examples 34 to 36)
A sample tape was prepared in the same manner as in Examples 28 to 30, except that a shield layer was not formed between the nonmagnetic support and the lower magnetic layer, and a shield layer was formed between the upper magnetic layer and the protective layer. . The shield layer is a 5 nm-thick Ti layer.
[0099]
(Examples 37 to 42 and Comparative Examples 17 and 18)
With two magnetic layers, the thickness of the upper magnetic layer and the thickness of the lower magnetic layer were set to the thickness shown in Table 4 so that the total laminated thickness of the magnetic layers became 100 nm. In Examples 37 to 42, a Ti layer having a thickness of 5 nm was formed as a shield layer at the positions shown in Table 4, respectively. In Comparative Examples 17 and 18, no shield layer was formed. Otherwise, a sample tape was produced in the same manner as in Example 1.
[0100]
[Table 4]

[0101]
(Examples 43 to 48 and Comparative Examples 19 and 20)
With two magnetic layers, the thickness of the upper magnetic layer and the thickness of the lower magnetic layer were set to the thicknesses shown in Table 5 so that the total laminated thickness of the magnetic layers was 75 nm. In Examples 43 to 48, a Ti layer having a thickness of 5 nm was formed as a shield layer at the positions shown in Table 5, respectively. In Comparative Examples 19 and 20, no shield layer was formed. Otherwise, a sample tape was produced in the same manner as in Example 1.
[0102]
[Table 5]

[0103]
(Example 49)
In Examples 49 to 52, as shown in Table 6, the number of magnetic layers was two, the thickness of the upper magnetic layer was 25 nm, and the thickness of the lower magnetic layer was 50 nm. A 5-nm-thick Ti layer was formed as a shield layer between the nonmagnetic support and the lower magnetic layer, and a 5-nm-thick Ti layer was formed between the lower magnetic layer and the upper magnetic layer as a shield layer. . Otherwise, a sample tape was produced in the same manner as in Example 1.
[0104]
[Table 6]

[0105]
(Example 50)
With two magnetic layers, the thickness of the upper magnetic layer was set to 25 nm, and the thickness of the lower magnetic layer was set to 50 nm. A 5-nm-thick Ti layer was formed as a shield layer between the lower magnetic layer and the upper magnetic layer, and a 5-nm-thick Ti layer was formed as a shield layer between the upper magnetic layer and the protective layer. Otherwise, a sample tape was produced in the same manner as in Example 1.
[0106]
(Example 51)
With two magnetic layers, the thickness of the upper magnetic layer was set to 25 nm, and the thickness of the lower magnetic layer was set to 50 nm. A 5-nm-thick Ti layer was formed as a shield layer between the nonmagnetic support and the lower magnetic layer, and a 5-nm-thick Ti layer was formed between the upper magnetic layer and the protective layer as a shield layer. Otherwise, a sample tape was produced in the same manner as in Example 1.
[0107]
(Example 52)
With two magnetic layers, the thickness of the upper magnetic layer was set to 25 nm, and the thickness of the lower magnetic layer was set to 50 nm. The lower magnetic layer and the upper magnetic layer were formed in the same manner as the single magnetic layer of Example 1. Forming a 5-nm-thick Ti layer as a shield layer between the nonmagnetic support and the lower magnetic layer, and forming a 5-nm-thick Ti layer as a shield layer between the lower magnetic layer and the upper magnetic layer; A 5 nm-thick Ti layer was also formed as a shield layer between the upper magnetic layer and the protective layer. Otherwise, a sample tape was produced in the same manner as in Example 1.
[0108]
(Examples 53 to 56)
The magnetic layer was a single layer having a thickness of 25 nm, and as shown in Table 1, in Example 53, the Ti layer of Example 2 was changed to a Ti—W alloy layer. In Example 54, the Ti layer of Example 10 was changed to a Ti-W alloy layer. In Example 55, the Al layer of Example 6 was changed to an Al-Mg alloy layer. In Example 56, the Al layer of Example 14 was changed to an Al-Mg alloy layer.
[0109]
Table 1 shows the results of examining the effect of the film formation position, material, and thickness of the shield layer when the magnetic layer was a single layer having a thickness of 25 nm. In Comparative Example 1 having no shield layer, the magnetization deterioration rate was as large as 62%. In contrast, when the Ti or Al shield layer is formed with a thickness of 1 to 30 nm, the amount of magnetization deterioration is extremely small. When the thickness of the shield layer is less than 1 nm, the effect of suppressing the deterioration of magnetization is small.
[0110]
When the shield layer having a thickness of 50 nm is at the interface between the nonmagnetic support and the magnetic layer, the amount of magnetization deterioration exceeds 10% and becomes NG. This is presumably because the thicker the shield layer, the worse the surface smoothness is, which affects the magnetic layer and the protective layer, resulting in an increase in the number of defects in the protective layer.
[0111]
When a shield layer having a thickness of 50 nm is at the interface between the magnetic layer and the protective layer, the rate of magnetization deterioration is acceptable, but the spacing loss in recording / reproducing increases, and high recording density cannot be achieved. It is thought that there is no. Therefore, the thickness of the shield layer is specified to be 1 nm or more and 30 nm or less. Further, in Examples 53 to 56, the shield layer is an alloy using Ti or Al as a base material, but similarly exhibits the effect of suppressing the magnetization deterioration. It is clear that the same effect is obtained when other elements are included.
[0112]
Table 2 shows the results of examining the effect when the magnetic layer is a single layer and a 30-nm-thick Ti layer is formed as a shield layer. From this result, it can be seen that the thinner the magnetic layer, the larger the amount of magnetization deterioration, but the presence of the shield layer significantly reduces the amount of magnetization deterioration. When the thickness of the magnetic layer is 125 nm, the magnetization deterioration rate is 10% or less even without the shield layer (Comparative Example 10). Therefore, in the present invention, the thickness of the single magnetic layer is specified to be 100 nm or less, but it is apparent that the magnetization degradation rate can be reduced by providing the shield layer even when the thickness is more than 100 nm.
[0113]
Tables 3 to 5 show the results obtained by examining the effects when a magnetic layer is laminated, the total thickness is 150 nm or less, and a 3 nm-thick Ti layer is formed as a shield layer. From the comparative examples in each table, as in the case where the magnetic layer is a single layer, the amount of magnetization deterioration tends to increase as the total thickness of the magnetic layer decreases, and the amount of magnetization deterioration significantly decreases in a sample having a shield layer. You can see that. In addition, from Table 3 when the total thickness of the magnetic layer is 150 nm and Table 4 when the total thickness of the magnetic layer is 100 nm, the shield is independent of the total thickness of the magnetic layer and the ratio between the upper and lower layers of the magnetic layer. It can be seen that when there is a layer, the magnetization deterioration rate can be made very small.
[0114]
It is obvious that the same effect is obtained even when the total thickness of the magnetic layer is 150 nm or more. However, if the total thickness exceeds 150 nm, for example, in a high-density magnetic recording system using a GMR head, the head is saturated, so There is no sex. Therefore, in the present invention, the total thickness of the laminated magnetic layers is specified to be 150 nm or less.
[0115]
Tables 5 and 6 show the results of examining the effect when a magnetic layer is stacked, the total thickness is 75 nm, and a 3 nm-thick Ti layer is formed as a shield layer. In this experiment, all combinations of the deposition positions of the shield layer were examined. As a result, it was found that if the shield layer was at least one interface, the magnetization deterioration rate could be made very small, and if the shield layer was increased, the magnetization deterioration amount could be made smaller.
[0116]
According to the magnetic recording medium of the embodiment of the present invention, oxygen that diffuses and permeates each layer from the nonmagnetic support side can be shielded at each interface, and storage characteristics under a high-temperature and high-humidity environment are significantly improved. In addition, by forming a shield layer at the interface between the magnetic layer and the protective layer, it is possible to shield oxygen that penetrates the protective layer and diffuses into the magnetic layer, and more effectively suppresses magnetization deterioration of the magnetic layer from the protective layer side. it can. The magnetic recording medium according to the embodiment of the present invention has excellent storage characteristics and enables high-density recording, and is therefore particularly suitable for data storage applications. Further, since the magnetic layer can be made thin, it is suitable for a recording / reproducing system using a high-sensitivity MR head.
[0117]
When a plurality of magnetic layers are stacked, magnetization deterioration is more likely to be more remarkable than when a single magnetic layer is formed. However, by providing at least one shield layer in contact with the magnetic layer, the magnetization can be reduced. Deterioration is effectively prevented. For example, a magnetic recording medium suitable for a linear recording / reproducing system in which two magnetic layers having different growth directions of an oblique columnar structure are stacked to reduce a difference in recording / reproducing characteristics in both directions of tape running. In addition, magnetization deterioration due to storage can be prevented.
[0118]
The present invention is not limited to the description of the above embodiment. For example, the shield layer material may be an alloy other than a Ti-W alloy or an Al-Mg alloy. Further, a magnetic recording medium suitable for the helical scan system may be provided with the above-described shield layer in which two magnetic layers having the same growth direction of the rhombic columnar structure are laminated. In addition, various changes can be made without departing from the spirit of the present invention.
[0119]
【The invention's effect】
According to the present invention, it is possible to obtain a magnetic recording medium which is excellent in storability, enables high-density magnetic recording, and is suitable for a recording / reproducing system using an MR head and a linear system.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of a magnetic recording medium of the present invention.
FIG. 2 is a schematic view of a sputtering apparatus used for forming a shield layer of the magnetic recording medium of the present invention.
FIG. 3 is a schematic view of a vacuum evaporation apparatus used for forming a magnetic layer of the magnetic recording medium of the present invention.
FIG. 4 is a diagram showing a relationship between a thickness of a magnetic layer and a magnetization deterioration rate.
FIG. 5 is a diagram showing changes in the magnetization deterioration rate and the coercive force depending on the thickness of the Ti shield layer.
FIG. 6 is a diagram showing changes in the magnetization deterioration rate and the coercive force depending on the thickness of the Al shield layer.
FIG. 7 is a sectional view of a conventional vapor deposition tape.
FIG. 8 is a cross-sectional view of a conventional vapor deposition tape.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support, 2a, 2b, 2c ... Shield layer, 3 ... Magnetic layer, 3a ... Lower magnetic thin film, 3b ... Upper magnetic thin film, 4 ... Protective layer, 5 ... Lubricant layer, 6 ... Back coat layer, DESCRIPTION OF SYMBOLS 10 ... Magnetic recording medium, 20 ... Magnetron sputtering apparatus, 21 ... Chamber, 22 ... Vacuum pump, 23 ... Valve, 24 ... Ar gas introduction pipe, 25 ... Supply roll, 26 ... Cooling can, 27 ... Take-up roll, 28 ... Electrode, 29 target, 30 vacuum deposition device, 31 vacuum chamber, 32 cooling can, 33 deposition source, 34 supply roll, 35 take-up roll, 36, 37 guide roller, 38 electron gun, 39: electron beam, 40: first shutter, 41: second shutter, 101: non-magnetic support, 102: magnetic layer, 102a, 102b: oblique deposition film.

Claims (4)

A non-magnetic support,
At least one magnetic layer formed on one surface side of the nonmagnetic support by a vacuum thin film forming technique and having a thickness of 100 nm or less per layer;
A metal or alloy containing at least one of aluminum and titanium formed on one or both surfaces of at least one magnetic layer, and at least one shield layer having a thickness of 1 nm or more and 30 nm or less. Magnetic recording medium. 2. The magnetic recording medium according to claim 1, comprising a plurality of the magnetic layers, wherein a total thickness of the plurality of the magnetic layers is 150 nm or less. 2. The magnetic recording medium according to claim 1, wherein the magnetic layer has an oblique columnar structure. 2. The magnetic recording medium according to claim 1, further comprising a protective layer on the uppermost magnetic layer.

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