JP2909766B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium with improved noise characteristics.

[Prior Art] At present, thin-film media in which a CoNi, CoPt or CoCrPt magnetic layer is provided on a Cr underlayer as a material for a small and large-capacity hard disk are being actively studied. In particular, recently, it has been reported that the noise characteristics are remarkably improved by using a laminated structure in which the magnetic layers and the nonmagnetic layers are alternately deposited, as compared with the case where the magnetic layer has a single-layer structure. There are several possible causes for this, such as miniaturization of magnetic particles by lamination, but this has not been clarified at present.

[Problems to be Solved by the Invention] Although the noise characteristics are greatly improved by increasing the number of magnetic layers, further noise reduction is desired in the case of high density recording in the future.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problem of high noise level of the prior art and to provide a magnetic recording medium having excellent high density recording characteristics.

Means for Solving the Problems To achieve the above object, according to the present invention, a columnar structure in which two types of layers having different saturation magnetizations are alternately stacked on a nonmagnetic substrate with or without a nonmagnetic layer interposed therebetween. In the magnetic recording medium having the recording layer, the thickness of the layer having a large saturation magnetization among the two types of layers is formed so as to decrease in order from the nonmagnetic substrate side to the recording layer surface layer side. A magnetic recording medium is provided.

It is preferable that the adjacent columnar recording layers are separated without contacting each other.

One of the two types of layers having different saturation magnetizations may be a non-magnetic layer.

[Operation] FIG. 1 shows a schematic sectional structure of the magnetic recording medium of the present invention.

As shown, in the magnetic recording medium 1 of the present invention, the high saturation magnetization layer 5 and the low saturation magnetization layer 7 are formed on the non-magnetic substrate 3.
When the magnetic recording layer 9 is formed by stacking
Are made thicker on the non-magnetic substrate side and thinner toward the recording layer surface layer side (that is, T ₄ > T ₃ > T ₂ > T ₁ ). Therefore, the adjacent columnar magnetic recording layers can maintain a separated state without contacting each other at any part from the root to the top. As a result, each of the columnar magnetic particles is magnetically separated, so that the generation of magnetic domains in the magnetization transition region can be suppressed, and the noise can be further reduced.

On the other hand, as shown in FIG. 2, when the high saturation magnetization layers 5 and the low saturation magnetization layers 7 having the same film thickness at t ₁ are alternately stacked, the columnar particles of each columnar magnetic recording layer become on the medium surface layer. The grains grow as they approach, and the columnar magnetic recording layers come into contact with each other near the surface layer of the medium. As a result, magnetic exchange interaction acts between the columnar magnetic particles near the surface layer of the medium, and a complex magnetic domain is generated in the magnetization transition region, causing an increase in noise.

The thickness of the low saturation magnetization layer or the non-magnetic layer alternately stacked with the high saturation magnetization layer is not particularly limited. In general, it is preferred that it be constant.

The medium structure of the present invention can be obtained by a dry method such as sputtering or vapor deposition, or a wet method by plating. In the dry method, a method of sequentially shortening the time for forming the high saturation magnetization layer is generally used. In the wet method by plating, a pulse plating method using a pulse power supply is suitable. The basic idea of pulse plating is to use an aqueous solution containing two or more types of metal ions having greatly different reduction potentials, and to supply a potential at which each metal ion is reduced and deposited alternately by a pulse wave. For example, in order to produce a laminated film of the present invention comprising a magnetic layer and a non-magnetic layer, the pulse application time for reducing the magnetic layer may be shortened sequentially. In pulse plating,
Since the thickness and number of layers of each layer can be freely controlled by the application time and period of the pulse wave, a laminated medium can be manufactured in a shorter time than a dry method such as a sputtering method in which a target must be replaced for each layer. There are advantages.

Non-magnetic substrates used in the magnetic recording medium of the present invention include, in addition to aluminum substrates, polymer films such as polyimide and polyethylene terephthalate; glasses; ceramics; metal plates such as anodized aluminum and brass; Plates and single-crystal Si plates whose surfaces are thermally oxidized.

Further, as the magnetic recording medium of the present invention, a disk or a drum composed of a magnetic tape or a magnetic disk, a synthetic resin film, an aluminum plate, a glass plate or the like based on a synthetic resin film such as a polyester film or a polyimide film as a base Various forms of a structure that slides on a magnetic head, such as a magnetic disk and a magnetic drum, are included.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 A 0.5 μm Cr underlayer was provided on a 3.5 ″ size Al substrate having a NiP nonmagnetic layer formed on the surface, and CoNi (200 Å (hereinafter referred to as “A”) / Pt (50A) / CoNi (150
A) A laminated film represented by Pt (50 A) / CoNi (100 A) / Pt (50 A) / CoNi (50 A) was formed by a sputtering method. As a result of examining the cross-sectional structure of this medium with a transmission electron microscope, it was confirmed that the columnar magnetic particles were not in contact with the medium surface layer as shown in FIG.

Example 2 Au was sputtered on a 3.5 ″ size Al disk at a thickness of 0.2 μm, and the same CoNi / Pt as in Example 1 was formed thereon by pulse plating.
A laminated film was performed. The plating bath is CoSO ₄ : 0.1 mol / l,
NiSO ₄ : 0.1 mol / l, H ₃ BO ₃ : 0.2 mol / l,
Glycerin: 2 ml / liter, K ₂ PtCl ₆ : 0.001 mol / liter, utilizing the fact that the potential for reduction precipitation of CO ²⁺ and Ni ²⁺ is sufficiently higher than the potential for reduction precipitation of Pt ⁴⁺ , Was alternately applied by a pulse wave, and the application time of the pulse potential for precipitating CoNi was shortened as the plating approached the end point. As a result of examining the cross-sectional structure of this medium with a transmission electron microscope, it was confirmed that the columnar magnetic particles were not in contact with the medium surface layer as shown in FIG.

Comparative Example 1 A 0.05 μm Cr underlayer was provided on the same substrate as in Example 1, and CoNi (200 A) / Pt (50 A) / CoNi (200 A) / Pt was formed thereon.
A laminated film represented by (50A) / CoNi (200A) was formed by a sputtering method. As a result of examining the cross-sectional structure of this medium with a transmission electron microscope, as shown in FIG. 2, the columnar magnetic particles were in contact near the surface layer of the medium.

Example 3 A carbon protective layer was formed on the medium surfaces prepared in Examples 1 and 2 and Comparative Example 1 by a sputtering method of 0.03 μm, and the gap length was changed.
Recording was performed using a 0.3 μm thin film magnetic head. The spacing between the magnetic head and the medium during recording was 0.14 μm including the carbon protective layer, and the recording density was 35 kFCI.
Table 1 below shows the S / N ratio of each medium. The noise band was set to 20 MHz.

As is clear from the results shown in Table 1 above, the magnetic recording medium of the present invention in which the magnetic columnar particles are not in contact is compared with the magnetic recording medium of the comparative example in which the magnetic columnar particles are in contact. Thus, the S / N ratio has been greatly improved.

[Effects of the Invention] As described above, in the magnetic recording medium of the present invention, the thickness of the surface layer side of the laminated high saturation magnetization film is made smaller than that of the lower layer side, and contact between the columnar magnetic particles is suppressed so that The noise of the media by increasing the spatial separation, and consequently the S / N
The ratio can be improved.

[Brief description of the drawings]

FIG. 1 shows a magnetic recording layer in which two types of layers having different saturation magnetizations are alternately stacked, and the thickness of the high saturation magnetization layer is formed so as to gradually decrease from the non-magnetic substrate side to the recording layer surface layer side. FIG. 2 is a schematic cross-sectional view of a magnetic recording medium according to the present invention. FIG. 2 shows a magnetic recording layer in which two types of layers having different saturation magnetizations are alternately stacked so that the thickness of the high saturation magnetization layer is constant. FIG. 4 is a schematic cross-sectional view of a formed magnetic recording medium of a comparative example. DESCRIPTION OF SYMBOLS 1 ... The magnetic recording medium of this invention, 3 ... Nonmagnetic base, 5 ... High saturation magnetization layer, 7 ... Low saturation magnetization layer, 9 ... Magnetic recording layer

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akihito Sakamoto 1-1-88 Ushitora, Ibaraki-shi, Osaka Inside Hitachi Maxell Co., Ltd. (72) Kunio Mizushima 1-1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Ltd. (56) References JP-A-57-179942 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/66

Claims (3)

(57) [Claims] 1. A magnetic recording medium having a columnar recording layer in which two types of layers having different saturation magnetizations are alternately laminated on a non-magnetic substrate with or without a non-magnetic layer interposed therebetween. A magnetic recording medium characterized in that the thickness of the layer having a large saturation magnetization is formed so as to decrease in order from the nonmagnetic substrate side to the recording layer surface layer side. 2. The magnetic recording medium according to claim 1, wherein the adjacent columnar recording layers are separated without contacting each other. 3. The magnetic recording medium according to claim 1, wherein one of the two types of layers having different saturation magnetizations is a nonmagnetic layer.