JP2909767B2 - 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, magnetic recording media having a magnetic layer such as Co-Ni or Co-Pt on a Cr underlayer are being actively studied as a material for a small and large-capacity hard disk. In particular, recently, it has been reported that noise characteristics are remarkably improved by using a laminated structure in which the magnetic layers and the nonmagnetic intermediate layers are alternately deposited, as compared with a single-layer structure. (For example, SElambert, JKHo
ward and ILSanders: “Reduction of media noise in
thin film metal media by lamination ": 1990 Digests
of INTERMAG'90, Lecture No. HB-02) There are several possible mechanisms for this, such as miniaturization of magnetic particles by lamination, but it has not been clarified so far.

[Problem to be Solved by the Invention] As described above, the noise characteristic of the recording medium is improved to some extent by the multilayer recording magnetic layer. However, if a higher density recording is aimed at in the future, further noise reduction is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium having excellent high-density recording characteristics by alleviating the disadvantage of the above-described prior art that the noise level is high.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, two types of layers having different saturation magnetizations are alternately laminated on a non-magnetic substrate with or without a non-magnetic underlayer. In a magnetic recording medium having a magnetic recording layer comprising: a magnetic recording medium, wherein a level difference occurs in a horizontal level of each layer at least near the surface of the magnetic recording layer.

It is preferable that the horizontal level step of each layer in the magnetic recording layer exists at least in the longitudinal direction of the recording track.

It is preferable that the repetition cycle of the horizontal level difference of each layer in the magnetic recording layer is 10 μm or less in the longitudinal direction of the recording track.

One of the two types of layers having different saturation magnetizations is preferably a nonmagnetic layer.

[Operation] FIG. 1 shows a schematic sectional structure of the magnetic recording medium of the present invention. This cross-sectional structure is viewed from the recording track width direction.

As shown in the figure, in the magnetic recording medium 1 of the present invention, two types of layers 5 and 7 having different saturation magnetizations are alternately laminated on the non-magnetic substrate 3 to form the magnetic recording layer 9. A feature of the magnetic recording medium of the present invention is that two types of layers 5 and 7 having different saturation magnetizations are laminated in a wave shape. That is, there is a step in the horizontal level of each layer. In particular, there is a horizontal level step in the longitudinal direction of the recording track. The repetition period of the horizontal level step is preferably 10 μm or less in the longitudinal direction of the recording track. If it exceeds 10 μm, inconveniences such as a small effect of noise reduction occur. On the other hand, the lower limit value of the repetition period is not particularly limited, but is preferably 0.05 μm or more from the viewpoint of securing a high reproduction output.

FIG. 2 shows a schematic step structure of a conventional multilayer magnetic recording medium viewed from the recording track width direction. In the conventional multilayer medium, two types of layers 5 and 7 having different saturation magnetizations are alternately stacked in a longitudinal direction of the recording track in a substantially complete layered structure to form the magnetic recording layer 9.

One of the two types of layers having different saturation magnetizations may be a nonmagnetic layer.

In the magnetic recording medium of the present invention, since there is a step in the magnetic recording layer, as shown in FIG. 3, in the magnetization transition region, the region where the magnetization in the opposite direction is reduced decreases, and the transition region due to the demagnetizing field Shape disorder is reduced. As a result, noise is significantly reduced.

On the other hand, in the conventional multilayer magnetic recording medium shown in FIG. 2, two types of magnetic layers having different saturation magnetizations are alternately laminated in the longitudinal direction of the recording track in a substantially complete layered structure to form a magnetic recording layer. As a result, as shown in FIG. 4, butting magnetic domains are formed in the recording magnetization transition region.
As a result, a strong demagnetizing field acts in the vicinity of the transition region in the direction opposite to the recording magnetization, and the shape of the transition region is disturbed to generate noise.

The magnetic recording medium of the present invention can also be obtained by depositing two types of magnetic materials having different saturation magnetizations on a non-magnetic substrate having a roughened surface by a vapor deposition method such as a sputtering method or a vacuum evaporation method. However, a convenient manufacturing method that most easily realizes the structure of the magnetic recording medium of the present invention is an AC or pulse plating method.

In this method, the plating bath contains two or more ions,
This is a method in which alternating current or a pulse is applied to the electrode and the composition is periodically modulated by utilizing the difference in the reduction potential of both ions. Therefore, by changing the applied voltage waveform,
The composition in the thickness direction can be modulated over a wide range. Although the exact mechanism has not been elucidated yet, the composition modulation film produced by such a plating method does not become a substantially flat layered structure film as shown in FIG. 2, but rather as shown in FIG. It has a structure close to a composition modulation film having a wavy shape. The pulse plating method can be applied to a non-magnetic substrate having a roughened surface.

Examples of the material used for manufacturing the corrugated layered magnetic recording medium of the present invention include materials in which Fe, Co, Ni or other elements are combined, and from the viewpoint of magnetic properties, Co- P, Co-Ni, Co-Ni-P, Co-Pt, Co-Pt-P,
Co-based materials such as Co-Ni-Pt, Co-W, Co-WP, and Co-Ni-WP are preferred.

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 On a 3.5-inch A1 disk, Au was sputtered at 0.2 μm to form a substrate electrode. This substrate was transferred to a plating bath containing CoSO ₄ : 0.1 mol / l, NiSO ₄ : 0.1 mol / l, H3BO ₃ : 0.2 mol / l, glycerin: 2 ml / l K ₂ PtCl ₆ : 0.001 mol / l,
CoNi / Pt multilayer film plating was performed using carbon as the counter electrode. The basic idea of this multilayer plating is that Co ²⁺ and
Potential Ni ²⁺ is reduced E ₀ Co, E ₀ Co ≒ E ₀ Ni between E ₀ potential Ni and Pt ⁴⁺ is reduced _{E 0 Pt, E 0 Co»E 0} Pt, E 0 Ni» Since there is a relationship of E ₀ Pt, the potential E _{1 at} which Co ²⁺ and Ni ²⁺ are reduced and precipitated together is
The potential E _{2 at} which Pt ⁴⁺ is reduced and precipitated is alternately applied. The thickness of the magnetic layer (CoNi) and the nonmagnetic layer (Pt) and the number of each layer can be controlled by the time and frequency of the applied potential. By this multilayer plating method, CoNi (200 Å (hereinafter referred to as “A”) / Pt) is formed on the substrate electrode.
A multilayer film of (40A) was formed so as to have a total thickness of about 700A.

When the structure of the cross section of the film of the magnetic recording medium obtained in this manner was analyzed by an electron microscope, the CoNi and Pt portions had a layered structure, but were not completely layered structures, and had a wavelength of 0.1 to 0.1 nm.
It was confirmed to have a mosaic wavy structure with a step at a period of 1 μm.

Comparative Example A 0.05 μm Cr underlayer was provided on a 3.5-inch size A1 substrate having a NiP nonmagnetic layer formed on the surface, and CoNi (20
A multilayer film of 0A) / Pt (40A) was formed to a total thickness of about 700A. In addition, all of the above film formation is performed by a DC magnetron sputtering method, and the substrate temperature during sputtering is
The temperature was adjusted to 120 ° C.

The structure of the cross section of the film of the magnetic recording medium thus obtained was analyzed with an electron microscope. As a result, it was confirmed that the magnetic recording medium had an almost completely flat layered structure.

Table 1 below shows the magnetic characteristics of each magnetic recording medium obtained in the above Examples and Comparative Examples. In the table, the average saturation magnetization is shown as a value obtained by dividing the saturation magnetic moment measured by the sample vibration magnetometer by the total volume including the non-magnetic portion.

Each of the magnetic recording media obtained in the above Examples and Comparative Examples was recorded by a thin film magnetic head having a permalloy magnetic pole (gap length: 0.3 μm). Magnetic head
The spacing between the recording media was 0.14 mm including the carbon sputter protection film thickness of 0.03 μm formed on the surface of the magnetic recording layer.
μm. The recording density of the recorded signal is 35kfci
(Flux change per inch), and the S / N ratio was evaluated. The evaluation results are shown in Table 2 below. The noise band is 20MHZ
z.

As is clear from the results shown in Table 2, the magnetic recording medium having the wavy layered structure of the present invention has a significantly improved S / N ratio as compared with the conventional magnetic recording medium having the flat layered structure. doing.

[Effects of the Invention] As described above, in the magnetic recording medium of the present invention, the magnetic recording layer formed by alternately laminating two types of layers having different saturation magnetizations has a horizontal level step of each layer, and has a wavy shape. Therefore, noise at the time of recording / reproducing is significantly reduced as compared with the conventional flat layered multilayer magnetic recording layer.

[Brief description of the drawings]

FIG. 1 is a schematic view of a cross-sectional structure of a magnetic recording medium of the present invention, FIG. 2 is a schematic view of a cross-sectional structure of a conventional magnetic recording medium, and FIG. FIG. 4 is a distribution diagram of the recording magnetization of the conventional magnetic recording medium. 1 ... magnetic recording medium of the present invention, 3 ... non-magnetic substrate, 5 ... high (or low) saturation magnetization layer, 7 ... low (or high) saturation magnetization layer, 9
.... magnetic recording layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihito Sakamoto 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Ltd. (58) Fields investigated (Int.Cl. ⁶ , DB name) G11B 5 / 66

Claims (4)

(57) [Claims] 1. A magnetic recording medium having a magnetic 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 underlayer interposed therebetween. A magnetic recording medium characterized in that a level difference occurs in the horizontal level of each layer near the surface. 2. The magnetic recording medium according to claim 1, wherein a horizontal level difference of each layer in the magnetic recording layer exists at least in the longitudinal direction of the recording track. 3. The magnetic recording medium according to claim 1, wherein the repetition period of the horizontal level difference of each layer in the magnetic recording layer is 10 μm or less in the longitudinal direction of the recording track. 4. The magnetic recording medium according to claim 1, wherein one of the two types of layers having different saturation magnetizations is a nonmagnetic layer.