JPS61194623A - Recording meidum - Google Patents

Abstract

PURPOSE:To provide overwrite S/N at about the same degree in the inside and outside circumferential parts of a disk and to permit recording of signals at high density to the disk by making the thickness of the medium in the outside circumferential part smaller than the thickness of the medium in the inside circumferential part. CONSTITUTION:The medium is formed to have the thickness smaller in the outside circumferential part than in the inside circumferential part. For example, a substrate 1 is a disk which has about 130mmphi outside diameter and 40mmphi inside diameter and is formed by subjecting the surface of Al having 1.9mm thickness to NiP plating to 50mum thickness. Co-20wt% Cr alloy is deposited thereon. The Co-Cr alloy 2 is a vertically magnetizable recording medium and permits recording and reproduction to the high density. The Co-Cr medium is formed to have 0.5mum thickness on the innermost circumference and 0.35mum thickness on the outermost circumference and in this manner the thickness on the outermost circumference is made smallest. Such distribution is obtainable by changing adequately the spacing between a sputter target and the substrate in the stage of sputtering the Co-Cr alloy.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a magnetic disk, and in particular to a recording medium suitable for high recording density, which is formed by depositing it on a substrate from a vapor phase using a sputtering method, a vapor deposition method, etc. Regarding.

[Background of the invention]

Conventional magnetic disks are manufactured by mixing magnetic powder with a binder material and applying it by rotation. Generally, coated disks made by this method have excellent durability, but they have the problem of not being able to perform high-density recording because the magnetic powder parasitic during recording and reproduction is diluted with a binder material. Recently, sputtering method,
γ-Fe, O made by depositing on a substrate from a gas phase using a vapor deposition method, etc.
, t Co-Cr, Ba ferrite, etc., have been developed for high-density recording, and have been reported to academic conferences. Regarding continuous media, for example, the Proceedings of the 1981 IEICE General Conference National Conference (229-231
, 193).

For fixed magnetic disk devices, for example,
As disclosed in Japanese Patent No. 96209, a disk is rotated at a constant speed at high speed, and a magnetic head is levitated above the disk at minute intervals. Since the relative movement speed of the head is greater at the outer circumference of the disk than at the inner circumference, the flying height is large, that is, the distance between the head and the disk is large. In a disk drive, when a new signal is recorded on top of an already recorded signal, the previous signal must disappear so that it does not become a loud sound. Such overwriting characteristics are evaluated as override S/N.

To ensure a sufficient value, a sufficiently strong magnetic field must be generated from the head through the entire thickness of the medium.

There has not been much research on the override S/N of continuous media, but according to research by the inventors, when the distance between the head and the disk increases.

I know it's going to get worse quickly. That is, in general,
Override S/N on the outer periphery of the disk than on the inner periphery
It's bad.

[Purpose of the invention]

The object of the present invention is to override S/
The object of the present invention is to provide a disk-shaped recording medium with good quality.

[Summary of the invention]

When the flying height of the head increases at the outer periphery, if the medium is thick, a sufficient recording magnetic field cannot be transmitted to the bottom of the medium.

Therefore, it can be seen that in order to make the override S/N of the outer circumferential part comparable to the override S/N of the inner circumferential part, it is sufficient to make the medium thickness of the outer circumferential part thinner than the medium thickness of the inner circumferential part. In the case of conventional coated media, since the disk is manufactured by a single-rotation coating method, the thickness of the medium tends to be larger at the outer circumference than at the inner circumference, but this does not pose much of a problem in practice regarding override S/N.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows a cross section of the magnetic disk of the present invention.

The substrate 1 is a circular plate having an outer diameter of about 130 Iφ and an inner diameter of 4 mm, which has a 1.9 wr thick AQ surface plated with NiP to a thickness of 50 μm, and is coated with a Co-20 wt % Cr alloy by RF sputtering. The Co-Cr alloy 2 is a perpendicular magnetization recording medium, and is capable of recording and reproducing up to high density. In this example, the thickness of the innermost Co-Cr medium is 0.5 μm,
The thickness of the Go-Cr medium at the outermost periphery was reduced to 0.35 μm. Such a distribution is Co
This can be obtained by appropriately changing the distance between the sputter target and the substrate when sputtering the -Cr alloy. Generally, as the distance between the target and the substrate increases, the thickness of the outer peripheral portion 3 of the magnetic disk tends to become thinner than the thickness of the inner peripheral portion 4 of the magnetic disk. Although the substrate was not rotated during sputtering in this example, it is possible to rotate the substrate in order to make the characteristics uniform. This medium was rotated at a rotational speed of 3600 rpm+, and recording and reproduction were evaluated using a Mn-Zn F↓ Wright Winchester type ring head with a magnetic gap length of 0.55 pm. The flying height at the innermost circumference is approximately 0.15 μm, and at the outermost circumference it is approximately 0.15 μm.
It was 23 μm. 2F 30kPC1, IF 1
As a result of selecting a recording current with a large override S/N as 6kPCI and measuring the override S/N from the inner circumference X to the outer circumference X, the overall result was as shown in curve 1 in Figure 2. A value of 28 dB or more can be obtained over the entire area, making it fully usable for magnetic disk drives (generally 28 dB or more).
It was found that 6 dB or more is required).

On the other hand, the thickness of the innermost periphery and the outermost periphery are approximately 0.
As shown by curve 2 in FIG. 2, for a medium with a constant diameter of 5 μm, the S/N is 28 dB at the inner circumference, but 18 dB at the outer circumference, indicating that there is a problem in the operation of the device.

Although it varies depending on the medium, head, and how the flying height changes, in the case of Co-Cr media, the override S/
It is possible to make N constant over the entire disk area. However, if it is made too thin, the reproduction output becomes too small, so it is actually difficult to reduce the thickness to 40% or less.

As perpendicular magnetization media, not only G o -Cr media but also double-layer media in which G o -Cr medium is formed on a high magnetic permeability layer such as Ni-Fe alloy are sometimes used. It is sufficient that the thickness of the G o -Cr perpendicular magnetization layer that participates in direct recording and reproduction satisfies the present invention.

In this example, an example of a Go-Cr medium was described, but the same applies to any continuous medium that is generally deposited from a gas phase, and it also applies to longitudinal magnetic recording media such as γ-Fe, 03, etc. The present invention can be applied. The present invention can also be applied to flexible disks, but the effect is particularly great for fixed disks that are used in a floating manner.

Further, in this embodiment, an M n -Z n ferrite head is used as the head, but if a thin film head is used, the dependence of the override S/N on the head-to-medium interval becomes greater, and thus the present invention is more effective.

〔Effect of the invention〕

According to the present invention, since the override S/N can be made to be the same at the inner circumference and the outer circumference of the disk, signals can be recorded on the disk at high density.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross section of a magnetic disk of the present invention, and FIG. 2 is a diagram for explaining the present invention in detail. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Go-Cr alloy, 3...
Magnetic disk outer circumference, 4... magnetic disk inner circumference. Iris 1 figure ytz mouth

Claims (1)

[Scope of Claims] 1. A disk-shaped recording medium characterized in that the medium thickness at the outer circumference is smaller than at the inner circumference. 2. The recording medium according to claim 1, which is formed by depositing it on a substrate from a vapor phase. 3. The recording medium according to claim 1 or 2, which is a Co--Cr perpendicular magnetization medium. 4. The recording medium according to claim 1, 2, or 3, which is a fixed disk. 5. The recording medium according to claim 1, 2, 3, or 4, characterized in that recording and reproduction are performed in combination with a thin film head.