JP2547994B2 - Magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a glass substrate type magnetic recording medium used in a magnetic disk device.

2. Description of the Related Art With the increase in capacity of magnetic disk recording devices, attention has been paid to spatter type magnetic disks, which are more advantageous than coating type magnetic disks in terms of magnetic characteristics and recording density. The coating type magnetic disk has a relatively large magnetic layer thickness of about 1 to 2 μm.
The surface property of the disk medium is not significantly affected by the surface property of the substrate. On the other hand, in the sputter type magnetic disk, since the magnetic layer thickness is as thin as 0.5 μm or less, the surface property of the substrate remarkably affects the surface property of the disk medium.
Therefore, the surface property of the thin film magnetic disk medium can be improved by using the substrate having excellent surface accuracy. As a result, the flying height of the magnetic head can be reduced, and the recording density can be improved.

On a spatter type magnetic disc
A Ni-P plating layer having a thickness of about 50 μm is formed and the surface is polished, or an alumite surface is anodized to form a hardened alumite layer having a thickness of about 2 μm, and the alumite surface is further polished. It is used as a substrate. With these substrates, a surface having a surface roughness (Rmax) of about 0.15 μm can be obtained.

When forming a magnetic thin film on these substrates, for example, Co
When forming a magnetic thin film containing -Ni as a main component, Cr is deposited on the substrate by about 2000 Å, and a magnetic thin film containing Co-Ni as a main component is deposited on this by about 1000 Å, and further C
Form a protective lubrication film such as 200 Å. The surface roughness (Rmax) of the surface of the medium thus obtained reflects the surface property of the substrate and is about 0.15 μm. When a magnetic thin film containing iron oxide as a main component is formed, a target containing Fe as a main component is sputtered in an Ar + O ₂ atmosphere and α-Fe ₂ O ₃
A sputtered film containing as a main component is formed on the substrate to a thickness of about 2000Å. This is heated to about 300 ℃ in a reducing atmosphere, and α-F
A film containing e ₂ O ₃ as a main component is a film containing Fe ₂ O ₄ as a main component,
Further, heat to about 300 ° C in an oxidizing atmosphere to produce γ-Fe ₂ O ₃
Is a film containing as a main component. A protective lubricating film is further formed on this to serve as a medium. The surface roughness (Rmax) of the surface of the medium thus obtained also reflects the surface property of the substrate.
It is about 0.15 μm.

In a substrate in which a Ni-P plating layer is formed on an aluminum alloy and the surface is polished, it is necessary to activate the aluminum alloy surface before performing Ni-P plating, which complicates the substrate forming process. Becomes Moreover, the process after the activation process occupies 50% or more of the board price, and the board becomes expensive. Further Ni-P
Since the plating layer is crystallized and becomes magnetic when heated to 150 ° C. or higher, this substrate cannot be used when a heating step is required as in the case of forming a magnetic iron oxide film.

A substrate having an alumite coating formed on an aluminum alloy has a drawback that cracks are likely to occur in the alumite coating due to the stress generated due to the difference in thermal expansion coefficient between the aluminum alloy and the alumite coating when heat-treated. Therefore, the heating temperature for forming the magnetic iron oxide film is limited to about 300 ° C. or lower. Further, the alumite coating has a large number of current-carrying holes and has a porous structure. Therefore, when a thin-film magnetic layer is formed on this substrate, magnetic defects are likely to occur in the current-carrying holes, and the surface accuracy has a Rmax of 0.
It is not sufficient, about 15 μm.

In view of the above drawbacks, the present inventors have a surface roughness (Rmax) of 10
A magnetic recording medium in which a magnetic thin film for magnetic recording is formed on a glass substrate that has been subjected to ultra-precision surface processing so as to be 0 Å or less (preferably 50 Å or less), and at least a part of the surface is strengthened or the surface roughness (Rmax ) Is less than 100Å (preferably 5
We have developed a magnetic recording medium in which a magnetic thin film for magnetic recording is formed on a glass substrate that has been subjected to ultra-precision surface processing so that it becomes 0 Å or less), and filed a patent application. (Japanese Patent Application No. 60-183022) Problems of Prior Art The glass substrate proposed in the above patent application uses high-grade glass such as aluminosilicate glass, quartz glass, and titanium silicate glass having high strength and high dimensional accuracy. In addition, a crystalline material that does not exist was required. Although these glass substrates have satisfactory functional characteristics and surface properties, they are expensive and are disadvantageous in cost in a disk type magnetic recording medium which is in large demand.

(Object of the Invention) Accordingly, an object of the present invention is to provide a magnetic recording medium which uses inexpensive glass as a non-magnetic substrate of a magnetic recording medium and has the same mechanical strength and surface accuracy as when high-grade glass is used. To do.

SUMMARY OF THE INVENTION The present invention is a magnetic recording medium in which a magnetic thin film is formed on a non-magnetic substrate, wherein the non-magnetic substrate has at least a part of a glass plate surface selected from soda quartz glass, lead alkali glass, and borosilicate glass. It is characterized in that a strengthening layer is formed by strengthening treatment, and an underlayer of a non-magnetic thin film is formed thereon. In this case, the non-magnetic thin film is SiO ₂ , Al.
_It is composed of inorganic materials such as ₂ O ₃ and TiO ₂ .

Structure of the Invention The present invention uses soda-lime glass, lead-alkali glass, or borosilicate glass as the non-magnetic substrate. However, these glasses have poor stability, and when the surface of the glass is polished and a magnetic metal thin film is directly formed on it, alkali and alkaline earth ions in the glass are deposited on the surface, which migrates into the magnetic thin film. However, there arises a problem of deteriorating the magnetic characteristics, particularly the squareness ratio (Br / Bm). As described above, when the heat treatment process is performed to form the iron oxide thin film, this deterioration tendency becomes even greater.

Therefore, the present invention, after the strengthening treatment such as ion substitution of the inexpensive glass substrate with a molten salt of potassium nitrate or the like, a nonmagnetic thin film such as SiO ₂ , Al ₂ O ₂ or TiO _{2 on the} surface thereof as an underlayer. Form. It is desirable to form this underlayer by a sputtering method, and since a dense film is formed by this method, alkali or alkaline earth ions in the glass will not diffuse into the magnetic thin film.

Since the surface roughness of the glass substrate is reflected on the surface roughness of the magnetic thin film through the underlying layer and the magnetic thin film formed on it, it should be finished with precision, for example, the mechanical strength of the polishing liquid containing colloidal silica. Also, by polishing using a chemical polishing action, the surface roughness (Rmax) is 40 to 100 Å. If it is less than 40 Å, an adsorption effect that hinders head levitation occurs, but this problem can be prevented by heat treatment of the magnetic surface (this point was the subject of the present application and the simultaneous application). Therefore, the glass substrate should be finished with high accuracy with a surface roughness of 100Å or less.

Further, since at least a part of the surface of the glass substrate is subjected to a strengthening treatment, it is possible to give a large resistance force to a large centrifugal force generated when the disk is subjected to high-speed rotation or to other external force. . For example, surface strengthening is generally performed by replacing the ions on the glass surface with larger ions at temperatures below the glass transition temperature. The ion substitution method is carried out by immersing the glass in a salt of potassium nitrate solution heated to about 450 ° C. By this substitution, a compressive stress layer having a steep distribution is formed on the surface, and the glass substrate surface is strengthened. The thickness of this stress layer is set to 10 to 200 μm by controlling the temperature and time during ion substitution.

Considering a magnetic disk, the portion to be surface-reinforced may be an inner diameter edge portion, an inner diameter edge portion, an outer diameter edge portion, an outer diameter edge portion, an appropriate combination thereof, or the entire surface.

When a glass substrate is used, it can be sufficiently used up to about 400 ° C., so that it can be particularly effectively used when a heating step is required as in the case of forming a magnetic iron oxide film.

On the other hand, the thickness of the underlayer formed on the surface of the glass substrate is
200 to 5000Å is suitable, and a uniform film is formed by the sputtering method. If it is less than 200Å, there is no sufficient barrier effect, and if it is more than 5000Å, it takes time and the effect is saturated.

 Next, examples of the present invention will be described.

[Reference example]

An underlayer of SiO ₂ , Al ₂ O ₃ , and TiO ₂ was formed on a disk-shaped glass substrate having an outer diameter of 130 mm, an inner diameter of 40 mm, and a thickness of 1.9 mm by 1000 Å by a sputtering method. Over this was iron and Tagetsuto Ar + O ₂ atmosphere (mixing ratio 50%, the degree of vacuum 5 × 10 ^-3 Torr) and α-Fe ₂ O ₃ film by sputter in to 2000Å formed. Next, the magnetic disk was completed by reducing in a hydrogen stream at 360 ° C. for 2 hours to form a Fe ₃ O ₄ film, and further oxidizing in air at 310 ° C. for 1 hour to form a γ-Fe ₂ O ₃ film. Squareness of this disk Br
/ Bm is shown in Table 1. For comparison, Table 1 also shows the squareness ratio when the underlayer is not formed. The example of aluminosilicate glass is an example of the prior application cited above, and proves that the present invention has a considerably high quality.

〔Example〕

The surface of a disk-shaped soda-lime glass substrate having the same shape as that of the reference example was strengthened. The strengthening was performed by bringing the molten salt of potassium nitrate to 450 ° C. and immersing it in it for 10 hours. The thickness of the reinforcing layer was 60 μm. When this substrate was subjected to mechanochemical polishing for 30 minutes using a polishing liquid containing colloidal silica, the surface roughness (Rmax) of the substrate was
It was 17Å.

It can be seen that the substrate thus formed is not destroyed even when rotated at 20,000 rpm, and has sufficient strength as a disk substrate used at 3600 rpm.

On top of this substrate, as in the reference example, an SiO ₂ underlayer, γ-Fe ₂ O
_{When three} magnetic layers were formed, the squareness ratio was 0.76 and the surface roughness (Rma
x) 45Å, and a magnetic disk with good magnetic characteristics and head floating stability was obtained.

 The squareness ratio is shown in Table 1.

Experiments were conducted in the same manner as in the examples using other glass materials and the base. The strength of the disc was similar to that of the example. The squareness ratio is shown in Table 1.

The squareness ratio is remarkably improved by forming the reinforcing layer and the underlayer. Although not as good as aluminosilicate glass, SiO ₂ is relatively good among SiO ₂ , Al ₂ O ₃ and TiO ₂ which is not a problem for practical use. By forming a non-magnetic inorganic oxide film by sputtering and subjecting at least part of the surface to a strengthening treatment, it is possible to further suppress the diffusion of ions in the glass into the magnetic film as compared with the case where only the underlayer is provided. I understand. As described above, it is possible to provide an advantage that a magnetic thin film having excellent characteristics can be formed, mechanically reinforced, and an inexpensive and high-performance magnetic recording medium.

Claims (3)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic thin film formed on a non-magnetic substrate, wherein the non-magnetic substrate is soda-lime glass.
A magnetic recording medium comprising a reinforcing layer formed on at least a part of the surface of a glass plate selected from lead-alkali glass and borosilicate glass, and an underlayer of a nonmagnetic thin film formed thereon. 2. The magnetic recording medium according to claim 1, wherein the non-magnetic thin film is a film selected from SiO ₂ , Al ₂ O ₃ and TiO ₂ . 3. The magnetic recording medium according to claim 1, wherein the surface of the glass plate is strengthened by ion substitution with a molten salt of potassium nitrate or the like.