JPH11306541A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the magnetic recording medium, in which a high density recording is made possible, by reducing the difference between the coercive forces of inner and outer peripheral portions of a substrate. SOLUTION: Fine grooves 5 are provided on the entire surface of a circular plate shape substrate 4 along the peripheral direction and a nonmagnetic thin film 3 and a magnetic thin film 2 are laminated on the substrate 4 having the grooves 5 to form the magnetic recording medium. The average number of the grooves 5 per unit length measured in the circular plate radial direction is varied from the inner peripheral to the outer peripheral portions. For an example, the average number of the grooves per unit length provided on the substrate 4 is reduced as it moves from the inner peripheral to the outer peripheral.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium used for a magnetic disk drive and the like.

[0002]

2. Description of the Related Art With the recent development of the advanced information society, the need for a small and large-capacity magnetic disk drive is rapidly increasing. To achieve high-density magnetic recording, high-performance magnetic heads and magnetic recording media and advanced signal processing technology are indispensable. In particular, high coercive force, low noise, and high coercive force squareness are required for magnetic recording media. Magnetic thin film is required.

The magnetic thin film is mainly classified into a coating type medium and a thin film medium. In order to increase the recording density, a thin film medium formed by a sputtering method is used. The thin-film medium has a non-magnetic underlayer formed on a substrate from one layer to several layers, a magnetic film on which recording is performed, a protective film for protecting the magnetic film, and lubrication for sliding with the magnetic head. It is configured by forming a film. As the magnetic film, a Co-based thin film having a large magnetic anisotropy is used, and as the nonmagnetic film, Cr, Mo, Ti, or the like is used as a main element in order to improve the crystal orientation and lattice matching of the magnetic film. Films are used.

As a substrate on which a nonmagnetic film or a magnetic film is formed, an aluminum alloy disk provided with a NiP (nickel-phosphorus) plating layer (NiP / Al substrate) or a glass disk whose surface is chemically strengthened are used. Used. On the surface of the NiP / Al substrate, a groove of about 2 to 10 nm is often formed along the circumferential direction. Hereinafter, this groove is called a texture. This has the purpose of reducing the frictional force when the magnetic head comes into contact with the magnetic recording medium and preventing the magnetic head and the substrate from sticking at the time of contact start / stop. This texture was uniformly applied to the substrate surface using diamond abrasive grains or the like. And, as shown in, for example, JP-A-6-243451, this texture also has the effect of controlling the magnetic properties by controlling the average roughness and the average number per unit length.

[0005]

Generally, the magnetostatic characteristics of a magnetic recording medium and the electromagnetic conversion characteristics when recording / reproducing with a magnetic head differ between an inner peripheral portion and an outer peripheral portion of a disk. This is because there is a difference in the substrate temperature during sputter deposition, there is a spatial distribution in the density and direction of the sputtered particles, and at the time of recording and reproduction, the peripheral speed due to the rotation of the disk is This is due to differences.

For example, the coercive force is generally lower at the outer periphery of the disk than at the inner periphery. Further, since the relative speed between the head and the disk increases at the outer peripheral portion of the disk, the flying height of the head increases, and the output resolution decreases. As described above, if there is a large difference in the magnetic characteristics between the inner and outer circumferences of the magnetic disk, a large margin is required when designing the magnetic recording medium, and it is difficult to design a high-performance magnetic recording medium.

An object of the present invention is to provide a magnetic recording medium that reduces the difference in magnetic properties, particularly the difference in coercive force, between the inner and outer circumferences of a disk.

[0008]

In order to achieve the above object, in the present invention, the average number of textures provided on the substrate per unit length in the radial direction of the disk is changed on the inner and outer circumferences of the disk.

The reason why the above object can be achieved by changing the average number of textures will be described below.

FIG. 1 is a schematic cross-sectional view of a magnetic recording medium formed on a textured substrate. In an actual magnetic recording medium, films are formed on both surfaces of a substrate.

The non-magnetic film and the magnetic film to be grown are Cr
The description will be given as a film and a CoCrPt film. If the NiP / Al substrate 4 has a texture 5, the Cr non-magnetic film 3, the CoCrPt magnetic film 2 grown on the non-magnetic film 3, and the protective film 1 grow along the irregularities of the substrate. Generally Ni
When Cr is formed at a high temperature on the P / Al substrate 4, the 001 orientation grows in the direction perpendicular to the substrate surface. Then, the CoCrPt magnetic film 2 is epitaxially grown on the Cr film 3, and (11.
0) or (10.0) orientation. That is, CoCr
The c-axis of the Pt magnetic film 2 is oriented in the film plane.

The degree of in-plane orientation depends on the thickness of the Cr film 3 and the CoC
It changes depending on the composition of the rPt magnetic film 2 and the like, but hardly changes on the inner and outer circumferences of the substrate 4. The coercive force of the magnetic recording medium largely depends on the degree of orientation of the crystal grains of the magnetic film 2 in the c-axis plane. The higher the degree of orientation, the larger the coercive force, and the smaller the degree of orientation, the smaller the coercive force. Here, the degree of in-plane orientation of the c-axis is defined as a percentage of a value obtained by dividing the area of the particles whose c-axis is in the film plane as viewed from the substrate vertical direction by the substrate surface area.

When texture 5 is applied to the substrate, the growing C
Since the r film 3 grows according to the unevenness of the substrate 4, FIG.
As shown in the figure, the 001 azimuth 7 is shifted from the direction perpendicular to the substrate surface. Therefore, CoCrP grown on the Cr film 3
The c-axis 6 of the t-magnetic film 2 has a component rising from within the substrate surface, and the degree of in-plane orientation decreases. The decrease in the degree of in-plane orientation of the c-axis 6 leads to a decrease in coercive force.

The shape of the texture 5 applied to the substrate 4 is a triangle as shown in FIG. 2, and the average roughness (groove depth) and the width of the groove are both about 3 nm. Then, assuming that the number of textures per 1 μm in the substrate radial direction (direction orthogonal to the groove) is 100, the ratio of the uneven portion to the entire substrate is about 30%. However, the average number of textures is 1
If the number is 10 per μm, the ratio to the whole becomes 3%. This ratio is proportional to the ratio of the c-axis oriented in the plane.

If a Cr film 3 and Co
50% c-axis orientation when CrPt magnetic film 2 is formed
In the case of a substrate having 100 textures, 10
In the case of this substrate, the degree of c-axis orientation is about 35% and about 48.5%, respectively. If the degree of c-axis orientation is so different, the coercive force will also differ greatly, and the coercive force of a magnetic recording medium having a degree of c-axis orientation of 35% will be greatly reduced. Therefore, if the number of textures is controlled on the inner and outer circumferences of the substrate, the magnitude of the coercive force can be controlled.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. The substrate 4 shown in FIG. 1 is a disc of aluminum alloy having a thickness of 0.8 mm and a diameter of 95 mm and a thickness of about 10 μm.
Is NiP plated. This substrate is polished with a polishing liquid containing diamond abrasive grains (average particle size 0.5 μm),
Fine grooves (texture 5) are provided. Use a tape polishing machine for polishing, apply polishing liquid to the polishing tape,
This is pressed against the substrate surface. Then, when the substrate is rotated, a texture is formed in the circumferential direction.

In order to form a fine texture having an average roughness of about 3 nm, the average grain size of the abrasive grains needs to be 1 μm or less. The polishing time is determined depending on the average number of textures to be formed. The size of the polishing tape is made smaller than the radius of the substrate, and a texture is formed on the entire surface by moving the disk from the inner circumference to the outer circumference and from the outside to the inside during polishing. The polishing tape is moved so that the polishing time at the inner peripheral portion of the substrate is longer than the polishing time at the outer peripheral portion of the substrate. In this embodiment, the polishing time for the inner peripheral portion is about 50 seconds, and the polishing time for the outer peripheral portion is about 10 seconds.

After polishing, an atomic force microscope is used to measure the depth to 1n.
When the number of textures of m or more is counted, the inner circumference is about 15
There were 0 and the outer circumference was about 10. After polishing, the abrasive grains attached to the substrate are removed by washing and dried. This substrate is placed in a magnetron sputtering apparatus, and a Cr film and CoCrPt
A membrane is formed. The composition ratio of Co, Cr, and Pt was 74, 20, and 6 in terms of the atomic ratio. The substrate temperature is heated to 250 degrees,
The Ar gas pressure was set at 2 mTorr. Thickness is 30n of Cr film
m, CoCrPt film was set to 20 nm. Finally, a carbon protective film of 20 nm was formed as a protective film.

The coercive force of the magnetic recording medium thus formed was measured using a vibration sample type magnetic force type. For comparison, the polishing time of the substrate was made uniform over the entire surface (polishing time: 10 seconds), and a magnetic recording medium formed under the same conditions was also prepared for comparison, and the coercive force was measured. The results are shown below.

FIG. 3 shows the coercive force of the magnetic recording medium of the present invention prepared by changing the average number of textures on the inner and outer peripheries of the substrate and the magnetic recording medium having a constant number of textures on the inner and outer peripheries of the substrate. This is a comparison between the inner peripheral portion and the outer peripheral portion of the plate. Obviously, the change in coercive force of the magnetic disk of the present invention is smaller than that of the conventional magnetic disk.
It is considered that this is because the coercive force, which increases as it goes toward the inner circumference of the disk, is increased by increasing the average number of textures, and the coercive force is reduced by decreasing the degree of c-axis orientation of crystal grains of the magnetic film, as described above. . As described above, according to the present invention, the in-plane distribution of the coercive force can be reduced. Therefore, the design specifications of the magnetic recording medium with respect to the coercive force can be strict, and a high-performance magnetic recording medium can be developed.

In the present invention, the in-plane distribution of the coercive force is made uniform on the inner and outer circumferences of the disk. However, changing the average number of textures may affect other magnetic characteristics, for example, the value of remanent magnetization. It is rare. At this time, for example, by combining the present invention with a method of changing the thickness of the CoCrPt film at the inner peripheral portion and the outer peripheral portion of the substrate and making the value of the remanent magnetization film thickness constant, a higher performance magnetic recording medium is obtained. Can be developed.

[0022]

As described in the above embodiments, the in-plane distribution of coercive force can be reduced by changing the average number of textures at the inner and outer peripheral portions of the magnetic disk.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a textured magnetic recording medium.

FIG. 2 shows a growth direction and c of a film grown in a texture groove portion.
FIG. 3 is an explanatory diagram showing an axial direction.

FIG. 3 is a measurement diagram showing the inner and outer peripheral dependencies of the coercive force of the magnetic recording media of the present invention and the conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Protective film, 2 ... CoCrPt magnetic film, 3 ... Cr nonmagnetic film, 4 ... NiP / Al substrate, 5 ... Texture, 6 ... c-axis direction, 7 ... 001 orientation.

Claims (2)

[Claims] A fine groove is provided along a substantially circumferential direction over the entire surface of a disk-shaped substrate, and a non-magnetic thin film and a magnetic thin film are laminated on the substrate provided with the groove. The magnetic recording medium according to claim 1, wherein an average number of grooves per unit length measured in a radial direction of the disk is changed from an inner peripheral portion to an outer peripheral portion of the disk. 2. The magnetic recording medium according to claim 1, wherein the average number of grooves per unit length provided in the substrate decreases from the inner circumference to the outer circumference of the disk.