JPH0656650B2 - Magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a magnetic recording medium, particularly to a magnetic recording medium having a magnetic layer of a Co—Cr metal thin film.

(2) Conventional Technology Conventionally, as magnetic recording media, there are so-called coating type media and metal thin film type magnetic recording media. Among the metal thin film type magnetic recording media, perpendicular magnetic recording has been attracting attention in recent years as a method suitable for high density recording. A magnetic recording medium of Co—Cr metal thin film is suitable for this perpendicular magnetic recording.
Research on magnetic recording media of o-Cr metal thin films has been conducted in various fields.

The perpendicular magnetic recording medium exhibits high performance by using a so-called perpendicular head, but is also effective for a ring head which has been conventionally used. When the recording wavelength dependence of the reproduction output is examined using the same ring head as the conventional magnetic recording medium, the perpendicular recording medium is superior in the short wavelength region and the in-plane recording medium is superior in the long wavelength region. Tends to.

As described above, since the reproduction output of the conventional perpendicular magnetic recording medium decreases in the long wavelength region, it is necessary to record a signal having a wide frequency band or to have a signal for controlling the system in the long wavelength region. However, it has been a problem to use a perpendicular magnetic recording medium while maintaining compatibility with the conventional method.

A countermeasure for the above problem is to use a magnetic recording medium having a high coercive force. However, in order to increase the coercive force in a Co-Cr magnetic recording medium, it is necessary to use a high temperature when forming a film by a sputtering method or an evaporation method. It is necessary to form a film. Therefore, when a flexible substrate such as a polymer film is used as the non-magnetic substrate, the selection of the material is extremely limited. Further, when the film is formed at a high temperature, the curl due to the difference in thermal expansion coefficient between the non-magnetic substrate and the magnetic layer is further increased, which is a serious problem for good recording.

Therefore, a perpendicular recording layer is overlaid on the in-plane recording layer to form a film.
A method of supplementing the reproduction output in the long wavelength region can be considered. In this case, a problem is a method of forming a Co—Cr thin film having a good vertical orientation on the in-plane recording layer.

The Co—Cr alloy has an hcp structure, and its C axis is oriented perpendicular to the film surface to form a perpendicular magnetization film. When the orientation of the C-axis is disturbed, the reproduction output in the short wavelength region is lowered, and the advantage of the perpendicular recording system is impaired.

It is known that the C-axis orientation of the magnetic layer is good when the polymer film uses an amorphous material such as glass as the base substrate, but is normally deteriorated when a crystalline material is used as the base substrate. Has been. In particular, in a medium by oblique vapor deposition of a Co-Ni alloy, which is currently being researched as a thin film medium for in-plane recording, the C axis of the hcp structure is inclined with respect to the film surface, and this is used as an upper layer as a lower layer. Co-Cr
Even if a layer is formed, only a Co—Cr layer having extremely poor vertical orientation can be obtained, and it is not possible to make a recording medium that makes full use of the advantages of the perpendicular recording system.

Therefore, it has been a problem to find a material for the lower in-plane recording layer which brings good orientation to the upper Co-Cr layer and at the same time has sufficient magnetic characteristics as the in-plane recording layer.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a magnetic recording medium having improved reproduction output in the long wavelength region while making the best use of the advantage of the perpendicular recording system in the short wavelength region.

(3) Means and Actions for Solving Problems The magnetic recording medium of the present invention has a Co—Cr magnetic layer formed on a non-magnetic substrate, and the Co—Cr magnetic layer comprises an upper magnetic layer and a lower magnetic layer. The upper magnetic layer has a Cr composition ratio and a perpendicular coercive force of 17 to 23 at.
%, 400 Oersted or more, and the Cr composition ratio and the in-plane coercive force of the lower magnetic layer are 3 to 12 at. %,
It is characterized by being 300 or more oersteds.

The magnetic recording medium of the present invention enables recording in a wide recording wavelength band by using the perpendicular magnetic film as the upper magnetic layer and the in-plane magnetic film as the lower magnetic layer.

In general, the magnetization of the magnetic layer is either perpendicular or in-plane
Or H of the magnetic layer_KAnd 4πMs (H_K: Anisotropic magnetic field, Ms:
It is almost determined by the magnitude relationship of (saturation magnetization). Co-Cr combination
In the case of gold, the composition ratio of Cr is 15 at. % Is the boundary
(For example, J. Appl. Phys.,52
(1981) 2453-2455). Cr is 15a
t. %, The magnetization is oriented in the perpendicular direction. Well
15 at. % Magnetic layer is in-plane
Turn to the direction.

The magnetic recording medium of the present invention is made under the above conditions. In the present invention, the upper magnetic layer is formed so that the C-axis is oriented sufficiently perpendicular to the film surface and the magnetization is oriented perpendicular to the film surface. The upper magnetic layer thus formed exhibits high output characteristics, especially in the short wavelength region. When the magnetization is oriented in the direction perpendicular to the film surface, the shorter the recording wavelength, the less loss due to self-demagnetization. Cr of the upper magnetic layer
It is necessary to determine the concentration so as to satisfy the above-mentioned condition of the perpendicular magnetization film, but if the Cr concentration is too high, the residual magnetic flux density is lowered and the reproduction output is deteriorated. Therefore, the Cr concentration of the upper magnetic layer is 17 to 23 at. % Is preferable,
Especially in this range, 18 to 20 at. % Range is preferred.

Further, in the upper magnetic layer of the present invention, the coercive force in the vertical direction of the upper magnetic layer is set to 400 Oersted or more so that the reproduction output does not drop even in the region on the long wavelength side to some extent. The coercive force can be determined by the substrate temperature during film formation.

In the present invention, the lower magnetic layer is formed so as to be an in-plane magnetic recording layer in which the C axis is oriented sufficiently perpendicular to the film surface. Since the C axis of the lower magnetic layer is oriented sufficiently perpendicular to the film surface, the upper magnetic layer can be provided with good orientation and the advantages of the upper magnetic layer can be fully brought out. Further, the lower magnetic layer of the in-plane magnetic recording has high output characteristics in the long wavelength region.

Thus, the lower in-plane magnetized film in which the C-axis is oriented perpendicular to the film surface is magnetically isotropic in the film surface, and therefore can be used for a disk-shaped medium. This is a point that cannot be realized by using an in-plane magnetized film formed by oblique vapor deposition.

The magnetic properties of the lower magnetic layer must be selected so that recording on the upper magnetic layer is not hindered. That is, if the coercive force of the lower magnetic layer is too small, the leak magnetic flux from the head is absorbed by the lower magnetic layer and spreads, resulting in insufficient recording on the upper magnetic layer. Therefore, the coercive force of the lower magnetic layer in the in-plane direction needs to be 300 Oersted or more.
In order for the lower magnetic layer to be an in-plane magnetized film having a desired coercive force, the Cr concentration is 3 to 12 at. %, But in this range, 5 to 10 at. % Range is preferred.

The magnetic recording medium of the present invention is formed by a thin film deposition method such as a vapor deposition method, an ion plating method, a sputtering method and a plating method.

(4) Examples Hereinafter, preferred examples of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an example of the magnetic recording medium of the present invention.
A lower magnetic layer 16 and an upper magnetic layer 17 made of a Co—Cr alloy are formed on the non-magnetic substrate 7. Examples of the non-magnetic substrate 7 include polyethylene terephthalate, polyimide,
A polymer film having relatively high heat resistance such as polyamide is used. The thickness of the polymer film is preferably about 7 to 35 μm.

FIG. 2 is a schematic view showing an example of a manufacturing apparatus for manufacturing the magnetic recording medium of the present invention. In the vacuum chamber 1, the non-magnetic substrate 7 of the polymer film is fed from the feeding roll 3 in the direction of arrow A. Sent to. After that, the non-magnetic substrate 7 moves along the intermediate free roller 5, the heating can 6, and the intermediate free roller 5, and is wound around the winding roll 4.

The magnetic layer is formed while the non-magnetic substrate 7 is moving along the heating can 6. That is, the crucibles 10, 11 and 12 are arranged at positions facing the outer peripheral side surface of the heating can 6, and a magnetic material is put in each of them. When these magnetic materials are heated by, for example, an electron beam or the like, the magnetic materials become a vapor flow and are deposited on the non-magnetic substrate 7 to form a magnetic layer. Numerals 8 and 9 are shielding plates that regulate the direction of the steam flow. Reference numeral 2 denotes an exhaust device which maintains the inside of the vacuum chamber 1 at a predetermined vacuum degree.

In this example, Cr was placed in the crucibles 10 and 12 and Co was placed in the crucible 11 to form the magnetic layer. As shown in FIG. 2, when the non-magnetic substrate 7 is moving in the direction of arrow A, Cr in the crucible 10 and Co in the crucible 11 form the lower magnetic layer 16, and Co in the crucible 11 is formed.
Cr in the crucible 12 forms the upper magnetic layer. The composition of Co and Cr of the magnetic layer can be adjusted by changing the amounts of Cr from the crucible 10 and Cr from the crucible 12.

Using this manufacturing apparatus, the magnetic tape (NO.
1) was produced. As shown in Table 1, the Cr composition ratio of the resulting magnetic tape was 20 at. %, 7 at. %Met. Nonmagnetic substrate 7 has a thickness of 10μ
m polyimide film was used.

In producing the magnetic tape of the present invention, the degree of vacuum during film formation was 1 × 10 ^{−4 to} 5 × 10 ⁻⁶ Torr. The thickness of the magnetic layer was 0.5 μm in the upper magnetic layer and 0.3 μm in the lower magnetic layer. As shown in Table 1, the coercive force of the magnetic layer has a perpendicular coercive force Hc ^⊥ of 42 in the upper magnetic layer.
0 Oersted, in-plane coercive force Hc ″ of lower magnetic layer
Was 350 Oersted.

Next, with respect to the magnetic tape of the present invention, the recording wavelength dependence of the reproduction output was measured. For comparison, a magnetic tape (NO. 2, N.
O. 3) and the magnetic layer is Co-20 at. % Ni magnetic tapes (NO. 4) were manufactured, and the recording wavelength dependence of the reproduction output of these was also measured. The results are shown graphically in FIG. The gap length of the head used in the experiment was 0.
3 μm, the relative speed between the head and the magnetic tape is 3.8.
It was m / sec. In addition, NO. For manufacturing the magnetic tape of No. 4, the manufacturing apparatus shown in FIG.

As is clear from FIG. 3, the magnetic tape of the present invention showed a high reproduction output in a wide recording wavelength band from a short wavelength region to a long wavelength region.

(5) Effects of the Invention As is clear from the above description, according to the present invention, by changing the Cr concentrations of the upper magnetic layer and the lower magnetic layer,
A perpendicular magnetic film and an in-plane magnetic film each having an appropriate coercive force can be formed, and a magnetic recording medium having comprehensively excellent characteristics in a wide recording wavelength band can be obtained.

[Brief description of drawings]

1 is a sectional view showing an example of the magnetic recording medium of the present invention, FIG. 2 is a schematic view showing an example of a manufacturing apparatus for producing the magnetic recording medium of the present invention, and FIG. 3 is a magnetic tape of the present invention. 5 is a graph showing the recording wavelength dependence of the reproduction output of Comparative Example. 1 ... Vacuum tank, 2 ... Exhaust device 3 ... Sending roll 4 ... Winding roll 5 ... Intermediate free roller 6 ... Heating can, 7 ... Non-magnetic substrate 10, 11, 12 ... Crucible 16 ...... Lower magnetic layer, 17 ...... Upper magnetic layer

Claims (1)

[Claims] 1. A magnetic recording medium in which a Co—Cr magnetic layer is formed on a non-magnetic substrate by a thin film deposition method, wherein
The Cr magnetic layer is composed of an upper magnetic layer and a lower magnetic layer, and the Cr composition ratio and the perpendicular coercive force of the upper magnetic layer are 17 to 23 at. %, 400 Oersted or higher,
The Cr composition ratio and the in-plane coercive force of the lower magnetic layer are 3 to 12 at. %, 300 oersteds or more, a magnetic recording medium.