JPH08335308A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To ensure satisfactory S-N ratio as well as to prevent the leak of magnetic flux in a magnetic layer from the underside of the magnetic layer and to increase reproduction output in a magnetic recording medium with a diagonally oriented vapor-deposited film as the magnetic layer. CONSTITUTION: A high permeability soft magnetic film 2 of a CoZrTa alloy is formed on a nonmagnetic substrate 1 and a magnetic layer 3 having an axis of easy magnetization inclined in a diagonal direction to the surface of the substrate 1 is formed on the soft magnetic film 2 by diagonal vapor deposition. The thickness of the film 2 is preferably regulated to <=100nm and it is desirable that the film 2 has a compsn. consisting of 85-95at.% Co, 2-5at.% Zr and 5-15at.% Ta.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an obliquely oriented magnetic recording medium, and more particularly to improvement of reproduction output.

[0002]

2. Description of the Related Art For example, in the field of video tape recorders, there is a strong demand for high density recording in order to achieve high image quality, and as a magnetic recording medium corresponding to this, metal or Co--Ni is used. Alloy, Co-Cr alloy, C
A ferromagnetic material made of an alloy material such as o-O is directly plated on a non-magnetic support such as a polyester film, polyamide, or polyimide film by plating or a vacuum thin film forming means (vacuum deposition method, sputtering method, ion plating method, etc.). A so-called metal magnetic thin film type magnetic recording medium in which a magnetic layer is formed by deposition is proposed and attracts attention.

This metal magnetic thin film type magnetic recording medium is excellent in coercive force, squareness ratio and the like, and the thickness of the magnetic layer can be made extremely thin, so that the thickness loss during recording demagnetization and reproduction is extremely small and electromagnetic waves at short wavelengths are reduced. Not only is it excellent in conversion characteristics, but since it is not necessary to mix a binder, which is a non-magnetic material, in the magnetic layer, it has various advantages such that the packing density of the magnetic material can be increased. That is, it is considered that this metal magnetic thin film type magnetic recording medium will become the mainstream as a magnetic recording medium for high density recording because of its superior magnetic characteristics.

In such a metal magnetic thin film type magnetic recording medium, a so-called oblique evaporation method has been proposed and put to practical use as a method for forming a magnetic layer in order to improve electromagnetic conversion characteristics and achieve higher output. ing.

The oblique vapor deposition method is a thin film forming method in which magnetic particles are vapor-deposited from a diagonal direction on a non-magnetic support that is moving and running. As a result, an obliquely oriented magnetic layer in which the easy axis of magnetization is inclined at an angle with respect to the surface of the non-magnetic support is formed. In this way, the magnetic tape in which the magnetic particles are oriented obliquely with respect to the surface of the non-magnetic support (oblique orientation vapor deposition tape) has a higher recording density than the conventional magnetic tape in which the magnetic particles are oriented in the longitudinal direction. Is possible. As such an obliquely oriented vapor deposition tape, a tape having an inclination angle of the easy axis of magnetization of the magnetic layer of about 20 ° is practically used.

Further, in the above obliquely oriented vapor deposition tape,
Generally, Co or N is used as the magnetic material forming the magnetic layer.
i is used. To form the magnetic layer by vapor deposition of Co and Ni, it is usual to use Co and Ni as the vapor deposition source and to blow oxygen gas onto the non-magnetic support. In this case, the magnetic layer is formed as a Co-Ni-O thin film or a Co-O thin film. Here, the introduction of oxygen gas into the film in this way reduces the medium noise by making the crystal grains finer, and increases the shape anisotropy in the oblique direction by making the crystal grains a columnar structure. This is to allow it.

[0007]

By the way, when a ring head is used for such an obliquely oriented vapor deposition tape, in order to achieve higher density recording, the orientation angle of the easy axis of magnetization of the magnetic layer is set. A higher angle is effective. As the orientation angle of the easy axis of magnetization of the magnetic layer increases and approaches the perpendicular, the recording magnetization in the medium can be more densely performed.

However, in the magnetic layer, the arc-shaped magnetization mode becomes more difficult to form as the orientation angle of the easy axis of magnetization becomes closer to perpendicular to the surface of the non-magnetic support. As a result, the magnetic flux in the magnetic layer does not form a closed magnetic path and leaks from the lower surface of the magnetic layer, thereby generating a magnetic pole on the lower surface of the magnetic layer. The magnetic pole on the lower surface of the magnetic layer weakens the recording magnetization by generating a demagnetizing field from the positive magnetic pole to the negative magnetic pole inside the magnetic layer. Further, outside the magnetic layer, a magnetic field that cancels the leakage magnetic field of the recorded magnetic signal is formed. For this reason, when such a magnetic pole appears, the reproduction output is reduced, and a practically sufficient S / N ratio cannot be obtained.

Therefore, the present invention has been proposed in view of such a conventional situation, and the magnetic flux in the magnetic layer has a lower surface of the magnetic layer even if it has an obliquely oriented vapor deposition film as the magnetic layer. It is an object of the present invention to provide a magnetic recording medium which is capable of high density recording while preventing leakage from the recording medium, preventing reduction in reproduction output, and ensuring a good SN ratio.

[0010]

Means for Solving the Problems The inventors of the present invention have made intensive studies as a result of achieving the above-mentioned object, and as a result, by providing a high magnetic permeability soft magnetic film between the non-magnetic support and the magnetic layer, Finding that a closed magnetic circuit is formed so that the magnetic flux leaked from the lower surface of the magnetic layer passes through the high magnetic permeability soft magnetic film and returns to the magnetic layer again, and the leakage of magnetic flux from the lower surface of the magnetic layer is prevented. Came to get.

The magnetic recording medium of the present invention has been proposed on the basis of such knowledge, and is a magnetic recording medium comprising a non-magnetic support and a magnetic layer comprising at least a metal magnetic thin film formed on the non-magnetic support. The magnetic layer has an easy axis of magnetization inclined in an oblique direction with respect to the surface of the non-magnetic support, and a high-permeability soft magnetic layer made of a CoZrTa-based alloy between the non-magnetic support and the thin metal magnetic thin film. It is characterized in that a film is formed.

In the magnetic recording medium of the present invention, the magnetic layer is formed having an easy axis of magnetization which is inclined in an oblique direction with respect to the surface of the non-magnetic support. The magnetic layer having such an easy axis of magnetization is formed by, for example, an oblique vapor deposition method in which metal magnetic particles are vapor-deposited from an oblique direction on a moving object to be processed.

As the non-magnetic support, a polymer support formed of a polymer material typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates, etc. Is mentioned.

Further, as a magnetic metal material for forming the magnetic layer, a ferromagnetic metal such as Fe, Co, Ni or Co--
Ni-based alloy, Co-Ni-Pt-based alloy, Fe-Co-N
Examples include i-based alloys, Fe-Ni-B-based alloys, Fe-Co-B-based alloys, Fe-Co-Ni-B-based alloys, and Co-Cr-based alloys.

When the film is formed by the oblique evaporation method using these metallic magnetic materials as the evaporation source, the inclination angle of the easy axis of magnetization of the magnetic layer is 20 to the surface of the non-magnetic support.
90 ° is desirable. In particular, setting the inclination angle of the easy axis of magnetization to a high angle is advantageous for high density recording. The easy axis of magnetization of the magnetic layer can be controlled by changing the incident angle of the vapor deposition particles to the non-magnetic support when the magnetic layer is formed by vapor deposition.

In performing the vapor deposition, oxygen gas is introduced into the vapor deposition atmosphere to form a magnetic layer, for example, a Co--O thin film,
It may be formed as a Co—Ni—O thin film or the like. As a result, the crystal grains of the magnetic layer become finer and the medium noise can be reduced. In addition, since the crystal grains have a columnar structure, the shape anisotropy of oblique orientation increases.

In the present invention, a high-permeability soft magnetic film is provided as an underlayer of the magnetic layer in which the easy axis of magnetization is inclined as described above.

This high-permeability soft magnetic film is made of a CoZrTa-based amorphous alloy, for example, a vacuum evaporation method,
It is formed on the non-magnetic support by a sputtering method, an ion plating method, or the like.

When this high-permeability soft magnetic film is provided as an underlayer of the obliquely oriented magnetic layer, the magnetic flux leaked from the lower surface of the magnetic layer passes through the high-permeability soft magnetic film and returns to the magnetic layer again. Such a closed magnetic circuit is formed. Therefore, the magnetic pole is not generated on the lower surface of the magnetic layer, and the generation of the demagnetizing field that cancels the recording magnetization and the leakage flux due to the magnetic pole on the lower surface of the magnetic layer is suppressed, and the reproduction output is increased.

In order to obtain a large demagnetizing field reducing effect with such a high magnetic permeability soft magnetic film, the relative magnetic permeability μ _r of the high magnetic permeability soft magnetic film is large, and the saturation magnetic flux density B _S and the film thickness are large. It is necessary that the product B _S · δ of δ be greater than or equal to a certain value (however, this B _S · δ is a value corresponding to the amount of magnetic flux passing through the high magnetic permeability soft magnetic film).

However, when a ring head is used for a magnetic recording medium having such a high magnetic permeability soft magnetic film, the high magnetic permeability soft magnetic film and the soft magnetic film of the head core are magnetically coupled over a wide range. However, as a result, the recording magnetic field distribution becomes broad, and there is a problem that the resolution deteriorates. In order to suppress such deterioration of resolution, it is necessary to suppress the film thickness of the high magnetic permeability soft magnetic film to about 100 nm or less.

Further, when the magnetic recording medium of the present invention is used as a magnetic tape, it is three-dimensionally wound and used. Therefore, if the film thickness δ of the high magnetic permeability soft magnetic film is too thick, It is disadvantageous in improving the volume recording density of the tape.

Here, the CoZrTa type amorphous alloy film used as the high magnetic permeability soft magnetic film in the present invention can have extremely high magnetic permeability μ and saturation magnetic flux density Bs, and even in a relatively thin film thickness range. B _S · δ can be set to a sufficiently high value.
Therefore, it is possible to suppress the broadening of the recording magnetic field distribution while obtaining a large magnetic field reducing effect, and to improve the reproduction output. In addition, if the high-permeability soft magnetic film can be formed in a thin film thickness range as described above, it is also advantageous in reducing the thickness of the medium and improving the volume recording density of the medium.

The performance of such a CoZrTa type amorphous alloy film as a high magnetic permeability soft magnetic film is further improved by optimizing its composition. That is, in general, in an amorphous alloy film, soft magnetism having the best composition with zero magnetostriction is obtained. On the other hand, in order to maintain high saturation magnetization, it is desirable to increase the Co content as much as possible. Here, in the CoZrTa-based alloy used as the high-permeability soft magnetic film in the present invention, the magnetostriction becomes 0 when Co is about 90 atomic%, because the atomic ratio of Ta is about twice the atomic ratio of Zr. It is when That is, CoZ
In the rTa-based amorphous alloy film, Co8 is preferable.
5 to 95 atom%, Zr 2 to 5 atom%, and Ta 5 to 15 atom%.

The above is the basic structure of the magnetic recording medium of the present invention. However, in the magnetic recording medium of the present invention, as in the case of a normal magnetic recording medium, a protective film may be formed on the magnetic layer if necessary. Or a top coat layer may be provided, or a back coat layer may be formed on the surface of the non-magnetic support opposite to the side on which the magnetic layer is formed.

As the protective film, carbon, Al ₂ O ₃ ,
Ti-N, Mo-C, Cr-C, SiO, SiO 2, S
Examples thereof include i-N and the like, but the material is not limited thereto, and any conventionally known material can be used.

The top coat layer is composed of a rust preventive or a lubricant, and the back coat layer is composed mainly of an antistatic agent and a binder. As the material used for the top coat layer and the back coat layer, any of those usually used in this kind of magnetic recording medium can be used.

[0028]

In a magnetic recording medium in which an obliquely oriented magnetic layer having an obliquely easy axis of magnetization is formed on a non-magnetic support, a high permeability of CoTaZr type amorphous alloy is used as an underlayer of the magnetic layer. When the magnetic susceptibility soft magnetic film is formed, a magnetic flux leaked from the lower surface of the magnetic layer passes through the high magnetic permeability soft magnetic film and returns to the magnetic layer again to form a closed magnetic circuit. As a result, the magnetic pole generated on the lower surface of the magnetic layer disappears, and the reproduction output increases.

[0029]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 The magnetic tape manufactured in this example is shown in FIG. Such a magnetic tape was produced as follows.

First, a high-permeability soft magnetic film 2 having a composition of Co ₉₀ Zr ₃ Ta ₇ (numerical values represent a composition ratio) is formed on a polymer film serving as the non-magnetic support 1 by a vapor deposition method. did. When forming the film, the incident angle of the vapor-deposited particles was around 0 °, and the film thickness of the high magnetic permeability soft magnetic film was 100 nm. As for the magnetic characteristics of the high magnetic permeability soft magnetic film 2, the saturation magnetic flux density B _S was 1.2 T, the coercive force H _C was 0.5 Oe, and the relative magnetic permeability μ _r was 1500.

Then, a Co—O type magnetic layer 3 was formed on the high magnetic permeability soft magnetic film 2 by introducing an oxygen gas by an oblique vapor deposition method. The orientation angle of the easy axis of magnetization of the magnetic layer was 60 °.

Then, the tape raw material on which the high magnetic permeability soft magnetic film 2 and the magnetic layer 3 were formed in this manner was cut into a predetermined tape width to produce a magnetic tape.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that the high magnetic permeability soft magnetic film 2 was not formed.

The magnetic tape produced as described above was subjected to signal recording at various recording frequencies and its reproduction output was measured. The relative speed between the head and the tape is 3.3 m / sec. The relationship between the recording frequency and the reproduction output is shown in FIG. Table 1 shows the reproduction output at a recording wavelength of 0.5 μm.

[0036]

[Table 1]

As can be seen from FIG. 2, the magnetic tape of Example 1 on which the high-permeability soft magnetic film was formed, was compared with the magnetic tape of Comparative Example 1 on which the high-permeability soft magnetic film was not formed.
A high reproduction output can be obtained over the entire wavelength range.

For example, the reproduction output at a recording wavelength of 0.5 μm is 0 dB for the magnetic tape of Comparative Example 1, whereas it is +2.3 dB for the magnetic tape of Example 1.

Therefore, providing the high magnetic permeability soft magnetic film between the non-magnetic support and the magnetic layer reduces the demagnetizing field,
It was found to be effective in increasing the reproduction output.

Orientation angle of easy axis of magnetization of magnetic layer and high permeability
Examination of Effect of High-Permittivity Soft Magnetic Film Here, the effect of the high-permeability soft magnetic film in each case was examined by changing the easy axis of magnetization of the magnetic layer.

Magnetic tapes (Experimental Examples 1 to 20) were prepared in the same manner as in Example 1 or Comparative Example 1 except that the orientation angle of the magnetic layer was changed as shown in Table 2.

Then, regarding the produced magnetic tape,
The reproduction output at a recording wavelength of 0.5 μm was measured. The results are shown in Table 2 together with the orientation angle of the easy axis of magnetization of the magnetic layer. The reproduction output is the magnetic tape of Experimental Example 11 (high magnetic permeability soft magnetic film: none, orientation angle of easy axis of magnetization of magnetic layer:
It was expressed as a relative value when the reproduction output at 0 °) was 0 dB.

[0043]

[Table 2]

In Table 2, the magnetic tapes of Experimental Examples 1 to 10 in which the high magnetic permeability soft magnetic film is formed and the magnetic tapes of Experimental Examples 11 to 20 in which the high magnetic permeability soft magnetic film is not formed are shown. Comparing the magnetic layers having the same easy axis of magnetization, it can be seen that the magnetic tapes of Experimental Examples 1 to 10 can obtain higher reproduction output than Experimental Examples 11 to 20. . From this, it was found that the effect of the high magnetic permeability soft magnetic film is exhibited regardless of the orientation angle of the easy axis of magnetization of the magnetic layer. Further, it was found that the effect of the high magnetic permeability soft magnetic film is remarkably exhibited especially when the orientation angle of the easy axis of magnetization of this magnetic layer is 20 to 90 °.

Investigation of Film Thickness of High Permeability Soft Magnetic Film Here, the optimum film thickness of the high magnetic permeability soft magnetic film was examined.

Magnetic tapes (Experimental Examples 21 to 25) were produced in the same manner as in Example 1 except that the film thickness of the high magnetic permeability soft magnetic film was changed as shown in Table 3.

Then, regarding the produced magnetic tape,
The reproduction output at a recording wavelength of 0.5 μm was measured. The results are shown in Table 3 together with the film thickness of the high magnetic permeability soft magnetic film of the magnetic layer. The reproduction output was expressed as a relative value when the reproduction output of the magnetic tape of Experimental Example 21 (high magnetic permeability soft magnetic film: none) was 0 dB.

[0048]

[Table 3]

As shown in Table 3, the reproduction output of a magnetic tape having a high magnetic permeability soft magnetic film that is too thick is lower than that of a magnetic tape having no high magnetic permeability soft magnetic film. The reason why the reproduction output is lowered by increasing the film thickness of the high magnetic permeability soft magnetic film is that the recording magnetic field distribution is broadened. From this, the high magnetic permeability soft magnetic film is 100 nm.
It has been found that it is suitable to form the film with a film thickness of the order.

Examination of Composition of High Permeability Soft Magnetic Film Here, the composition of the high permeability soft magnetic film was examined.

A high-permeability soft magnetic film having the composition shown in Table 4 was formed, and its soft magnetic characteristics (relative permeability μ _r , saturation magnetization) were measured. The results are shown in Table 4.

[0052]

[Table 4]

As shown in Table 4, the high magnetic permeability soft magnetic film is
When the composition is around 90 at% Co, 3 at% Zr, and 7 at% Ta, the relative permeability μ _r and the saturation magnetization are high. From this, in order to obtain an excellent effect of reducing the demagnetizing field, the composition of the high magnetic permeability soft magnetic film is 90 at% Co, Zr
Composition near 3 at% and Ta at 7 at%, ie Co85
~ 95 atom%, Zr2-5 atom%, Ta5-15 atom%
It was found that it is preferable to set it within the range.

[0054]

As is apparent from the above description, in the present invention, in the magnetic recording medium of the oblique orientation type, which has the magnetic layer on which the easy axis of magnetization is inclined on the non-magnetic support, Since the high-permeability soft magnetic film made of a Co—Zr—Ta-based amorphous alloy is provided as the underlayer, the demagnetizing field inside and outside the magnetic layer can be reduced, and the reproduction output can be increased.

Therefore, it can be said that the present invention greatly contributes to the improvement of the performance of such an oblique orientation type magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one structural example of a magnetic tape to which the present invention is applied.

FIG. 2 is a characteristic diagram showing reproduction output characteristics of a magnetic tape on which a high magnetic permeability soft magnetic film is formed and a magnetic tape on which a high magnetic permeability soft magnetic film is not formed, for comparison.

[Explanation of symbols]

 1 non-magnetic support 2 high permeability soft magnetic film 3 magnetic layer

Claims (3)

[Claims] 1. A magnetic recording medium in which a magnetic layer made of at least a metal magnetic thin film is formed on a non-magnetic support, wherein the magnetic layer has an easy axis of magnetization inclined in an oblique direction with respect to the surface of the non-magnetic support. And a high magnetic permeability soft magnetic film made of a CoZrTa-based alloy formed between the non-magnetic support and the metal magnetic thin film. 2. The high magnetic permeability soft magnetic film has a thickness of 100 n.
m or less and the composition thereof is Co85 to 95 atomic%,
The magnetic recording medium according to claim 1, wherein Zr is in the range of 2 to 5 atomic% and Ta is in the range of 5 to 15 atomic%. 3. The magnetic recording medium according to claim 1, wherein the easy axis of magnetization of the magnetic layer is inclined by 20 to 90 ° with respect to the surface of the non-magnetic support.