JPS6233321A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce the anisotropy by forming a permalloy thin film of a soft magnetic substance layer with a laminated film comprising a low coercive force layer having a small coercive force and a low isotropy layer having a small planer magnetic anisotropy. CONSTITUTION:The permalloy thin film of the soft magnetic layer is constituted with the low coercive force layer having a low coercive force and a low anisotropy layer having a small planer magnetic anisotrpy in a vertical magnetic recording medium having the permalloy thin film and a magnetic recording layer having a magnetization easy axis in vertical direction to the film face on a nonmagnetic base. As the permalloy thin film, a film having 1.0-12.0 Oe of the planer coercive force is preferred, and the anisotropic ratio is in the range of 0.90-1.10 in this range and excellent isotropy is attained. The low anisotropy layer is a layer formed under inactive gas atmosphere including 1.0-10vol% of oxygen, and as the low coercive layer, a layer formed under inactive gas environment including no oxygen or <=0.5vol% of oxygen is preferred. Thus, the permalloy thin film with a low coercive force and small anisotropy is obtained over a wide range.

Description

[Detailed Description of the Invention] [Field of Application] The present invention is an improvement of a perpendicular magnetic recording medium in which a permalloy thin film is used as a soft magnetic layer and a perpendicular magnetic layer having an axis of easy magnetization perpendicular to the film surface is used as a magnetic recording layer. Regarding.

[Prior Art] The above-described two-layer 11jJ magnetic recording medium consisting of a soft magnetic layer and a perpendicular magnetization layer has f! Direct electromagnetic recording media have been proposed in Japanese Patent Publication No. 1983-1989, Japanese Patent Publication No. 10764-1983, etc. This proposed perpendicular magnetic recording medium with a two-layer film structure (hereinafter referred to as "the double-layer medium") is specifically created by the RF bipolar sputtering method. cobalt)-Cr
It is composed of a (chromium) alloy film, and is excellent in that it can obtain high recording sensitivity and human playback output, but in terms of recording sensitivity.

Further improvements are desired in terms of playback output, etc.

[Objective of the Invention 1] The present invention provides that the characteristics of the above-mentioned two-layer film medium are the soft magnetic layer f and the N
It was developed by focusing on the characteristics of permalloy thin films whose main component is Fe (iron), and aimed at perpendicular magnetic recording media with low anisotropy and high output. be.

[Configuration 1 of the invention: Effects] The above objects are achieved by the invention as follows.

However, the present invention provides a perpendicular magnetic recording medium in which a soft magnetic layer made of a permalloy thin film and a magnetic recording layer having an axis of easy magnetization perpendicular to the film surface are arranged on a non-magnetic substrate. This perpendicular magnetic recording medium is characterized in that the permalloy thin film of the layer is a laminated film of a low coercive force layer having a low coercive force and a low anisotropy layer having a small in-plane magnetic anisotropy.

The present invention described above was accomplished as follows. It is said that the smaller the coercive force of the soft magnetic layer of a two-layer film medium is, the more advantageous it is in terms of recording sensitivity and the like. Therefore, when we created and evaluated a magnetic recording medium using a permalloy thin film as a soft magnetic layer with a small coercive force of 20e (oersted) or less, we found that the envelope of the playback output changed, and in the end it became difficult to achieve stable playback. We encountered the problem of being restricted to the lowest point and not improving the reproduction output much, and after various studies, we discovered that the cause was the in-plane magnetic anisotropy of the permalloy thin film that constitutes the soft magnetic layer. It is.

In other words, in the above-mentioned magnetic recording medium in which Permalloy 1tli2 is used as a soft magnetic layer, the reproduction output is higher when recording and reproduction is performed by running the permalloy thin film in the direction of the hard magnetization axis than when it is traveling in the direction of the easy magnetization axis. It exhibits good characteristics especially in the high frequency range of high-density recording.

In other words, in order to make the in-plane reproduction output uniform, the in-plane magnetic anisotropy of the soft magnetic layer as a whole is reduced, the lowest point of the reproduction output is upper bound, and the envelope is made uniform in the plane. It is necessary. As a result, a magnetic recording medium suitable for the disk system with high recording density and uniform recording/reproducing characteristics in the plane can be obtained.

Note that in-plane magnetic anisotropy refers to magnetic anisotropy in a plane parallel to the film surface.

However, it is difficult to make the in-plane magnetic anisotropy uniform using normal methods, and the anisotropy is particularly large when a soft magnetic layer is formed by transferring the substrate in one direction. It was common for this to occur.

Based on the above knowledge, the present inventors conducted extensive research and found that if the permalloy film is formed in an atmosphere containing oxygen, the magnetic anisotropy becomes uniform.

In the permanent OIA I9 film formed in such an M atmosphere, the anisotropy is greatly improved [1], and therefore an excellent soft magnetic layer with uniform magnetic properties in the plane can be obtained, but its coercive force is normally larger than in an oxygen-free atmosphere.

Therefore, perpendicular magnetic recording media in which the permalloy thin film formed by this method is used as a soft magnetic layer have good modulation, but the reproduction output is still insufficient, and a medium with small modulation and even higher reproduction output is desired. was. In order to achieve this objective, a permalloy thin film is required which has generally contradictory properties such as low coercive force and low anisotropy. The inventors of the present invention conducted extensive research to solve these problems, and found that the permalloy thin film is a laminated film consisting of a low coercive force layer with a small coercive force and a low anisotropic layer with a small in-plane magnetic anisotropy. The inventors discovered that permalloy thin films with low coercive force and small anisotropy can be obtained over a wide range by doing this, and came up with the present invention.

In view of the above, the perpendicular magnetic recording medium of the present invention has a soft magnetic layer made of permalloy (Mo(T: liveden), CLl(
Since it is a thin film containing a third component such as copper (copper), etc., it can be selected from a wide range in the vA range where the coercive force and in-plane magnetic anisotropy are sufficiently small for practical use, and it is suitable for the system in the case of disks. This has the great effect of providing a medium in which the modulation of various levels is small and the playback output is relatively large. The magnetic permeability of the Permalloy 77g film is also selected depending on the system, but from the standpoint of recording sensitivity and reproduction output, a film with high magnetic permeability is preferably used.

In addition, in the present invention, from a practical point of view, the reduction in the playback output level is small and the modulation when used as a disc satisfies the 5% or less that is said to be practically necessary.
The permalloy thin film as a whole has an in-plane coercive force of 1.0~
A range of 12.0 Q e (Oersted) is preferred. In this range, the anisotropy ratio is 0.90 to 1,1
It is in the range of 0 and has good isotropy. Here, the anisotropy ratio is calculated by dividing the in-plane coercive force HCE in the direction of the easy axis by the in-plane coercive force HCH in the direction of the hard axis.
-I CH. In addition, in the above-mentioned Permanent [1] thin film, each layer is formed by a physical deposition method in terms of production and film characteristics, and the low orientation layer has an oxygen content of 1.0. ~10 volume LO% M rope S 15 A layer formed under an inert gas atmosphere, and the low coercive force layer does not contain oxygen, or even if it does, the content is 0.5 volume % or less The layer is preferably formed under a low oxygen-containing inert gas atmosphere.

In the present invention described above, the magnetic recording layer is made of Co as in the embodiment.
-In addition to the perpendicular magnetization layer made of a Cr alloy film, the G
It is clear from the spirit of the present invention that an o-Cr alloy and its well-known perpendicular magnetization layer can be applied.

Hereinafter, the details of the above-mentioned present invention will be explained based on examples.

Note that although the embodiments of this invention were made using the facing target sputtering method, from the perspective of the spirit of the invention,
Obviously other methods, e.g. vapor deposition.

It is clear that so-called physical deposition methods (PVD methods) such as sputtering and inblating can be applied.

Note that the above-mentioned facing target sputtering method is
Using a sputtering method known in Japanese Patent No. 7-158380, etc., a substrate is placed on the side of a pair of opposing targets, and a magnetic field for plasma trapping is applied perpendicularly between the targets to perform sputtering, thereby sputtering onto the substrate. Refers to the sputtering method for forming a film.

FIG. 1 is a structural diagram of a facing target type sputtering apparatus used in carrying out the present invention.

As is clear from the figure, this device is based on the aforementioned Japanese Unexamined Patent Publication No. 57-15
It has basically the same configuration as the facing target type sputtering apparatus known in Japanese Patent No. 8380.

That is, in the figure, 10 is a vacuum chamber, and 20 is a vacuum chamber 10.
Exhaust system consisting of a vacuum pump, etc. 30 is a vacuum! This is a gas introduction system that introduces a predetermined gas into the ri 10 and sets the pressure in the vacuum Piio to a predetermined gas pressure of about 10-1 to 10''4 Torr.

In the vacuum chamber 10, a pair of targets T+ and Tz are sputtered by a target holder 15.16 fixed to a copper plate 71.12 of the vacuum chamber 10 via an insulating member 13.74 as shown in the figure. ru-r + s
.

The T2S are arranged so as to face each other in parallel across a space. The target boulders 15 and 16 for attaching the targs t"T+ and Tz are the cold water pipes 151 and 161.
Cooling water is circulated through the target T1. The permanent magnets 152 and 162 are cooled. , magnet 152.16
2 through target T1.1-2.

The south poles are arranged so as to face each other, so that the magnetic field is applied to the target T'1. It is formed in the direction perpendicular to T2 and only between the targets. Note that 17.18 indicates the insulating member 13.
14 and target holders 15 and 16 from plasma particles during sputtering, and to prevent exposure to parts other than the target surface.

Further, the substrate holding means 41 holding the substrate 40 on which the magnetic thin film is formed is placed in the vacuum chamber 1σ.

The substrate holding means 41 are feed rolls 41a which are rotatably supported by support brackets (not shown) and are supported parallel to each other.

The substrate 40 is held in a direction substantially perpendicular to the sputtering surface TI9.1'7S so as to face the space between the targeters 1 to T+ and -[2. It is arranged as follows.

Therefore, the substrate 40 can be moved in a direction perpendicular to the sputtering surfaces TIS and T2S by the substrate holding means 41c. Note that the surface density of the support roll 41b can be adjusted.

On the other hand, a power supply means 50 consisting of a DC power source for supplying sputtering power has its positive side connected to ground and its negative side connected to targets T+ and T2, respectively. Therefore, the sputtering power from the power supply means 50 is supplied between the anode and the cathode, with the ground as the anode and the targets T+ and T2 as the cathodes.

Note that in order to protect the substrate 40 during pre-sputtering, the substrate 4
A shutter (not shown) is provided between T0 and targets T+ and T2.

As described above, the structure is basically the same as that of the above-mentioned Japanese Patent Application Laid-Open No. 57-158380, and high-speed low-temperature spucking is possible as is known. Zunawara, target hT+,T
Sputter gas ions are generated in the space between the two by the action of the magnetic field.

γ electrons etc. emitted by the sputtering are bound and a high-density plasma is formed.

Therefore, the sputtering of targets T+ and T2 is promoted, the distance between the deposits increases from the space, and the deposition rate on the substrate 40 increases, allowing high-speed sputtering, and the substrate 40 is located on the side of the targets T+ and T2. Therefore, low-temperature sputtering is also possible.

J′3, the facing target sputtering system of the present invention is
The method is not limited to the above-mentioned apparatus, but as described above, a substrate is placed on the side of a pair of targeters 1 facing each other, and a perpendicular magnetic field is applied between the targets to perform sputtering, and sputtering is performed on the substrate. Refers to the sputtering method for forming a film. Therefore, the magnetic field generating means may also be an electromagnet instead of a permanent magnet. Further, the magnetic field may be of any type as long as it can entrain γ electrons and the like into the space between the targets, and therefore includes the case where it is generated not over the entire surface of the target but only around the target laser 1.

Next, an example of a perpendicular magnetic recording medium according to the present invention, which was implemented using the above-mentioned facing target type sputtering apparatus, will be described.

J5, the crystal structure of the obtained alloy film was identified using a Rigaku-type tFi numerical X-ray diffraction device, and the vertical orientation was a hexagonal close-packed structure and the rocking curve of the (002) plane peak was determined using the X-ray diffraction method. It was determined using a device, and its half width Δθ has already been evaluated.

The film thickness and composition were determined from a curve calibrated in advance using a fluorescent X-ray device.

The magnetic properties of the medium were determined using a moving sample magnetometer.

The recording/reproducing characteristics of the double-layer film media are as follows:
Evaluation was carried out using a vertical magnetic head similar to that known in Japanese Patent No. 91 and the like.

[Examples and Comparative Examples] Various permalloy thin films were created on substrates under the following conditions, and their coercive force and magnetic anisotropy were evaluated. At the same time, perpendicular magnetization layers made of Go-Cr were sequentially formed on people's permalloy thin films. A two-layer film medium was formed and its playback characteristics were evaluated.

Δ, equipment conditions Δ-1, soft magnetic layer a, Target T+, T2 material: 1-1. Between T22.

-4wt%, Ni -78wt%, Fc -18w
t% permalloy B, substrate 40: 50μ surface thickness polyethylene terephthalate (PET) film C, target T+, -rz spacing: 120#d, magnetic field on target surface: 100-200 Gauss C, target T+, T2 shape: 100INR1 -X 150mmWX12mj
Rectangle ", Distance between substrate 40 and target L, -r2 end: 20°A-2, C0-Cr perpendicular magnetization layer a, Target material: T1. Both T2 are Co 80wt%
.

Cr-20wt% alloy target b, target t゛T+, Tz spacing: 160mC, target surface magnetic field: lOO~200 Gauss d, target 'r+, T2 shape: 100mIRL x 150mW x 12NR
The following operations were performed under the conditions of rectangle e of t, distance between substrate 40 and target -It, and end of T2: 20 #B, and operating procedures A-1 and Δ-2.

a. After installing the substrate, the degree of vacuum reached in the vacuum chamber 10 is 1 x
Evacuate to below 10' Torr.

b. Gas was introduced to a predetermined pressure, press sputtering was performed for 3 to 5 minutes, the shutter was opened, and film formation was performed while moving the substrate 40 in the opposite direction of targets T+ and -rz as shown. The gas pressure during sputtering is 4 x
It was set to 10' Torr.

The gases were 100% Ar (argon) and 0.1% oxygen (02). 0,3.1.3゜5
, 10.15. A film was formed using Ar gas mixed with 20% by volume (hereinafter abbreviated as ``%'') as follows. That is, first, the first low anisotropic layer was formed in a predetermined atmosphere. A film is formed to a predetermined thickness while being transferred, and then the second low coercive force layer is formed in the same manner as the first layer while changing the gas to 100% Ar gas and transferring the film in the opposite direction. The films were laminated. The film thickness of each layer was adjusted by changing the film transport speed. In the case of laminating three or more types of films, the film may be formed by repeating this method.

In the case of majc A-2 (7), ArloO% (3N) was used.

C, sputter 111 input power is 3 for both A-1 and A-2.
I did KW'c.

C9 results Figure 2 shows the characteristic magnetization characteristics of the permalloy thin film of the comparative example. The magnetization characteristics in the running direction of the substrate (MD force direction and substrate width direction (T I) direction) are different, and magnetic anisotropy occurs in the plane.
The D direction was the axis of difficult magnetization.

In FIG. 2, G indicates the strength of the applied magnetic field, and B indicates the magnetization of the soft magnetic layer.

Table 1 shows the measurement results of the in-plane coercive force of each permalloy thin film obtained.

These results are the measurement results of the single-layer film of the comparative example and the permalloy thin film with a two-layer structure, which is a stack of a low anisotropy film formed in an oxygen-containing atmosphere and a low coercive force film formed in an oxygen-free atmosphere. It is. The thickness of each film was adjusted to a total of 0.4 μm. Table 1 shows the measurement results of the coercive force, where column A is the oxygen concentration (%), BIIgl is the thickness (μm) of the low anisotropic film formed in an oxygen atmosphere, and Of[l
II is the measurement direction of the in-plane coercive force of the same sample, E is the easy axis direction of magnetization, ]] is the direction of the hard axis of magnetization.

Therefore, the values in column E in the table are Al111. In-plane coercive force in the easy axis direction of the sample specified in column B 1-I
CE, and the column ( ) is the in-plane coercive force HCH in the direction of the hard magnetization axis of the sample, which is in Oersteds (Oe).

In addition, in order to obtain a perpendicular magnetic recording medium, C0 was formed under the conditions of A-2 on each permalloy thin film having the characteristics shown in Table-1.
Table 2 shows the characteristics of the perpendicular magnetization layer consisting of the -0r layer.

Table 1: In-plane coercive force of permalloy thin film Table 2: Characteristics of perpendicular magnetic layer shows the coercive force of The coercive force was measured by separating the soft magnetic layer of the 2-4Itφ medium. The half-width Δθ cut was measured using the two-layer film medium as it is.

D, Electromagnetic Conversion Characteristics As shown in FIG. 3, M
Rectangular samples in the Dh and TD force directions were cut out, and their respective reproduction outputs were measured at J'3 at a recording density of 50KFRPI to evaluate electromagnetic conversion characteristics.

Table 3 shows the measurement results.

In addition, the electromagnetic conversion characteristics are 4.75 when the tape runs during recording.
cni/sec, and 9.5 cm/sec during playback.

Further, the numerical values in the table are shown as relative values obtained by dividing each measured value by the measured value of an appropriate sample. The Δ column and B column of the table are the same as Table-1, and the C column shows the cutting direction of the sample.

Furthermore, Table 4 shows the output ratio of each sample in the MD force direction and TDh direction.

Table-3 Reproduction output of two-layer media (Note) *marks indicate standard measurement values Table-4MD force direction TD force direction output ratio Table-3 J: sea urchin, 11-layer permalloy thin film It can be seen that the two-layer structure of the low coercive force layer and the low anisotropy layer satisfies the required characteristics over a much wider range than the permalloy film of the tli layer in the comparative example. In order to achieve the modulation of 5% or less, which is said to be practically necessary, it is necessary that the output ratio in the MD force direction 1" and the D direction is 0.90 to 1.10. As is clear from the results in Table 32 and Table 4, for the two-layer medium of the comparative example of single-layer permalloy thin film, the output that satisfies the above dicolation condition is compared to the standard measurement value. On the other hand, in the two-layer medium of the multilayer permalloy film of the present invention, there is a wide range in which the output does not decrease significantly as long as the above modulation conditions are satisfied. As described above, according to the present invention, it is possible to achieve moji correction without causing any practical problems without significantly reducing the output.

In particular, as is clear from the results in Table 1, a multilayer Pernloy thin film whose overall in-plane coercive force is in the range of 1.0 to 12.0 Q e in both the hard axis direction and the easy axis direction, The two-layer medium has a modulation ratio of 5% or less and an output of 10% or more of the standard sample, which is preferable since it has practically sufficient performance.

Furthermore, from Table 1, it can be seen that the multilayer permalloy thin film described above can be obtained by a combination of a low anisotropy layer and a low coercive force layer formed in an atmosphere with an oxygen content of 1.0% or more.

Note that the low coercive force layer has an oxygen content of 0.5 as described later.
% or less is sufficient.

As described above, it can be seen that by forming a laminated permalloy thin film of a low anisotropy layer and a low coercive force layer, the characteristics of the two-layer medium are greatly improved compared to the comparative example.

The effect of such lamination can be achieved by suitably changing the thickness of two or more films made under different atmospheric conditions. However, permalloy films made in an oxygen atmosphere with an oxygen content of more than 10% actually undergo reactive sputtering, forming oxides of permalloy's constituent atoms - iron and nickel, and the sputtering rate becomes slower. This is not desirable from the point of view of production efficiency.

Furthermore, the object of the present invention can be achieved even if the number of laminated thin film layers is three or more, but the number of layers in the process is 17! lisa, 1q
Considering the characteristics, two layers are sufficient.

In the case of two layers, it is more preferable that the lower layer is a low anisotropy layer formed in an oxygen atmosphere, and the upper layer is a low coercive force layer formed in an oxygen-free atmosphere.

This is because when a vertical magnetization layer mainly made of Co-Cr is formed on a permalloy layer, the GO-Cr film is affected by the crystals of the permalloy layer, so the boundary is made of a permalloy film with as good crystallinity as possible. Because it is better to be.

Furthermore, the atmosphere in which the permalloy layer of the low coercive force layer is formed must have an oxygen concentration of less than 0.5%. In other words, in an oxygen atmosphere of less than 0.5%, the crystallinity of the permalloy film is not substantially impaired, and it exhibits almost the same characteristics as a film formed in an oxygen-free system.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a facing target type sputtering apparatus used in carrying out the present invention, FIG. 2 is an explanatory diagram of magnetic characteristics, and FIG. 3 is an explanatory diagram of one number extraction.

Claims (1)

[Claims] 1. A perpendicular magnetic recording medium having a soft magnetic layer made of a permalloy thin film on a nonmagnetic substrate and a magnetic recording layer having an axis of easy magnetization perpendicular to the film surface, wherein the permalloy of the soft magnetic layer is 1. A perpendicular magnetic recording medium characterized in that the thin film is composed of a laminated film of a low coercivity layer having a small coercive force and a low anisotropy layer having a small in-plane magnetic anisotropy. 2. The permalloy thin film has an in-plane coercive force of 1.0 to 12.
2. The perpendicular magnetic recording medium according to claim 1, wherein the perpendicular magnetic recording medium is 0 oersted (Oc). 3. Both the low anisotropy layer and the low coercive force layer are formed by a physical deposition method, and the low anisotropy layer has an oxygen concentration of 1.
．． It is a layer formed in an atmosphere of 0 to 10% by volume, and the low coercive force layer is a layer formed in an atmosphere that does not contain oxygen, or even if it does, its concentration is 0.5% by volume or less. A perpendicular magnetic recording medium according to claim 1 or 2. 4. The perpendicular magnetic recording medium according to claim 1, 2 or 3, wherein the outermost layer of the permalloy thin film on the magnetic recording layer side is a low coercive force layer. 5. The perpendicular magnetic recording medium according to claim 1, 2, 3, or 4, wherein the permalloy thin film is formed by a sputtering method. 6. The perpendicular magnetic recording medium according to claim 5, wherein the permalloy thin film is formed by a facing target sputtering method.