JPH05143952A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a perpendicular magnetic recording medium having a ferromagnetic metal thin film excellent in perpendicular magnetic anisotropy. CONSTITUTION:The perpendicular magnetic recording medium consists of a ferromagnetic metal thin film essentially comprising Co and formed on a nonmagnetic supporting body. The grain size of the ferromagnetic metal thin film measured by thin film X-ray diffraction method satisfies the relation of (grain size with respect to 002 plane of alpha-Co)/(grain size with respect to 100 plane of alpha-Co) >= 3.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film as a magnetic layer, and more particularly to a magnetic recording medium suitable for a perpendicular magnetic recording system with improved magnetic characteristics.

[0002]

2. Description of the Related Art In recent years, improvements in magnetic recording media have been earnestly pursued in order to meet the demand for high density recording. Above all,
As a medium for which the improvement in recording density is most expected, there is a so-called metal thin film type medium in which a metal thin film is used for a magnetic layer.

On the other hand, from the aspect of the recording system, magnetic recording is roughly classified into an in-plane magnetization type having an easy magnetization axis in the in-plane direction of the magnetic layer and a perpendicular magnetization type having an easy magnetization axis in a direction perpendicular to the film surface. However, since the perpendicular magnetization type recording method is capable of further increasing the recording density and is an optimum method for digital recording, it is under intensive development.

Regarding the perpendicular magnetization type ferromagnetic metal thin film, J. Vac. Sci. Technol. A4
(1), p1 to p13 (1986), etc., CoCr and Co formed by a sputtering method.
A thin film containing Co as a main component such as CrTa has been widely studied because of its excellent perpendicular magnetic anisotropy. On the other hand, improvement of characteristics as a medium for perpendicular magnetic recording, in particular, improvement of perpendicular magnetic anisotropy has been promoted from various viewpoints.
Vac. Sci. Technol. A4 (6), p29
75-p2987 (1986), a technique is known in which epitaxial growth is performed on a Ti underlayer having the same hcp structure as a CoCr alloy. In addition, IEEE Tran
s. Mag. , MAG-21, 5, p1426-142
8 (1985), it is reported that columnar crystals of CoCr having highly oriented C-axis can be formed on the amorphous Ge underlayer from the interface of the underlayer.

However, these conventional layer structures have a problem that, for example, when the film is formed, heating at about 150 ° C. is required, and the nonmagnetic support is required to have heat resistance. The characteristics as a magnetic recording medium are still insufficient, and further improvement of the ferromagnetic metal thin film itself or improvement by a new material has been demanded.

On the other hand, as a method for improving the characteristics of a magnetic recording medium having a ferromagnetic metal thin film as a magnetic layer from the shape and size of particles constituting the thin film, a Co--Ni alloy is used as a non-magnetic support in an oxidizing atmosphere. Attempts have been made to reduce the noise by finely crystallizing the ferromagnetic metal thin film by vapor-depositing the ferromagnetic metal thin film, and various methods of devising an oxygen introduction method have been proposed. For example, in JP-A-58-41442 and JP-A-58-83328, Co-Ni is disclosed.
A method of introducing oxygen gas from the high incident angle side when obliquely vapor-depositing an alloy is also disclosed in JP-A-58-41443 and 58-83327. A method of introducing gas is disclosed. Further, in Japanese Patent Laid-Open No. 2-306425, the corrosion resistance is determined by specifying the ratio of the peak intensity of the (110) plane and the peak intensity of the (211) plane by X-ray diffraction of a chromium film provided on a ferromagnetic metal thin film. The invention for providing an excellent magnetic recording medium is disclosed. However, it does not suggest anything about improving the ferromagnetic metal thin film itself. Further, in JP-A-3-73410, by reducing the crystallite size obtained by the thin film X-ray diffraction method below a specific value, noise is reduced and in-plane magnetization with excellent S / N is obtained. An invention relating to a mold medium is described. However,
There is no description about the perpendicular magnetization characteristic, and no description suggesting it.

As described above, the ferromagnetic metal thin film containing Co as a main component is relatively excellent as a magnetic layer of a perpendicular magnetic recording medium, but still has many problems in terms of perpendicular magnetic anisotropy, and is still unsolved. No means for effectively solving it has been proposed.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and provides a perpendicular magnetic recording medium having a ferromagnetic metal thin film excellent in perpendicular magnetic anisotropy. Has a purpose.

[0009]

In order to achieve the above object of the present invention, the inventors of the present invention have considered the shape and size of a ferromagnetic metal thin film containing Co as a main component while considering the growth of particles constituting the thin film. As a result of repeating the experiment while paying attention to this, the following invention was able to be achieved. That is, the object of the present invention is to provide a perpendicular magnetic recording medium having a ferromagnetic metal thin film mainly composed of Co on a non-magnetic support, and to measure the crystallite size of the ferromagnetic metal thin film from the thin film X-ray diffraction method. With respect to the ratio (1) to (3), it is achieved by a perpendicular magnetic recording medium characterized in that (crystallite size of 002 plane of α-Co) / (crystallite size of 100 plane of α-Co) is 3.0 or more. It

The crystallite size of α-Co with respect to the 002 plane obtained by the thin film X-ray diffraction method is the same as α-C.
The perpendicular anisotropic magnetic field and the vertical coercive force could be increased by setting the crystallite size of o to 100 times the crystallite size or more. The characteristic of the present invention is that
The ratio of the crystallite size to a specific plane, rather than the crystallite size itself, is effective for improving the perpendicular magnetic anisotropy. The reason for this is not clear, but it is presumed that the columnar structure of the fine particles forming the ferromagnetic metal thin film probably contributes to the shape anisotropy.

The thin film X-ray diffraction method referred to in the present invention is carried out by setting the incident angle of X-rays on the thin film to 1 degree or less.
In the magnetic recording medium of the present invention, regarding the crystallite size ratio of the ferromagnetic metal thin film obtained by the thin film X-ray diffraction method, (crystallite size with respect to the 002 plane of α-Co) /
(Crystallite size for 100 plane of α-Co) is 3.0
The above is desirable.

That is, the crystallite size ratio value of 3.0
The perpendicular magnetic anisotropy greatly changes at the boundary of, and if it is less than 3.0, the perpendicular magnetic anisotropy cannot be increased so much that the object of the present invention cannot be sufficiently achieved.

The size of the crystallite size itself does not directly affect the achievement of the object of the present invention, but the size of the crystallite size with respect to the 100 face of α-Co and the size of the crystallite size with respect to the 002 face of α-Co are large. It is desirable that the difference in height be 250 angstroms or more.

The ferromagnetic thin film mainly composed of Co in the present invention usually contains at least 50 at% or more of Co, and as a component other than Co, Co--Ni, Co
-Pt, Co-Ni-Pd, Co-Fe, Co-Ni-
Fe, Co-Cr-Ta, etc. can be introduced. Further, by adding Al, B, Cr or the like to these compositions, other characteristics as a metal thin film can be improved.

The thickness of the metal thin film of the magnetic layer of the present invention is usually in the range of 200 to 10,000 A (angstrom).

There are various methods in which the crystallite size of the ferromagnetic metal thin film is the same as that of the magnetic recording medium of the present invention. The composition of the ferromagnetic metal thin film, the base material of the ferromagnetic metal thin film, the film forming atmosphere and the film forming speed. It is possible to use a method such as adjustment. Above all,
As a method mainly based on the composition of a ferromagnetic metal thin film, C
A ferromagnetic metal thin film obtained by forming an o-Pd-Cr alloy thin film by sputtering is most preferable.

In particular, the alloy is made of (Co100-xPdx) 100-
When expressed as yCry (x and y are at.% (atomic%)), it is preferable that 10 ≦ x ≦ 40 and 5 ≦ y ≦ 25. Co-Pd-Cr alloy thin film is Co-P
It is considered that the high magnetostriction of the binary alloy of d effectively acts and the ratio of the crystallite size is likely to be the condition as in the present invention.

Further, oxygen is added to the component {(Co100-
xPdx) 100-yCry} 100-zOz (10 ≦ x ≦ 40, 5
≦ y ≦ 25, 0.5 ≦ z ≦ 15, x, y and z are a
t.% (atomic%). The ferromagnetic metal thin film having the composition represented by (4) is also effective for the present invention, and the ferromagnetic metal thin film having this composition can further improve the perpendicular magnetic anisotropy.

The Co-Pd-Cr alloy thin film is
Since it is possible to form a film at a relatively low temperature of from room temperature to about 350 ° C. at most, the range of selection of the non-magnetic support is wider than in the case of using Co as the main component such as Co—Cr system. There is an advantage that the film forming apparatus may be relatively inexpensive.

In order to further improve the characteristics of the thin film magnetic layer, oxygen, nitrogen, carbon of 10 at.
An additive element such as an inert gas, a metal, or a semimetal may be added. Above all, oxygen is added to the thin film magnetic layer having the above composition at 0.5 to 15 at. %, Preferably 1 to 10 at.
%, The perpendicular magnetic anisotropy can be further increased.

[0021] Usually, the value of at% of the metal element in the ferromagnetic metal thin film is determined by the ICP (Inductivel)
It is a value specified by quantifying by XRF (fluorescent X-ray analysis) calibrated by y Coupled Plasma Analysis).

On the other hand, the at% of oxygen can be measured by a value obtained by reading the obtained metal thin film from the profile in the depth direction of the film obtained by Auger electron spectroscopy (AES).

In the magnetic recording medium of the present invention,
By providing a nonmagnetic layer as an underlayer between the magnetic layer having the above composition and the nonmagnetic support, a magnetic layer having a further improved coercive force can be obtained. Examples of the composition of the non-magnetic layer include Cr, Mo, W, V, Nb, Ta, Si,
A thin film of a metal such as Ge or Ti, an oxide, a nitride, or a carbide can be used. When the composition for the non-magnetic layer is a simple metal, oxide, nitride or carbide of Cr, Ge and Ti, the perpendicular magnetic anisotropy of the metal thin film formed thereon is further improved. ..

The effect of the non-magnetic layer provided on the non-magnetic substrate is an epitaxial effect, or impurities from the non-magnetic substrate are prevented from mixing into the magnetic thin film, and the magnetic layer has an excellent perpendicular magnetic structure. It is thought that this is to facilitate the formation of.

The thickness of the non-magnetic layer is 200 to 10,
It may be 000A. As a method for forming the non-magnetic layer,
Similar to the magnetic layer, a vacuum film forming method such as sputtering or vacuum evaporation is preferable in order to reflect the effect of the nonmagnetic layer in the thin film magnetic recording layer.

The metal thin film magnetic layer of the magnetic recording medium of the present invention can be formed by a vacuum film forming method such as sputtering or vacuum evaporation. In order to obtain an alloy thin film having a predetermined composition, an alloy target having a composition close to that of the thin film may be used for sputtering film formation, or a plurality of targets may be simultaneously sputtered (multiple simultaneous sputtering) to produce a non-magnetic substrate. You may form the alloy thin film of a predetermined composition on it.

When oxygen is introduced into the metal thin film, it may be added in advance to any of the above target compositions or starting materials to be formed, or in a vacuum gas atmosphere during the film forming process. It may be incorporated into the metal thin film formed on the non-magnetic substrate by mixing it as a gas containing a trace amount of oxygen. Usually, the introduction of oxygen can be performed by introducing a gas in which a small amount of oxygen is mixed in an inert gas such as Ar into the vacuum chamber.

Further, the multi-source simultaneous sputtering method is a desirable method for obtaining the magnetic recording medium of the present invention since it enhances the separation property of the grain boundaries and easily induces magnetic anisotropy. For example,
By combining a CoPd alloy target and a Cr target and performing binary simultaneous sputtering in a vacuum atmosphere containing a small amount of oxygen, the segregation effect of Cr and oxygen is further enhanced,
A metal thin film having excellent magnetic anisotropy can be obtained. Further, in order to further improve the characteristics of the thin film magnetic recording layer, for example, a residual gas atmosphere in a vacuum during sputtering film formation, the substrate temperature, removal of adsorbed substances on the substrate surface, reduction of degassing from the substrate,
Of course, it is desirable to optimize the film forming speed.

In the present invention, it is considered that the magnetostriction effect due to the internal stress of the thin film magnetic recording layer is effective, and the magnetic field obtained by the pressure of the inert gas in the vacuum chamber of the film forming chamber during sputtering is obtained. Since the characteristics change, it is desirable to pay attention to the gas pressure during manufacturing. For example, when Ar is used as the inert gas, the Ar gas pressure is 5 × 10 ⁻³ To.
It is desirable to be rr or more. When Ar is used as the inert gas, the sputtering gas pressure is preferably 5 × 10 ⁻³ Torr or more, and the oxygen-containing gas partial pressure is 2 or more.
It is desirable that it be not more than × 10 ^-4 Torr.

In order to further improve the characteristics of the thin film magnetic recording layer, for example, a residual gas atmosphere in a vacuum during sputtering film formation, the substrate temperature, removal of adsorbed substances on the substrate surface, reduction of degassing from the substrate, film formation Of course, optimization of speed, etc. is desirable.

As the non-magnetic substrate in the magnetic recording medium of the present invention, a non-magnetic substrate made of metal such as Al or Al alloy, glass, ceramics, synthetic resin or the like, or a non-magnetic substrate having a surface treatment or an underlayer. Is used. For example, Al alloy, Al substrate with Ni-P underlayer,
Various tempered glass, various ceramics, polyethylene terephthalate, polyimide, polyetherimide, inorganic / organic composite materials and the like are used.

In particular, in the present invention, since it is not necessary to heat the nonmagnetic substrate to a high temperature during film formation, it can be applied to a material having low heat resistance such as plastic. As the form of the non-magnetic substrate, besides the disc-like form, it is of course applicable to the tape-like form.

Further, a so-called two-layer structure in which a low coercive force magnetic layer having an easy axis of magnetization is provided in the film plane directly or through an intermediate layer under the thin film magnetic recording layer having the perpendicular magnetic anisotropy described above. It is also possible to implement it as a structured perpendicular magnetization medium. As the low coercive force magnetic layer, an in-plane magnetized film having an in-plane coercive force of 100 oersted or less, particularly preferably a soft magnetic thin film having high magnetic permeability is desirable. For example, permalloy alloy, Co-Cr-Ta, Co-Cr-Nb, Co-N
Examples thereof include thin films such as b-Zr. As the intermediate layer, for example, a material and a film structure similar to those of the nonmagnetic layer can be used.

The film thickness of the resistance magnetic force magnetic layer is 20
It is selected from 0 to 10,000A. As a film forming method,
Although a plating method or the like is possible, a vacuum film forming method such as sputtering or vacuum deposition is more preferable.

In order to carry out the present invention more effectively, a protective layer and a lubricating layer may be provided on the thin film magnetic layer. For example, as the protective layer, a carbon thin film, an oxide film, a nitride film, a carbide film, a metal thin film, an alloy thin film, or the like is used. As the lubricant layer, various compounds known as lubricants for metal thin film magnetic recording media can be used. Of these, perfluorocarbon-based lubricants are desirable in terms of lubrication effect. The novel effects of the present invention will be specifically described with reference to the following examples.

[0036]

【Example】

(Example 1) 1 in a vacuum chamber of a magnetron sputtering apparatus
An alloy target having a composition of Co80Pd20 (at%) with a diameter of 25 mm and a Cr target were set, and then argon gas was introduced into the vacuum chamber until the gas pressure became 5 × 10 ⁻³ Torr. Then, the Co80Pd20 target was supplied with an RF power of 2.0 kW, and the Cr target was supplied with 1 RF power.
DC power of 50W is applied, diameter 86mm, thickness 1.2
C with a thickness of 2000 angstroms on a glass substrate of mm
A sample of a magnetic recording medium was obtained by sputtering a ferromagnetic metal thin film of an oPdCr alloy.

(Example 2) In Example 1, Co80P
Change to an alloy target with a composition of d20 (at%), Co
A magnetic recording medium sample was prepared under the same conditions as in Example 1 except that an alloy target having a composition of 75 Pd25 (at%) was used.

Example 3 In Example 1, Co80P
Change to an alloy target with a composition of d20 (at%), Co
A magnetic recording medium sample was prepared under the same conditions as in Example 1 except that an alloy target having a composition of 70 Pd30 (at%) was used.

Comparative Example 1 In Example 1, Co80P
Change to an alloy target with a composition of d20 (at%), Co
A magnetic recording medium sample was prepared under the same conditions as in Example 1 except that the single metal target of No. 1 was used.

(Comparative Example 2) In Example 1, Co80P
Change to an alloy target with a composition of d20 (at%), Co
A magnetic recording medium sample was prepared under the same conditions as in Example 1 except that an alloy target having a composition of 90 Pd10 (at%) was used.

(Comparative Example 3) In Example 1, Co80P
Change to an alloy target with a composition of d20 (at%), Co
A magnetic recording medium sample was prepared under the same conditions as in Example 1 except that an alloy target having a composition of 85 Pd15 (at%) was used.

The crystallite size and the magnetic properties of the samples of the magnetic recording medium prepared as described above were measured and evaluated using the thin film X-ray diffraction method and the vibrating sample magnetometer (VSM), respectively.

In the measurement by the thin film X-ray diffraction method, the incident angle of the X-ray with respect to the ferromagnetic metal thin film of the sample of each magnetic recording medium is 1
I did it less than once. In addition, a vibrating sample magnetometer (VS
The applied magnetic field at the time of measurement by M) was set to 15 (kOe). The measurement results are shown in Table 1.

[0044]

[Table 1]

From the above results, when the ratio of (crystallite size for 002 plane of α-Co / size of crystallite size for 100 plane of α-Co) is 3.0 or more, the magnitude of perpendicular magnetic anisotropy is large. Was found to be good. In particular, it was found from the measurement of the coercive force in the vertical direction that only an in-plane magnetized film could be obtained.

Example 4 An alloy target having a composition of 125 mm Co80 Pd20 (at%), a Cr target, and a Ti target were placed in a vacuum chamber of a magnetron sputtering apparatus, and then a gas pressure of 5 was set in the vacuum chamber. × 10
Argon gas was introduced until the pressure reached ^-3 Torr. Then, first, 500 W of electric power was applied to the Ti target, and 1 was placed on a glass substrate having a diameter of 86 mm and a thickness of 1.2 mm.
A nonmagnetic layer of Ti having a film thickness of 000 angstrom was formed.
Then, an RF power of 2.0 kW was applied to the Co80Pd20 target and a DC power of 150 W was applied to the Cr target, and while the glass substrate was heated and held at 180 ° C., sputtering was performed to form a 2000 angstrom film. A ferromagnetic metal thin film of CoPdCr-based alloy was formed into a thick film to obtain a sample of a magnetic recording medium.

(Example 5) In Example 4, CoPd
A magnetic recording medium sample was obtained under the same conditions as in Example 4 except that the temperature at which the substrate was heated and held at the time of forming the ferromagnetic metal thin film of the Cr-based alloy was 100 ° C.

(Example 6) In Example 4, CoPd
A sample of a magnetic recording medium was obtained under the same conditions as in Example 4 except that the temperature at which the substrate was heated and held when forming the ferromagnetic metal thin film of a Cr-based alloy was 250 ° C.

(Example 7) In Example 4, CoPd
A magnetic recording medium sample was obtained under the same conditions as in Example 4 except that the temperature at which the substrate was heated and held at the time of forming the ferromagnetic metal thin film of a Cr-based alloy was 350 ° C.

(Comparative Example 4) In Example 4, CoPd
A sample of a magnetic recording medium was obtained under the same conditions as in Example 4 except that the substrate was not heated and was kept at room temperature when forming the ferromagnetic metal thin film of the Cr-based alloy. Table 2 shows the measurement and evaluation results of the crystallite size and the perpendicular magnetic characteristics of the prepared sample.

[0051]

[Table 2]

[0052]

In a perpendicular magnetic recording medium having a ferromagnetic metal thin film mainly composed of Co on a non-magnetic support, with respect to the crystallite size ratio of the ferromagnetic metal thin film obtained by thin film X-ray diffraction, By setting (crystallite size with respect to 002 plane of α-Co) / (crystallite size with respect to 100 plane of α-Co) of 3.0 or more, a magnetic recording medium excellent in perpendicular magnetic anisotropy can be obtained. it can. In particular, CoPdC in which the composition ratio of each atom is specified as a ferromagnetic metal thin film
The ternary alloy of r was effective.

Claims (2)

[Claims] 1. In a perpendicular magnetic recording medium having a ferromagnetic metal thin film mainly composed of Co on a non-magnetic support, with respect to the crystallite size ratio of the ferromagnetic metal thin film obtained by thin film X-ray diffraction, A perpendicular magnetic recording medium characterized in that (crystallite size of 002 plane of α-Co) / (crystallite size of 100 plane of α-Co) is 3.0 or more. 2. The perpendicular magnetic recording medium according to claim 1, wherein the ferromagnetic metal thin film is a ternary alloy of CoPdCr.