JPS63201912A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To permit sufficient magnetic recording from the front to the rear surface part of a medium and to improve recording and reproducing characteristics by using the medium which is increased in the coervice force on the front side of the medium and is successively decreased toward the rear face. CONSTITUTION:The perpendicular magnetic recording medium formed by changing the coercive force in the perpendicular direction of a magnetic Co-Cr alloy film formed on a nonmagnetic substrate continuously or stepwise in such a manner that the coercive force on the boundary side of the substrate is decreased and the coercive force on the front face side of the magnetic film is increased is used. Stepwise changing of the coercive force is permitted simply by laminating multi-layered films having the different coercive forces on the substrate. Recording and reproduction efficiency are thereby improved and the high density magnetic recording is permitted. The similar effect is further obtd. as well by using, for example, Co-V, Co-Mo, Co-W, Co-Ru, etc., in addition to Co-Cr as the Co-base alloy which is the perpendicularly magnetized film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, particularly a magnetic recording medium suitable for perpendicular magnetic recording, and a method for manufacturing the same.

[Conventional technology]

First, the perpendicular magnetic recording method will be explained. This method performs magnetic recording in a direction perpendicular to the film surface of a magnetic recording medium, and is suitable for increasing magnetic recording density because the demagnetizing field within each bit is small during high-density magnetic recording. The magnetic recording medium used for this purpose is Co
-Cr,C.

-V, Co-Mo, Co-W, Co-Rn, C.

-Re, Co-0, Co-Cr-Rh, Co-Cr-
Some use Co-based alloy thin films such as Ru and Co-Ni-0. The Co-based alloy that makes up these magnetic thin films is
Close-packed hexagonal lattice (HAP) structure.

It has the characteristic that the microcrystalline grains constituting the thin film are easily oriented along the C axis. These Co-based alloy thin films have strong magnetocrystalline anisotropy in the C-axis direction. Using these perpendicular magnetic recording media, magnetic recording characteristics (such as recording density,
In order to increase the sensitivity of recording and reproduction, it is necessary to improve the degree of C-axis orientation of the film and to increase the coercive force (in the perpendicular direction of the film) of the film. In order to increase the magnetic recording sensitivity, it is necessary to
E E Trans, Magntics, M
AG-15).

As discussed in the paper entitled “Perpendicular Magnetic Recording Media” by Iwasaki et al. in 1456 (1979),
A method is known in which a thin film layer of a soft magnetic material such as permalloy is provided below a Co-based alloy thin film.

Currently used perpendicular magnetic recording media are made by directly depositing a Co-based alloy thin film on plastic films such as polyimide or polyethylene terephthalate, or on non-magnetic substrates such as AQ or glass plates, or by directly depositing a Co-based alloy thin film on the above substrate. A Co-based alloy thin film is formed through a soft magnetic thin layer such as permalloy. Furthermore, in the method of forming a Co-based alloy thin film, efforts have been made to keep the substrate temperature, formation speed, and composition of the Co-based alloy as constant as possible during thin film formation.

In order to make a magnetic recording medium high in density, it is desirable that the film thickness of the medium be as thin as possible, that the degree of C-axis orientation be excellent, and that the size of the columnar crystal grains be uniform. In order to improve the magnetic recording and reproducing sensitivity, it is necessary to increase the vertical coercive force of the Co-based alloy thin film and increase the film thickness of the medium. However, in this case, there was a drawback that recording and reproducing using a magnetic head became extremely difficult.

[Problem that the invention seeks to solve]

In the above-mentioned conventional technology, no consideration was given to the magnitude of the coercive force in the vertical direction of the Co-based alloy thin film.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to provide a perpendicularly magnetized film for a perpendicular magnetic recording medium.
The degree of C-axis orientation and columnar crystal grain size of a Co-based alloy thin film formed on a non-magnetic substrate or a non-magnetic substrate provided with a soft-magnetic thin film layer are controlled.

In particular, by forming a Co-based alloy thin film by controlling the magnitude of the coercive force in the film thickness direction of the Co-based alloy thin film, a perpendicular magnetic recording medium suitable for high-density magnetic recording with excellent magnetic recording and reproducing sensitivity is provided. There is a particular thing.

[Means for solving problems]

The present invention was completed based on the findings shown below. In other words, Co with a close-packed hexagonal lattice structure (hereinafter referred to as HCP structure) has large crystal magnetic anisotropy in the C-axis direction, and by adding elements such as crtvtMo to it, a Co-based alloy is formed on a non-magnetic substrate. If a thin film is formed, a perpendicularly magnetized film with the C-axis oriented perpendicular to the film surface can be obtained, and the saturation magnetization and coercive force can be adjusted by changing the composition of additive elements and the film formation temperature. It is known that it is possible to change The present invention will now be described in detail by taking a Co--Cr alloy film as an example of a Co-based alloy thin film.

A Co-Cr alloy magnetic film is formed on a nonmagnetic substrate, and the relationship between the magnetic properties, composition, and microstructure of the magnetic film is investigated using a vibrating sample magnetometer, Kerr rotation angle measurement, X-ray microanalyzer, and Auger electron spectroscopy. It was also investigated by cross-sectional R observation using electronic i*gi. As a result, the magnitude of the coercive force can be controlled by the composition of the Cr additive concentration, and the magnitude of the coercive force in the vertical direction of the Co-Cr alloy magnetic film and the film composition can be controlled from 15 to 28 W.
In the Go-Cr alloy composition in the range of t%Cr, the magnitude of the vertical coercive force can be controlled almost proportionally, and Cr
It has been found that the coercive force can be increased by reducing the amount added. In addition, as a result of investigating the relationship between the vertical coercive force and the fine structure of the Co-Cr alloy magnetic film, we found that C
It has been found that there is a correlation between the grain size of columnar crystals in an o-Cr alloy film and the magnitude of coercive force, and that as the grain size increases, the coercive force increases. Furthermore, it was found that the grain size of the columnar crystals can be controlled by changing the formation temperature and formation rate of the magnetic film, and that increasing the formation temperature and slowing the formation rate increases the columnar crystal grain size.

Based on the above findings, the present inventors have developed a method for depositing Co on a non-magnetic substrate.
- The vertical coercive force of the Cr alloy magnetic film is increased continuously or
By using a perpendicular magnetic recording medium in which the coercive force is changed stepwise to reduce the coercive force on the substrate interface side and increase the coercive force on the surface side of the magnetic film, it is possible to reduce the coercive force when using a magnetic head, especially a ring-type magnetic head. It has been found that the recording and reproducing efficiency of the magnetic field can be improved and high-density magnetic recording is possible. In order to change the coercive force in stages, it is sufficient to laminate multilayer films having different coercive forces.

Furthermore, the present inventors used Co-based alloys, which are perpendicularly magnetized films, in addition to Co-Cr, such as Co-V.

Similar effects have been confirmed using Co-Mo, Co-We, Co-Ru, and the like.

In addition, the present inventors added a Co-based amorphous soft magnetic thin film, for example, a Go
-Mo -Zr, Co -Mo -Nb
.

Even in magnetic recording media formed with Co-W-Nb, Co-Nb-Zr thin films, or other high permeability magnetic thin films,
It has been confirmed that recording and reproducing efficiency can be improved by forming the above-mentioned Co-based alloy perpendicularly magnetized film so as to change the coercive force.

In the present invention, when forming a multilayered Co-based alloy magnetic film, the thickness of one layer is insufficient to form a continuous film for each layer if less than 20 people are used, and it is preferable to set the thickness to 20 Å or more. Desirably, even if the thickness of one layer is 5000 Å or more, 1
Although the effects of the present invention are the same, since the total film thickness is used for a perpendicular magnetic recording medium of about 3000 people, it is desirable that the film thickness be 3000 Å or less, and from a practical standpoint, it is even more desirable to have a single layer. The film thickness range is 50 to 100
There are 0 people.

As a method for forming a thin film in the magnetic recording medium of the present invention, a physical vapor deposition method such as a vacuum evaporation method, a high frequency sputtering method, or an ion beam sputtering method can be used. In addition to controlling the substrate temperature during thin film formation and adjusting the thin film formation rate.

For example, when forming by sputtering, the magnitude of the coercive force can be controlled by changing the sputtering output, Ar pressure, etc.

[Effect]

The strength of the magnetic field of the head decreases in inverse proportion to the distance from the end face. For this reason, in a recording medium with a large coercive force compared to the magnetic field strength of the head, magnetic recording is performed only on the surface of the medium, resulting in poor recording and reproducing characteristics.6 On the other hand, with a medium with a small coercive force, the Magnetic recording is performed to the bottom surface, but sufficient reproduction output cannot be obtained. According to the present invention, the coercive force is increased on the surface side of the medium in accordance with the distribution of the head magnetic field strength, and the coercive force is gradually increased toward the bottom surface. By using a medium with a reduced magnetic field, sufficient magnetic recording can be performed from the surface to the bottom of the medium, so that the recording and reproducing characteristics can be improved.

〔Example〕

An embodiment of the present invention will be described below in more detail with reference to the drawings. In the drawings, the same reference numerals indicate parts having the same performance characteristics.

Example 1 A Co--Cr perpendicular magnetic recording medium consisting of a multilayer magnetic film having the structure shown in FIG. 1 was fabricated using a Galai substrate by high-frequency sputtering according to the procedure shown below.

In the high-frequency sputtering bag layer used in this example, four types of Co-Cr alloy targets with different compositions can be installed.
In this example, Co-27wt%Cr, Co-24wt%
%Cr, Co-21wt%Cr, Co-18wt%Cr
A Co-Cr alloy target consisting of was used. First, set the substrate 1 at a temperature of 120°C and an Ar pressure of 5 mTorr.
The first magnetic layer 2 made of Co-27wt%Cr was formed to a thickness of 5% under the condition of a high frequency output of 4W/a# in sputtering.
00 people were formed. Next, in the same atmosphere and under the same conditions as above, a second magnetic layer 3 made of Co-24wt%Cr was formed, and then a third magnetic layer 4 made of Co-21wt%Cr was formed.
Next, a fourth magnetic layer 5 made of Co-18 wt % Cr was formed to a thickness of 300 layers each to produce a Co--Cr perpendicular magnetic recording medium 6 consisting of a multilayer magnetic film with a total thickness of 1400 layers.

In addition, in the Co--Cr perpendicular magnetic recording medium 6 made of four magnetic layers, each of the first and second layers is made of four layers of magnetic films. Second. A medium was prepared in which no magnetic film was formed on the upper layer of the third magnetic layer, and the coercive force in the perpendicular direction of each magnetic layer was measured using the Kerr effect. An example of the results is shown in Table 1. .

Table 1 As shown in Table 1, multilayer Co with different compositions
By forming the -Cr magnetic film, it was possible to form a film in which the coercive force in the perpendicular direction was controlled in each magnetic layer.

Also, for comparison, C. under the same conditions as above.

- Using an alloy target of 21 wt% Cr, a Co.
-Cr perpendicular magnetic recording medium 6 was produced. The perpendicular coercive force of this magnetic film was 8500e.

Table 2 shows an example of the results of measuring the recording and reproducing characteristics of the multilayer G o -Cr perpendicular magnetic recording medium in which the coercive force was changed by changing the composition prepared in this example, and the medium consisting of a single layer.

Table 2 As shown in Table 2, by changing the composition of each layer, increasing the coercive force of the upper layer compared to the lower layer, and forming a multilayer C0-Cr magnetic film, the recording and reproducing characteristics in perpendicular magnetic recording can be greatly improved. I was able to improve.

Example 2 Using a polyimide film as the substrate 1, a Co-Cr perpendicular magnetic recording medium consisting of a multilayer magnetic film having a structure similar to that shown in FIG. 1 was fabricated by the vacuum evaporation method shown in FIG. 3 in the following steps. .

IX: In a vacuum of L 0-BTorr, the first can roller 7 is heated to 110° C., and Co-22wt% Cr is deposited at a rate of 1000 persons/S at a rate of 500° C. from the first vapor deposition source 8.
Deposited to the thickness of a person. Next, the second can roller 7 is heated to 150° C. in the same vacuum to remove Co from the second evaporation source 8.
-22,wt%Cr was deposited to a thickness of 300 mm at a rate of 1000 mm/S. Furthermore, the third can roller 7 is heated to 190° C. in the same vacuum, and Co is removed from the third evaporation source 8.
-22wt% Cr was deposited to a thickness of 300 mm at a rate of 1000 mm/S. Finally, the fourth can roller 7 is heated to 230° C. in the same vacuum, and the fourth evaporation source 8 is heated to
-22wt% Cr was deposited to a thickness of 300 layers at a rate of 1000 layers per second to produce a Co--Cr perpendicular magnetic recording medium 6 with a total film thickness of 1400 layers.

A cross-sectional sample of the Co--Cr perpendicular magnetic recording medium 6 in this example was prepared by the Ar ion thinning method, and the grain size of the Co--Cr columnar crystals was measured by observation with a transmission electron microscope. Further, the magnitude of the coercive force of each of the first to fourth layers was measured using the Kerr effect in the same manner as in Example 1, and an example of the results are shown in Table 3.

Table 3 In the multilayer Co--Cr magnetic film formed, it was possible to sequentially control the columnar crystal grain size in each magnetic film, and it was also possible to form a film in which the magnitude of coercive force was controlled.

For comparison, using the same evaporation apparatus as above, the can roller 7 was heated to 190'C, and the evaporation source 8 was heated to 190'C.
o-22wt%Cr at a rate of 1000 people/S to 1400
A single-layer Co--Cr perpendicular magnetic recording medium 6 was fabricated by vapor deposition to a thickness of about 100 mL. The perpendicular coercive force of this magnetic film is 82
It was 00a.

Table 4 shows an example of the results of measuring the recording and reproducing characteristics of a multilayer Co-Cr perpendicular magnetization film whose coercive force was changed by changing the columnar crystal grain size produced in this example, and a single-layer medium. .

Table 4 shows that by forming a multilayer Co-Cr magnetic film in which the upper layer has a larger coercive force and the upper layer has a larger coercive force than the lower layer,
The recording and reproducing characteristics of perpendicular magnetic recording were significantly improved.

Example 3 As shown in FIG. 4, in the lower layer (upper layer of the substrate 1) of the multilayer Go-Cr magnetic film 6,
A perpendicular magnetic recording medium provided with an alloy amorphous soft magnetic thin film 9 is heated to a substrate temperature of 150° C. using a high frequency sputtering device.
, Ar pressure of 5 mTorr, high frequency output in sputtering of 4 W/a#, Co -0,2at%Z
It was produced by the same procedure as in Example 1 above, except that an amorphous soft magnetic M [9 made of r-0.7 at% Mo was formed to a thickness of 5000 mm.

In this case as well, the coercive force and recording/reproducing characteristics of the Co--Cr magnetic film of each layer are the same as those in Example 1. Performance characteristics almost equivalent to those shown in Table 2 could be obtained.

In the above embodiments, as an example of a Co-based alloy magnetic film, C
Although the case of o-Cr magnetic WIIIi has been described, other Co-based alloy magnetic thin films such as Go-Ru eCo-V,
Co-Mow Co-W, Co-Re.

Co-0s Co-Cr-Rh, Co-Cr-Ru.

A similar effect could be obtained using Co-Ni-0 or the like.

Also, soft magnetic! [As, Co -Mo -Zr
In addition to the amorphous film, other Co-based amorphous Ix'fa films, such as Co-Mo-Nb, Co-W-Nb, Co-Nb
- Equivalent effects could be obtained even with other high magnetic permeability materials such as Zr.

〔Effect of the invention〕

As explained in detail above, in the magnetic recording medium of the present invention, in forming a Co-based alloy thin film which is a perpendicularly magnetized film, a multi-layered Co-based alloy thin film in which the coercive force of the Co-based alloy thin film is larger in the upper layer than in the lower layer. By using the Co-based alloy thin film, magnetic recording and reproducing efficiency such as linearity and reproducing output in perpendicular magnetic recording can be greatly improved. In this case, it is effective even if there is a soft magnetic thin film as the underlayer or a non-magnetic substrate, and it is possible to obtain a perpendicular magnetic recording medium suitable for high-density magnetic recording, which has extremely high industrial value. big.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a perpendicular magnetic recording medium in Example 1 of the present invention, FIG. 2 is a sectional view showing the structure of a perpendicular magnetic recording medium for comparison, and FIG. 3 is an example of the present invention. FIG. 4 is a cross-sectional view showing the structure of a perpendicular magnetic recording medium in Example 3 of the present invention.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a ferromagnetic metal thin film is formed on a non-magnetic substrate or a non-magnetic substrate provided with a soft magnetic thin film, a A magnetic recording medium characterized in that the magnetic force is greater than the coercive force of the lower layer of the film. 2. A magnetic recording medium according to claim 1, characterized in that the ferromagnetic metal thin film is a laminated film in which the coercive force decreases sequentially from the surface toward the bottom layer. 3. A method for producing a magnetic recording medium in which a ferromagnetic metal thin film of a Co-based alloy consisting of Co and another metal is formed on a non-magnetic substrate or a non-magnetic substrate having a soft magnetic thin film, in which A method for manufacturing a magnetic recording medium, characterized in that the ferromagnetic metal thin film is formed by increasing its ratio to metal.