JP2715783B2 - Magnetic recording media - Google Patents

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 based on a polymer film such as a video tape, a floppy disk and a magnetic tape for a computer, and more particularly to a magnetic recording medium capable of improving recording characteristics.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable improvement in recording characteristics of a magnetic recording medium, and a metal thin film medium has been put to practical use in place of a coating type medium, and furthermore, a perpendicular magnetic recording system is expected to be promising and active. R & D is underway. The reason is that the self-demagnetization effect decreases as the recording density increases in the perpendicular magnetic recording method as compared with the in-plane recording method, so that the formation of a so-called rotational magnetization mode is suppressed, and a large reproduction output is obtained even in shorter wavelength recording. In that they can do it. In this type of perpendicular magnetic recording system, a material that is easy to be magnetized perpendicular to the medium surface is required, and a CoCr film, CoOx
Materials such as a film and a hexagonal Ba ferrite film having a large uniaxial anisotropy and an axis of easy magnetization easily oriented perpendicular to the film surface are used. Further, in order to improve magnetic recording characteristics, a recording medium having a multilayer film structure in which a permalloy or Co-based amorphous soft magnetic film is formed as a base film between a perpendicular magnetization film and a nonmagnetic substrate has been proposed.

[0003]

However, as described above, forming a soft magnetic film of permalloy or the like as a base layer and then forming a magnetic film of metal or alloy to form a multi-layer structure has a problem in recording characteristics. Although improvement can be achieved, there is a problem that not only cost for equipment and material is increased, but also productivity is reduced. The present invention has been devised in view of the above problems and effectively solving them. An object of the present invention is to improve the same recording characteristics without forming an underlayer by forming a metal or alloy magnetic film having a soft magnetic transition region on a nonmagnetic substrate such as a polymer film. It is to provide a magnetic recording medium which can be used.

[0004]

Generally, in a magnetic recording medium having a perpendicular magnetic film formed thereon, for example, when a CoCr perpendicular magnetic film is formed on a polyimide film, C
Even if the composition ratio of o and Cr is constant, the recording characteristics vary greatly depending on the film forming conditions. This is due to the difference in the film structure of the perpendicular magnetization film. The present inventor observed a so-called snake-shaped loop in the in-plane direction hysteresis loop by the magnetostatic measurement in the difference of the film structure, and thought that this plays the role of the underlayer described above. The present invention was completed by finding that a magnetized film was formed under the film formation conditions described above and that the snake-shaped loop was caused by the transition region of the magnetic film on the polymer substrate.
That is, the present invention provides a magnetic recording medium in which a magnetic film having a magnetic anisotropy perpendicular to the film surface is formed on a non-magnetic substrate in order to solve the above-mentioned problems. A part thereof is such that a soft magnetic transition region exists on the non-magnetic substrate side.

More specifically, as shown in FIG. 1, a magnetic recording medium 2 according to the present invention is formed on a non-magnetic substrate 4 made of a polymer film, for example, by a magnetic material perpendicular to the film surface by a metal or alloy. It is formed by forming a magnetic film 6 having anisotropy. A part of the magnetic film 6 on the non-magnetic substrate side is formed as a soft magnetic transition region 8 where a jump of magnetization occurs where the external magnetic field (magnetic field) is small in the initial magnetization curve in the in-plane direction. The magnitude of the jump of the magnetization is proportional to the thickness of the transition region 8, and there is a strong correlation between the thickness of the transition region and the magnetic recording characteristics. The thickness L2 of the transition region 8 with respect to the entire thickness L1 of the magnetic film 6 is set to 15% or less, preferably in the range of 5 to 10%.

In order to form the magnetic film 6, for example, a Co film is formed on a non-magnetic substrate 4 made of a polymer film.
It is formed by laminating a Cr alloy in an argon gas atmosphere by sputtering or vapor deposition. When activated sputtered particles or metal vapor are deposited on the polymer film in this manner, the polymer film is damaged by the particles, and the polymer film is damaged by the particles. It is considered that a transition region in which carbon or the like of the film is mixed is formed, and this transition region becomes amorphous and exhibits soft magnetism. Therefore, the present invention can be applied not only to a magnetic film formed using a CoCr alloy, but also to a perpendicular magnetic film made of another metal or alloy.

[0007]

As described above, for example, when a CoCr perpendicular magnetization film is formed on a polymer film, the film structure of the perpendicular magnetization film differs depending on the film forming conditions even if the composition ratio of Co and Cr is kept constant. Therefore, magnetic recording characteristics are greatly different.
When a magnetostatic measurement was performed to examine the difference in the film structure, a snake-shaped loop A as shown in FIG. 2 was observed in the in-plane direction hysteresis loop. The conditions at this time were as follows: the thickness of the CoCr magnetic film was 2000 ° C., the substrate temperature Ts was 210 ° C., and the argon gas pressure PAr was 0.5 m.
Torr, target current It is 5.8 A (constant voltage)
It is. The snake-shaped loop A exhibits a magnetic field or a jump 10 in the vicinity of zero magnetic field, and it is considered that this magnetization characteristic plays a role of the underlayer. Then, a magnetized film was formed under various film forming conditions, and the characteristics were examined. As a result, it was found that the snake-shaped loop A was caused by the transition region of the magnetic film on the polymer nonmagnetic substrate.

[0008] This transition region is considered to be a soft magnetic material, and the jump of magnetization 10 occurs as described above where the external magnetic field is small in the initial magnetization curve in the in-plane direction. The magnitude of the jump in magnetization is proportional to the thickness of the transition region. Based on this, various magnetic films were formed, and the relationship between the thickness of the transition region and the magnetic recording characteristics was examined. There is a correlation, and it has been found that when the thickness of the transition region is 15% or less with respect to the total thickness of the magnetic film, the reproduction output can be improved. That is, if this property is used, the same effect can be obtained without forming a conventionally used base film. As a result, the recording characteristics can be improved even when a single magnetic film is used without forming a multilayer structure, and the productivity can be greatly improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the magnetic recording medium according to the present invention will be described in detail. Example 1 Using a CoCr (Cr: 18 at%) alloy target,
A polyimide film substrate was used as a nonmagnetic substrate, and a CoCr perpendicular magnetic film was formed thereon by sputtering. Only the substrate temperature and the argon gas pressure were changed as the sputtering conditions. As a preliminary experiment, first, the argon gas pressure was kept constant and the thickness of the CoCr perpendicular magnetic film was increased from 250 ° to 1500 °.
サ ン プ ル Make a sample that has been changed to VSM (Vibrati
The initial magnetization curves in the in-plane direction were measured using ng Sample Magnetometry, and the jump of magnetization was measured by the method shown in FIG. 3 to determine the relationship between the total thickness of the magnetic film and the jump of magnetization. The result is shown in FIG. M
relationship j / Ms and 1 / t has become a good linear relationship regardless substrate temperature Ts, the thickness t _in the transition region can be determined as shown in the following formula from the slope of the linear relationship. t _in = t × Mj / Ms

Here, t is the total thickness of the magnetic film, Mj is the value of the inflection point of the magnetization, and Ms is the saturation magnetization. Further, as is clear from the above equation and FIG. 4, the thickness of the transition region can be controlled by changing the substrate temperature. Next, a CoCr perpendicular magnetic film having a total thickness t of 2000 ° was formed under various sputtering conditions, and the thickness t _in of the soft magnetic transition region was determined based on the results of the preliminary experiment. Was measured. A drum tester was used for the measurement, and the recording wavelength λ was fixed at 0.5 μm. The rectangular wave recorded by the optimum recording current was reproduced and standardized to obtain a reproduction output.
The magnetic head uses a ring-type sendust head,
The relative speed between the head and the medium is 2 m / s, the head gap is 0.19 μm, and the number of turns is 20 turns. FIG. 5 shows the relationship between the thickness t _{in of the} transition region and the reproduction output Vpb. I in the figure
t indicates a target current. According to FIG.
On the other hand, if the thickness t _{in of the} transition region is 300 ° or less, that is, if the transition region is 15% or less of the total thickness of the magnetic film, the reproduction output Vpb becomes 200 or more, and the reproduction output increases. It was found that the recording characteristics were improved. The thickness t _in of this transition region is about 160 ° or about 8
% Is more preferably controlled in the range of 5 to 10% with the peak as the top. Then, it was found that when the thickness t _{in of the} transition region exceeded 15%, the reproduction output was considerably reduced, and the recording characteristics were not sufficiently improved.

[0011]

As described above, according to the present invention, the following excellent functions and effects can be exhibited. Since the soft magnetic transition region is formed in a part of the magnetic film on the non-magnetic substrate side, recording characteristics can be improved without having a multilayer structure. Therefore, not only can the productivity be improved, but also an increase in equipment and material costs can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a magnetic recording medium according to the present invention.

FIG. 2 is a graph showing a snake-shaped loop.

FIG. 3 is a graph showing a magnetization curve for explaining a jump of magnetization.

FIG. 4 is a graph showing the relationship between the thickness of a transition region and Mj and Ms.

FIG. 5 is a graph showing a relationship between a transition region thickness and a reproduction output.

[Explanation of symbols]

2 ... magnetic recording medium, 4 ... non-magnetic substrate, 6 ... magnetic film, 8 ...
Soft magnetic transition region, 10 ... jump of magnetization, L1, L2 ... thickness.

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic film having a magnetic anisotropy perpendicular to a film surface formed on a nonmagnetic substrate , wherein the magnetic film has a soft magnetic transition region on the nonmagnetic substrate side.
Wherein the thickness of the soft magnetic transition region is the entirety of the magnetic film.
A magnetic recording medium having a thickness of 15% or less of the thickness of the magnetic recording medium.