JPH04311008A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To suppress the thermal structure relaxation of the magneto-optical recording material consisting of an amorphous rare-earth transition alloy, and to lessen the lowering of vertical magnetic anisotropy after a repeated rewriting. CONSTITUTION:Th dependency of composition of the time, wherein magnetic anisotropy becomes 50% of initial value of a {Tb0.22(Fe0.5Co0.5)0.78}1-XAX film (A=B, C, P) by conducting the annealing at 250 deg.C, is shown in the diagram separately mentioned. The deterioration of vertial magnetic anisotropy is suppresed substantially by adding B, C and P. A magneto-optical recording medium, in which the deterioration in strength of a reproduced signal is not observed, can be manufactured.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magneto-optical recording in which information is recorded, reproduced and erased using an energy beam such as a laser beam.

0002

2. Description of the Related Art Amorphous rare earth transition metal alloys having an axis of easy magnetization perpendicular to the film surface are generally used as magneto-optical recording materials. This alloy has a large coercive force at room temperature, is superior to other material systems in terms of stable retention of recorded information, and low media noise.

0003

[Problem to be solved by the invention] In magneto-optical recording,
In order to improve read durability, power margin, and tolerance to fluctuations in medium environmental temperature, it is desirable to increase the Curie temperature of the recording film and perform recording and erasing at a high temperature. In particular, in recent years, as the output of semiconductor lasers has increased, it has become possible for recording devices to perform recording at high temperatures. However, it is known that the amorphous rare earth-transition metal alloy commonly used as a magneto-optical recording film undergoes thermal structural relaxation when exposed to high temperatures, resulting in a decrease in the reproduced signal after repeated recording and erasing many times. The reason for this is that the perpendicular magnetic anisotropy decreases due to structural relaxation of the amorphous recording film due to heating by laser light, and the axis of easy magnetization shifts in the in-plane direction at the track center position, which reaches the highest temperature in the recording film. It is known that this is because the person collapses (Japan Journal of Applied Physics Japan J.Appl.Phy
s. ) vol. 28, Suppl. 28-3, pp61
). An object of the present invention is to eliminate the above-mentioned drawbacks and provide a magneto-optical recording medium that exhibits relatively slow structural relaxation and less decrease in perpendicular magnetic anisotropy even after being exposed to high temperatures by laser beam irradiation. .

0004

[Means for Solving the Problems] The above object is to provide a magneto-optical recording medium whose composition is {Ra(FebCo1-b)1-a}1-xAx, but
R is a rare earth element containing at least one of Tb and Dy; A
is an element containing at least one of B, C, and P, 0.1
This is achieved by using a magnetic film that satisfies the following relationships: 5<a<0.35, b<0.8, 0.2<x<0.4.

[0005]

[Effect] The mechanism by which perpendicular magnetic anisotropy decreases due to heating is that structural relaxation occurs in the amorphous film, and the atomic arrangement attempts to shift to a more stable amorphous state. This is thought to be because the perpendicular magnetic anisotropy that was formed at the time is lost.

[0006] It is thought that this structural relaxation can be suppressed by adding elements. Elements to be added include B, C, P, Si, and Ge, which form an amorphous alloy with transition metals.
etc. are promising. These elements are known to have the effect of stabilizing the amorphous state and preventing crystallization when alloyed with transition metal elements. However, crystallization and
The phenomenon of relaxation to a more stable state within an amorphous state does not necessarily correspond one-to-one. That is, an additive element that is effective in inhibiting crystallization does not necessarily have an effect in suppressing structural relaxation.

[0007] As a result of studying various additive elements,
It has become clear that the addition of B, C, and P is effective in suppressing structural relaxation. What these elements have in common is that they have smaller atomic radii than transition metals. That is, Fe
, the atomic radius of Co is 1.25 Å, whereas the atomic radius of B is 0.98 Å, C is 0.91 Å, and P is 1.10 Å.
It is. Therefore, these additive elements fill the gaps in the amorphous structure and make it difficult for atoms to move, which is thought to contribute to suppressing structural relaxation.

Comparing the three elements B, C, and P as additive elements, C, P, and B are more expensive in this order. The deterrent effect of structural relaxation is ranked in descending order of magnitude: B
, C, P in that order. Regarding the magneto-optic effect, B, C
, P, the degree of decrease in the Kerr effect due to addition increases gradually. Taking all these into account, addition of B is the most excellent in terms of performance, and addition of C is the most preferable in terms of economy.

Next, the above composition range will be explained. In order to stably direct the magnetization in the direction perpendicular to the film surface, the rare earth R contains at least one of Tb and Dy, and the ratio of R to the transition metal is 0.15<a<0. .35
It is known that there is a need for
-23927).

[0010] Regarding the amounts of B, C, and P added, there are the following restrictions. If x>0.4, the Kerr rotation angle at room temperature will be 0.15° or less, making it difficult to reproduce magneto-optical recording signals and making it unsuitable as a magneto-optical recording material. x<0
．． In the case of 2, the effect of suppressing structural relaxation by the additive element is insufficient. The Fe to Co ratio determines the Curie point;
The larger b is, the lower the Curie point is, but in the case of the present invention, the Curie point has already been lowered by the addition of B, C, and P, so in a composition where b≧0.8, the Curie point is 100°C.
If b<0.8, there is a possibility that the recording will be destroyed by irradiation with the read light.

[0011]

EXAMPLES The present invention will be explained in detail with reference to Examples below. Composition {Tb0.22(Fe0.5Co0.5)0.
A series of films represented by 78}1-xAx, (A=B, C, P) were prepared, and changes in perpendicular magnetic anisotropy after annealing were investigated. In Figure 1, the time τ for the perpendicular magnetic anisotropy to drop to 50% of the initial value of the film after annealing at 250°C is plotted against the amount x of B, C, and P added in these films. . When the amount of B, C, and P added is x<0.2, τ increases only about three times as much as when no additive is added. However, 0.2<x
In the case of , the relaxation suppressing effect becomes significant. In comparing the additive elements, B has the greatest effect, followed by C, and the effect of P addition is about half that of B.

Next, the magneto-optical effect of the above film was investigated. In FIG. 2, {Tb0.22(Fe0.5Co0.5)0.
78} The composition dependence of the Kerr rotation angle θK at room temperature of the 1-xAx film (A=B, C, P) is shown. As the amount of added elements increases, the Kerr rotation angle decreases monotonically. While x is small, the rate of decrease is small, but when x exceeds 0.3, it decreases rapidly, and when x is between 0.4 and 0.5, the Curie point becomes below room temperature. The degree of decrease in the Kerr rotation angle gradually increases in the order of B, C, and P. In order to use it for magneto-optical recording, the amount x added needs to be 0.4 or less, since reproduction becomes difficult unless the Kerr rotation angle is 0.15 degrees or more.

[0013] Next, a series of films with different ratios of Fe to Co were prepared, and changes in their Curie temperatures were investigated. In Figure 3, {
(Tb0.5Dy0.5)0.22(FebCo1-b
)0.0.78}0.4A0.6 membrane (A=B,C,P)
shows the composition dependence of the Curie temperature. As the proportion of Fe increases, the Curie temperature decreases. If the Curie temperature is 100° C. or lower, the magneto-optical recording domain will be destroyed during reading by laser light, making it unsuitable as a recording medium. Therefore, it can be seen from this figure that b<0.7 is required.

Based on the above study results, a magneto-optical disk using a recording film doped with B and C was prepared, and its repeated recording and erasing characteristics were measured. The recording medium is S on a glass 2P substrate.
iNx lower protective film/recording film/SiNx upper protective film,
It was created by laminating layers in this order. The recording film thickness was 100 nm. Record erasure is performed at a linear velocity of 10 m/sec.
The erasing laser power was 8 mW at the film surface. At this time, the maximum temperature reached by the medium is estimated to be about 300°C.

FIG. 4 shows {Tb0.22(FebCo1−
b) Using a recording film with a composition of 0.78}1-xBx, the decrease ΔC in the reproduced signal after repeated recording and erasing is shown under the above conditions. In order to correct the decrease in Curie point due to the addition of B and unify the recording sensitivity, x = 0, 0.1, 0.2.
, 0.3, b=0.5, 0.45, respectively.
0.4, 0.35. If B is not added, 1
The signal began to deteriorate after 05 times, and after 107 rewrites, the signal decreased by 4 dB. As the B addition amount x increases, the signal drop becomes smaller, and when x=0.3, no drop in the reproduced signal was observed even after 107 rewrites. Considering that magneto-optical disk products are required to be rewritten 106 to 107 times, x must be 0.2 or more.

Evaluations similar to those described above were also conducted for C-added recording films. In FIG. 4, {Tb0.22(FebCo1
-b) Using a recording film having a composition of 0.78}1-xCx and under the above conditions, the decrease ΔC in the reproduced signal after repeated recording and erasure is shown. In order to correct the decrease in the Curie point due to C addition and unify the recording sensitivity, b = 0.5, 0.44 for x = 0, 0.1, 0.2, 0.3, respectively. ,0.38,
It was set to 0.32. As in the case of B addition, as the C addition amount x is increased, the reproduction signal decrease becomes smaller, and when x=0.3, no decrease in the reproduction signal was observed even after 107 rewrites. Regarding the addition of C, x must be 0.2 or more in order to ensure a rewritable number of 106 to 107 times.

As described above, by using a recording film containing appropriate amounts of B and C, it was possible to increase the rewritable number of times of the magneto-optical disk to 106 or more.

[0018]

[Effects of the Invention] According to the present invention, thermal structural relaxation can be suppressed by adding B, C, or P to a magneto-optical recording material made of an amorphous film of a rare earth transition metal alloy. Take. Utilizing this, it has become possible to create a magneto-optical disk that suppresses the decline in perpendicular magnetic anisotropy due to laser beam heating during recording and erasing, and to increase the number of rewrites to 106 or more.

[Brief explanation of drawings]

[Figure 1] By annealing at 250°C, {Tb0.22(Fe0
．． 5Co0.5)0.78}1-xAx film (A=B,C
, P) is a diagram showing the composition dependence of the time τ at which the perpendicular magnetic anisotropy becomes 50% of the initial value.

FIG. 2 {Tb0.22(Fe0.5Co0.5)0.
78} A diagram showing the composition dependence of the Kerr rotation angle θK of a 1-xAx film (A=B, C, P) at room temperature.

[Figure 3] {(Tb0.5Dy0.5)0.22(Feb
Co1-b)0.78}0.4A0.6 film (A=B,C
, P) is a diagram showing the composition dependence of the Curie temperature.

FIG. 4 {Tb0.22(FebCo1-b)0.78
} A diagram showing a reproduction signal drop ΔC after repeated recording and erasing of a magneto-optical disk using a 1-xBx film.

FIG. 5 {Tb0.22(FebCo1-b)0.78
} A diagram showing a reproduction signal decrease ΔC after repeated recording and erasing of a magneto-optical disk using a 1-xCx film.

Claims (1)

[Claims] Claim 1: An amorphous magnetic film having an axis of easy magnetization in a direction perpendicular to the film surface, the composition of which is {Ra(FebCo1-
b) 1-a}1-xAx, where R is a rare earth element containing at least one of Tb and Dy, A is an element containing at least one of B, C, and P, and 0.15<a<0. 35,b
A magneto-optical recording medium characterized by being expressed by <0.8, 0.2<x<0.4.