JPS60185237A - Photothermomagnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a photothermomagnetic recording medium which has large vertical anisotropy and a defect-free Bi-substd. magnetic garnet film of a large area having high coercive force by forming said garnet film by a sputtering method on a substrate then subjecting the film to a heat treatment to form a vertical magnetized film. CONSTITUTION:The Bi-substd. magnetic garnet film expressed by the formula (0<x<=2.0, 0<=y<5, R is yttrium or rare earth element, A is an element which can be substd. with Fe) is formed by a sputtering method on a substrate. The film is then subjected to a heat treatment to crystallize the sputtering film formed in the amorphous state by utilizing the difference in the lattice constant between said film and the substrate or the difference in the coefft. of thermal expansion, thereby forming the vertical magnetized film consisting of the (111) bismuth-substd. magnetic garnet Nonmagnetic garnet such as neodium gallium garnet or gadolinium gallium garnet or the like is used for the substrate. The photothermomagnetic recording medium having the higher coercive force, larger Faraday rotating angle and better performance than in the prior art is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a photothermal magnetic recording medium, and particularly to a photothermal magnetic recording medium comprising a bismuth-substituted garnet epitaxial film having a large perpendicular anisotropy.

Background of the technology Photothermal magnetic recording, which performs thermomagnetic writing using Rade beam irradiation and reads out records using magneto-optic effects, mainly the Kerr effect and Faraday effect, has features such as being rewritable and capable of high-density rewriting. There is. Currently, such photothermal magnetic recording media materials include GdCo, TbFe, G
Amorphous (non-crystalline) consisting of rare earth elements such as dFe and iron group
It can be said that membranes have been mainly studied and have entered the practical stage.

Prior Art and Problems Conventionally, magnetic garnet films as photothermal magnetic recording materials have been mainly formed by liquid phase epitaxial method (LPE method). It is a well-established theory that the perpendicular anisotropy of a magnetic garnet film induced by the LPE method is caused by growth-induced magnetic anisotropy, which requires at least two types of rare earth elements. As a photothermal magnetic recording medium, it requires a large coercive force (He > 1 kOe) and therefore a large perpendicular anisotropy, but in the magnetic Ga-I film formed by the LPE method, rare ions with a large difference in ion radius,
For example, the coercive force is increased by using Sm and Er.

However, its coercive force is at most about 3QOOe, which is not sufficient for use as a photothermal magnetic recording medium.

So-called bismuth-substituted garnet (Bix
It is well known that R3-xFe5012) is a promising photothermal recording medium because it has a very large Faraday rotation. It is possible to form a bismuth-substituted garnet film by the LPE method.

However, in this case, since the melting point of the bismuth-substituted material is low, the amount of bismuth substitution is large (x>1), and it is difficult to obtain a large-area film with good crystallinity.

The crystal structure of magnetic garnet is cubic, and its magnetocrystalline anisotropy is small, so a perpendicularly magnetized film cannot be obtained by itself. In addition to the above-mentioned LPE method, there is a chemical vapor deposition method (CVD method) as a method for obtaining a perpendicularly magnetized film of magnetic garnet. The perpendicular anisotropy of magnetic garnet obtained by the CVD method is said to be strain-induced magnetic anisotropy. This is because there is a difference in the lattice constant and B expansion coefficient between the magnetic garnet film and the substrate, which causes negative stress in the magnetic garnet film and causes perpendicular anisotropy due to the reverse magnetostriction effect.

OBJECTS OF THE INVENTION In view of the above drawbacks, it is an object of the present invention to provide a photothermal magnetic recording medium comprising a bismuth-substituted non-sputtered film having a large perpendicular anisotropy, that is, a high magnetic force.

Composition of the invention The object of the present invention is bismuth-substituted magnetic garnet.

BixR6-XAyFe5-XOl. (0(xku2.0
．． o<y<s, R is yttrium or a rare earth element,
In a method for manufacturing a photothermal magnetic recording medium comprising a film of A (A is an element that can be substituted with F'e), the bismuth-substituted magnetic garnet film is formed on a non-magnetic garnet substrate by a sawing or tuttering method, and then heat treatment is performed. This is achieved by a photothermal magnetic recording medium characterized in that the bismuth-substituted magnetic garnet perpendicularly magnetized film is formed by applying this method.

Normally, when a garnet film is formed by strut ringing, the garnet film is in an amorphous state as it is, and is then subjected to heat treatment to obtain a magnetic garnet.

Considering that the magnetostrictive effect that contributes to perpendicular anisotropy is associated with the orientation of the crystal, the garnet sputtering film, which is amorphous when deposited by the sputtering method as described above, has the same effect as the CVD method. It is not easy to think of a method for inducing such vertical anisotropy. However, the present inventors found that under appropriate film formation conditions for the above-mentioned garnet sputtered film, B
It was discovered that vertical anisotropy can be imparted using a mechanism similar to that of the CVD method.

In order to induce vertical anisotropy, there are two methods that utilize the difference in lattice constant or the difference in thermal expansion coefficient between the garnet film and the substrate, which will be explained below.

First, we will show a method that utilizes the difference in lattice constant between the garnet film and the substrate.

Nonozome gallium garnet (hereinafter N) is used as a substrate.
GG), an amorphous film having a composition of (BiY)3Fe50.2 is formed on the (11I) plane by sputtering, and then an amorphous film having a composition of (BiY)3Fe50.2 is formed at a high temperature of about 700 to 800 °C to about 180 to 300 °C. The amorphous film of (BiY)3Fe501□ was crystallized by heat treatment for 1 minute, L, (1
11) A bismuth-substituted YIG (yttrium iron garnet) film.

Here, the process of crystallization of the garnet film through the heat treatment step will be considered. The lattice constant of NGG is bismuth substitution YI
The difference between G and C is also large, but the difference is small. This crystallization occurs from the interface with NGO, but when the lattice constants of both are very close, the 110-plane lattice is forced to align with the substrate lattice, and as a result, the garnet film has a tensile force. Since the magnetostriction constant of bismuth-substituted YIG is negative, υ perpendicular anisotropy is induced by the inverse magnetostriction effect.

The lattice constant of gadolinium Φ gallium garnet (hereinafter referred to as GGG), which is usually used as a substrate for magnetic garnet films, is also smaller than that of bismuth-substituted YIG.
Vertical anisotropy cannot be induced using GG. N
Although GG was developed to form a film with a large lattice constant such as bismuth-substituted YIG, there is no example in which it has been used primarily for the purpose of inducing vertical anisotropy as described above.

Next, an example will be shown in which vertical anisotropy is induced using the difference in thermal expansion between the garnet film and the substrate.

V) (BiY)sFe5o1 was deposited on the GGG(11) surface of the substrate by sputtering method while heating the substrate to about 5000℃.
An amorphous film having a composition of □ is formed. Next, heat treatment is performed at a temperature of about 800° C. to crystallize it. In this case, since the thermal expansion coefficient of bismuth-substituted YIGO is larger than that of GGG, tensile stress is applied to the garnet film by heat treatment. This combines with the negative magnetostriction of bismuth-substituted YI'G to induce perpendicular anisotropy. However, in this case, the quality of the crystal is poor due to the large difference (mismatch) in lattice constants and the stress caused by the difference in thermal expansion coefficients, and furthermore, cracks are likely to occur in the garnet film. To prevent this, the substrate is heated during film formation by sputtering. That is, by heating the substrate, defects are not introduced into the garnet film, and a state is created in which crystal growth is facilitated. By doing so, vertical anisotropy can be induced by effectively exerting tensile stress within a range that does not cause defects in the garnet film.

Example 1 BiY2GaFe4o1 by high frequency sputtering method
A 1 μm thick layer of Bi is deposited on the (111) plane of an NGO substrate heated to 500°C using a sintered targut having a composition of 2.
A Y2GaFe401° amorphous film was formed. A bismuth-substituted garnet epitaxial film was obtained by heat-treating this in air at a temperature of 800°C.

FIG. 1 shows the hysteresis loop of the Faraday rotation of this film, indicating that it is a perpendicularly magnetized film. The Faraday rotation angle θ2 was approximately 0.6 deg, and the coercive force was 1400 e.

Example 2 By high frequency sputtering method! 0 BiY2GaFe4
500 using sintered garnet with a composition of 0.2
An amorphous film of Biy2GaFe401□ with a thickness of 1 μm was formed on the (111) plane of the GGG substrate heated to ℃. A bismuth-substituted garnet epitaxial film was obtained by heat-treating this in air at a temperature of 800°C. Figure 2 shows the hysteresis loop of the Faraday rotation of the film, indicating that it is a perpendicularly magnetized film. The Faraday rotation angle θ2 was approximately 1 degree, and the coercive force was 3000 degrees.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show the hysteresis loop of the garnet films formed in Example 1 and Example 2, respectively, with one revolution of 7 degrees. g;+, 2 drawings.

Claims (1)

[Claims] 1. Bismuth-substituted magnetic garnet. BixR5-xAye 5-Xol 2 (0<X≦2
．． In a method for manufacturing a photothermal magnetic recording medium comprising a film of 0.0≦y<5゜Ril' yttrium or a rare earth element, A is an element that can be replaced with Fe), the bismuth-substituted magnetic garnet film is spun on a substrate. ? A photothermal magnetic recording medium characterized in that a bismuth-substituted magnetic garnet perpendicularly magnetized film is formed by vine ringing and subsequent heat treatment. 2. The photothermal magnetic recording medium according to item 1, wherein the substrate is made of nonmagnetic garnet.