JPS6055535A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the coercive force of a recording medium larger than the original coercive force of a vertically magnetized film, by forming this film on a nonmagnetic substrate via a foundation layer with use of a material layer having the distortion anisotropy which increases the coercive force of the vertically magnetized film. CONSTITUTION:A photomagnetic record layer is formed on a nonmagnetic substrate via a foundation layer, and the distortion anisotropy Ksigma is applied to the photoelectric recording layer by the foundation layer. This improves the anisotropy K and coercive force Hc and reduces the bubble diameter (d). Furthermore, the recording density and image resolution are improved. In other words, the foundation layer is attached under a vertically magnetized film, i.e., the photomagnetic record layer by vapor deposition, etc. The foundation layer is made of a material which has the volumetric expansion when it is attached on the substrate and solidified. The anisotropy Ksigma is made positive at the recording layer by said volumetric expansion. While the anisotropy K is increased. The foundation layer is formed by sputtering Tb, for example, to 25Angstrom thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical recording medium, such as a magneto-optical disk on which rewritable recording can be performed using laser light.

BACKGROUND TECHNOLOGY AND PROBLEMS Amorphous magneto-optical disks made of rare earth metals and transition metals are used as rewritable magneto-optical disks that can be read and written using laser light, such as semiconductor laser light.
A method using a perpendicularly magnetized film made of an amorphous (amorphous) alloy has been proposed. Such a magneto-optical disk, that is, a magneto-optical recording medium, is usually made by sputtering or vapor depositing an alloy of rare earth metals and transition metals mentioned above, or by sputtering or vapor-depositing each element alone, on a non-magnetic substrate. It is formed.

This type of magneto-optical recording medium generally requires a high coercive force Hc in order for its magnetization film to exist as a stable perpendicular magnetization film.

A rare earth-transition metal magnetized film has contradictory properties in that as the coercive force increases, the magnitude of magnetization M decreases.

In magneto-optical recording, in order to realize high-density recording (micro-recording), both magnetization M and coercive force l-1c are required to be large. That is, The diameter d of the recording magnetic bubble is: (C is the domain wall energy) Purpose of the Invention The present invention provides a magneto-optical recording medium whose coercive force is greater than the coercive force originally possessed by the magnetic material of the recording layer of this medium, that is, the perpendicularly magnetized film. An object of the present invention is to provide a magneto-optical recording medium that can be made sufficiently large.

Summary of the Invention In the present invention, a perpendicularly magnetized film, that is, a magneto-optical recording layer, is formed on a nonmagnetic substrate by vapor deposition, sputtering, etc. via an underlayer formed by vapor deposition, sputtering, etc. This underlayer is made of a material capable of imparting anti-anisotropy to the magneto-optical recording layer thereon, increasing the magnetic anisotropy therein. That is, the anisotropic magnetic field HK in the basic material is originally the magnetic anisotropy Ka
and magnetization Ms.

a HK=■ ...(1) On the other hand, in order to make the bubble diameter d as small as possible in order to obtain high recording density and high resolution, the coercive force He It is desired that the magnetization and magnetization Ms are as large as possible.

The magnitude of the anisotropy K, which affects the magnetic flux of the magnetized film deposited on the substrate, especially the magnitude of the coercive force, depends on the anisotropy Ka that the magnetic material originally has, as well as the relationship between the substrate and the magnetism. is involved in the φ anisotropy caused by the mutual relationship with the body.

to K, Ka + Ka... (31 In the present invention, as mentioned above, on a non-magnetic substrate,
By forming a magneto-optical recording layer through an underlayer, this underlayer is used to influence the optical 71h recording layer to Ii anisotropy. This aims to improve the bubble diameter d, reduce the bubble diameter d, and ultimately improve the recording density and resolution.

That is, when an amorphous magnetic thin film is formed by directly sputtering a rare earth-transition metal alloy such as Th-Fe on a non-magnetic substrate such as a glass substrate, σ=E(α1- α2) A stress of ΔT...f4+ is generated, and a strain anisotropy of Kσ=−−λσ (5) (λ is the magnetostriction constant of the magnetic thin film) is generated in the magnetic thin film. Due to the involvement of this strain anisotropy, the anisotropy K'' of the magnetic thin film is obtained from Equation 31, and the anisotropic magnetic field HK or coercive force H, c is determined. In a magnetic thin film made of a film, since σ in equation (3) is negative, the anisotropy KS' is relatively small.However, in the present invention, the underlayer is formed by sputtering, vapor deposition, etc. That is, it is deposited under the magneto-optical recording layer, and the underlayer is made of, for example, a material that expands in volume when it solidifies when deposited on the non-extractable substrate.
In this way, the strain caused by the volume expansion affects the magneto-optical recording layer formed thereon, and the bud anisotropy of the above formula (3) in this magneto-optical recording layer is changed by setting σ to be positive. Make the meal bigger. However, this underlayer is not limited to the case where it is made of a material that expands in volume during solidification, and as described above, a magneto-optical recording layer of a rare earth-transition metal is directly deposited on a non-magnetic substrate. It can also be made of a material that has the effect of buffering the negative anisotropy in the case, such as Fe.

Examples Example I A base layer is formed by sputtering Tb to a thickness of 251 nm on a glass substrate, and then 22 at % Tb-
The remaining Fe alloy was sputtered to form a perpendicular magnetization film. FIG. 1 shows the magnetization B-magnetic field I characteristic curve in the film thickness direction of the magneto-optical recording medium thus obtained. The coercive force H,c in this case was 6KOe.

FIG. 2 shows a magnetization curve in the film thickness direction when a perpendicularly magnetized film similar to that in Example 1 is directly formed on a glass substrate without forming an underlayer.

Example 2 A magneto-optical recording medium was obtained in the same manner as in Example 1, except that Bi, Ge, and Pb were used as the underlayer instead of Tb. In either case, the holding force H
c was increased compared to the conventional one in which no underlayer was formed.

Example 3 Fe was evaporated at 150× on a glass substrate, and a perpendicular magnetization film of Tb-Fe similar to that in Example 1 was formed thereon. Hc in this case was twice that of the conventional one.

Curves (1) and (2) in FIG. 3 show the relationship between the thickness of Tb and Fe in the underlayer and Hc in Examples 1 and 3. In this case @111, when the thickness becomes too thick, a decrease in Hc is observed. This is thought to be due to the fact that if the thickness is too thick, the underlayer itself absorbs the strain and becomes -CL.
It can be seen that it is good to adhere to 90X1, preferably IOX to 80X.

In the above example, the non-magnetic substrate is a glass substrate, but other acrylic substrates, polymer films such as polyethylene tereftate, polyamide, polyamideimide, and polyimide films may also be used! You can also

Effects of the Invention As described above, according to the present invention, by providing the underlayer, it is possible to obtain the effect of increasing the anisotropy of the thin film, thereby improving the nc and thereby reducing the bubble diameter.

[Brief explanation of the drawing]

1 and 2 are magnetization curve diagrams of the present invention and a conventional magneto-optical recording medium, respectively, and FIG. 3 is a measurement curve diagram of the film thickness of the underlayer versus the sharpening force. Figure 1 Figure 3 s: (A)

Claims (1)

[Claims] A perpendicularly magnetized film mainly composed of rare earth metals and transition metals is formed on the nonmagnetic substrate via an underlayer, and the underlayer can provide strain anisotropy that increases the coercive force of the perpendicularly magnetized film. A magneto-optical recording medium consisting of a material layer.