JPS5873030A - Optical magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain recording at a low power and a high optical reproducing output, by providing the gradient of composition toward the film thickness direction, so as to attain an excellent composition in readout characteristics at the optical readout side of a single thin film, and the excellent composition in excellent recording characteristics at the opposite side. CONSTITUTION:An photomagnetic recording medium 2 is formed on a substrate 1 made of glass or the like. This medium consists of a recording medium region (a) with low Curie point and high coercive force, a recording medium region (b) with high Curie point, small coercive force and high Kerr rotary angle, and a transition region (c), which plays a role of transmission of the information stored in the region (a) into the region (b). Recording is done with temperature rise due to light irradiated from the (b) side, with decreased coercive force of the region (a) and the part 5 of the decreased coercive force rotated in the direction of external magnetic field, and the information is transferred to the region (b) through the region (c). This information is read out with the Kerr effect of the reflected light of light irradiated rom the (b). Thus, efficient recording and readout can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magneto-optical recording medium used in magneto-optical memories, magnetic recording display elements, etc. Specifically, the present invention relates to a magneto-optical recording medium that has a direction of easy magnetization perpendicular to the film surface, and has a circular shape. Alternatively, the present invention relates to a magnetic thin film recording medium in which information can be recorded by creating reversed magnetic domains of arbitrary shapes and read out using magneto-optic effects such as the magnetic Kerr effect.

In a ferromagnetic thin film whose axis of easy magnetization is perpendicular to the film surface,
It is possible to create a small reversal magnetic domain having a uniform magnetization polarity in the plane of the film that is uniformly magnetized to the S pole or the N pole and the magnetic pole in the opposite direction. If the presence or absence of this inverted magnetic domain corresponds to rlJ and rOJ, such a ferromagnetic thin film can be used as a high-density magnetic recording medium. Among these ferromagnetic thin films, it has a large coercive force at room temperature and is a key
In a thin film whose IJ point or magnetic compensation temperature is relatively close to room temperature, information can be recorded by creating an inverted magnetic domain at an arbitrary position with a light beam using the Curie point or magnetic compensation temperature. Generally used as a beam addressable φ file.

Conventionally known ferromagnetic thin films that have an axis of easy magnetization in the direction perpendicular to the film surface and can be used as beam-addressable files include polycrystalline metal thin films typified by MnB1 and ferromagnetic thin films typified by GIG. Compound single crystal thin film, Gd
-Co, Gd-Fe, TbFe, Dy
There are amorphous metal thin films such as Fe, but each has advantages and disadvantages as described below. A polycrystalline metal thin film, represented by MnBjK, which performs writing using a single Curie point, is excellent as a magnetic recording medium in that it has a large coercive force of several KOe at room temperature. Since the temperature is high (Te=360° C. for MnBi), there is a drawback that a large amount of energy is required for writing. In addition, since it is a polycrystalline substance, it is necessary to create a thin film with a stoichiometric composition, which is technically difficult to create, and in addition, MnB+ has two phases: a high temperature phase and a low temperature phase. It also has the disadvantage of being thermally unstable due to its tendency to undergo phase transitions. Furthermore, compound single crystal thin films typified by GIG have a major drawback in that they are extremely expensive compared to other types.

On the other hand, a monocrystalline metal thin film such as Gd-Co, Gd-Fe, etc., which performs writing using magnetic compensation points, is amorphous, so it can be fabricated on any substrate, and some impurities are added. Although it has the advantage that the magnetic compensation temperature can be arbitrarily controlled to some extent, it has the disadvantage that the coercive force at room temperature is small (300 to 5 oooe) and the recorded information is unstable.

Furthermore, in order to produce a thin film having such a coercive force, it is necessary to control the composition within tY 1 atom 1, which is not easy in terms of thin film production. On the other hand,
15 atoms to 30 atoms proposed to eliminate the drawbacks of the technique in 1 with the same amorphous thin film.
TbFe or DyFe containing m Tb or Dy has the following advantages.

■Has a large coercive force of several KOe at room temperature,
It is possible to record high-density information and write magnetic domains in a desired shape, and the recorded information is extremely stable.

(2) It has excellent properties as a recording medium, such as a large coercive force.It has a wide composition range, and it is not necessary to make a thin film with a strictly limited composition, so it is very easy to produce and has a high yield.

■One cucumber is 120'C in TbFe, DyFe
Since the temperature is as low as 60° C., when performing thermal writing using a single Curie point, writing can be performed with extremely small energy.

However, this amorphous alloy thin film such as TbFe or DyFe has the following drawbacks. That is, if the Curie point is low, it is true that writing can be performed with small energy, but the S/N during reading is conversely reduced. Figure 1 shows the optical reproduction output (S) and signal-to-noise ratio (S/N) during optical reproduction of an amorphous alloy thin film as a function of the irradiated laser power ('Io), which has good characteristics as a recording medium. It can be seen that TbFe and DyFe, which have the following properties, are worse than GdFe, which is not good as a recording medium, in terms of optical reproduction. This is a very serious drawback when this recording medium is used as a magneto-optical memory.

In order to eliminate this drawback, GdTbFe (patent application
5-30251) and GdDyTbFe (see Japanese Patent Application No. 55-170239). The former is (GdxTb 1-z) y” *-y as 0
．． 00≦X≦1.00, 0.15≦y≦0.35, the latter is ((GdzDy 1-z) z T
b 1-zlyFel as 0.00 (x(1,
00,0,15≦y<o,as.

y O800(z (1,00 range), both of which have good recording characteristics such as TbFe and DyFe and G which have good optical reproduction characteristics.
It has the advantages of both dFe. The single key point and coercive force are located between TbFe or DyFe and GdFe, but the optical regeneration output S is simply TbFe as shown in Figure 2.
e.

GdTbFe and GdDyFe have a large coercive force at room temperature, are not located between DyFe and GdFe, and have a large coercive force. Shows excellent properties as a medium.

Magneto-optical recording media are naturally required to have both excellent recording and reproduction characteristics.
The conditions for the former are that the Curie point is low and the coercive force is large, and for the latter that the Kerr rotation angle is large. Looking at the relationship between the single point of the Curie and the Kerr rotation angle in Figure 3, these conditions are contradictory in conventional binary systems, and it is not possible to obtain a medium that satisfies both. In other words, it was desired to improve the direction of the arrow in the figure. The GdTbFe ternary system and the GdDyTbFe quaternary system were considered as media that would satisfy this direction. These multi-component systems are TbFe, which is a binary system and has excellent recording properties.
.

By mixing DyFe and GdFe, which has excellent readout characteristics, it was designed to take advantage of the advantages of both. Although this objective has been achieved to a large extent as shown in the figure, it cannot necessarily be said that the recording characteristics and reproduction characteristics of the two sources are utilized to the fullest due to the multiplexing. The reason for this is the attempt to obtain a uniform film for a medium that requires contradictory conditions for recording and reproduction.

The object of the present invention is to obtain the above binary Gd-Fe, Tb-F
e, DyFe and ternary GdTbFe, GdD
yFe, TbDyFe and quaternary GdDyThFe
By creating a composition gradient in the film thickness direction within a single film such as, the composition has excellent readout characteristics on the optical readout side and the composition has excellent recording characteristics on the other side. It is an object of the present invention to provide a magneto-optical recording medium in which recording characteristics and reading characteristics are not influenced by each other and the performances of the medium suitable for each are maximized.

The present invention will be explained in detail below.

In the magneto-optical recording medium of the present invention, the axis of easy magnetization is perpendicular to the film surface, and the recording medium with a low Curie point and high coercive force is mounted on the substrate side such as glass and has a high key on the light incident surface side. One point is that it is a thin film magneto-optical recording medium that has a composition gradient in the film thickness direction so as to be a readout medium with a low coercive force and a large Kerr rotation angle.

In order to have sufficient magnetic anisotropy to orient the magnetization perpendicular to the film surface, it is necessary to make the thin film amorphous, but this condition requires that the thin film be made amorphous on a substrate kept at a temperature below room temperature. This is achieved by fabricating a thin film using a sputtering method or a vacuum evaporation method. In order to stably direct the magnetization in the direction perpendicular to the film surface, the thickness of the film must be 10
It needs to be 0A or more.

An example of the structure of the magneto-optical recording medium of the present invention is shown in FIG.

1 is a substrate such as glass, 2 is a magneto-optical recording medium, which has a recording area a, a reading area and a transition area C between them.
It consists of A medium with a low Curie point and high coercive force is suitable for the recording medium region a. On the other hand, in the reading medium area of the area, a medium having a high key point and a small coercive force and a large Kerr rotation angle .theta. is required. The transition region of C plays the role of transmitting the information stored in region a to region A through exchange interaction.The recording of 0 information is achieved by increasing the temperature of the medium by a light beam irradiated from the region side, and transferring the information stored in region A to region A. This is done by reducing the coercive force of a and rotating that part in the direction of the external magnetic field. Information recorded in area a is transferred to area 2 through area C by exchange interaction. In this way, the information transferred to the area is read out by the Kerr effect of the reflected light from the area of the beam irradiated from the side of the area. During recording, a beam passes through area A and enters area a, but since area a accounts for a very small proportion of the total thickness, it is assumed that there is almost no effect on the recording power. Guessed.

As an example, region a is TbFe and region a is GdFe.
Examples of the composition distribution in the film thickness direction of the medium when the ternary alloy TbGdFe is used are shown in FIGS. 5(a) and 5(b).

The media used in regions a and b and the thickness of their layers can be changed independently to improve recording and reading characteristics. For example, if a medium that can be written with lower power is required, the Curie point of area a can be lowered by one point, and the reading characteristics of area a are not affected by this, which is the greatest feature of the present invention. .

For example, TbGdFe is used as the magneto-optical recording medium according to the present invention.
In the case of a ternary alloy film, in the sputtering method, the RF power of Fe is kept constant and the RF powers of Gd and Tb are controlled to vary over time, and in the evaporation method, the temperature of the evaporation source is controlled. By doing so, it can be easily manufactured.

As explained above, the magneto-optical recording medium of the present invention has three regions: a recording region, a readout region, and a transition region between them. The alloy thin film has an axis of easy magnetization in the direction perpendicular to the film surface. Since a separate region is in charge, it is possible to obtain both low-power recording and high optical reproduction output.Therefore, the so-called beam 7-dres coupler writes using a light beam and reads using the Kerr effect. - If used as a magneto-optical memory medium such as a file memory, an excellent memory device with extremely high density and high S/N can be realized.

It goes without saying that the writing method used in the present invention is not limited to a light beam, but may be performed by any method that supplies the energy necessary to generate a reversed magnetic domain, such as a nail-shaped magnetic head, a thermal pen, or an electron beam. stomach.

[Brief explanation of the drawing]

Figure 1 shows the optical regeneration characteristics of conventional binary amorphous alloy thin films, Figure 2 shows the optical regeneration characteristics of ternary and binary amorphous alloy thin films, and Figure 3 shows quaternary and ternary amorphous alloy thin films. 4 is a cross-sectional view showing a configuration example of a thin film recording medium of the present invention, and FIG. 5 is an embodiment of the present invention. FIG. 3 is a composition distribution diagram in the film thickness direction when TbGdFe is used as the film. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Magneto-optical recording medium, a... Recording area, b... Reading area, C... Transition area. Patent applicant: International Telephone and Telephone Co., Ltd. Representative: Otsuka 1 person from outside the university

Claims (1)

[Claims] In a thin film magneto-optical recording medium that has an axis of easy magnetization perpendicular to the film surface, the composition within a single film has excellent readout characteristics on the optical readout side, while the composition has excellent recording characteristics on the other side. 1. A magneto-optical recording medium characterized by having a composition gradient in the film thickness direction such that