JPS63317944A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve recording, reproducing and erasing characteristics by maintaining the saturation magnetization in the direction perpendicular to the film plane of a recording layer always at <=50emu/cc at the temp. at which the coercive force in the direction perpendicular to the film plane of the recording layer is <=1kOe. CONSTITUTION:The recording layer of a recording medium which is formed by using a thin magnetic film essentially consisting of a rare earth metal and transition metal as the recording layer and executes recording, reproducing and erasing of information by light is formed in the following manner in order to improve the recording, reproducing and erasing characteristics: The saturation magnetization in the direction perpendicular to the film plane of the recording layer is always maintained at <=50emu/cc at the temp. at which the coercive force in the direction perpendicular to the film plane is <=1kOe in the 18<=X<=25, 0.55-Y<=1.00 range of X, Y when the compsn. of the recording layer is expressed in atomic ratio by the formula and in the temp. range from 25 deg.C up to the Curie temp. of the recording layer. Since the thin magnetic film having a small floating magnetic field is used as the recording layer, the recording, reproducing and erasing characteristics are improved and the high CN is obtd. with the low bias magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium on which information can be recorded, reproduced and erased using light.

[Conventional technology]

While heating the recording layer with a laser beam spot, information is recorded and erased by applying a bias magnetic field to form and eliminate reversed magnetic domains, and then irradiating the laser beam with linearly polarized light of lower power than during recording. In magneto-optical recording in which information is reproduced using the Kerr effect or the Faraday effect, the magnetic thin film that is the recording layer is small (and must satisfy the following properties).

(1) It is a perpendicular magnetization film.

(2) The Curie temperature is low enough to allow recording and erasing with a semiconductor laser, and the Curie temperature is sufficiently high compared to the normal usage environment.

(3) Low media noise.

(4) The magneto-optical effect is large.

For example, JP-A-57-94
Heavy rare earth metals Tb, Dy like 948.

Amorphous alloys formed of one or more of Gd and one or more of Fe or Co have been used.

[Problem that the invention seeks to solve]

Magneto-optical recording is a method of recording and erasing information by heating a part of the recording film to a temperature above the Curie temperature by irradiating it with laser light, and at the same time forming or eliminating reversal domains by applying a bias magnetic field. conduct. Heavy rare earth metal 6
In an amorphous alloy whose main component is a transition metal, in a composition system in which there is more transition metal than in a compensating composition where magnetization apparently disappears at room temperature, the magnetic domain that is reversed when forming a magnetic domain and the magnetization around it are created. A magnetic field (stray magnetic field) acts in a direction that helps form reversed magnetic domains. Therefore, the bias magnetic field applied to form reversed magnetic domains can be small. On the other hand, since the floating magnetic field acts in a direction that prevents the formation of reversed magnetic domains when a magnetic domain is eliminated, the bias magnetic field must be large in order to eliminate reversed magnetic domains. Also, from compensation organizations.

In a composition system rich in heavy rare earth metals, a stray magnetic field acts in the opposite direction to that in a composition system rich in transition metals than in a compensation composition, so a large bias magnetic field is required to form a reversal domain, and a small bias field is required to eliminate it. A magnetic field is sufficient.

As described above, by applying a bias magnetic field larger than the floating magnetic field, reversed magnetic domains are formed and disappeared.

The bias magnetic field applied during recording and erasing using the magneto-optical recording method usually has an R of 500 to eoo.

It never exceeds -e. Therefore, it is essential that the magneto-optical recording medium has the property of being able to perform saturation recording and complete erasing at several hundred Oe. In a composition system in which there is more transition metal than in the compensation composition, if the stray magnetic field is large, saturation recording can be achieved during recording, but complete erasure may not be possible during erasing. In a composition system in which the amount of heavy rare earth metal is higher than that of the compensation composition, if the stray magnetic field is large, complete erasure can be achieved during erasing, but saturation recording may not be possible during recording. In other words, unless the stray magnetic field is sufficiently small, recording and erasing with a low bias magnetic field cannot be performed completely.

In addition, since the laser beam irradiated during recording and erasing has a strong distribution, the temperature of the recording layer is highest at the center of the laser beam irradiated area, and as it cools down toward the outer periphery (with a lower temperature distribution). To go.

For this reason, the outer periphery of the portion that had been heated above the Curie temperature gradually becomes below the Curie temperature and magnetization appears. Therefore, a floating magnetic field is formed by the magnetization of the surrounding area of the inverted magnetic domain and the newly appeared magnetization, and when this floating magnetic field is large, a minute inverted magnetic domain is formed within the inverted magnetic domain during recording, and during erasing, It will remain unerased.

Therefore, if the stray magnetic field is sufficiently small, it is possible to form uniform recording bits without minute inverted magnetic domains within inverted magnetic domains, and thus a signal with a high carrier level can be obtained when reproducing information. Also, if the stray magnetic field is small enough,
Since complete erasure is possible, a signal with a low noise level can be obtained during playback.

Therefore, an object of the present invention is to provide a magneto-optical recording medium with excellent recording, reproducing and erasing characteristics by using a magnetic thin film with a small stray magnetic field as a recording layer.

[Means for solving problems]

The magneto-optical recording medium of the present invention is a magneto-optical recording medium in which a magnetic thin film having magnetic anisotropy in a direction perpendicular to the film surface is formed as a recording layer on a transparent substrate, and information is recorded, reproduced and erased using light. In the recording medium, when the composition of the recording layer is expressed as HRx (FeyCo+-/)too-X in atomic ratio (however, HR represents one or more of the heavy rare earth metals Gd, Tb, and DV), Among those in which Y is in the range of 18≦X≦25 0.55≦Y≦1.00, in the temperature range from 25°C to the Curie temperature of the recording layer, in the direction perpendicular to the film surface of the recording layer. When the coercive force of
It is characterized by being below u/cc.

〔Example〕

(Example 1) Recording films having five types of compositions were created by sputtering five types of targets with different ratios of heavy rare earth metals and other metals under the conditions shown below. After evacuating the chamber to an initial vacuum level of 5.0XIO or less, Ar was introduced as a carrier gas, and a
High frequency power of 5 is applied to the cathode, and 5 is applied to the glass substrate.
It was made to have a film thickness of 0 nm. In order to prevent oxidation of the magnetic film, the mixture of aluminum nitride and silicon nitride was continuously heated for 11 minutes without breaking the vacuum.
00n was formed. Table 1 shows the composition of the recording film produced. Figure 1 (a), (b), (c), (d), and (e) respectively show the magnetization (hereinafter magnetization) perpendicular to the film surface of the recording film with the composition of sample number 1.2.3.4.5. The temperature dependence of the coercive force in the direction perpendicular to the film surface (hereinafter referred to as coercive force) is shown. Table 2 shows sample number 1.2.3.4.5
The Faraday rotation angle of a recording film with a composition of is shown. Next, a mixture of aluminum nitride and silicon nitride was applied to the polycarbonate substrate with guide grooves as a second protective surface layer.
Sample No. 1.2.3 was formed continuously with a film thickness of 00n.
．． A recording film having one composition among 4.5 was formed to a thickness of 40 nm, and a second protective layer having the same composition as the first protective layer was formed to a thickness of 1100 nm. A magneto-optical recording medium was fabricated. Table 3 shows the CN ratio of the reproduced signal by the Farade single method for five types of recording media. Linear speed 4.
7m/Ss recording frequency IMHz, resolution band 30
Evaluation was performed under the condition of KH2N bias magnetic field of 3000e.

As is clear from Table 3, Figure 1, the recording media with the compositions of sample numbers 1 and 2 do not satisfy the condition that the magnetization is always 50 em u / cc or less at a temperature where the coercive force is 1 KOe or less. , the CN ratio is inferior compared to other recording media. On the other hand, the recording medium with the composition of sample number 5 always has a magnetization of 50 e at a temperature where the coercive force is 1 KOe or less.
Similarly, the magnetization is always 50 emu/c at a temperature where the coercive force is below 1 KOe, although it is below mu/cc.
The CN ratio is inferior compared to sample numbers 3 and 4, which are below c. This is because, as shown in Table 3, as the ratio of heavy rare earth metal increases in the order of sample numbers 1, 2, 3, 4, and 5, the magneto-optic effect decreases in that order. From the above, in a magneto-optical recording medium with a high C/N ratio, it is possible to form recording bits that are uniform and have no reversed magnetic domain due to the small floating magnetic field in the vicinity of the Curie temperature, that is, in the temperature range where the coercive force is 1 KOe. In addition, it is desirable that the magneto-optic effect be large.

(Example 2) In order to examine the erasing characteristics of the five types of magneto-optical recording media used in Example 1, the CN ratio was measured while changing the laser power in each bias magnetic field during erasing. Figure 2 (a) (b)
)(c)(d)(e) is sample number 1.2.8.4.5
These are the results of the erasing characteristics for the composition recording medium. The recording media with the compositions of sample numbers 1 and 2 require a bias magnetic field of 5000 e for erasing, whereas sample numbers 3.4.5 can be erased with a bias magnetic field of 2000 e. For the recording medium with the composition of Sample No. 8.4.5, in which the floating magnetic field is smaller than that of Sample Nos. 1 and 2, a bias magnetic field of 2000e is sufficient for erasing, and according to Example 1, a bias magnetic field of 3000e is sufficient for recording. Therefore, it is considered that the recording medium of sample number 3.4.5 realizes recording and reproduction using a low bias magnetic field, which is desired for a magneto-optical recording medium.

〔Effect of the invention〕

As described above, according to the present invention, in a magneto-optical recording medium whose recording layer is a magnetic thin film containing rare earth metals and transition metals as the main components, recording and erasing with a low bias magnetic field and a high CN ratio can be achieved. exists.

[Brief explanation of drawings]

Figures 1, (a), (b), (c), (d), and (e) are diagrams showing the temperature dependence of magnetization and coercive force of magnetic films with compositions of sample numbers 1, 2, 3, 4, and 5, respectively. In each figure, (0) indicates the temperature dependence of coercive force, and (Δ) indicates the temperature dependence of magnetization. Figure 2, (a), (b), (c), (d), and (e) show the CN ratio at each bias magnetic field during erasing of the magneto-optical recording medium with the composition of sample number 1.2.8.4.5, respectively. This is a diagram showing the laser power dependence of
000e1 (Δ) is 5500e, (X) is 6000e
represents the bias magnetic field of In Figure 2 (b) (0)
is 4500e1 (△) is 5000e N (X
) is a diagram representing the bias magnetic field of 5500e, and Figure 2 (
In C), (○) is 1500e, (Δ) is 2000e
. (x) represents a bias magnetic field of 2500e. In Figure 2(d), (○) is 1000e1(Δ)
is 1500e1 (x) represents a bias magnetic field of 2000e. In Fig. 2(e), (○) is 1000e, (
Δ) does not represent the bias magnetic field of 1500e1(X) and 2000e. Applicant: Seiko Epson Corporation 4φ5,! ;, 0 5. %l,,o
6. ”;Signal power [Object W] Fig. 2 α Nozzle power [m1] Fig. 2 (b, 1 4, da 5.o5.5G, o6,5 racer L no. Guwa [m mouth r] 21st!I(C) 2nd figure (dn

Claims (1)

[Claims] In a magneto-optical recording medium in which a magnetic thin film having magnetic anisotropy in a direction perpendicular to the film surface is formed as a recording layer on a transparent substrate, and information is recorded, reproduced, and erased using light. , the composition of the recording layer is HR_x(Fe_yCo_1
____y)_1_0_0_-_x (however, H
R represents one or more of the heavy rare earth metals Gd, Tb, and Dy), and X and Y are each in the range of 18≦X≦25 0.55≦Y≦1.00, from 25°C to the above In the temperature range up to the Curie temperature of the recording layer, when the coercive force in the direction perpendicular to the film surface of the recording layer is 1 KOe or less, the saturation magnetization in the direction perpendicular to the film surface of the recording layer is always 50 em.
1. A magneto-optical recording medium characterized in that it is less than u/cc.