JPH04205740A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium for high density and high speed access by using specified compsn. of TbDyFeCo films as first and second layers of the recording layer. CONSTITUTION:The magneto-optical recording medium has a functional separating type two-layer structure, comprising a transparent substrate 1, interference layer 2, and a first recording layer 3a and a second recording layer 3b of the recording layer 3. Both of the first and second layers consist of amorphous magnetic alloy films expressed by (TbxDy1-x)z(FeyCo1-y) 1-z, having the axis of easy magnetization perpendicular to the film plane. In the above formula, 0.5<x<1, 0.6<y<0.85, 0.1<z<0.3 for the first layer, and for the second layer, 0<x<0.5, 1>y>=0.85, and 0.15<z<=0.25. With this constitution, the obtd. magento-optical recording medium has high C/N and high sensitivity, which realizes high-density recording and high access speed.

Description

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

[Conventional technology and problems to be solved by the invention] Magneto-optical disks use laser light to record, reproduce, and erase information, so they have a large storage capacity and are rewritable because the recording film uses a magnetic material. It is. It also has excellent reliability because it can record and reproduce without contact and is not affected by dust. The materials used for this magneto-optical recording layer (hereinafter referred to as recording layer) include TbFeCo, NdDyFeC
Rare earth transition metal amorphous alloys (RIE-TM) such as o, TbDyFeCo are known, and have no grain boundary noise.
Since perpendicular magnetization cylinders can be easily obtained by using sputtering, etc., development has been actively carried out.
Since it was commercialized several years ago, it has rapidly spread to the market.

This RE-TM film must have a large Kerr rotation angle θ□, which greatly influences the reproduction C/N of the disc, and a small Curie point Tc, which influences recording sensitivity, of 180° C. or less. This characteristic is particularly important for high-speed rotation in order to increase the transfer rate of information, which is required as a replacement for hard disks and the like. Furthermore, in order to perform high-density recording, the material must have a large coercive force He to hold small bits (magnetic domains) of 1 μm or less. However, to date, there is no RE-TM film that satisfies all of these characteristics at the same time. Therefore, a magneto-optical recording medium with a functionally separated two-layer structure has been proposed in which the RE-TM film serving as the recording layer has a two-layer structure, and recording and erasing and reproduction are separated. In other words, in this medium, a first layer with a high Curie point Tc, a low coercive force Hc, and a large magneto-optic effect is used for reproduction, and a second layer with a low Curie point Tc and a large coercive force Hc is used for recording and erasing. is used. Conventionally, the following materials have been proposed as materials for the recording layer used in media with such a structure. That is, the first layer is GdFe,
GdFeCo, Bi-substituted YIG, etc. are used. GdF
e, GdFeCo, etc., use the Kerr effect (0,); Bi-substituted YIG, etc. use the Faraday effect (OF). As the layer of Bunsetsu 2, TbFe, TbFe
Co, etc. have been proposed.

However, when TbFe or TbFeCo is used for the second layer, the Curie point Tc can only be lowered to about 180°C at most, and there is still a long way to go to achieve high sensitivity during high-speed rotation to support high-density and high-speed access. Not enough.

The present invention has been made in view of the actual state of the prior art, and an object of the present invention is to provide a magneto-optical recording medium that can sufficiently cope with high-density and high-speed access.

[Means to solve the problem]

As a result of extensive research, the present inventors found that in a magneto-optical recording medium with a functionally separated two-layer structure, the first layer and the second layer are the same 71)[)yFeCo film, but each has a specific composition. We have discovered that the above problems can be solved by using By optimizing the composition of the TbDyFeCo film, the Curie point Tc can be lowered to 130°C to 160°C, and the coercive force 11c is sufficiently large, so when used as a second layer, high sensitivity can be achieved, and By using the composition as the first layer, high C/
Furthermore, it was confirmed that Dy contained in the film has excellent corrosion resistance compared to other rare earth elements (Tb, Gd, Nd, etc.), so it was possible to provide a highly reliable medium with less deterioration over time. .

That is, according to the present invention, a recording layer is provided on a transparent substrate via an interference layer, and a protective layer is further provided as necessary, and the recording layer has a high Curie point and a low coercive force. In a magneto-optical recording medium comprising a first layer having a large magneto-optic effect and a second layer having a low Curie point and a large coercive force, the first layer and the second layer are both perpendicular to the film plane. A magneto-optical recording medium is provided which is characterized by being made of an amorphous magnetic alloy film having an axis of easy magnetization in the direction and represented by the general formula shown below.

(T b x D y] −y, ) z (F e
yCO]-Y)]-Z(first layer=0.5≦
X<1.0.6≦Y<0.85, 0.1<Z≦0.3; Second layer: O<X<0.5, ]>Y≧0.85.0.1
5<Z≦0.25) The configuration of the present invention will be described in detail below with reference to FIG.

FIG. 1 is a sectional view showing an example of the configuration of a magneto-optical recording medium according to the present invention, in which an interference layer N2 and a first layer 3a are placed on a transparent substrate l.
It has a structure in which a recording layer 3 and a protective layer 4 consisting of a second layer 3b and a second layer 3b are sequentially laminated. Each configuration will be explained below.

(Substrate) The transparent substrate used in the present invention includes polycarbonate (PC), polymethylmethacrylate-1-(PMMA),
Examples include a plastic substrate made of a resin such as amorphous polyolefin (APO), or a substrate made of glass such as aluminosilicate, barium borosilicate, etc., on which a grooved resin is formed. These substrates are disk-shaped and have a thickness of about 1 to 2 mm.

(Interference M) In the present invention, an interference layer 2 is first provided on the substrate 1''. This interference layer 2 has a high refractive index (1.8 or higher).
2) Kerr rotation angle θ due to light interference effect using dielectric film
The objective is to raise the carrier (C) level by enhancement of Cr, lower the noise (N) level by lowering the reflectance, and improve the Cr in total. In addition, RE- such as TbDyFeCo film
When eJ'13 is formed by TM, corrosion such as oxidation is likely to occur, so this interference layer 2 must also serve as a protective film to prevent corrosion of the recording layer 3. For this purpose, it is necessary to prevent water and oxygen from entering from the substrate 1, to have high corrosion resistance itself, and to have low reactivity with the recording layer 3. The specific material is 5iO1Si
n□,AQ,,0. , Ta, , O, etc. metal oxides,
Metal nitrides with Sl, AQ, Zr, Ge, etc., 84C,
Examples include inorganic carbides such as SiC and metal sulfides such as ZnS, and these may be composites (Example 5ilQON, 5i
ZrN) or a multilayer film (eg SiN/5in). Although the optimum value of the film thickness varies depending on the refractive index, it is usually 500 to 2000, preferably 800 to 1200.

(Recording M) The feature of the present invention lies in the recording layer 3. As described above, this recording layer 3 consists of the first layer 1j3a for reproduction and the second layer 13b for recording and erasing, and the composition of each layer is as expressed by the following general formula.

First layer: 0.5≦X<1.0.6≦Y<0.85.0
．． 1<Z≦0.3 Second layer: O<X<0.5.1. >Y≧0.85, 0.
15<Z≦0.25 The reason why the ranges of X, V, and Z in the first layer 3a are defined as above is because the first layer 3a has a high Curie point Tc, a small coercive force He, and a magneto-optic effect. This is due to the fact that it is required to be large. On the other hand, in the second M3b
, Y, and Z are defined as above because the second i
3b is due to the fact that a low Curie point Tc and a large coercive force He are required.

The optimal value for the film thickness of both M3a and 3b is determined by the values of coercive force HC and saturation magnetization Ms.
Preferably it is about 150 to 500 people.

The TbDyFeCo film contains various elements (Tb, Dy, Fe, C
It has the advantage that Tc, θ□, and He can be freely changed by adjusting the content of o) (Figures 2 to 4).
(see figure).

In particular, by adjusting the content of oy, the Curie point Tc can be lowered to 130°C without changing other properties, and this can be said to be a feature not found in other RE-TM films (TbFeCo films, etc.). Figure 2). Therefore, the first M3a (for regeneration), which has a high Curie point Tc, a high coercive force He, and a large Kerr rotation angle θ, has a high Curie point Tc and a large Kerr rotation angle θ.
(Fig. 3) and by controlling the amount of TbDy to an appropriate value (Fig. 4), and the Curie point Tc
The second layer 3b (for recording and erasing) with a low coercivity and a large coercive force 1+c has a large Oy content (Figure 2), a small Co content (Figure 3), and a TbDy content close to the compensation composition. do(
(Fig. 4).

The first
Even if a nonmagnetic thin film (such as a SiO□ film) or a soft magnetic horizontally magnetized film (such as a NiFe film) is provided between the layer and the second layer, the effects of the present invention will not be impaired.

(Protection N) In the present invention, a protective film 4 is usually provided on the recording layer 3.

This protective layer 4 prevents harmful substances such as water, oxygen, or halogen elements from entering the recording layer from the air (in the case of a single-sided disc) or the adhesive layer (in the case of a double-sided disc), and Since it is provided for the purpose of protecting the interference layer 2, it needs to have high corrosion resistance itself and low reactivity with the recording layer 3, just like the interference layer 2.

In addition to the materials listed for the interference layer 2, the materials include Cr, Fe,
It may be a metal such as Ni, Mo, or Pt, or an alloy made of these metals.

As means for forming the interference layer 2, the recording layer 3, and the protective layer 4 on the substrate 1, physical vapor deposition methods such as sputter linking and ion blasting, chemical vapor deposition methods such as plasma CVD, etc. are used.

In addition to the layer structure shown in Fig. 1, the protective layer 4'' may be further provided with an organic protective film (cover N) with a thickness of 5 to 10 μm, or the film surfaces may be bonded together using an adhesive. However, the effect of the present invention is not impaired.

〔Example〕

The present invention will now be described in more detail with reference to Examples.

Examples 1 to 6 A polycarbonate substrate with a pregroup having a diameter of 130 mm and a thickness of 1 to 2 rnrn was set in a vacuum chamber of a sputtering apparatus and evacuated to a pressure of 5 x 10'' Torr or less.

First, a mixed gas of Ar and N2 was introduced into a vacuum chamber, the pressure was adjusted to 5 X IO-'' Torr, and high-frequency sputtering was performed using Si as a target with a discharge power of 2 KW (4 W/cd) to form SiN as an interference layer. 1,000 films were deposited.Next, the recording layer was formed by direct current sputtering using TbDyFeco alloy as a target.
The bDyFeCo membrane was used as the first layer (400 layers) and the second layer
(400 people) to form two layers (see Table 1 for each composition). Furthermore, drying as a protective layer: S by the same method as am.
A recording medium was obtained by depositing 800 iN films.

Comparative Example A drying layer, a recording layer and a protective layer were formed using the same means as in the previous example, but the recording layer was made of a conventional material (the first layer
・GdFeCo11 (400 people), second layer - TbF
eC.

A recording medium was obtained using a film (400 people) (see Table 1 for detailed composition).

The film surfaces of these recording media were bonded together to form a double-sided disc, and the relationship between recording power and C was investigated. The recording sensitivity was determined as the recording power at which the second harmonic was minimized with respect to the fundamental wave. Note that the recording and reproducing conditions were as follows.

・Recording frequency 3.7MHz ・Laser wavelength 780 nm ・Disc rotation speed
180Orpm(CAV)・Reproduction laser i power
1 mW・Recording magnetic field 2500e・Erasing magnetic field 2000e・Recording radius
30 mm From Table 1 1 According to the present invention, a magneto-optical recording medium with high C/N and high sensitivity can be realized by using two layers of optimized TbDyFeCo films with different compositions as the recording layer. It can be seen that higher density and faster access than before is possible. Moreover, Example 1~
As a result of an accelerated life test of the media of Comparative Example 6 and Comparative Example under the environmental conditions of 80°C and 15% R1, the media of Comparative Example
After 000 hours, the pit error rate (BER) is approximately 1
In contrast, no significant change in BEH was observed in any of the media of Examples 1 to 6 even after 2000 hours. In other words, as in the present invention, both of the two layers are Tb.
It has been found that the stability over time is also improved when using a DyFeCo membrane.

〔Effect of the invention〕

According to the present invention, since the magneto-optical recording medium with the functionally separated two-layer structure is configured as described above, a magneto-optical recording medium with high C and high sensitivity can be realized, and high density and high speed access can be realized. Furthermore, stability over time is also improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the layer structure of a magneto-optical recording medium according to the present invention, and FIGS. 2 to 4 show changes in magnetic properties when the Dy, Co, and TbDy contents of the TbDyFeCo film are changed, respectively. It is a diagram. 1 ・Transparent substrate 2 ・・Interference layer 3 ・・Recording layer 3a ・First layer 3b 2nd layer 4 Protective layer

Claims (1)

[Claims] (1) A recording layer is provided on a transparent substrate via an interference layer, and a protective layer is provided as necessary, and the recording layer has a high Curie point, a small coercive force, and a large magneto-optical effect. In a magneto-optical recording medium comprising a first layer and a second layer having a low Curie point and a high coercive force, the first layer and the second layer both have an axis of easy magnetization in a direction perpendicular to the film surface. 1. A magneto-optical recording medium comprising an amorphous magnetic alloy film having the following general formula: (Tb_XDy_1_-_X)_Z(Fe_YCo_1
_-_Y)_1_-_Z (first layer: 0.5≦X<1, 0.6≦Y<0.85,
0.1<Z≦0.3; Second layer: 0<X<0.5, 1>Y≧0.85, 0.1
5<Z≦0.25)