JPH06309716A - Magneto-optical recording medium and reproducing method of the medium - Google Patents

Abstract

(57) [Summary] [Object] The present invention is also applicable to a conventional magneto-optical recording / reproducing apparatus.
Provided are a magneto-optical recording medium capable of reproducing a signal having a period equal to or shorter than a diffraction limit of light and improving linear density and track density, and a reproducing method thereof. [Structure] A first magnetic layer which is an in-plane magnetized film, a second magnetic layer which is an in-plane magnetized film having a Curie temperature higher than that of the first layer and which is a room temperature magnetized film at room temperature and which becomes a vertically magnetized film, and a perpendicular magnetized layer. A magneto-optical recording medium having at least a third magnetic layer made of a film, and an optical magneto-optical effect while transferring the minute magnetic domains recorded in the third magnetic layer of the magneto-optical recording medium to the second magnetic layer. A signal reproducing method in a magneto-optical recording medium, characterized in that the signal is converted and read.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording / reproducing information with a laser beam by utilizing a magneto-optical effect, and a magneto-optical reproducing method and a magneto-optical recording capable of increasing the density of the medium. It concerns media.

[0002]

2. Description of the Related Art As a rewritable high density recording system,
Using the thermal energy of a semiconductor laser to write magnetic domains in a magnetic thin film to record information, using the magneto-optical effect,
Attention has been paid to a magneto-optical recording medium for reading this information.

In recent years, there is an increasing demand for increasing the recording density of this magneto-optical recording medium to make it a recording medium having a larger capacity.

By the way, the linear recording density of an optical disk such as a magneto-optical recording medium is mainly determined by the S / N of the reproducing layer, which is the period of the signal bit string, the laser wavelength of the reproducing optical system, and the aperture of the objective lens. Depends heavily on the number.

That is, when the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens are determined, the bit period f which is the detection limit is determined by the following equation.

[0006]

F = λ / 2NA On the other hand, the track density is limited mainly by crosstalk. This crosstalk is mainly determined by the distribution (profile) of the laser beam on the medium surface, and is represented by a function of λ / 2NA as with the bit period.

Therefore, in order to realize high density in the conventional optical disk, it is necessary to shorten the laser wavelength of the reproducing optical system and increase the numerical aperture NA of the objective lens.

However, there is a limit to the improvement of the laser wavelength and the numerical aperture of the objective lens. Therefore, a technique for improving the recording density by devising the configuration of the recording medium and the reading method has been developed.

For example, in Japanese Patent Laid-Open No. 3-93058, a medium composed of a reproducing layer and a recording layer is used, and before the reproduction of a signal, the magnetization direction of the reproducing layer is aligned in one direction, and then the recording layer is held. The signal is transferred to the reproduction layer to reduce intersymbol interference during reproduction, and it is possible to reproduce (super-resolution) a signal having a period equal to or shorter than the diffraction limit of light, in an attempt to improve recording quality.

[0010]

However, in the above-described conventional magneto-optical reproducing method, the magnetization of the reproducing layer must be aligned in one direction before being irradiated with laser light. Therefore, it is necessary to add a reproducing layer initialization magnet to the conventional device. Therefore, the reproducing method has problems that the magneto-optical recording device is complicated, the cost is high, and it is difficult to reduce the size.

In view of the above problems, the present invention eliminates the need for initialization of the reproducing layer, so that even a conventionally used magneto-optical recording / reproducing apparatus can reproduce a signal having a period equal to or shorter than the diffraction limit of light. The purpose is to enable improvement of the density and the track density.

[0012]

In view of the above problems, the present invention has made extensive studies and found that the first magnetic layer, which is an in-plane magnetized film, and the in-plane magnetized film, which has a Curie temperature higher than that of the first layer, at room temperature. A second magnetic layer that becomes a perpendicular magnetization film when the temperature rises,
A magneto-optical recording medium having at least a third magnetic layer made of a perpendicularly magnetized film, wherein the minute magnetic domain recorded in the third magnetic layer of the magneto-optical recording medium is transferred to the second magnetic layer and read out. It has been found that the above can solve the above problems.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed description will be given below with reference to the drawings.

1A and 1B are schematic views showing the film structure of the present invention, FIG. 2 is an explanatory view showing the magneto-optical reproducing method of the present invention, and FIG. 3 is a magneto-optical recording medium of the present invention. FIG. 4 is a diagram showing a magnetization state after recording in one example, and FIG. 4 shows a demagnetizing field energy 2πMs ² of the second magnetic layer and a perpendicular magnetic anisotropy energy ku
5A shows the temperature dependence of the residual θ _K (magnetic field 0) of the magneto-optical recording medium of the present invention, and FIG. 5B shows the light of the comparative example. Residual θ _{K of} magnetic recording medium
The figure showing the temperature dependence of (magnetic field 0). The magneto-optical recording medium of the present invention has a first magnetic layer which is an in-plane magnetized film and an in-plane magnetized film having a Curie temperature higher than that of the first layer at room temperature. A magneto-optical recording medium having at least a second magnetic layer to be a perpendicular magnetization film when heated and a third magnetic layer to be a perpendicular magnetization film is provided, and a minute magnetic domain recorded in the third magnetic layer is recorded. The above object is achieved by transferring the data to the second magnetic layer and reading the data.

<Structure and Composition of Medium> As shown in FIG. 1A, first, second and third magnetic layers were prepared as follows.

The first magnetic layer has a stable in-plane magnetic anisotropy until reaching the Curie temperature, for example, a rare earth-iron group amorphous alloy such as GdCo, GdFeCo, GdTbFe.
Co, GdDyFeCo, NdGdFeCo, etc. are preferable. The Curie temperature is preferably near the medium temperature during reproduction.

The second magnetic layer is, for example, a rare earth-iron group amorphous alloy such as GdCo, GdFeCo, GdTbFeCo, GdDy.
FeCo, NdGdFeCo, etc. are desirable. Those having a compensation temperature between room temperature and Curie temperature are mentioned as examples of preferable ones.

The third magnetic layer has a large perpendicular magnetic anisotropy and can maintain a stable magnetization state, for example, a rare earth-iron group amorphous alloy such as TbFeCo, DyFeCo, TbDyFeCo.
, Or garnet, or a platinum group-iron group periodic structure film, for example, Pt / Co, Pd / Co platinum group-iron group alloy,
For example, PtCo and PdCo are desirable.

Further, these magnetic layers may be added with elements such as Cr, Ti and Pt for improving the corrosion resistance.

In addition to the above magnetic layer, the interference effect is enhanced.
For SiN, AlN_x, AlO_x, TaO_x, SiO _x Such as dielectric
It may be provided.

In order to improve thermal conductivity, Al, AlTa, AlTi,
AlCr, Cu, etc. may be provided.

Further, an intermediate layer for adjusting the exchange coupling force or the magnetostatic coupling force, and an auxiliary layer for assisting recording and reproducing may be provided. Further, a protective coat made of the dielectric layer or polymer resin may be provided as a protective film.

The recording / reproducing process of the present invention will be described below. In the following description, the first magnetic layer is called an auxiliary layer, the second magnetic layer is called a reproducing layer, and the third magnetic layer is called a recording layer.

As shown in FIG. 3, first, a data signal is recorded on the recording layer of the magneto-optical recording medium of the present invention. Recording is performed by irradiating the external magnetic field while irradiating the laser beam with the power such that the recording layer becomes the Curie temperature or higher, or after erasing once, the laser power is modulated while applying the magnetic field in the recording direction. To do. Alternatively, the laser power is modulated while applying an external magnetic field. At this time, if the intensity of the laser light is determined in consideration of the linear velocity of the recording medium so that only a predetermined area within the light spot is near the Curie temperature of the recording layer, a recording magnetic domain smaller than the diameter of the light spot can be formed. As a result, it is possible to record a signal having a period less than the diffraction limit of light.

At the time of data reproduction, the medium is irradiated with reproduction laser light, and at this time, the temperature of the irradiated portion rises. Since the medium moves at a constant speed, the temperature distribution on the medium has a shape extending in the moving direction of the medium, and the temperature distribution is such that a part of the light spot has a high temperature.

With respect to a single-layer magnetic thin film, when the saturation magnetization is Ms and the perpendicular magnetic anisotropy constant is Ku, the following equation is obtained.

[0027]

It is known that the main direction of magnetization is determined by the effective perpendicular magnetic anisotropy constant K⊥ defined by K⊥ = Ku−2πMs ² . When K⊥ is positive, it is a perpendicular magnetization film, and when it is negative, it is an in-plane magnetization film.

Here, 2πMs ² is the demagnetizing field energy. Therefore, as shown in FIG. 4, at room temperature (RT),

[0029]

## EQU3 ## When Ku <2πMs ² and K⊥ <0 are satisfied, that is, when the film becomes an in-plane magnetized film and the temperature becomes high during reproduction,

[0030]

## EQU4 ## If Ku> 2πMs ² and K⊥> 0 are satisfied, that is, if the saturation magnetization Ms and perpendicular magnetic anisotropy constant Ku of the magnetic thin film are set so as to form a perpendicular magnetic film, the high temperature part of the light spot Only becomes the perpendicular magnetization film that can transfer the magnetization of the recording layer, and super resolution is realized.

When this magnetic thin film is laminated with the perpendicularly magnetized film and the in-plane magnetized film directly or through an intermediate layer or the like, exchange coupling force, magnetostatic coupling force and the like from these films work, and apparently. Although Ku changes, if the perpendicular magnetization temperature region in the single-layer film is set to be slightly higher or lower, even when stacked with other layers, the perpendicular magnetization film is increased by the in-plane magnetization film at room temperature when it is heated. The situation is established.

In the magneto-optical recording medium of the present invention, in addition to the recording layer, an auxiliary layer is further laminated on the reproducing layer directly or via an intermediate layer. Since this auxiliary layer remains an in-plane magnetized film from room temperature to the Curie temperature, the magnetization direction of the reproducing layer is stably in-plane until the medium reaches the Curie temperature of the auxiliary layer due to the exchange coupling force from the auxiliary layer. Orient.

Therefore, if the Curie temperature of the auxiliary layer is set to be substantially equal to the temperature at which the magnetization direction of the reproducing layer transitions, the detection region of the reproducing layer has an exchange coupling force that promotes in-plane magnetization orientation from the auxiliary layer. Does not work, it becomes easier to magnetize vertically.

Since this auxiliary layer is arranged on the side opposite to the recording layer, that is, on the light incident side, the film thickness is made thin (200 angstroms or less, more preferably 100 angstroms) so that the reproduction output does not deteriorate due to absorption of light. The thickness is preferably angstroms or less, most preferably 60 angstroms or less, and thick enough (20 angstroms or more) so that the exchange power to the reproducing layer does not deteriorate.

Therefore, by providing the above-mentioned auxiliary layer, the boundary between the in-plane magnetized portion and the perpendicular magnetized portion of the reproducing layer becomes clear and C / N is improved. Further, according to the present invention, since reproduction can be performed without being affected by adjacent bits in the track direction and the radial direction, bits recorded by increasing both the linear recording density and the track density can be reproduced with good C / N.

Although the magnetic layers are magnetically coupled by exchange interaction in the above description, they may be magnetically coupled by magnetostatic coupling.

Further, in order to make the transfer clearer, an intermediate layer having a different Curie temperature may be provided.

The present invention will be described in detail below with reference to experimental examples, but the present invention is not limited to the following experimental examples as long as the gist thereof is not exceeded.

(Experimental Example 1) Each target of Si, Tb, Gd, Fe, and Co was attached to a DC magnetron sputtering apparatus, and a polycarbonate substrate was fixed to a substrate holder, and then a high vacuum of 1 × 10 ^-6 Pa or less was obtained. The inside of the chamber was evacuated by a cryopump until it became.

Ar gas was supplied to 0.4 Pa while evacuating.
After being introduced into the chamber until
An iN layer is formed in a thickness of 780 angstroms, a GdCo layer that is an auxiliary layer is formed, and then a GdF that is a reproduction layer is formed.
An eCo layer was formed, a TbFeCo layer as a recording layer was formed, and then a SiN layer was formed as a protective layer in a thickness of 700 angstroms to obtain a laminated film having the configuration of FIG. 1 (b).

At the time of forming the SiN layer, N ₂ is added in addition to Ar gas.
A gas was introduced, and a film was formed by direct current reactive sputtering of a Si target. The GdFeCo layer and the TbFeCo layer are G
A DC power was applied to each target of d, Fe, Co, and Tb to form a film.

The film thickness of the GdFe auxiliary layer was 50 Å, and the composition was set to be RE rich from room temperature to the Curie temperature and the Curie temperature around 140 ° C.

The thickness of the GdFeCo reproducing layer was 400 Å, and the composition was set so that the compensation temperature was 280 ° C. and the Curie temperature was 350 ° C. or higher.

The thickness of the TbFeCo recording layer was 400 angstroms, the composition was TM rich at room temperature, the compensation temperature was below room temperature, and the Curie temperature was 220 ° C.

When the residual θ _K when the magnetic field was 0 was measured while raising the temperature of this laminated film, the Kerr effect appeared near 140 ° C. as shown in FIG. Was confirmed.

(Experimental Example 2) Next, using the magneto-optical recording medium described in Experimental Example 1, the recording / reproducing characteristics were measured.

N.V. of the objective lens of the measuring device. A. Is 0.5
5. The laser wavelength was 780 nm. Recording power is 8
-10mW, linear velocity 9m / s (rotation speed 2400rp
m, radius 36 mm) and 5.8 to 15 MH in the recording layer
The z carrier signal was written by the magnetic field modulation method, and the recording frequency dependence of the C / N ratio was examined. Applied magnetic field is ± 150O
e.

The reproducing power was set to a value at which the C / N ratio was max.

The results are shown in Table 1.

[0050]

[Table 1] (Experimental Example 3) Similar to Experimental Examples 1 and 2, a magneto-optical recording medium was prepared by forming a thin film on a polycarbonate and evaluated under the same conditions.

A SiN layer which is an interference layer is formed in a thickness of 780 Å, a GdCo layer which is an auxiliary layer is formed, a GdFeCo layer which is a reproducing layer 1 is formed, and a TbFeCo layer which is a recording layer is formed. Then, a SiN layer as a protective layer is formed to a thickness of 700 angstroms.
A laminated film having the structure of (b) was obtained.

At the time of forming the SiN layer, in addition to Ar gas, N ₂
A gas was introduced, and a film was formed by direct current reactive sputtering of a Si target. The GdFeCo layer and the TbFeCo layer are G
A DC power was applied to each target of d, Fe, Co, and Tb to form a film.

The thickness of the GdCoAl auxiliary layer was 30 Å, and the composition was set to be RE rich from room temperature to the Curie temperature and the Curie temperature around 130 ° C.

The thickness of the GdFeCo reproducing layer was 400 Å, and the composition was set so that the compensation temperature was 270 ° C. and the Curie temperature was 350 ° C. or higher.

The thickness of the TbFeCo recording layer was 300 Å, the composition was TM rich at room temperature, the compensation temperature was below room temperature, and the Curie temperature was 200 ° C.

The results are shown in Table 1.

(Experimental Example 4) Similar to Experimental Examples 1 and 2, a magneto-optical recording medium was prepared by forming a thin film on polycarbonate and evaluated under the same conditions.

A SiN layer which is an interference layer is formed in a thickness of 780 Å, a GdCo layer which is an auxiliary layer is formed, a GdFeCo layer which is a reproducing layer 1 is formed, and a DyFeCo layer which is a recording layer is formed. Then, a SiN layer as a protective layer is formed to a thickness of 700 angstroms.
A laminated film having the structure of (b) was obtained.

At the time of forming the SiN layer, in addition to Ar gas, N ₂
A gas was introduced, and a film was formed by direct current reactive sputtering of a Si target. The GdFeCo layer and the TbFeCo layer are G
A DC power was applied to each target of d, Fe, Co, and Tb to form a film.

The film thickness of the GdCoSi auxiliary layer was 40 Å, and the composition was set to be RE rich from room temperature to the Curie temperature, and the Curie temperature was around 160 ° C.

The thickness of the GdFeCo reproducing layer was 400 Å, and the composition was set so that the compensation temperature was 260 ° C. and the Curie temperature was 350 ° C. or higher.

The thickness of the TbFeCo recording layer was 400 Å, the composition was set to be TM rich at room temperature, the compensation temperature was below room temperature, and the Curie temperature was 200 ° C.

The results are shown in Table 1.

(Experimental Example 5) A magneto-optical recording medium was prepared by forming a thin film on polycarbonate in the same manner as in Experimental Examples 1 and 2, and evaluated under the same conditions.

A SiN layer which is an interference layer is formed in a thickness of 780 Å, a GdFeCo layer which is an auxiliary layer is formed, and then a GdFeCo layer which is a reproducing layer 1 is formed.
A TbFeCo layer that is a recording layer is formed, and then a SiN layer is formed as a protective layer at 700 angstroms.
A laminated film having the structure of (b) was obtained.

At the time of forming the SiN layer, N ₂ is added in addition to Ar gas.
A gas was introduced, and a film was formed by direct current reactive sputtering of a Si target. The GdFeCo layer and the TbFeCo layer are G
A DC power was applied to each target of d, Fe, Co, and Tb to form a film.

The film thickness of the GdFeCo auxiliary layer was 40 Å, and the composition was set to be RE rich from room temperature to the Curie temperature and the Curie temperature around 160 ° C.

The thickness of the GdFeCo reproducing layer was 400 Å, and the composition was set so that the compensation temperature was 220 ° C. and the Curie temperature was 350 ° C. or higher.

The film thickness of the TbFeCo recording layer was 400 Å, the composition was set to be TM rich at room temperature, the compensation temperature was below room temperature, and the Curie temperature was 240 ° C.

The results are shown in Table 1.

COMPARATIVE EXPERIMENTAL EXAMPLE 1 A magneto-optical recording medium was prepared by forming a thin film on a polycarbonate in the same manner with the same film-forming machine and film-forming method except that the auxiliary layer of Experimental Example 1 was deleted. , And evaluated under the same conditions.

The results are shown in FIG. 5 (b). From these, the method of the present invention suppresses the occurrence of θ _K at room temperature as compared with the comparative example, and the rise of θ _K at the time of temperature rise becomes sharp,
An improvement in the super-resolution detection effect can be seen.

(Comparative Experimental Example 2) Next, using the magneto-optical recording medium described in Comparative Experimental Example 1, recording / reproducing characteristics were measured in the same manner as in Comparative Experimental Example 1. The results are shown in Table 1.

[0074]

According to the magneto-optical recording method of the present invention, a simple device (conventional device) that does not require an initialization magnet can be used.
It became possible to reproduce by enlarging a magnetic domain smaller than the beam spot diameter, and it became possible to achieve high density recording with further improved linear recording density and track density.

[Brief description of drawings]

1A and 1B are schematic views showing a film structure of the present invention.

FIG. 2 is an explanatory diagram showing a magneto-optical reproducing method of the present invention.

FIG. 3 is a diagram showing a magnetized state after recording on an example of the magneto-optical recording medium of the present invention.

FIG. 4 is a demagnetizing field energy 2πMs ² and a perpendicular magnetic anisotropy energy K of the second magnetic layer of the magneto-optical recording medium of the present invention.
It is the figure which showed the temperature change of u.

FIG. 5A is a residual θ _{K of the} magneto-optical recording medium of the present invention.
It is the figure which showed the temperature dependence of (magnetic field 0). (B) is
FIG. 7 is a diagram showing the temperature dependence of residual θ _K (magnetic field 0) of the magneto-optical recording medium of the comparative example.

[Explanation of symbols]

 1 substrate 2 dielectric layer 3 first magnetic layer 4 second magnetic layer 5 third magnetic layer 6 dielectric layer

Claims (2)

[Claims] 1. A first magnetic layer formed of an in-plane magnetized film, and a second magnetic layer which is an in-plane magnetized film having a Curie temperature higher than that of the first layer at room temperature and which becomes a perpendicular magnetized film when heated. A magneto-optical recording medium having at least a third magnetic layer made of a perpendicularly magnetized film. 2. The magneto-optical recording medium according to claim 1, wherein the magnetic signal recorded in the third magnetic layer is transferred to the second magnetic layer while being converted into an optical signal by the magneto-optical effect and read. And a signal reproducing method in a magneto-optical recording medium.