JPH06274958A - Magneto-optical recording medium, method for recording and reproducing information using the medium - Google Patents

Abstract

PURPOSE:To prevent formation of crescent-shape recording pits and to improve S/N for reproducing by constituting the medium to have a magnetic layer which is an intra-plane magnetization film at room temp. but changes into a perpendicular magnetization film by heating, a magnetic. layer which is always a perpendicular magnetization film, and a thermally conductive layer. CONSTITUTION:This magneto-optical recording medium consists of at least a reproducing layer 3, recording layer 4, and thermally conductive layer 6 which well transfers heat and is directly or indirectly deposited on the recording layer 4. The reproducing layer 3 is an intra-plane magnetization film at room temp. but changes into a perpendicular magnetization film when heated. The recording layer 4 is a perpendicular magnetization film both at room temp. and higher temp. The reproducing layer is, for example, a rare earth-iron group amorphous alloy preferably. More preferably, a material having small anisotropy and compensation temp. between the room temp. and Curie temp. is used. The recording layer 4 is preferably such a material having large perpendicular magnetic anisotropy such as rare earth-iron group amorphous alloy, garnet, platinum group-iron group periodical structure film, and platinum group-iron group alloy. The thermally conductive layer 6 is preferably Al, A/Nx, AlTa, AlTi, AlCr Cu, etc.

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 an information recording / reproducing method using the medium.
In particular, the present invention relates to a magneto-optical recording medium capable of improving the linear recording density and the track density to increase the density of the medium and a method of recording or reproducing information using the medium.

[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 which becomes the detection limit is determined to be 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 like the bit period.

Therefore, in order to realize high density in the conventional optical disc, the laser wavelength of the reproducing optical system is shortened,
It is necessary to 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 Laid-Open Patent Publication No. 3-93058, a medium composed of a reproducing layer and a recording layer is used, and the magnetization direction of the reproducing layer is aligned in one direction before reproducing information, and then the information is held in the recording layer. Information is transferred to the reproducing layer to reduce intersymbol interference at the time of reproducing, information of a period below the diffraction limit of light can be reproduced, and an attempt is made to improve linear recording density and track density.

[0010]

[Patent Document 1] Japanese Unexamined Patent Application Publication No.
In the magneto-optical information reproducing method described in -93058, the magnetization of the reproducing layer must be aligned in one direction before being irradiated with the laser beam. 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 / reproducing apparatus becomes complicated, the cost becomes high, and it is difficult to reduce the size.

When performing magnetic field modulation recording on the magneto-optical recording medium described in JP-A-3-93058, the recording layer is heated to a Curie temperature or a compensation temperature or higher by a laser beam and recorded information is recorded in this state. Accordingly, the external magnetic field is applied while reversing the polarity. The shape of the recording pit formed by this magnetic field modulation recording is as shown in FIG.
As shown in (b), it is on a circular arc having a steep curve that bulges and bulges in the transfer direction of the recording medium, or a crescent shape.

This is due to the heat storage effect due to the relatively low thermal conductivity of the magnetic layer including the reproducing layer and the recording layer. That is, as shown in FIG. 4A, the isothermal distribution near the laser beam irradiation position is an elliptical distribution having a major axis in the direction of travel of the laser beam, and the rear end of the laser beam Since the temperature becomes high at the end portion, the distribution thereof has a steep curvature on the rear end portion side, and the recording pit shape also exhibits a steep curved shape, that is, a crescent shape.

When such a shape of the recording pit becomes a prominent crescent shape, as shown in FIG. 6, in addition to one recording pit in the high temperature area which is a reproducible area of the reproducing laser beam, And the tails of both ends of the recording pit of the other side adjacent to come in and the S / N (C /
N) is brought about. That is, the original improvement in resolution is hindered.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to reduce the size of an apparatus and to record a recording pit even if information is recorded using a magnetic field modulation recording system. (EN) Provided are a magneto-optical recording medium capable of improving resolution at the time of reproducing information, that is, improving S / N (C / N), and an information recording method and a reproducing method using the medium, without forming a remarkable crescent moon shape. To aim.

The above object is to provide an in-plane magnetized film at room temperature, a first magnetic layer which becomes a perpendicular magnetized film when the temperature is raised, a room temperature, and a second magnetic layer which is a perpendicular magnetized film when the temperature is raised and a heat conduction layer. It is achieved by the magneto-optical recording medium having.

Further, a magneto-optical recording having an in-plane magnetized film at room temperature, a first magnetic layer which becomes a perpendicular magnetized film when the temperature is raised, a second magnetic layer which is a perpendicular magnetized film when the temperature is raised, and a heat conduction layer. This is achieved by applying an external magnetic field modulated according to information while irradiating the medium with a light spot, and recording information only in a temperature rising region in the light spot of the second magnetic layer.

Further, a magneto-optical recording having an in-plane magnetized film at room temperature, which has a first magnetic layer which becomes a perpendicular magnetized film when heated, and a second magnetic layer which is a perpendicular magnetized film when heated, and a heat conduction layer. The medium is irradiated with a light spot, the first magnetic layer is made to be a perpendicular magnetization film only in a temperature rising region in the light spot, the first magnetic layer and the second magnetic layer are exchange-coupled, and the second magnetic layer is formed. Information is reproduced by aligning the magnetization of the first magnetic layer in a direction that is stable with respect to the magnetization direction based on the above information, and magneto-optically changing the reflected light of the light spot due to the influence of the perpendicularly magnetized film portion of the first magnetic layer. It is achieved by performing.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The magneto-optical recording medium, information recording method and information reproducing method of the present invention will be described in detail below with reference to the drawings.

The magneto-optical recording medium of the present invention is shown in FIG.
As shown in a schematic cross-sectional view of an example thereof in (b), a reproducing layer (first magnetic layer) which is an in-plane magnetized film at least at room temperature and becomes a perpendicularly magnetized film when heated, and a perpendicularly magnetized film when heated to room temperature. A recording layer (second magnetic layer) and a heat conductor layer which is directly or indirectly laminated on the recording layer and which propagates heat well.

As the reproducing layer, for example, a rare earth-iron group amorphous alloy such as GdCo, GdFeCo, GdTbFeCo, GdDyFeCo, NdGd.
FeCo or the like is preferable. It is preferable that the magnetic anisotropy is small and the compensation temperature is between room temperature and the Curie temperature.

The recording layer has a large perpendicular magnetic anisotropy, for example, a rare earth-iron group amorphous alloy such as Tb.
FeCo, DyFeCo, TbDyFeCo, etc., or garnet, or platinum group-iron group periodic structure film, for example, Pt / Co, Pd / Co
Platinum group-iron group alloys such as PtCo and PdCo are desirable.

The reproducing layer and the recording layer are made of Cr, Al, Ti, Pt, Nb.
It is also possible to add elements for improving corrosion resistance such as.

The heat conductor layer is made of Al, AlNx, AlTa, AlTi, Al.
Cr, Cu and the like are preferable. Further, as shown in FIG. 1A, a dielectric layer may be provided between the heat conductor layer and the recording layer. As this dielectric layer, SiNx, AlNx, AlOx, TaOx, SiOx
And so on.

The information recording and reproducing method of the present invention will be described below.

First, an information signal is recorded on the recording layer of the magneto-optical recording medium of the present invention. Recording is performed by modulating the external magnetic field while irradiating a laser beam with a power that causes the recording layer to have a Curie temperature or higher. At this time, since the thermal conductor layer is provided according to the above-described magneto-optical recording medium of the present invention,
Due to the heat radiation effect, the isothermal distribution curve is shown in FIG.
As shown in (a), since it is an isotropic and almost perfect circular curve, it is possible to prevent the recording pit shape from becoming a sharp curved shape, that is, a crescent shape.

Therefore, the recording pit formed by the magnetic field modulation recording has a gently curved shape as shown in FIG. 3 (b).

Next, at the time of reproducing information, the medium is irradiated with a reproducing laser beam. At this time, the temperature of the irradiated portion rises and has a temperature distribution as shown in FIG. 3 (a). in this case,
The highest temperature is near the center of the light spot.

With respect to a single-layer magnetic thin film, when the saturation magnetization is M _S and the perpendicular magnetic anisotropy constant is Ku, the effective perpendicular magnetic anisotropy constant K defined by K⊥ = Ku-2πM _S ² It is known that ⊥ determines the main direction of magnetization. Here, 2πM _s ² is the demagnetizing energy.

If a reproducing layer having a compensation temperature between room temperature and the Curie temperature is used, at room temperature, M
_{Although S} is large and K⊥ <0, it is an in-plane magnetized film, but since the temperature rises during reproduction, 2πM _S ² suddenly becomes small and the magnitude relationship with Ku is reversed, and K⊥> 0 and in-plane magnetized film is obtained. Can be (Ku also decreases slightly as the temperature rises, but the decrease rate is generally small compared to 2πMs ^2. )

That is, the saturation magnetization M _{S of the} reproducing layer is taken into consideration in consideration of the intensity and linear velocity of the laser beam during reproduction so that the magnetization of the reproducing layer becomes a perpendicularly magnetized film only in the high temperature portion which is a part of the light spot. If the perpendicular magnetic anisotropy constant Ku is set,
Only the high temperature part in the light spot becomes the perpendicular magnetization film, and the other part becomes the in-plane magnetization film. Since the reproducing layer, which is a perpendicularly magnetized film, is magnetically coupled to the recording layer by exchange coupling, the magnetization direction of the reproducing layer is aligned with the magnetization direction based on the information of the recording layer. That is, the information recorded in the recording layer is transferred to the reproducing layer. Then, the transferred information is converted into an optical signal and detected by the magneto-optical effect of the reproducing layer (specifically, the magneto-optical effect of the laser beam reflected from the reproducing layer). In this case, the magneto-optical effect does not occur in the portion where the reproducing layer in the light spot is the in-plane magnetized film.

As described above, in the information reproducing method using the magneto-optical recording medium of the present invention, even when the bit period is smaller than the beam diameter of the laser beam without requiring an initializing magnetic field, the intersymbol Interference is suppressed, and information can be reproduced with high C / N.

When the recording pits recorded on this magneto-optical recording medium are read by a reproducing laser beam, as shown in FIG. 5, for example, reproduction of a laser beam spot for reading (reproducing) by laser light is performed. It is possible to allow only one originally recorded bit to be read out in a possible window area, and to prevent the end of another adjacent recorded bit from entering.

Therefore, it is possible to improve the S / N (C / N) and eventually the reproduction resolution.

[Experimental Example 1] Each target of Si, Tb, Gd, Fe, Co, and Al was attached to a DC magnetron sputtering apparatus, a polycarbonate substrate with a pre-groove of φ130 mm was fixed to a substrate holder, and then 1 × 10. ^The interior of the chamber was evacuated with a cryopump until a high vacuum of ^-5 Pa or less was obtained.

Ar gas is supplied to 0.4 Pa while evacuating.
After being introduced into the chamber until
An iN layer of 800 Å was formed, and then a reproduction layer of GdFe was formed.
Co layer of 400 Å is formed, and then TbFe which is a recording layer is formed.
Co layer of 400Å is deposited, then SiN layer of 300Å is deposited as an interference layer, and AlCr layer of 600 is deposited as a heat conduction layer.
A film was formed to obtain a magneto-optical recording medium having the structure shown in FIG.

When the SiN layer is formed, N ₂ is added in addition to Ar gas.
A gas was introduced, and a film was formed by DC reactive sputtering. G
The dFeCo layer and the TbFeCo layer are composed of Gd, Fe, Co,
A DC power was applied to each target of Tb to form a film.

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

The composition of the TbFeCo recording layer is TM at room temperature.
Rich (compensation temperature is below room temperature) and Curie temperature is 210
The temperature was set to be ° C.

Next, the recording / reproducing characteristics were measured using this magneto-optical recording medium.

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 ± 200O
e.

The results are shown in Table 1. Playback power is C
The value was set so that the / N ratio was max.

[Experimental Example 2] Each target of Si, Tb, Gd, Fe, Co and Al was attached to a DC magnetron sputtering apparatus, and a polycarbonate substrate having a pre-groove of 130 mm in diameter was fixed to a substrate holder and then 1 × 10. ^The interior of the chamber was evacuated with a cryopump until a high vacuum of ^-5 Pa or less was obtained.

Ar gas was supplied at 0.4 Pa while evacuation was performed.
After being introduced into the chamber until
An iN layer of 800 Å was formed, and then a reproduction layer of GdFe was formed.
Co layer of 400 Å is formed, and then TbFe which is a recording layer is formed.
Co layer of 400Å is formed, and then AlC is used as a heat conduction layer
An r layer of 600 Å was formed to obtain a magneto-optical recording medium having the structure shown in FIG.

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 DC reactive sputtering. G
The dFeCo layer and the TbFeCo layer are composed of Gd, Fe, Co,
A DC power was applied to each target of Tb to form a film.

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

The composition of the TbFeCo recording layer is TM at room temperature.
Rich (compensation temperature is below room temperature) and Curie temperature is 220
The temperature was set to be ° C.

Next, the recording / reproducing characteristics were measured using this magneto-optical recording medium.

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 ± 180O
e.

The results are shown in Table 1. Playback power is C /
The N ratio was set to a value that maximized.

[Comparative Experimental Example] Si, Tb, Gd, Fe, Co, and Al targets were attached to a DC magnetron sputtering apparatus, and a polycarbonate substrate having a pre-groove of 130 mm in diameter was fixed to a substrate holder, and then 1 × 10. ^The interior of the chamber was evacuated with a cryopump until a high vacuum of ^-5 Pa or less was obtained.

Ar gas was supplied at 0.4 Pa while evacuation was performed.
After being introduced into the chamber until
An iN layer of 800 Å was formed, and then a reproduction layer of GdFe was formed.
Co layer of 400 Å is formed, and then TbFe which is a recording layer is formed.
A Co layer of 400 Å was formed, and then a SiN layer of 300 Å was formed as a protective layer to obtain a magneto-optical recording medium having the structure of FIG.

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 DC reactive sputtering. G
The dFeCo layer and the TbFeCo layer are composed of Gd, Fe, Co,
A DC power was applied to each target of Tb to form a film.

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

The composition of the TbFeCo recording layer was TM at room temperature.
Rich (compensation temperature is below room temperature) and Curie temperature is 220
The temperature was set to be ° C.

Next, using this magneto-optical recording medium, 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 ± 180O
e.

The results are shown in Table 1. Playback power is C /
The N ratio was set to a value that maximized.

[0058]

[Table 1]

[0059]

By using the magneto-optical recording medium and the information recording method and reproducing method of the medium of the present invention, it is possible to reproduce a magnetic domain smaller than the laser beam spot diameter by using a simple device which does not require an initializing magnet. Therefore, it is possible to achieve high density recording with further improved linear recording density, and C / N is improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a film structure of a magneto-optical recording medium of the present invention.

FIG. 2 is a schematic diagram showing another film configuration of the magneto-optical recording medium of the present invention.

3A is a diagram showing isotherms during recording in the magneto-optical recording medium of the present invention. FIG. 3B is a diagram showing recording pit patterns in the magneto-optical recording medium of the present invention.

FIG. 4A is a diagram showing an isotherm at the time of recording in a conventional magneto-optical recording medium. FIG. 4B is a diagram showing a pattern of recording pits in the conventional magneto-optical recording medium.

FIG. 5 is a diagram showing a relationship between recording pits formed on a magneto-optical recording medium of the present invention and a reproducible area of a laser beam.

FIG. 6 is a diagram showing a relationship between recording pits formed on a conventional magneto-optical recording medium and a reproducible area of a laser beam.

Claims (3)

[Claims] 1. An in-plane magnetized film at room temperature, which comprises a first magnetic layer which becomes a perpendicular magnetized film when the temperature is raised, a room temperature, a second magnetic layer which is made of a perpendicular magnetized film when the temperature is raised, and a heat conduction layer. And a magneto-optical recording medium. 2. A magneto-optical recording comprising an in-plane magnetized film at room temperature, a first magnetic layer which becomes a perpendicular magnetized film when heated, and a second magnetic layer which is a perpendicular magnetized film when heated, and a heat conduction layer. Information is recorded only in a temperature rising region in the light spot of the second magnetic layer by applying an external magnetic field modulated according to information while irradiating the medium with a light spot. Information recording method for magnetic recording medium. 3. A magneto-optical recording comprising an in-plane magnetized film at room temperature, a first magnetic layer which becomes a perpendicular magnetized film when heated, and a second magnetic layer which is a perpendicular magnetized film when heated, and a heat conductive layer. The medium is irradiated with a light spot, and the first magnetic layer is formed as a perpendicular magnetization film only in the temperature rising region in the light spot and the first magnetic layer is formed.
The magnetic layer and the second magnetic layer are exchange-coupled with each other, and the first magnetic layer is oriented in a stable direction with respect to the magnetization direction based on the information of the second magnetic layer.
An information reproducing method for a magneto-optical recording medium, characterized in that the magnetizations of the magnetic layers are aligned and information is reproduced by magneto-optical change of reflected light of the light spot under the influence of the perpendicularly magnetized film portion of the first magnetic layer.