JPH0714230A - Magneto-optical recording medium and its reproduction method - Google Patents

Abstract

PURPOSE:To stabilize the movement of a magneto-optical recording medium which information is recorded on and reproduced from by using such light beam as laser beam, etc., at the time of reproduction with a simple structure. CONSTITUTION:A magneto-optical recording medium has a reproducing layer 2, intermediate layer 3, and recording layer 4 which are magnetically coupled with each other and the intermediate layer 3 is an intrasurface magnetized film at a room temperature, and, the compensation temperature of the layer 3 is higher than the temperature at which the pattern of magnetization of the layer 4 starts to be transferred to the layer 2 and the Curie temperature of the layer 3 is such a temperature that the magnetization of the layer 3 disappears by the temperature rise at the time of reproduction. Therefore, the number of the layers constituting the magneto-optical medium can be reduced and the exchanging connecting force between the layers can be easily controlled as compared with the conventional medium. Moreover, When the compensation and Curie temperature of the layer 3 are adjusted, the movement of the medium can be stabilized at the time of reproduction.

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 using light such as laser light and a reproducing method thereof.

[0002]

2. Description of the Related Art With the rapid increase in the amount of information processing in an information processing system, a recording medium having a large recording capacity, especially a magneto-optical recording medium, has been attracting attention.

In recording on a magneto-optical recording medium, the temperature of the recording film is locally heated to a Curie temperature or higher by laser light irradiation, and the recording film in the irradiated portion is magnetized in the direction of the external magnetic field to form a recording magnetic domain. (Thermomagnetic recording). The reproduction of the recording signal is performed by irradiating a laser beam having a power lower than the laser power at the time of recording and erasing, and the polarization plane of the reflected light or the transmitted light rotates depending on the recording state of the recording film (direction of magnetization of recording magnetic domain). (Magneto-optical effect) It is performed by detecting the situation.

When the recording magnetic domain becomes smaller than the spot diameter of the reproducing light, the recording magnetic domains before and after the recording magnetic domain to be reproduced are also included in the detecting range of the reproducing light, and the reproduction signal becomes small due to interference from them, so that S There is a problem that / N decreases. As a solution to this problem, when the recorded domain is sufficiently smaller than the spot diameter of the laser light, two or more domains are included in the spot of the laser light, so that the C / N at the time of reproduction is deteriorated. There is a method of reproducing only one of the domains in the laser light spot (for example, Nikkei Electronics 1991.
10.28 (No. 539)).

A conventional magneto-optical recording medium will be described below. As shown in FIG. 6, the magneto-optical recording medium has a reproducing layer 2
1, a reproduction auxiliary layer 22, an intermediate layer 23, and a recording layer 24 are composed of four exchange-coupled layers.

The exchange coupling force between the reproduction layer 21 and the reproduction auxiliary layer 22 is H1-2, and the exchange coupling force between the reproduction auxiliary layer 22 and the recording layer 24 acting through the intermediate layer 23 is H2-4. Since the intermediate layer 23 is an in-plane magnetized film, H2-4 becomes smaller than the exchange coupling force when the reproduction auxiliary layer 22 and the recording layer 24 are directly laminated.

The reproducing layer 21 is made of GdFeC having a low coercive force Hc1.
The perpendicular magnetization film made of o film has Hc1 of about 50 to 100 Oe.
The auxiliary reproduction layer 22 is made of Tb having a low Curie temperature Tc.
Perpendicular magnetic film made of FeCo film with Tc of 130 to 160 ° C
Then, the coercive force Hc2 is set to 4 kOe or less. The intermediate layer 23 for controlling the exchange coupling force at room temperature is made of a GdFeCo film, the recording layer 24 is a perpendicular magnetization film made of a TbFeCo film having a high coercive force Hc4, and Hc4 is 10 kOe or more.

In the figure, 25 is an initializing magnetic field Hi, 26 is a reproducing magnetic field Hr, 27 is reproducing light, and 28 is a recording magnetic domain.

The reproducing operation of the magneto-optical recording medium having the above structure will be described below.

Information is previously thermomagnetically recorded on a magneto-optical recording medium, and a method of reproducing the recorded recording domain will be described.

First, the reproduction layer 21 and the reproduction auxiliary layer 22 are initialized. That is, the magnetizations of the reproducing layer 21 and the recording layer 24 are oriented in the direction of the initializing magnetic field Hi25. As a result, the recording magnetic domain 28 of the reproducing layer 21 disappears. The conditions for this are Hi> Hc1 + H1-2 for the reproduction layer 21, and Hi> Hc2 + H2-4-H for the reproduction auxiliary layer 22.
1-2. The composition and film forming conditions are set so as to satisfy this condition.

In order to maintain the state of uniform magnetization, Hc2> H2-4-H1-2 is set to be satisfied. The recording magnetic domain 28 of the reproducing layer 21 becomes an erasing magnetic domain 29.

Next, the reproducing light 27 is irradiated. During playback,
The reproduction layer 21 and the reproduction auxiliary layer 2 are irradiated by the reproduction light 27.
The temperature of the portion 30a of 2 is equal to or higher than the temperature Td1 and is equal to the temperature Td2.
When the temperature rises below, the magnetization of the recording layer 24 is changed to the reproducing layer 21.
And the reproduction assisting layer 22. H2-4 + Hr> Hc2 +
When it is set to satisfy H1-2, the magnetization of the recording layer 24 is transferred to the reproduction assisting layer 22. Further, since the coercive force Hc1 of the reproducing layer 21 is originally small, the magnetization of the reproducing layer 21 is aligned with the direction of the reproducing auxiliary layer 22 by setting H1-2> Hc1.

The portion 30b of the reproducing layer 21 and the reproducing auxiliary layer 22 rises to a temperature Td2 higher than the Curie temperature Tc, but since Tc <Td2, the magnetization of the reproducing auxiliary layer 22 disappears (reproducing auxiliary layer 22). Part of the layer 22b) H2-4 is zero. At this time, the reproducing magnetic field Hr is set so that Hr> Hc1. Therefore, the magnetization of the reproducing layer 21 is aligned in the direction of the reproducing magnetic field Hr.

Therefore, the stored information can be read out as a reproduction signal only from a portion of the spot of the reproduction light 27 having a temperature of Td1 or more and Td2 or less. This is reproduction light 2
The recording magnetic domain 28 smaller than the spot size of 7 can be reproduced without waveform interference from the recording magnetic domains 28 before and after.

[0016]

However, in the above-mentioned conventional structure, the structure of the magneto-optical recording medium has four layers, which is complicated and difficult to control between the layers, and the composition, film thickness and film forming conditions are slightly changed. However, the exchange coupling force changes and the operating conditions for regeneration fluctuate, and stable regeneration becomes impossible and operation cannot be performed. Also, since four layers must be formed, it takes time and effort to form the film, which is low. It had a problem that the cost could not be reduced.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a magneto-optical recording medium having a simple structure capable of stable reproducing operation and a reproducing method thereof.

[0018]

In order to achieve this object, a magneto-optical recording medium and a reproducing method thereof according to the present invention have a magnetically coupled recording layer, an intermediate layer and a reproducing layer, and the intermediate layer is It is an in-plane magnetized film at room temperature, and the compensation temperature of the intermediate layer is higher than the temperature at which the magnetization of the recording layer starts transferring to the reproducing layer, and the Curie temperature of the intermediate layer is The structure is such that the temperature is at a loss, and a part of the intermediate layer of the magneto-optical recording medium reaches the Curie temperature of the intermediate layer, and a part of the temperature of the intermediate layer is equal to the compensation temperature and the Curie temperature of the intermediate layer. This is a method of reproducing with a laser beam having an intensity so as to be in the range.

[0019]

In this structure and method, when the Curie temperature of the intermediate layer is lowered to approach the temperature that rises during reproduction, a region having a Curie temperature or higher is generated during reproduction, so that the magnetization disappears in that region. The exchange coupling force between the recording layer and the reproducing layer does not work.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, the magneto-optical recording medium has a reproducing layer 2 made of a GdTbFeCo film having a Curie temperature Tc1 and a coercive force Hc1 formed on a substrate 1 made of polycarbonate, and a surface at room temperature. Curie temperature T in the inner magnetized film
Intermediate layer 3 made of GdFeCo film having c2 and compensation temperature Tcomp, and TbFe having Curie temperature Tc3 and coercive force Hc3
Recording layer 4 made of Co film and protective layers 5a, 5b made of silicon nitride
The reproducing layer 2 and the recording layer 4 are exchange-coupled via the intermediate layer 3. Each layer is formed by a sputtering method or a vacuum evaporation method, and the thickness of each layer is 40 n
m, the intermediate layer 3 was set to 1 to 10 nm, and the recording layer 4 was set to 50 nm. Curie temperature Tc1 is about 300 ° C,
c2 is 200 ° C., Tc3 is about 300 ° C., coercive force is Hc1 of 1.5 to 2 kOe and Hc3 is rare earth dominant (RE-r at room temperature).
ich) It was set to 5 kOe. The compensation temperature Tcomp of the intermediate layer 3 is about 150 ° C.

In the figure, 6 is an initializing magnetic field Hi, 7 is a reproducing magnetic field Hr, 8 is reproducing light (including a shaded portion), 9 is a recording magnetic domain, 1
0 indicates a recording magnetic domain which disappeared by the initializing magnetic field.

The operation of the magneto-optical recording medium having the above structure will be described below. Information is thermomagnetically recorded on the recording layer 4 as a recording magnetic domain 9 under a recording magnetic field (about 300 Oe). At room temperature, the recording magnetic domain 9 from the recording layer 4 to the reproducing layer 2 is suppressed by the exchange coupling suppressing action of the intermediate layer 3.
The transfer force of, that is, the exchange coupling force H1-3 is weakened. That is, since the magnetization of the intermediate layer 3 is thin, the magnetization is oriented in the vertical direction due to the exchange coupling force from the recording layer 4 and the reproduction layer 2, but the magnetization originally intended to be in-plane is forced to be oriented in the vertical direction. For that, power is taken there.
For this reason, the exchange coupling force between the recording layer 4 and the reproducing layer 2 is weaker than when the recording layer 4 and the reproducing layer 2 which are perpendicularly magnetized films are directly laminated. As can be seen from the exchange coupling force shown in FIG. 3 based on the exchange coupling force when the thickness of the intermediate layer 3 is zero, the intermediate layer 3
When the thickness is 3 nm, the exchange coupling force can be reduced to about 60% of that when the intermediate layer 3 is not inserted. The exchange coupling force between the reproducing layer 2 and the recording layer 4 without the intermediate layer 3 is about 1.5.
Since it is kOe, when the thickness of the intermediate layer 3 is 3 nm, H1-3
Can be reduced to about 900 Oe at room temperature, and Hc1 is 1.5 kO
If it is about e, the relationship of Hc1> H1-3 and Hc1 + H1-3 <Hi <Hc3 can be easily set even if the initialization magnetic field Hi is reduced to 3 kOe or less. Therefore, the magnetization of the reproducing layer 2 is aligned in the direction of the initializing magnetic field Hi, the recording magnetic domain 10 disappears, and the reproducing layer 2 does not exist. During reproduction, when the temperature of the portion 2a of the reproducing layer 2 rises to about 150 ° C. or more due to the irradiation of the reproducing light 8, the temperature becomes close to the compensation temperature (150 ° C.) of the intermediate layer 3, and the demagnetizing field is greatly reduced due to the decrease in magnetization. (The magnetization is zero and the demagnetizing field is zero.) The effect of suppressing the exchange coupling is reduced and the exchange coupling force H1-3 is increased to about 0.5 kOe, so that Hc1 <H1-3 + Hr, H3-1 + Hr < The relationship of Hc3 can be easily established. Therefore, the magnetization of the portion 2a of the reproducing layer 2 is aligned with the magnetization direction of the recording layer 4, so that the recording layer 4
The recording magnetic domain 9 is transferred to the reproducing layer 2.

Further, in the portion 2b of the reproducing layer 2, the temperature is 2
When the temperature exceeds 00 ° C and the Curie temperature Tc2 of the intermediate layer 3 is 20
Since the temperature exceeds 0 ° C., the magnetization of the part 11 of the intermediate layer 3 disappears. Therefore, the exchange coupling force H1-3 becomes zero. Therefore, the coercive force Hc1 of the reproducing layer 2 is originally small, so
c1 <Hr (reproducing magnetic field), and the reproducing layer 2 is aligned again in the direction of the reproducing magnetic field Hr in the part 2b of the reproducing layer 2. Therefore, the recording magnetic domain 9 of the recording layer 4 is formed only in the part 2a of the reproducing layer 2.
Are transferred to the reproduction layer 2.

When this magneto-optical recording medium is reproduced, the temperature of the magneto-optical recording medium rises due to the irradiation of the reproducing light 8. Since the intensity of the focused reproducing light 8 has a Gaussian distribution and the magneto-optical recording medium moves in the direction indicated by the arrow A with respect to the reproducing light 8, the temperature distribution in the reproducing light spot is the center of the reproducing light 8. The part 2a of the reproducing layer 2 is displaced from the vicinity to the rear by 15
The temperature rises from about 0 ° C. to 200 ° C., and the portion 2b of the reproduction layer 2 reaches a high temperature of 200 ° C. or higher. That is, the exchange coupling force H1-3 increases to about 0.5 kOe in a part of the reproduction light 8 where the temperature is 150 ° C. or higher and 200 ° C. or lower, and the relationship of Hc1 <H1-3 + Hr, H3-1 + Hr <Hc3 is established. Then, the magnetization of the portion 2a of the reproducing layer 2 is aligned with the magnetization direction of the recording layer 4, so that the recording magnetic domain 9 of the recording layer 4 is transferred to the reproducing layer 2.

The portion 2b having a high temperature of 200 ° C. or higher
Then, the magnetization of the intermediate layer 3 disappears (a part of the intermediate layer 1
1) The exchange coupling force H1-3 becomes zero, the reproducing magnetic field Hr becomes larger than the coercive force Hc1 of the reproducing layer 2, and the magnetization of the reproducing layer 2 is aligned in the direction of the reproducing magnetic field Hr again.

As shown in FIG. 4, at room temperature, the coercive force Hc1 of the reproducing layer 2 is 1.5 kOe and the exchange coupling force H1-3 converted into a magnetic field is 0.8 kOe. Hc1> H1-3, 3.
It can be initialized with an initializing magnetic field Hi of about 5 kOe. Both the coercive force Hc1 and the exchange coupling force H1-3 decrease as the temperature rises, and become the same value at the temperature To (about 150 ° C.). This temperature To
In the above, Hc1> H1-3, and the magnetization of the recording layer 4 is transferred to the reproducing layer 2. When the temperature further rises to Tc2, the magnetization of the intermediate layer 3 disappears and the exchange coupling force H1-3 becomes zero.

Next, a reproducing method of this magneto-optical recording medium will be described. FIG. 5 shows the reproduction output dependency of noise and the reproduction output of a magneto-optical recording medium having a recording magnetic domain 9 size of 0.4 μm, a linear velocity of 5.6 m / s, and a reproduction power of 1 to 3.5 mW. As can be seen from the above, when the reproducing power is 1 mW, the reproducing output is low, but as the reproducing power increases, the temperature of the magneto-optical recording medium also rises, and at 1.5 mW, the temperature exceeds the temperature To shown in FIG. The magnetization is transferred to the reproducing layer 2 and the output increases sharply. When the reproducing power is further increased, the Curie temperature Tc2 of the intermediate layer 3 is exceeded in a part of the region, so that the reproducing layer 2 of FIG.
The area indicated by a part 2b of 1 appears, and the output further increases. That is, when reproducing, the reproducing power of 1.5 mW becomes the temperature of the magneto-optical recording medium at which the transfer of the magnetization of the recording layer 4 to the reproducing layer 2 starts. Further, when the output is further increased, a part of the intermediate layer 3 that exceeds the Curie temperature Tc2 of the intermediate layer 3 appears.

Since the temperature of the region where the magnetization of the recording layer 4 is transferred to the reproducing layer 2 is set near the compensation temperature Tcomp of the intermediate layer 3, the magnetization of the recording layer 4 is transferred to the reproducing layer 2. Transfer becomes easy. The relationship between the reproducing power and the temperature rise temperature of the intermediate layer 3 is not uniquely determined because it changes depending on the linear velocity at which the magneto-optical recording medium moves and the structure of the magneto-optical recording medium. Therefore, the recording magnetic domain 9 is analogized from the power at which erasing is started under the condition that the external magnetic field is zero. With this erasing start power, the recording magnetic domain 9
It can be inferred that a part of has reached the Curie temperature Tc2,
If the supplied laser power and the temperature at which the recording magnetic domain 9 is heated are in a proportional relationship, the power required to raise the temperature at which the recording magnetic domain 9 is raised to the compensation temperature Tcomp of the intermediate layer 3 can be estimated.

As described above, according to this embodiment, the intermediate layer 3
When the Curie temperature Tc2 of is decreased to approach the temperature that rises during reproduction, a region having a Curie temperature Tc2 or higher is generated during reproduction, so that the magnetization disappears in that region, and the recording layer 4 and the reproduction layer 2 The exchange coupling force between them does not work. This is the role of the conventional reproduction auxiliary layer. In this embodiment, the conventional reproduction auxiliary layer is not necessary, and the exchange coupling force between the recording layer 4 and the reproduction layer 2 may be controlled. Therefore, the parameters to be controlled are reduced, stable operation can be ensured, and the cost can be reduced by reducing one regeneration assisting layer. Further, the Curie temperature and the coercive force of each magnetic layer constituting the magneto-optical recording medium can be relatively easily changed by selecting the composition and adding various elements that change the magnitude of the perpendicular magnetic anisotropy. An optimum magneto-optical recording medium can be manufactured even if the recording / reproducing conditions required for the magnetic recording medium change.

Further, in this embodiment, since the reproducing operation is performed while transferring the magnetization of the recording layer 4 to the reproducing layer 2, the maximum temperature reached by the reproducing layer 2 during reproduction is such that the magnetization of the recording layer 4 is transferred to the reproducing layer 2. Transfer occurs in a region which is higher than the starting temperature To and is higher than the temperature To and lower than the Curie temperature Tc2. Further, the compensation temperature Tcomp of the intermediate layer 3 is Tc, where To is the temperature at which the magnetization of the recording layer 4 starts transferring to the reproducing layer 2.
When omp> To is desirable and the relationship of Tc2>Tcomp> To is established, the intermediate layer 3 is in a region which is higher than the temperature To and lower than the Curie temperature Tc during the reproducing operation.
Is near the compensation temperature Tcomp. Compensation temperature Tcomp
In the vicinity, since the magnetization is small, the demagnetizing field becomes small, and a force acts in the direction of increasing the exchange coupling force, and the recording magnetic domain 9 of the recording layer 4 is easily transferred to the reproducing layer 2. Therefore, the exchange coupling force becomes strong even at the operating temperature, and the recording is performed. The transferability of the magnetic domains 9 is improved. Further, since the intermediate layer 3 is an in-plane magnetized film, the recording layer 4 is formed at room temperature.
Since the exchange coupling force of the reproducing layer 2 is weakened, the initializing magnetic field can be reduced.

Further, the composition of each magnetic film and the exchange coupling force for favorably performing the initialization operation and the transfer operation can be easily controlled, and the stability of the operation can be expanded.

Although the intermediate layer 3 is made of a GdFeCo film, the compensation temperature of the other intermediate layers 3 is Tcomp, and the recording layer 4 is made.
Of the magnetic material film satisfying the condition of To <Tcomp when the temperature at which the magnetization of the layer starts to be transferred to the reproducing layer 2 is To, and having a Curie temperature at which the magnetization is lost due to a temperature rise during reproduction. Good.

[0034]

As is apparent from the above description, the present invention has a magnetically coupled recording layer, intermediate layer and reproducing layer,
The intermediate layer is an in-plane magnetized film at room temperature, the compensation temperature of the intermediate layer is higher than the temperature at which the magnetization of the recording layer starts transferring to the reproducing layer, and the Curie temperature of the intermediate layer is the temperature rise during reproduction. The temperature is such that the magnetization is lost due to, and a part of the intermediate layer of the magneto-optical recording medium reaches the Curie temperature of the intermediate layer, and the temperature of a part of the intermediate layer is the compensation temperature of the intermediate layer. It is possible to realize a magneto-optical recording medium having a simple structure capable of stable reproducing operation and a reproducing method thereof by a reproducing method using a laser beam having an intensity that is between the Curie temperature and the Curie temperature.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a magneto-optical recording medium according to an embodiment of the present invention.

2A is a schematic plan view for explaining a reproducing operation of the magneto-optical recording medium, and FIG. 2B is a cross-sectional view of a main part of FIG.

FIG. 3 is a diagram showing a relationship between a film thickness of an intermediate layer of the magneto-optical recording medium and an exchange coupling force.

FIG. 4 is a diagram showing the temperature dependence of the exchange coupling force of the magneto-optical recording medium and the coercive force of the reproducing layer.

FIG. 5 is a diagram showing reproduction output dependence of the magneto-optical recording medium and reproduction power dependence of noise.

6A is a schematic plan view for explaining a reproducing operation of a conventional magneto-optical recording medium, and FIG. 6B is a cross-sectional view of a main part of FIG.

[Explanation of symbols]

 2 playback layer 3 intermediate layer 4 recording layer

Claims (2)

[Claims] 1. A recording layer, an intermediate layer, and a reproducing layer which are magnetically coupled to each other, and a signal is recorded in the recording layer, and the reproducing layer is aligned after the magnetization directions of the reproducing layer are aligned. A magneto-optical recording medium used in a reproducing method which is heated by irradiation of laser light and is converted into an optical signal by a magneto-optical effect while reading the magnetic signal recorded in the recording layer onto the reproducing layer, The intermediate layer is an in-plane magnetized film at room temperature, the compensation temperature of the intermediate layer is higher than the temperature at which the magnetization of the recording layer starts transferring to the reproducing layer, and the Curie temperature of the intermediate layer is A magneto-optical recording medium characterized in that the temperature is such that the magnetization is lost by the temperature rise during reproduction. 2. A magnetically coupled recording layer, an intermediate layer, and a reproducing layer, wherein the intermediate layer is an in-plane magnetized film at room temperature, and the compensation temperature of the intermediate layer is the magnetization of the recording layer. A magneto-optical recording medium having a Curie temperature higher than the temperature at which transfer is started to the reproducing layer and at a temperature at which the magnetization of the intermediate layer is lost due to a temperature increase during reproduction is used. A magneto-optical recording medium is characterized in that reproduction is performed with a laser beam having an intensity that reaches the Curie temperature and a temperature of a part of the intermediate layer is between the compensation temperature of the intermediate layer and the Curie temperature. How to play.