JPH06168494A - Magneto-optical recording medium and recording and reproducing method therefor - Google Patents

Abstract

PURPOSE:To greatly improve a recording density by executing reproduction of smaller recording pits. CONSTITUTION:A magneto-optical disk 10 has a 4-layered structure formed by exchange bonding of first to fourth magnetic layers. The first magnetic layer is a reading out layer 3 for magneto-optical signals, the second magnetic layer is an auxiliary layer 4 lower in Curie temp. than the other magnetic layers, the third magnetic layer is a transfer layer 5 which exhibits intra-surface magnetization at room temp. and shifts from the intra-surface magnetization to perpendicular magnetization with an increase in temp. and the 4th magnetic layer is a recording layer 6 holding information. Such magneto-optical disk is used. The disk is subjected to recording and reproducing by impressing a magnetic field for initialization for unifying the magnetization direction of the reading out part 3 to one direction in the parts exclusive of the parts irradiated with a laser and impressing the auxiliary magnetic field of the same direction as the direction of the magnetic field for initialization in the parts irradiate with the laser at the time of recording and reproducing. As a result, the previous recording pits in the reproducing beam 12 are masked and are no longer reproduced. The intrusion of the signals from the adjacent pits which are the cause for noise is thus prevented.

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 such as a magneto-optical disk, a magneto-optical tape, a magneto-optical card used in a magneto-optical recording / reproducing apparatus and a recording / reproducing method thereof.

[0002]

2. Description of the Related Art In recent years, optical memory devices such as magneto-optical disks have been attracting attention as high-density and large-capacity memory devices capable of rewriting information.

The recording density of the optical memory element depends on the size of the laser beam used for recording and reproducing on the recording medium. Usually, in optical recording, since the laser beam is focused to the diffraction limit by a condenser lens, its light intensity distribution becomes Gaussian distribution, and the temperature distribution on the recording medium also becomes substantially Gaussian distribution. Therefore, if it is possible to involve only the region having a certain temperature or higher in the reproduction, the recording density will be improved. Recently, a method of reproducing recorded bits smaller than the size of a laser beam using this principle has been proposed.

Now, with reference to FIG. 11, a magneto-optical disk 20 capable of reproducing a recording bit smaller than the size of the above laser beam will be described below. The magneto-optical disk 20 is mainly configured by laminating a reading layer 22 and a recording layer 23 on a substrate 21. Recording layer 23
Has a high coercive force at room temperature. Also, the readout layer 2
No. 2 has a small coercive force at room temperature. When the temperature of the reproducing portion of the read layer 22 rises, the magnetization direction is affected by the recording layer 23, and the magnetization direction matches the magnetization direction of the recording layer 23. That is, the magnetization of the recording layer 23 is transferred to the reading layer 22 by the exchange coupling force between the two layers of the reading layer 22 and the recording layer 23.

According to the above arrangement, recording is performed by the usual photothermal magnetic recording method. In order to reproduce the recorded bits, an initialization magnetic field generator 24 applies an initialization magnetic field to the read layer 22 in advance, and the magnetization direction of the read layer 22 is aligned in a predetermined direction (upward in FIG. 11). Need to be initialized. Next, the magneto-optical disk 20 is irradiated with the laser beam 31 narrowed down to the analysis limit by the condensing lens 32 to raise the temperature of the local portion of the recording layer 2.
The magnetization information of No. 3 is transferred to the read layer 22. By doing so, it is possible to reproduce the information of only the part where the temperature rises in the central part of the part irradiated with the laser beam 31. Therefore, even a recording bit smaller than the laser beam 31 can be read.

On the other hand, the need for a magneto-optical memory device capable of double-sided recording and optical modulation overwriting which facilitates multi-beam writing without the need to erase information when rewriting information is increasing year by year.

In the above light modulation overwrite, Jpn.J.Ap
As described in pl. Phys., Vol. 26 (1987) Suppl. P155-159, a magneto-optical memory element having a memory layer made of a perpendicular magnetization film and an auxiliary layer is used. The memory layer has a high coercive force and a low Curie point for holding and reading information, and the auxiliary layer has a lower coercive force and a higher Curie point than the memory layer, and the information in the memory layer is Is transferred to perform overwriting. Information is recorded or erased by utilizing the exchange coupling force acting between the memory layer and the auxiliary layer. In this case, prior to the recording of information, it is necessary to initialize the auxiliary layer by aligning the magnetization direction of the auxiliary layer in one direction by using an initialization magnetic field.

In the above-mentioned light modulation overwrite system, for example, as shown in FIG. 12, the information is rewritten by overwriting while switching the laser beam between the high level power P _H and the low level power P _L.

That is, by irradiating the laser beam of high level power P _H , the temperature of the magneto-optical memory element rises to near the Curie point of the auxiliary layer, and the magnetization direction of the auxiliary layer is reversed by the recording magnetic field. When the laser spot is removed and the memory layer is cooled to near the Curie point, the magnetization direction of the memory layer matches the magnetization direction of the auxiliary layer due to the exchange force acting on the interface between the memory layer and the auxiliary layer.

On the other hand, when the laser beam of low level power P _L is irradiated, the temperature of the magneto-optical memory element rises only up to near the Curie point of the memory layer, and the magnetization direction of the auxiliary layer is recorded. It does not reverse due to the influence of the magnetic field,
When the magnetization direction of the memory layer does not match the magnetization direction of the auxiliary layer, the magnetization of the memory layer is inverted so as to match the magnetization direction of the auxiliary layer.

Further, at the time of reproduction, a laser beam having a lower intensity (reproduction level power P _R ) than that at the time of recording is irradiated so that the information recorded in the magneto-optical memory element is reproduced by utilizing the magneto-optical effect. It has become.

[0012]

However, in the structure of the magneto-optical disk 20 having the read layer 22 and the recording layer 23 as in the above-described conventional case, the recording transferred from the recording layer 23 to the read layer 22 at the time of reproduction. Bit, laser beam 3
It will remain as it is even after 1 is transferred. Therefore, when the recording density is further increased, as shown in FIG. 13, when the laser beam 31 is moved to reproduce the next recording bit,
Since the previous recorded bit is still present in the laser beam 31, the remaining bit is also reproduced, which causes noise and deteriorates the signal quality.

Further, in the above-mentioned conventional optical modulation overwrite method for a magneto-optical recording medium, since the material having a low Curie temperature is used for the memory layer, the magneto-optical effect is reduced and the read signal level is lowered. I have a problem.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a magneto-optical recording medium capable of reproducing higher density recording bits and a recording / reproducing method thereof.

[0015]

The magneto-optical recording medium according to claim 1 of the present invention takes the following means in order to solve the above problems.

That is, a magneto-optical recording medium having a four-layer structure in which a first magnetic layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer are exchange-coupled, and the first magnetic layer is a magneto-optical signal. Of the information is read out, the second magnetic layer is an auxiliary layer having a lower Curie temperature than other magnetic layers, and the third magnetic layer exhibits in-plane magnetization at room temperature. The fourth magnetic layer is a transfer layer that shifts from in-plane magnetization to perpendicular magnetization as the temperature rises, and the fourth magnetic layer is a recording layer that holds information of a magneto-optical signal.

A magneto-optical recording medium according to a second aspect is
In order to solve the above problems, the following means are taken in the magneto-optical recording medium according to claim 1.

That is, the magnetization direction of the second magnetic layer is transferred to the first magnetic layer by the exchange coupling force between room temperature and the Curie temperature of the second magnetic layer.

A magneto-optical recording medium according to a third aspect is
In order to solve the above problems, the following means are taken in the magneto-optical recording medium according to claim 1.

That is, the temperature at which the third magnetic layer changes from in-plane magnetization to perpendicular magnetization is between room temperature and the Curie temperature of the second magnetic layer.

Further, the recording / reproducing method according to claim 4 uses the magneto-optical recording medium according to claim 1 so that the magnetization directions of the first and second magnetic layers are aligned in one direction outside the laser irradiation portion. Is applied, and an external magnetic field in the same direction as the initialization magnetic field is applied at the laser irradiation portion at the time of recording and reproducing information.

A magneto-optical recording medium according to a fifth aspect is
The following measures are taken to solve the above problems.

That is, the magneto-optical recording medium has a five-layer structure in which the first magnetic layer, the second magnetic layer, the third magnetic layer, the fourth magnetic layer, and the fifth magnetic layer are exchange-coupled, and the first magnetic layer is the same. Is a readout layer from which information of the magneto-optical signal is read out,
The second magnetic layer is an auxiliary layer having a lower Curie temperature than the other magnetic layers, and the third magnetic layer exhibits in-plane magnetization at room temperature, and changes from in-plane magnetization to perpendicular magnetization as the temperature rises. The fourth magnetic layer is a recording layer that holds information of a magneto-optical signal, and the fifth magnetic layer has a lower coercive force and a higher Curie temperature than the fourth magnetic layer. It is an initialization layer.

The magneto-optical recording medium according to claim 6 is
In order to solve the above problems, the following means are taken in the magneto-optical recording medium according to claim 5.

That is, the magnetization direction of the second magnetic layer is transferred to the first magnetic layer by the exchange coupling force between room temperature and the Curie temperature of the second magnetic layer.

The magneto-optical recording medium according to claim 7 is
In order to solve the above problems, the following means are taken in the magneto-optical recording medium according to claim 5.

That is, the temperature at which the third magnetic layer changes from in-plane magnetization to perpendicular magnetization is between room temperature and the Curie temperature of the second magnetic layer.

The magneto-optical recording medium according to claim 8 is
In order to solve the above problems, the following means are taken in the magneto-optical recording medium according to claim 5.

That is, between the fourth magnetic layer and the fifth magnetic layer, there is provided an in-plane magnetization, perpendicular magnetization, or an intermediate layer which changes to perpendicular magnetization by room temperature in-plane magnetization due to temperature rise.

Further, the recording / reproducing method according to claim 9 uses the magneto-optical recording medium according to claim 5 so that the magnetization directions of the first and second magnetic layers are aligned in one direction outside the laser irradiation portion. Is applied, and an external magnetic field in the same direction as the initialization magnetic field is applied at the laser irradiation portion at the time of recording and reproducing information.

[0031]

According to the structure of the magneto-optical recording medium described in claims 1 to 3, the magnetic layers including the read layer, the auxiliary layer, the transfer layer, and the recording layer are sequentially exchange-coupled to each other, and the magnetic layers are assisted from room temperature. During the Curie temperature of the layer, the magnetization direction of the auxiliary layer is transferred to the readout layer, and the transfer layer shifts from in-plane magnetization to perpendicular magnetization. Therefore, as in the recording / reproducing method according to claim 4, an initialization magnetic field for aligning the magnetization directions of the readout layer and the auxiliary layer in one direction is applied outside the laser irradiation section, and the initialization magnetic field is applied in the laser irradiation section. By applying an external magnetic field in the same direction at the time of recording and reproducing information, the previously recorded bit in the laser beam is masked and cannot be reproduced, and a signal from an adjacent bit which causes noise is not mixed. As a result, smaller recording bits can be reproduced, and the recording density is significantly improved.

Further, according to the structure of the magneto-optical recording medium according to claims 5 to 8, the magnetic layers including the read layer, the auxiliary layer, the transfer layer, the recording layer, the intermediate layer and the initialization layer are sequentially exchange coupled. Then, between the room temperature and the Curie temperature of the auxiliary layer, the magnetization direction of the auxiliary layer is transferred to the read layer, and the transfer layer shifts from in-plane magnetization to perpendicular magnetization. Therefore, as in the recording / reproducing method according to claim 9, an initialization magnetic field for aligning the magnetization directions of the read layer and the auxiliary layer in one direction is applied outside the laser irradiation part, and the initialization magnetic field is applied in the laser irradiation part. By applying an external magnetic field in the same direction at the time of recording and reproducing information, the previously recorded bit in the laser beam is masked and cannot be reproduced, and a signal from an adjacent bit which causes noise is not mixed. As a result, smaller recorded bits can be reproduced,
Recording density is significantly improved. Further, in the magneto-optical recording medium according to the fifth to eighth aspects, the overwrite operation is performed by irradiating the laser beam whose intensity is modulated into two levels of high and low. Moreover, since it is not necessary to use a material having a low Curie temperature for the read layer, a good reproduction performance can be obtained without a decrease in signal level.

[0033]

【Example】

[Embodiment 1] An embodiment of the present invention will be described with reference to FIGS.
The explanation is based on the following. In this example, the case where the magneto-optical recording medium is applied to a magneto-optical disk is illustrated.

As shown in FIG. 1, the magneto-optical disk 10 according to this embodiment has a substrate 1, a first transparent dielectric film 2, a read layer 3, an auxiliary layer 4, a transfer layer 5, a recording layer 6 and a second layer. The transparent dielectric film 7 and the overcoat film 8 are laminated in this order.

The read layer 3 and the auxiliary layer 4 are perpendicular magnetization films of rare earth transition metals, and are exchange-coupled to each other, so that the magnetization direction of the auxiliary layer 4 is transferred to the read layer 3. There is.

The auxiliary layer 4 has a lower coercive force than other magnetic layers and is initialized by applying an initialization magnetic field described later from outside the laser irradiation portion. Therefore, the read layer 3 is also initialized at the same time. Further, the Curie temperature of the auxiliary layer 4 is lower than that of other magnetic layers. Therefore, the auxiliary layer 4 reaches the Curie temperature due to the temperature rise accompanying the irradiation of the reproducing power.

The readout layer 3 is, for example, Dy.
_0.21 (Fe _0.8 Co _0.2 ) _0.79 is used, and the film thickness is 20
and the Curie temperature is set to 150 to 250 ° C. The auxiliary layer 4 may be, for example, D
y _0.17 Fe _0.83 is used, the film thickness is 40 nm, and the Curie temperature is set to 80 ° C to 100 ° C.

The magnetic phase diagram of the rare earth transition metal used as the transfer layer 5 is as shown in FIG. 2, and the range A showing the perpendicular magnetization is very narrow. This is because the perpendicular magnetization appears only near the compensating composition (indicated by P in the figure) in which the magnetic moments of the rare earth metal and the transition metal are balanced.

By the way, the magnetic moments of the rare earth metal and the transition metal have different temperature characteristics, and the magnetic moment of the transition metal becomes larger than that of the rare earth metal at high temperatures. Based on this, in the transfer layer 5 at room temperature, the content of the rare earth metal is set to be larger than the compensation composition.
Therefore, at room temperature, the transfer layer 5 does not exhibit perpendicular magnetization but exhibits in-plane magnetization. On the other hand, when the temperature of the portion irradiated with the laser beam rises, the magnetic moment of the transition metal is relatively increased. As it becomes larger, it comes to balance with the magnetic moment of the rare earth metal, and as a whole exhibits perpendicular magnetization.

FIGS. 3 to 6 show the relationship (hysteresis characteristic) between the externally applied magnetic field H _ex applied to the transfer layer 5 and the magnetic Kerr rotation angle θ _k . Magnetic properties up to ₁ , magnetic properties from temperature T ₁ to temperature T ₂ , magnetic properties from temperature T ₂ to temperature T ₃ , and magnetic properties from temperature T ₃ to Curie temperature T _c are shown.

In the range from the temperature T ₁ to the temperature T ₂ , the hysteresis characteristic with a sharp rise is shown, but in the range from the room temperature to the temperature T ₁ and from the temperature T ₃ to the Curie temperature T _c , the hysteresis characteristic is shown respectively. It turns out that it does not show.

In the present embodiment, for example, Gd _0.28 (Fe _0.8 Co _0.2 ) _0.72 is used as the transfer layer 5, and the film thickness is 50 nm. The Curie temperature is about 300 to 400 ° C. For the above reason, the content of the rare earth metal is set to be higher than the compensating composition at room temperature so that the compensating composition is achieved (transition from in-plane magnetization to perpendicular magnetization) at around 70 ° C.

The recording layer 6 is a rare earth transition metal perpendicular magnetization film, for example, Dy _0.23 (Fe _0.82 Co _0.18 ) _0.77 is used, and the film thickness is 20 nm. The Curie temperature is set to 150 ° C to 250 ° C.

The first transparent dielectric film 2 is made of Al N, S, for example.
It is made of a dielectric film such as iN or AlSiN, and its film thickness is set to a value about 1/4 of the wavelength of the reproduction light divided by the refractive index. For example, when the wavelength of the reproduction light is 780 nm, the film thickness of the transparent dielectric film 2 is about 10 nm to 80 nm. The second transparent dielectric film 7 is a protective film made of nitride and has a film thickness of 50 nm.

In the above structure, the present magneto-optical disk 1
The recording of 0 is performed by a usual photothermal magnetic recording method.
Next, the reproducing operation will be described with reference to FIG.

First, the magnetization directions of the readout layer 3 and the auxiliary layer 4 are aligned in one direction (downward in FIG. 7) by the initialization magnetic field generator 11 provided outside the laser irradiation section. At this time, the transfer layer 5 exhibits in-plane magnetization, the recording layer 6 has a higher coercive force than the initializing magnetic field, and is not affected by the initializing magnetic field.

Subsequently, since the reproducing beam 12 is narrowed down from the substrate 1 side to the analysis limit by the condenser lens 13, the light intensity distribution becomes a Gaussian distribution, and the magneto-optical disk 10
The temperature distribution of the upper regenerated part also becomes a substantially Gaussian distribution. At this time, areas a to c corresponding to the vicinity of the central portion of the reproduction beam 12
Then, the temperature of the magneto-optical disk 10 becomes around 70 ° C,
Further, in the region b, the temperature of the magneto-optical disk 10 reaches 100 ° C. or higher. The area b is a position displaced in the traveling direction B of the magneto-optical disk 10 with respect to the peak position of the light intensity distribution, and constitutes the actual peak position of the temperature distribution.

In the regions a to c, the magnetization of the transfer layer 5 shifts from the in-plane magnetic field to the vertical magnetic field. Then, the exchange coupling force acts between the two layers of the recording layer 6 and the transfer layer 5, and the direction of the magnetic field of the recording layer 6 is transferred to the transfer layer 5. Furthermore, in the areas a and c,
It is transferred to the auxiliary layer 4 and the readout layer 3. In the region b, since the auxiliary layer 4 reaches the Curie temperature and loses its magnetization, the transfer to the read layer 3 is not performed, and the magnetization direction of the read layer 3 is the direction of the magnetic field applied from the auxiliary magnetic field device 14 (see FIG. 7 down). Therefore, the information of the recording layer 6 is transferred to the reading layer 3 only in the areas a and c, and is not reproduced from the low temperature portion (area d) and the high temperature portion (area b).

Therefore, when the recording density is increased, as shown in FIG. 8, when the reproducing beam 12 is moved to reproduce the next recording bit, the previous recording bit enters the high temperature portion (region b), It will not be reproduced and signals from adjacent bits, which cause noise, will not be mixed. As a result, smaller recording bits can be reproduced and the recording density can be remarkably increased.

[Embodiment 2] The following will describe another embodiment of the present invention in reference to FIGS. 9 and 10.
In the present embodiment, the case where the magneto-optical recording medium is applied to a magneto-optical disk is illustrated, and regarding the member having the same function as that of the magneto-optical disk 10 of the first embodiment,
8 and 12 are reused for convenience of explanation.

The magneto-optical disk 10 'according to this embodiment is
As shown in FIG. 9, the substrate 1, the first transparent dielectric film 2, the readout layer 3, the auxiliary layer 4, the transfer layer 5, the recording layer 6 ′, the initialization layer 9, the second transparent dielectric film 7, and the overcoat. Coat layer 8
However, the recording layer 6'has a structure in which they are laminated in this order.
And, except for the initialization layer 9, the structure is the same as that of the first embodiment.

That is, as the read layer 3, for example, Dy
_0.21 (Fe _0.8 Co _0.2 ) _0.79 is used, the film thickness is 20 nm, and the Curie temperature is set to 150 ° C to 250 ° C. As the auxiliary layer 4, for example, Dy _0.17 Fe _0.83 is used, the film thickness is 40 nm, and the Curie temperature is 8
The temperature is set to 0 ° C to 100 ° C.

As the transfer layer 5, for example, Gd _0.28 (Fe _0.8
Co _0.2 ) _0.72 is used, the film thickness is 50 nm,
The Curie temperature is about 300 to 400 ° C. Further, the transfer layer 5 has a rare earth metal content higher than the compensating composition at room temperature so as to have the compensating composition at about 70 ° C. (transition from in-plane magnetization to perpendicular magnetization).
Further, the first transparent dielectric film 2 is made of, for example, Al S, Si.
It is made of a dielectric film such as N or Al Si N and has a film thickness of 10 n.
It is about m to 80 nm. In addition, the second transparent dielectric film 7
Is a protective film made of nitride and has a film thickness of 50 nm.

The recording layer 6'is a perpendicularly magnetized film of rare earth transition metal, for example, Dy _0.23 (Fe _0.82 Co _0.18 ) _0.77 is used, and the film thickness is 20 nm. However, the Curie temperature is set to 150 ° C.

The initialization layer 9 is a rare earth transition metal perpendicular magnetization film, has a compensation temperature, has a lower coercive force and a higher Curie point than the recording layer 6 ', and transfers information to the recording layer 6'. Overwriting is performed. Information is recorded or erased by utilizing the exchange coupling force acting between the recording layer 6 ′ and the initialization layer 9.

As the initialization layer 9, for example, Dy
_0.27 (Fe _0.48 Co _0.52 ) _0.73 is used, and the film thickness is 5
It is 0 nm. The compensation temperature is set to 120 ° C to 180 ° C, and the Curie temperature is set to 200 ° C to 300 ° C.

In the above structure, the present magneto-optical disk 1
The recording operation of 0'will be described below with reference to FIG.

First, the direction of the magnetic field of the initialization layer 9 is aligned in one direction (downward in FIG. 10) by the initialization magnetic field generator 11 provided outside the laser irradiation section. In this state, as shown in FIG. 12, information is rewritten by overwriting while switching the reproducing beam 12 between the high level power P _H and the low level power P _L.

That is, the reproduction beam 1 of high level power P _H
By irradiating with 2, the temperature of the magneto-optical disk 10 ′ rises to near the Curie point of the initialization layer 9, and the magnetization direction of the initialization layer 9 is reversed by the magnetic field applied from the auxiliary magnetic field generator 14. When the laser spot is removed and the recording layer 6 ′ is cooled to near the Curie point, the magnetization direction of the recording layer 6 ′ is changed by the exchange force acting on the interface between the initialization layer 9 and the recording layer 6 ′. 9 matches the direction of magnetization.

On the other hand, the reproduction beam 1 of low level power P _L
2 is irradiated, the temperature of the magneto-optical disk 10 'rises only up to near the Curie point of the recording layer 6', and the magnetization direction of the initialization layer 9 is applied by the auxiliary magnetic field generator 14. Although it is not inverted due to the influence of the magnetic field, if the magnetization direction of the recording layer 6 ′ and the magnetization direction of the initialization layer 9 do not match, the magnetization direction of the initialization layer 9 may match. Then, the magnetization of the recording layer 6'is reversed. By the above operation,
Overwriting can be performed on the recording layer 6 '.

On the other hand, the reproducing operation of the present magneto-optical recording medium 10 'is the same as that of the first embodiment. Therefore, as in the case of the first embodiment, when the recording density is increased and the reproducing beam 12 is moved to reproduce the next recording bit as shown in FIG. 8, the previous recording bit is masked. It will not be reproduced and signals from adjacent bits, which cause noise, will not be mixed. As a result, smaller recording bits can be reproduced and the recording density can be remarkably increased.

The first and second embodiments are not intended to limit the present invention, and various modifications can be made within the scope of the present invention. Although the magneto-optical recording medium is applied to the magneto-optical disk in each of the first and second embodiments, the present invention is not limited to this, and may be applied to a magneto-optical tape, a magneto-optical card and the like. It is possible.

Further, although the materials, compositions, and film thicknesses of the respective layers constituting the magneto-optical recording medium are shown in the above-mentioned first and second embodiments, the present invention is not limited to these, and is described in the embodiments. What is necessary is just to satisfy the characteristics of each layer. For example, as the transfer layer 5, GdFe, GdCo, GdFe
Co, Tb Fe Co, etc. can be used. The read layer 3, the recording layers 6 and 6 ′, and the initialization layer 9 are T
bFeCo, GdDyFeCo, GdFeCo, etc. can be used. Further, as the auxiliary layer 4, TbFe,
GdFe, GdTbFe, GdDyFe, etc. can be used.

Further, in the above-mentioned first and second embodiments, the magneto-optical recording medium is shown as sandwiched between the first and second transparent dielectric films 2 and 7, but the second transparent dielectric film 7 is used. A structure in which a reflective film is inserted between the overcoat film 8 and the overcoat film 8 may be used. Further, in the magneto-optical disk 10 'of the second embodiment, in-plane magnetization for adjusting the exchange coupling force, perpendicular magnetization, or in-plane magnetization at a predetermined temperature or more is provided between the recording layer 6'and the reading layer 3. It is also possible to have a configuration in which an intermediate layer that shifts from a to perpendicular magnetization is sandwiched.

[0065]

As described above, the magneto-optical recording medium according to claim 1 of the present invention has four layers in which the first magnetic layer, the second magnetic layer, the third magnetic layer, and the fourth magnetic layer are exchange-coupled. In the magneto-optical recording medium having a structure, the first magnetic layer is a reading layer for reading information of a magneto-optical signal, and the second magnetic layer is an auxiliary layer having a lower Curie temperature than other magnetic layers. The third magnetic layer is a transfer layer that exhibits in-plane magnetization at room temperature and shifts from in-plane magnetization to perpendicular magnetization as the temperature rises, and the fourth magnetic layer stores information of a magneto-optical signal. It is a recording layer to hold. And as described in claim 2, the second
The magnetization direction of the magnetic layer is transferred to the first magnetic layer by the exchange coupling force between room temperature and the Curie temperature of the second magnetic layer,
According to a third aspect of the present invention, the temperature at which the third magnetic layer changes from in-plane magnetization to perpendicular magnetization is between room temperature and the Curie temperature of the second magnetic layer.

Therefore, as in the recording / reproducing method according to the fourth aspect, an initialization magnetic field for applying the magnetization directions of the first and second magnetic layers to one direction outside the laser irradiation portion is applied, and the laser irradiation portion is applied. By applying the external magnetic field in the same direction as the initializing magnetic field at the time of recording and reproducing information by using the magneto-optical recording medium according to claim 1, the previous recording bit in the laser beam is masked. It will not be reproduced and signals from adjacent bits, which cause noise, will not be mixed. As a result, smaller recording bits can be reproduced, and the recording density is significantly improved.

Further, the magneto-optical recording medium according to claim 5 is
A magneto-optical recording medium having a five-layer structure in which a first magnetic layer, a second magnetic layer, a third magnetic layer, a fourth magnetic layer, and a fifth magnetic layer are exchange-coupled, and the first magnetic layer is a magneto-optical signal. Is a read layer from which information is read, and the second magnetic layer is
An auxiliary layer with a lower Curie temperature than other magnetic layers,
The third magnetic layer is a transfer layer that exhibits in-plane magnetization at room temperature and shifts from in-plane magnetization to perpendicular magnetization as the temperature rises, and the fourth magnetic layer is a recording layer that retains information of a magneto-optical signal. The fifth magnetic layer is an initialization layer having a lower coercive force and a higher Curie temperature than the fourth magnetic layer. The magnetization direction of the second magnetic layer is transferred to the first magnetic layer by an exchange coupling force between room temperature and the Curie temperature of the second magnetic layer. As described in claim 7, the temperature at which the third magnetic layer shifts from in-plane magnetization to perpendicular magnetization is between room temperature and the Curie temperature of the second magnetic layer, and further, according to claim 8, Fourth
Between the magnetic layer and the fifth magnetic layer, there is provided an in-plane magnetization, a perpendicular magnetization, or an intermediate layer in which the in-plane magnetization shifts to a perpendicular magnetization due to a temperature rise at room temperature.

Therefore, as in the recording / reproducing method according to the ninth aspect, an initialization magnetic field for aligning the magnetization directions of the first and second magnetic layers to one direction outside the laser irradiation portion is applied, and the laser irradiation portion is applied. The improvement of the recording density according to any one of claims 1 to 4 by applying the external magnetic field in the same direction as the initialization magnetic field at the time of recording and reproducing information by using the magneto-optical recording medium according to claim 5 in In addition to the effect, an overwrite operation is performed by irradiating a laser beam whose intensity is modulated into two levels, high and low. Moreover, since it is not necessary to use a material having a low Curie temperature for the readout layer, there is an effect that a good reproduction performance can be obtained without a decrease in signal level.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a magneto-optical disk according to an embodiment of the present invention.

FIG. 2 is a magnetic state diagram of a transfer layer forming the magneto-optical disk.

FIG. 3 is a graph showing the relationship between the externally applied magnetic field applied to the transfer layer and the magnetic Kerr rotation angle from room temperature to temperature T ₁ .

FIG. 4 is a graph showing a relationship between an externally applied magnetic field applied to the transfer layer and a magnetic Kerr rotation angle from temperature T ₁ to temperature T ₂ .

FIG. 5 is a graph showing a relationship between an externally applied magnetic field applied to the transfer layer and a magnetic Kerr rotation angle from temperature T ₂ to temperature T ₃ .

FIG. 6 is a graph showing the relationship between the externally applied magnetic field applied to the transfer layer and the magnetic Kerr rotation angle from the temperature T ₃ to the Curie temperature T _c .

FIG. 7 is an explanatory diagram showing a reproducing operation of the magneto-optical disk.

FIG. 8 is an explanatory diagram showing a positional relationship between a reproduction beam and a recording bit in the above reproduction operation.

FIG. 9 is a vertical sectional view showing a magneto-optical disk according to another embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a recording operation of the magneto-optical disk.

FIG. 11 is an explanatory diagram showing a reproducing operation of a magneto-optical disk in a conventional example.

FIG. 12 is a graph showing the relationship between the intensity of a recording laser beam and the irradiation time according to the light modulation overwrite method.

FIG. 13 is an explanatory diagram showing a positional relationship between a reproduction beam and a recording bit in a conventional magneto-optical recording method.

[Explanation of symbols]

 3 read-out layer 4 auxiliary layer 5 transfer layer 6 · 6 'recording layer 9 initialization layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichiro Nakayama 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (9)

[Claims] 1. A magneto-optical recording medium having a four-layer structure in which a first magnetic layer, a second magnetic layer, a third magnetic layer, and a fourth magnetic layer are exchange-coupled, and the first magnetic layer is a magneto-optical signal. Is a read layer from which information is read, the second magnetic layer is an auxiliary layer having a lower Curie temperature than other magnetic layers, and the third magnetic layer exhibits in-plane magnetization at room temperature, A magneto-optical recording medium, which is a transfer layer that shifts from in-plane magnetization to perpendicular magnetization as the temperature rises, and the fourth magnetic layer is a recording layer that holds information of a magneto-optical signal. 2. The magnetization direction of the second magnetic layer is transferred to the first magnetic layer by an exchange coupling force between room temperature and the Curie temperature of the second magnetic layer. Magneto-optical recording medium. 3. The magneto-optical recording medium according to claim 1, wherein the temperature at which the third magnetic layer changes from in-plane magnetization to perpendicular magnetization is between room temperature and the Curie temperature of the second magnetic layer. . 4. An initialization magnetic field for aligning the magnetization directions of the first and second magnetic layers to one direction outside the laser irradiation part is applied, and an external magnetic field in the same direction as the initialization magnetic field is informationed in the laser irradiation part. 2. The recording / reproducing method using the magneto-optical recording medium according to claim 1, wherein the voltage is applied during recording and reproducing. 5. A magneto-optical recording medium having a five-layer structure in which a first magnetic layer, a second magnetic layer, a third magnetic layer, a fourth magnetic layer, and a fifth magnetic layer are exchange-coupled, and the first magnetic layer is the same. Is a read layer from which information of a magneto-optical signal is read, the second magnetic layer is an auxiliary layer having a lower Curie temperature than other magnetic layers, and the third magnetic layer is a surface layer at room temperature. The fourth magnetic layer is a transfer layer that exhibits internal magnetization and shifts from in-plane magnetization to perpendicular magnetization as the temperature rises, the fourth magnetic layer is a recording layer that holds information of a magneto-optical signal, and the fifth magnetic layer is Has a lower coercive force than the fourth magnetic layer,
A magneto-optical recording medium characterized by being an initialization layer having a high Curie temperature. 6. The magnetization direction of the second magnetic layer is transferred to the first magnetic layer by an exchange coupling force between room temperature and the Curie temperature of the second magnetic layer. Magneto-optical recording medium. 7. The magneto-optical recording medium according to claim 5, wherein the temperature at which the third magnetic layer changes from in-plane magnetization to perpendicular magnetization is between room temperature and the Curie temperature of the second magnetic layer. . 8. An intermediate layer is provided between the fourth magnetic layer and the fifth magnetic layer, which has in-plane magnetization, perpendicular magnetization, or in-plane magnetization at room temperature which changes to perpendicular magnetization due to temperature rise. A magneto-optical recording medium according to claim 5. 9. An initialization magnetic field for aligning the magnetization directions of the first and second magnetic layers to one direction outside the laser irradiation portion is applied, and an external magnetic field in the same direction as the initialization magnetic field is informed in the laser irradiation portion. 6. The recording / reproducing method using the magneto-optical recording medium according to claim 5, wherein the voltage is applied during recording and reproducing.