JPH07240039A - Overwrite magneto-optical recording medium - Google Patents

Abstract

(57) [Summary] [Object] It is an object of the present invention to provide a magneto-optical recording medium capable of overwriting information by light intensity modulation and capable of super-resolution reproduction. A transparent substrate 14, a magnetic reproducing layer 16 laminated on the transparent substrate 14 for reading information having an in-plane easy magnetization direction at room temperature, and laminated on the magnetic reproducing layer 16. A magnetic memory layer 18 for holding information having a magnetization easy direction perpendicular to the film surface and having a compensation temperature equal to or lower than room temperature, and a magnetic memory layer 18 stacked on the magnetic memory layer 18 and perpendicular to the film surface. An overwrite magneto-optical recording medium comprising a magnetic recording layer 20 for recording information having a direction of easy magnetization, wherein the thickness of the magnetic reproducing layer 16 is within a range of 20 nm to 60 nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a magneto-optical recording capable of overwriting by using an in-plane magnetized film as a reproducing layer, which has a resolution smaller than the diffraction limit of a reproducing laser wavelength. Regarding the medium.

Although a magneto-optical disk is known as a high density recording medium, a higher density is demanded as the amount of information increases. Higher density can be realized by narrowing the intervals of recording marks, but recording and reproduction thereof are limited by the size of the light beam (beam spot) on the medium.

When it is set that only one recording mark exists in the beam spot, output waveforms corresponding to "1" and "0" can be observed as a reproduction signal depending on whether or not there is a recording mark.

However, if the recording marks are closely spaced so that a plurality of recording marks are present in the beam spot, the reproduction output does not change even if the beam spot on the medium moves, so that the output waveform becomes a straight line. The presence or absence of recording marks cannot be identified.

In order to reproduce a small recording mark having a period less than such a beam spot, the beam spot may be narrowed down. The size of the beam spot depends on the wavelength λ of the light source and the numerical aperture NA of the objective lens. It is restricted by and cannot be narrowed down sufficiently.

[0006]

2. Description of the Related Art Recently, there has been proposed a reproducing method using a magnetic induction super-resolution technique for reproducing a recording mark below a beam spot by using the existing optical system as it is. This is a reproducing method in which one mark in the beam spot is reproduced while another mark is masked to improve the reproducing resolution.

Therefore, in the super-resolution disc medium, in addition to the recording layer for recording marks, a mask layer or reproducing layer for hiding other marks so that only one mark is reproduced at the time of signal reproduction. Is the minimum required.

A magneto-optical recording medium using a perpendicularly magnetized film as a reproducing layer is proposed in Japanese Patent Laid-Open No. 3-88156. However, the conventional technique described in this publication has a problem that the device cannot be miniaturized because an initializing magnetic field of about several kilo Oersted is required to initialize the reproducing layer.

On the other hand, a magneto-optical recording medium using a magnetic film having a direction of easy magnetization in the plane at room temperature and a direction of easy magnetization perpendicular to the film surface at a temperature higher than a predetermined temperature is disclosed in Japanese Patent Application Laid-Open No. HEI 5-1993.
No. 81717.

The reproducing principle of this prior art will be briefly described with reference to FIG. As shown in FIG. 14C, the magneto-optical disk 2 is formed by laminating a magnetic reproducing layer 6 and a magnetic recording layer 8 on a transparent substrate 4.

The magnetic reproducing layer 6 has an in-plane easy magnetization direction at room temperature, but the easy magnetization direction changes vertically when the reproducing power is irradiated to reach a predetermined temperature or higher. The magnetic recording layer 8 is a perpendicular magnetization film. Reference numeral 10 indicates a light beam.

Since the intensity distribution of the light beam has a Gaussian distribution as shown in FIG. 14A, when the disc is stationary, the temperature distribution on the disc is higher in the central portion than in the peripheral portion. Has become.

However, since the disk 2 is actually rotating in the direction of arrow R, the temperature distribution on the disk is as shown in FIG.
As shown in (B), the front side of the beam spot in the disc movement direction has a high temperature.

Since the temperature distribution is generated as described above, the easy magnetization direction of the magnetic reproducing layer 6 is in-plane in the region where the temperature in the beam spot is low, so that the Kerr rotation angle of the reflected light is almost zero. Become. In the high temperature region, the easy magnetization direction of the magnetic reproducing layer 6 changes from in-plane to perpendicular.

At this time, the perpendicular magnetization of the magnetic reproducing layer 6 is coupled with the magnetization of the magnetic recording layer 8 by the exchange force and is aligned in the magnetization direction of the magnetic recording layer 8. Therefore, the magnetization recorded in the magnetic recording layer 8 is aligned. Can be transferred to. The width of this transfer area can be changed by the reproduction laser beam power.

By controlling the size of the mask of the magnetic reproducing layer in such a manner that only one recording mark can be reproduced, the same effect as that of substantially reducing the area of the beam spot can be obtained. The resolution is improved and high density can be realized.

Therefore, by using the technique described in Japanese Patent Laid-Open No. 5-81717, crosstalk between recording marks on adjacent tracks or on the same track can be suppressed, and the magneto-optical disk currently in practical use can be used. The recording density can be increased several times.

[0018]

Although super-resolution reproduction is possible by using the above-mentioned technique, when writing new data, the old data still has to be erased. Therefore, it is necessary to increase the data transfer rate. There is a problem that you can not.

Therefore, a technique for directly overwriting old data with new data is required. Magnetic field modulation methods and light intensity modulation methods have been proposed as technologies for directly overwriting old data with new data.

The magnetic field modulation system enables overwriting by irradiating a medium having a single-layer magnetic film with a laser beam and further applying an alternating magnetic field. However, in this method, since a magnetic head for generating an alternating magnetic field must be installed near the disk, a so-called head crash may occur in which the magnetic head contacts the disk, and it is difficult to improve reliability. Is.

On the other hand, in the light intensity modulation method, a low level (for erasing data by a laser beam to be irradiated onto a recording medium having a memory layer for retaining data and a recording layer for recording data) is used. PL) and a high level (PH) for recording data, which enables overwriting.

This light intensity modulation method has been proposed by Mitsubishi Electric Corporation at the 16th Scientific Lecture Meeting of the Japan Institute of Applied Magnetics (9pG-18). However, seven magnetic layers are laminated and each magnetic layer is formed. It is very difficult to realize this magneto-optical disk from the viewpoint of the manufacturing process, because the exchange coupling force must be controlled accurately.

JP-A-5-12732 discloses a magneto-optical recording medium having a structure in which a magnetic layer (reproducing layer) exhibiting in-plane magnetization at room temperature is provided on the structure of a conventional overwrite medium.

A supplementary test of the magneto-optical recording medium disclosed in this publication discloses that exchange coupling between the reproducing layer and the memory layer (referred to as the recording layer in the above publication) is induced at a predetermined temperature. It has been found that it is extremely difficult and depends largely on the composition of the memory layer. Further, it was found that the reproduction signal output greatly depends on the film thickness of the reproduction layer, and the film thickness of the reproduction layer must be controlled within the optimum range in order to obtain a large reproduction signal output.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magneto-optical recording medium capable of simultaneously realizing super-resolution reproduction and overwrite by a light intensity modulation method. That is.

[0026]

According to the first aspect of the present invention, a transparent substrate and a magnetic reproducing layer laminated on the transparent substrate for reading information having an in-plane easy magnetization direction at room temperature. And a magnetic memory layer laminated on the magnetic reproducing layer for holding information having an easy magnetization direction perpendicular to the film surface and having a compensation temperature of room temperature or less, and laminated on the magnetic memory layer A magnetic recording layer for recording information having an easy magnetization direction perpendicular to the film surface, and the film thickness of the magnetic reproducing layer is 20 nm to 60 nm.
Provided is an overwrite magneto-optical recording medium characterized by being in the range of nm.

According to the second structure of the present invention, the transparent substrate, the magnetic reproducing layer laminated on the transparent substrate for reading information having the in-plane easy magnetization direction at room temperature, and the magnetic reproducing layer. A magnetic memory layer laminated on the magnetic memory layer for holding information having an easy magnetization direction perpendicular to the film surface and having a compensation temperature equal to or lower than room temperature, and a magnetic memory layer laminated on the magnetic memory layer on the film surface. A magnetic recording layer for recording information having a perpendicular easy magnetization direction, and a magnetic initialization layer having a perpendicular easy magnetization direction with respect to a film surface for initializing the magnetization of the magnetic recording layer; A magnetic switch inserted between the magnetic recording layer and the magnetic initialization layer and having an easy magnetization direction perpendicular to a film surface for controlling an exchange coupling force between the magnetic recording layer and the magnetic initialization layer. And layers,
The Curie temperatures of the magnetic memory layer, the magnetic recording layer, the magnetic switch layer and the magnetic initializing layer are Tc1, Tc2 and Tc2, respectively.
When Tc3 and Tc4 are set, Tc3 <Tc1 <Tc2
<The relationship of Tc4 is satisfied, and the thickness of the magnetic reproducing layer is 20.
There is provided an overwrite magneto-optical recording medium characterized by being in the range of 60 nm to 60 nm.

Preferably, each of the magnetic layers is made of a rare earth-transition metal amorphous alloy, and the rare earth element of the memory layer contains terbium (Tb) as a main component.

[0029]

When recording data on the magneto-optical recording medium of the first structure by overwriting using light intensity modulation, the bias magnetic field is set in the direction opposite to the recording direction prior to recording, By raising the temperature above the Curie temperature of the recording layer, the memory layer and the recording layer are initialized and the magnetization directions are aligned in one direction.

When writing data, the light beam is intensity-modulated according to the presence or absence of data, high power is emitted when data is present, and low power is emitted when there is no data. When irradiated with high power, the temperature is raised to above the Curie temperature of the recording layer, and the direction of magnetization of the recording layer is aligned with the direction of the bias magnetic field applied from the outside.

When cooled to room temperature, it falls below the compensation temperature of the recording layer, so the magnetization direction of the recording layer is reversed, but by applying an initializing magnetic field in the same direction as the bias magnetic field at the time of recording, the recording layer and the memory. The magnetization directions of the layers are aligned with the direction of the initializing magnetic field.

When irradiated with low power, the magnetization direction of the recording layer is raised to a temperature above the temperature at which it is transferred to the memory layer and below the Curie temperature of the recording layer. As a result, the magnetization direction of the recording layer, that is, the initialized magnetization direction is transferred to the memory layer by the exchange coupling force between the two layers of the memory layer and the recording layer.

Therefore, by adjusting the irradiation intensity of the light beam, overwriting can be performed on the magneto-optical recording medium. At this time, since the reproducing layer exhibits in-plane magnetization,
Does not affect the recording operation.

When the reproducing power is irradiated, a low temperature region and a high temperature region are formed in the beam spot, and an in-plane mask in which the magnetization direction of the reproducing layer is in the in-plane direction is formed in the low temperature region.
In the high temperature region, the magnetization direction of the memory layer is transferred to the reproducing layer, so that super-resolution reproducing within the diffraction limit of the reproducing laser wavelength is possible.

When recording is performed on the magneto-optical recording medium of the second structure by overwriting using light intensity modulation, the bias magnetic field direction is set to the direction opposite to that of the recording prior to recording while the initializing layer is formed. The recording medium is initialized by raising the temperature above the Curie temperature.

In the medium of the second structure, since the initialization layer having a very high Curie temperature and the switch layer having a very low Curie temperature are provided, the magnetization of the initialization layer can be used as an initialization magnetic field. The initialization magnet required in the first configuration can be omitted. The overwrite process according to the second configuration is similar to the above-described first configuration.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown a configuration diagram of a recording medium according to a first embodiment of the present invention. The magneto-optical recording medium 12a includes a magnetic reproducing layer 16 and a magnetic memory layer 18 on a transparent substrate 14.
And the magnetic recording layer 20 are laminated in this order. Each magnetic layer is formed of a rare earth-transition metal amorphous alloy.

The easy magnetization direction of the reproducing layer 16 is parallel to the film surface at room temperature, and the reproducing layer 16 is an in-plane magnetized film at room temperature. On the other hand, the easy magnetization directions of the memory layer 18 and the recording layer 20 are perpendicular to the film surface, and these magnetic layers are perpendicular magnetization films. The memory layer 18 has room temperature or a compensation temperature below room temperature.

Referring to FIG. 2, there is shown a configuration diagram of a recording medium according to the second embodiment of the present invention. The magneto-optical recording medium 12b of this embodiment has a magnetic intermediate layer 22 interposed between the memory layer 18 and the recording layer 20 of the recording medium 12a of the first embodiment. The intermediate layer 22 may be either an in-plane magnetized film or a perpendicular magnetized film.

The intermediate layer 22 may be made of a rare earth-transition metal amorphous alloy to which any metal is added. The composition of the intermediate layer 22 may be any composition that enables super-resolution reproduction and overwrite, and is not generally limited to a narrow range.

The intermediate layer 22 controls the exchange coupling force between the memory layer 18 and the recording layer 20, and has a Curie temperature higher than the Curie temperature of the recording layer 20. Referring to FIG. 3, there is shown a configuration diagram of a recording medium according to a third embodiment of the present invention. The magneto-optical recording medium 12c of this embodiment
Is a magnetic switching layer 24 and a magnetic initialization layer 26 laminated on the recording layer 20 of the recording medium 12a of the first embodiment.

The switch layer 24 and the initialization layer 26 are perpendicular magnetization films like the memory layer 18 and the recording layer 20, and are made of a rare earth-transition metal amorphous alloy. Memory layer 18, recording layer 20, switch layer 24, and initialization layer 26
If the Curie temperatures of Tc1, Tc2, Tc3, and Tc4 are respectively, the relationship of Tc3 <Tc1 <Tc2 <Tc4 is satisfied.

The compensation temperature of the reproducing layer 16 is room temperature or below room temperature, the compensation temperature of the recording layer 20 is below Curie temperature of the switch layer 24, and the compensation temperature of the initialization layer 26 is the Curie temperature of the memory layer 18 and the recording. Between the Curie temperatures of layer 20.

Referring to FIG. 4, there is shown a configuration diagram of a recording medium according to the fourth embodiment of the present invention. Magneto-optical recording medium 12d
Is an intermediate layer 22 interposed between the memory layer 18 and the recording layer 20 of the recording medium 12c of the third embodiment. The intermediate layer 22 has the same composition and characteristics as the intermediate layer 22 of the second embodiment shown in FIG.

Regarding the magneto-optical recording media 12a to 12d of the above-mentioned first to fourth embodiments, the relationship between the composition of the memory layer 18 and the signal output was examined. This is because the memory layer 18 and the reproducing layer 16 need to be exchange-coupled at the time of temperature rise, and the optimum composition of the memory layer 18 was investigated. The results are shown in Table 1.
Shown in.

[0046]

[Table 1]

Table 1 shows the maximum output when a mark having a length of 0.5 μm is recorded on the disc. The structure of layers other than the memory layer 18 is the same as that of Example 1 described later. As is clear from Table 1, the terbium (T
It was found that the one containing b) as the main component is optimal, and that a large signal output can be obtained in a composition having a compensation temperature below room temperature. The compensation composition when Tb is the main component is when Tb is about 20, and the compensation composition when the main component is Dy is when Dy is about 21 to 22.

Next, the thickness of the reproduction layer 16 and the reproduction signal output were examined. The results are shown in Table 2.

[0049]

[Table 2]

As is clear from Table 2, the thickness of the reproducing layer 16 is optimally in the range of 20 to 60 nm in order to obtain a large signal output. This is because if the thickness of the reproducing layer 16 is thin, incident light is transmitted and a large reproduced signal output cannot be obtained, and if it is too thick, the magnetization from the memory layer 18 is not sufficiently transferred to the reproducing layer 16. This is because a large reproduced signal output cannot be obtained.

Next, the process for overwriting information (data) on the recording medium 12a of the first embodiment will be described with reference to FIG. Regarding the dominant of each magnetic layer used in the recording medium of FIG. 5, the reproducing layer 16 is rare earth element rich (RE rich), the memory layer 18 is transition metal rich (TM rich), and the recording layer 20 is RE rich. In principle, the type of dominant of each magnetic layer is not limited at all.

In FIG. 5, Troom is room temperature, Tcompw is the compensation temperature of the recording layer 20, Tcm is the Curie temperature of the memory layer 18, Tcw is the Curie temperature of the recording layer 20, and Tcopy1 is the magnetization direction of the memory layer 18 in the reproducing layer 16. Temperature transferred to
Tcopy2 is the temperature at which the magnetization direction of the recording layer 20 is transferred to the memory layer 18.

With reference to FIG. 5, the overwrite function and the super-resolution reproducing function will be described in association with the magnetization direction of each magnetic layer. First, the direction of the bias magnetic field is opposite to the direction at the time of recording, that is, the bias magnetic field is set downward, and the temperature is raised to the Curie temperature of the recording layer 20 or higher to initialize the memory layer 18 and the recording layer 20. At this time, the reproduction layer 16
The magnetization direction of is in-plane at room temperature (state a).

In FIG. 5, the arrows indicate the spin direction of the transition metal in each magnetic layer, and the outlined arrows indicate the magnetization direction of each magnetic layer. The magnetization direction of each magnetic layer is reversed at the compensation temperature.

When there is a data signal at the time of overwriting, the medium is irradiated with a high power (PH) laser beam, and when there is no data, the medium is irradiated with a low power (PL) laser beam.

When the medium is irradiated with a high power laser beam, the medium is heated to the Curie temperature of the recording layer 20 or higher,
When irradiated with a low power laser beam, the medium becomes Tco
When py2 or more, the temperature is raised to below the Curie temperature of the recording layer 20.

In FIG. 5, the writing process and the erasing process are described separately, but the writing process and the erasing process are performed when there is data at the time of a series of overwrites, and when there is no data. Means

Writing Process When writing data, the medium is heated to the Curie temperature Tcw of the recording layer 20 or higher. The shaded area shows the state in which each magnetic layer is heated to the Curie temperature or higher and has no magnetization. At the time of overwriting, the bias magnetic field is applied upward, and the initialization magnetic field is also applied upward as shown by the outline arrow.

When writing is performed from the state of a, the magnetization directions of the magnetic layers are ab-c-g-h-i-j-k.
Change in the order of -l. In the state of 1, the magnetization direction of the recording layer 20 changes, but this is due to
This is because the temperature is below the compensation temperature.

At room temperature, an initializing magnet is provided as an external magnetic field, and the disk medium passes through the initializing magnet.
Then, the data is recorded in the memory layer 18 and the recording layer 20 is initialized.

On the other hand, when writing is performed from the state of d, the magnetization direction of each magnetic layer is d-e-f-g-h-i-.
It changes in the order of jk-1. Then, by passing through the initialization magnet, it returns to the original state, that is, the state of d.

Erase Process When erasing without write data, a medium is irradiated with a low power laser beam, and the medium is transferred from the temperature Tcopy2 at which the magnetization direction of the recording layer 20 is transferred to the memory layer 18 to the Curie temperature Tcw of the recording layer 20. The temperature is raised below.

When the temperature is raised from the state of a to the temperature at which the erasing process is performed and lowered to room temperature, the magnetization directions of the respective magnetic layers are in the order of ab-c-b-a or a.
The data changes in the order of -b-c-g-c-b-a, returns to the original state, that is, the state of a, and the data in the memory layer 18 is erased. Then, though passing through the initializing magnet, the magnetization directions of the memory layer 18 and the recording layer 20 do not change.

When the temperature is raised from the state of d to the temperature at which the erasing process is carried out and is lowered to room temperature,
The magnetization direction of each magnetic layer changes in the order of d-e-f-c-b-a or d-e-f-g-c-b-a, and the data in the memory layer 18 is erased.

Reproduction Process The reproduction process will be described with reference to FIG. It is assumed that the recording medium is rotating in the direction of arrow R as shown in FIG. The reproducible temperature is within the range of Tcopy1 to Tcopy2. At this time, by adjusting the reproduction power PR, the T spot is formed in the beam spot 30 as shown in FIG.
A low temperature region 30a lower than copy1 and a high temperature region 30b higher than Tcopy1 are formed.

In the low temperature region 30a, an in-plane mask 16a is formed in the reproducing layer 16 as shown in FIG. 6B, and in the high temperature region 30b, an opening 16b is formed in which the magnetization direction of the reproducing layer 16 is aligned with the memory layer 18. To be done.

As described above, in the high temperature region 30b of the beam spot 30, the magnetization direction of the memory layer 18 is transferred to the reproducing layer 16, so that the information recorded in the memory layer 18 is reproduced in the opening 16b of the reproducing layer 16. Is possible.

Since the in-plane mask 16a is formed on the reproducing layer 16 in the low temperature region 30a in the beam spot 30, a so-called super-resolution reproducing for reproducing a recording mark having a size less than the diffraction limit of the reproducing laser wavelength. Is possible.

The above-mentioned processes are directly applied to the medium of the second embodiment having the intermediate layer 22. This is because the intermediate layer 22 is only for controlling the exchange coupling force between the memory layer 18 and the recording layer 20, and is not involved in the basic idea of each process.

Next, the process of overwriting data on the recording medium of the third embodiment will be described with reference to FIG. In the description of FIG. 7, Troom is room temperature, T
compw is the compensation temperature of the recording layer 20, Tcompi is the initialization layer 2
6 compensation temperature, Tcs is Curie temperature of the switch layer 24,
Tcm is the Curie temperature of the memory layer 18, and Tcw is the recording layer 20.
Curie temperature of, Tci is the Curie temperature of the initialization layer 26,
Tcopy1 indicates the temperature at which the magnetization direction of the memory layer 18 is transferred to the reproducing layer 16, and Tcopy2 indicates the temperature at which the magnetization direction of the recording layer 20 is transferred to the memory layer 18.

In the first and second embodiments shown in FIGS. 1 and 2, the initialization magnet was required to align the magnetization directions of the recording layer 20, but the third and the third embodiments shown in FIGS. Fourth
In an embodiment, the initialization magnet can be eliminated by providing the switch layer 24 and the initialization layer 26.

That is, in the recording media of the third and fourth embodiments, the initialization layer 26 functions as an initialization magnet. The switch layer 24 includes the recording layer 20 and the initialization layer 2 at a predetermined temperature or higher.
It has a lower Curie temperature than Tcopy1 in order to prevent exchange coupling with 6.

The dominant of each magnetic layer used in the medium of FIG. 7 is that the reproducing layer 16 is RE-rich and the memory layer 18 is TM-rich.
Rich, recording layer 20 is RE rich, and switch layer 24 is T
The M-rich and initialization layer 26 is RE-rich.

First, the bias magnetic field is directed downward in the direction opposite to that at the time of recording, and the disc is initialized by raising the temperature above the Curie temperature of the initialization layer 26 (state a).

Writing Process When writing is performed from the state of a, the magnetization directions of the respective magnetic layers are a-b-c-d-e-j-l-m-n-o-p.
It changes in the order of -q-r. In the state of q, the recording layer 20
There is an interface domain wall between the switch layer 24 and the switch layer 24, but in the state of r cooled to room temperature, the interface domain wall moves between the memory layer 18 and the recording layer 20, data is written in the memory layer 18, and The recording layer 20 is initialized by the magnetization of the conversion layer 26.

When writing from the state of r, the magnetization direction of each magnetic layer is r-f-g-h-i-j-l-m.
It changes in the order of-n-op-q-r and returns to the original state. When the temperature is raised from the state of the erasing process a to a temperature at which the erasing process is performed and is lowered to room temperature, the magnetization directions of the respective magnetic layers are a-b-c-d-e-j-e-d-. It changes in the order of c-b-a or a-b-c-d-e-d-c-b-a, returns to the original state, that is, the state of a, and the data in the memory layer 18 is erased.

When the temperature is raised from the state of r to the temperature at which the erasing process is carried out and is lowered to room temperature,
The magnetization direction of each magnetic layer is r-f-g-h-i-j-e-
The data in the memory layer 18 is erased by changing in the order of d-c-b-a.

Reproducing Process With reference to FIG. 8, a reproducing method of the information recorded on the medium of the third embodiment will be described. It is assumed that the recording medium is rotating in the arrow R direction as shown in FIG.

Beam spot 3 irradiated with reproduction power
Within 0, as shown in FIG. 8A, a low temperature region 30a below Tcopy1 and a high temperature region 30b above Tcopy1 are formed. In the low temperature region 30 a of the beam spot 30, the in-plane mask 16 a is formed on the reproducing layer 16, and the high temperature region 30 a
At b, the opening 16b is formed so that the magnetization direction of the reproducing layer 16 is aligned with the memory layer 18.

Therefore, the information recorded in the memory layer 18 can be reproduced through the opening 16b of the reproducing layer 16, and the in-plane mask 16a is formed on the reproducing layer 16 irradiated with the beam spot 30. , Super-resolution reproduction of information becomes possible.

Example 1 First, in order to investigate whether super-resolution reproduction can be performed using an in-plane magnetized film, as shown in FIG. 9, a glass-photopolymer (2p) having grooves of 1.2 μm pitch was used. Board 14
The protective film 32, the reproducing layer 16, the memory layer 18, and the protective film 34 are formed on the upper surface by DC sputtering.

At this time, the protective film 32 was formed at an ultimate vacuum degree of 5 × 10 ⁻⁵ Pa, and the vacuum was evacuated to the ultimate vacuum degree again to continuously form the reproducing layer 16 and the memory layer 18. Further, a protective film 34 was formed.

The protective films 32 and 34 are made of Y: SiO and have a film thickness of 90 nm. The composition of the reproducing layer 16 is Gd ₂₅ Fe ₇₀ Co ₅ , and its film thickness is 30 nm. The composition of the memory layer 18 is Tb ₂₀ Fe ₇₄ Co ₆ ,
Its film thickness is 40 nm.

Next, the reproduction characteristics were examined. As a result, wavelength 7
The C / N when reading a mark of 0.5 μm with a laser of 80 nm is about 10 dB in the recording medium having the conventional single-layer magnetic film as shown in FIG. 10, but has the configuration of FIG. About 45 dB could be obtained in the layer film medium. This means that super-resolution reproduction could be performed with the medium having the configuration of FIG.

Example 2 A magneto-optical recording medium capable of simultaneously realizing overwriting and super-resolution reproduction was manufactured by the same method as in Example 1. A magneto-optical recording medium having the composition shown in FIG. 11 was produced on the glass-2p substrate 14 having grooves of 1.2 μm pitch by the DC sputtering method.

The compositions and film thicknesses of the protective films 32 and 34, the reproducing layer 16 and the memory layer 18 are the same as in Example 1 shown in FIG. 9, and the composition of the recording layer 20 is Dy ₂₅ Fe ₅₂ Co ₂₃ .
Its film thickness is 50 nm.

When the reproduction characteristics were examined, the same results as in FIG. 10 were obtained. Further, the overwritable power margin was about 2 mW for each of the high power PH and the low power PL, as shown in FIG. 12, where the C / N was 40 dB or more.

Example 3 In order to eliminate the need for an initializing magnet installed outside the magneto-optical recording medium, a magneto-optical recording medium provided with a switch layer and an initializing layer and capable of realizing overwriting and super-resolution reproduction at the same time. I made a prototype.

The manufacturing method is the same as in Example 1 and Example 2, and a medium having the composition and film thickness shown in FIG. 13 was manufactured by the DC sputtering method. Protective films 32, 34, reproduction layer 16,
The composition and film thickness of the memory layer 18 and the recording layer 20 are the same as those in the second embodiment shown in FIG.

The composition of the switch layer 24 is Tb _20.5 Fe _79.5.
And the film thickness is 15 nm. The composition of the initialization layer 26 is Tb _28.2 Co _71.8 , and its thickness is 30 nm. As a result, the reproduction characteristic similar to that of FIG. 10 was obtained, and the overwritable power margin similar to that of FIG. 12 was realized without providing the initialization magnet.

[0091]

As described above, according to the present invention, a magneto-optical recording medium having both functions of super-resolution reproduction and overwrite can be easily realized, and the magneto-optical recording medium currently put into practical use. The recording density and the data transfer speed can be significantly improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a recording medium according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a recording medium according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a recording medium according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a recording medium according to a fourth embodiment of the present invention.

FIG. 5 is a diagram illustrating a process of overwriting information on the recording medium of the first embodiment.

FIG. 6 is a diagram illustrating a method of reproducing information recorded on the recording medium of the first embodiment.

FIG. 7 is a diagram illustrating a process of overwriting information on a recording medium according to a third embodiment.

FIG. 8 is a diagram illustrating a method of reproducing information recorded on the recording medium of the third embodiment.

FIG. 9 is a configuration diagram of a recording medium of Example 1.

FIG. 10 is a diagram showing the mark length dependency of C / N of the medium of Example 1 compared with the conventional example.

FIG. 11 is a configuration diagram of a recording medium according to a second embodiment.

FIG. 12 is a diagram showing an overwritable power margin of the medium of Example 2;

FIG. 13 is a configuration diagram of a recording medium according to a third embodiment.

FIG. 14 is a diagram illustrating a reproduction principle of a conventional example.

[Explanation of symbols]

 16 reproducing layer 18 memory layer 20 recording layer 22 intermediate layer 24 switch layer 26 initialization layer 30 beam spot 30a low temperature region 30b high temperature region

Claims (3)

[Claims] 1. A transparent substrate (14) and a magnetic reproducing layer (1) laminated on the transparent substrate (14) for reading information having an in-plane easy magnetization direction at room temperature.
6), and a magnetic memory layer (18) laminated on the magnetic reproducing layer (16) for holding information having an easy magnetization direction perpendicular to the film surface and having a compensation temperature of room temperature or less. A magnetic recording layer (20) laminated on the magnetic memory layer (18) for recording information having a direction of easy magnetization perpendicular to a film surface, and the magnetic reproducing layer (16) 2. The overwrite magneto-optical recording medium having a film thickness of 20 nm to 60 nm. 2. A transparent substrate (14) and a magnetic reproducing layer (1) laminated on the transparent substrate (14) for reading information having an in-plane easy magnetization direction at room temperature.
6), and a magnetic memory layer (18) laminated on the magnetic reproducing layer (16) for holding information having an easy magnetization direction perpendicular to the film surface and having a compensation temperature of room temperature or less. A magnetic recording layer (20) laminated on the magnetic memory layer (18) for recording information having a direction of easy magnetization perpendicular to the film surface, and the magnetization of the magnetic recording layer (20). A magnetic initialization layer (26) having a magnetization easy direction perpendicular to the film surface for initialization, and inserted between the magnetic recording layer (20) and the magnetic initialization layer (26), A magnetic switching layer (24) having an easy magnetization direction perpendicular to a film surface for controlling an exchange coupling force between the magnetic recording layer (20) and the magnetic initialization layer (26), The Curie temperatures of the layer (18), the magnetic recording layer (20), the magnetic switch layer (24) and the magnetic initializing layer (26) are Tc1, Tc2, Tc3 and Tc4, respectively. At this time, the overwrite magneto-optical recording medium is characterized in that the relationship of Tc3 <Tc1 <Tc2 <Tc4 is satisfied, and the film thickness of the magnetic reproducing layer (16) is within a range of 20 nm to 60 nm. 3. The magnetic memory layer (18) and the magnetic recording layer
The magnetic intermediate layer (22) inserted between the magnetic memory layer (18) and the magnetic recording layer (20), which is inserted between the magnetic intermediate layer (22) and the magnetic recording layer (20). Overwrite magneto-optical recording medium.