JP2000215535A - Magneto-optical recording medium with overwrite function - Google Patents

Abstract

(57) Abstract: To improve the recording performance of a magneto-optical recording medium having an overwrite function. A magneto-optical recording medium of the present invention comprises a disk-shaped substrate and at least a memory layer on the substrate. And the recording layer,
The recording layer is irradiated with a laser beam, the information is recorded by changing the direction of magnetization, the memory layer is transferred with the information recorded on the recording layer, the initialization layer is In a magneto-optical recording medium having a function of aligning the magnetization of the recording layer in one direction and having a light modulation direct overwrite function, the recording layer is formed of a plurality of layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magneto-optical recording medium having a light modulation direct overwrite (LIM-DOW) function.

[0002]

2. Description of the Related Art A recording method in a rewritable optical disk system includes a light modulation recording in which recording is performed by modulating an irradiation intensity of a laser beam irradiated according to recording information, and a direction of an external magnetic field to be applied is modulated in accordance with recording information. There is magnetic field modulation recording for recording. To achieve high-density recording,
Recording by the pen tip recording method of light modulation recording is effective. In the pen tip recording method, recording is performed in a central region of an irradiation spot formed on a recording medium by a laser beam irradiated at the time of recording.

If a magneto-optical recording medium having a light modulation direct overwrite function is used, a higher-performance magneto-optical recording medium can be obtained. The light modulation direct overwrite function modulates the irradiation intensity of a laser beam irradiated at the time of recording to a high level and a low level according to recording information, and erases previously written information and simultaneously writes a recording mark. . In writing the mark, the mark is once written on the recording layer and then transferred to the memory layer. The recording mark is held by this transfer. After that, the recording layer is initialized under the influence of the initialization layer,
Since the recording mark is transferred to the memory layer as described above, the recording mark does not disappear.

[0004] Reproduction is performed by irradiating a laser beam for reproduction to a magneto-optical film whose magnetization direction has changed in accordance with information and detecting reflected light. The Kerr rotation angle changes in the reflected light in accordance with the direction of the magnetization changed according to the recorded information. Information is reproduced by detecting the reflected light having the different Kerr rotation angles. In order to perform high-density recording, it is effective to make the size of the recording mark smaller. However, there is a limit to the size of a reproducible recording mark. This is due to the fact that there is a limit to the minimum diameter of the irradiation spot of the laser beam irradiated during reproduction.

[0005] Normally, reproduction is performed in such a state that one recording mark enters the irradiation spot. However, if the recording marks are made smaller for higher density and the interval between the marks becomes narrower, a plurality of recording marks will enter the irradiation spot of the reproducing laser beam. In such a state, reflected light from a plurality of recording marks is generated, a plurality of recorded information is reproduced, and information other than the information to be reproduced is detected, and the reproduction becomes impossible.

An irradiation spot is formed by narrowing a laser beam with an objective lens. The diameter of the irradiation spot depends on the wavelength of the laser beam and cannot be made smaller than the wavelength of the laser beam. Therefore, even if the size of the recording mark is reduced to increase the recording density, the irradiation spot cannot be reduced to correspond to the size of the recording mark.

As a method of reproducing a recording mark smaller than that of the related art, reproduction by MSR (magnetic super-resolution) is known. When reproducing information recorded on a magneto-optical recording medium that can be reproduced by the MSR, a laser beam applied to the medium is irradiated with a laser beam having a higher intensity than when a general magneto-optical recording medium is used. in this case,
In the irradiation spot, a region having a relatively low temperature is formed in a region having a relatively high temperature and a region other than the high temperature region. Further, by dividing the temperature distribution into three, it is possible to divide the temperature distribution into a high-temperature region having a relatively high temperature, a low-temperature region having a relatively low temperature, and a medium-temperature region sandwiched between these two regions. Thereby, only the recorded information in one of the high-temperature region and the low-temperature region, or the medium-temperature region between the high-temperature region and the low-temperature region is to be reproduced.

[0008] Such MSRs include CAD, FAD,
There is a method such as a double mask (D-RAD). For example, C
The AD method uses a material that is an in-plane magnetized film at room temperature as a reproducing layer, but becomes perpendicularly magnetized when irradiated with a laser beam and becomes high temperature, and reproduces only a region in the perpendicularly magnetized state. . Further, there is a magnetostatic coupling CAD system.
This method has a film configuration in which a nonmagnetic layer such as SiN is formed between a reproducing layer and a memory layer. With this configuration, higher-density reproduction can be performed than in the above-described normal CAD system.

Japanese Patent Application Laid-Open No. 4-255946 proposes a double mask method (D-RAD method) in which reproduction is performed in an area between a high temperature area and a low temperature area. The mark length of a conventional magneto-optical recording medium having an overwrite function was about 0.54 μm.

[0010]

When recording is performed on a magneto-optical recording medium having a light modulation direct overwrite function by a pen tip recording method in order to achieve high-density recording, recorded information is lost. A point has arisen. Therefore, high-density recording cannot be performed on a magneto-optical recording medium having a light modulation direct overwrite function by a pen tip recording method.

[0011]

The inventor of the present invention has investigated the cause of the loss of recorded information when recording is performed on a magneto-optical recording medium having a light modulation direct overwrite function by a pen tip recording method. As a result, it was found that the cause was that the information recorded on the recording layer first was not transferred to the memory layer in a satisfactory manner. Then, it was found that the reason why the transfer to the memory layer is not performed favorably is that the pen tip recording method is caused by the feature that the recording is performed using the smiling area of the irradiation spot.

Therefore, the inventor tried to change the composition of the material constituting the memory layer in order to transfer the recording mark to the memory layer satisfactorily. However, if the composition of the material of the memory layer is changed, the recording layer becomes difficult to be initialized, causing a problem that the overwrite operation is deteriorated. Therefore, the present inventor has decided to solve the above-mentioned problem by replacing the single recording layer with a plurality of recording layers.

Accordingly, the present invention provides a disk-shaped substrate having at least a memory layer, a recording layer, and an initialization layer on the substrate, wherein the recording layer is irradiated with laser light to change its magnetization direction. Information is recorded, the memory layer transfers information recorded on the recording layer, and the initialization layer has a light modulation direct overwrite function having a function of aligning the direction of magnetization of the recording layer in one direction. A magneto-optical recording medium, wherein the recording layer is formed of a plurality of layers (claim 1). 2. The magneto-optical recording apparatus according to claim 1, wherein each of the plurality of layers is made of a rare earth metal and a transition metal, and the layers have different compositions of the rare earth metal and the transition metal. Media (claim 2). " Third, among the plurality of layers, a layer formed on the memory layer side is a layer that promotes transfer of recording information of the recording layer to the memory layer, and is formed on the initialization layer side. 2. The magneto-optical recording medium according to claim 1, wherein the layer is a layer that promotes initialization of recording information of the recording layer. Fourth, the magneto-optical recording medium according to claim 1, wherein the plurality of layers include at least a layer made of a material predominant in rare earth and a layer made of a material predominant in transition metal. . Fifthly, there is provided "a magneto-optical recording medium according to claim 1, wherein the plurality of layers include at least a layer made of a rare earth-dominated material and a layer made of a transition metal-dominated material." . Sixthly, there is provided "a magneto-optical recording medium according to claim 1, wherein the plurality of layers have layers having at least different composition ratios of Co." Seventhly, there is provided an overwritable magneto-optical recording medium characterized by having a recording mark having a mark length smaller than about 0.54 μm (claim 7).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A magneto-optical recording medium according to the present invention has at least an optical modulation direct overwrite function. The magneto-optical recording medium has at least a memory layer, a recording layer, and an initialization layer made of a magnetic film of a rare earth metal and a transition metal, and the recording layer includes a plurality of layers having different functions.

Tb, Fe, Co can be used for the memory layer, Dy, Fe, Co, etc. can be used for the recording layer, and Tb, Fe, C can be used for the initialization layer.
o etc. can be used. Further, a reproducing intermediate layer may be formed between the memory layer and the recording layer. The reproduction intermediate layer is Gd,
The magnetic layer is preferably made of Fe or the like. Further, a switch layer may be formed between the recording layer and the initialization layer.
The switch layer is preferably a magnetic layer made of Tb, Fe, Co or the like. The Curie temperature is preferably higher in the order of the initialization layer, the recording layer, and the memory layer.

As described above, the recording layer of the magneto-optical recording medium of the present invention is characterized in that it comprises at least two layers. Of these two recording layers, one layer is a layer having a performance of good transfer of recording marks to the memory layer, and the other layer is a layer having excellent initialization characteristics of the initialization layer with respect to the recording layer. It is preferable to use a layer having the performance of

When the recording layer is composed of two layers,
Domain walls may occur between layers. Even if a recording layer is formed of a plurality of layers, if it functions as a recording layer, it must function as a single layer.If a domain wall occurs, there may be a problem in function, and there is a problem in stability of recording / reproducing performance. May occur. In such a case, if the recording layer is formed of three or more layers, the problem of the domain wall can be solved and more stable recording / reproducing characteristics can be provided.

The performance of the recording layer can be controlled by changing the composition of the material forming each layer of the recording layer. Specifically, the recording layer formed closer to the memory layer has a composition having a compensation temperature near the Curie temperature of the memory layer in order to improve the transfer performance of the recording mark from the recording layer to the memory layer. The Curie temperature as described above can be controlled by changing the composition ratio of Co in the layers constituting the recording layer.

By setting the recording layer close to the initialization layer to the above-described composition, the recording layer can be almost completely initialized. In the present invention, the thickness of the recording layer is preferably about 300 °. Further, the magneto-optical recording medium having the optical modulation direct overwrite function of the present invention may be further provided with an MSR (magnetic super-resolution) function as described in the description of the related art. In this case, the reproducing layer and the reproducing intermediate layer have an MSR function. As the MSR function, functions of the type described in the above-mentioned conventional technology can be applied.

By adding the MSR function in this way, it is possible to further increase the recording density of a magneto-optical recording medium having an optical modulation direct overwrite function that provides an almost reliable overwrite function.

[0021]

EXAMPLE (Production of a magneto-optical recording medium) Si was formed on a circular substrate having a diameter of 86 mm by magnetron sputtering.
A lower protective film made of N is formed to a thickness of about 70 nm.
At this time, a target containing Si as a main component is used.

In the sputtering, the gas pressure in the vacuum chamber of the sputtering device is temporarily reduced to 1 × 10 ⁻⁶ Torr.
After evacuation, a mixed gas of argon and nitrogen was introduced, and the gas pressure in the chamber was set to 5 × 10 ⁻³ Torr, and sputtering was performed. After forming the lower protective film, a reproducing layer was formed thereon. GdFeCo was used for the reproducing layer. The composition is 25 atm% of Gd and 60 atm of Fe.
% And Co at 15 atm%. The film thickness was about 30 nm.

A reproducing intermediate layer was formed on the reproducing layer. GdFe was used for the reproducing intermediate layer. The composition is Gd at 30at.
m% and Fe at 70 atm%. The film thickness was about 30 nm. A cut layer was formed on the reproduction intermediate layer. T for cutting layer
bFe was used. The composition was Tb at 21 atm% and Fe at 79 atm%. The film thickness was about 20 nm.

A memory layer was formed on the cutting layer. TbFeCo was used for the memory layer. The composition is Tb 21a
tm%, Fe was 79 atm%, and Co was 15 atm%. The film thickness was about 30 nm. An intermediate layer was formed on the memory layer. GdFeCo was used for the intermediate layer. The composition was 24 atm% for Gd, 66 atm% for Fe, and 10 atm% for Co. The film thickness was about 10 nm.

A recording layer was formed on the memory layer. The recording layer is used for improving the recording performance of the magneto-optical recording medium of the present embodiment having the optical modulation direct overwrite function.
A layer structure was adopted. First, the recording layer 1 near the reproducing layer is formed. For the recording layer 1, DyFeCo was used. The composition is Dy
28 atm%, Fe 59 atm%, Co 13 at
m%. The film thickness was about 10 nm.

The recording layer 2 was formed on the recording layer 1. DyFeCo was used for the recording layer 2 similarly to the recording layer 1. The composition is
Dy 25 atm%, Fe 61 atm%, Co 14
atm%. The film thickness was about 10 nm. In this embodiment, the recording layer was formed by using co-sputtering. Then, the composition of the recording layers 1 and 2 was changed by lowering the power applied to the target when forming the recording layer 2 than when the recording layer 1 was formed.

A switch layer was formed on the recording layer 2. TbFeCo was used for the switch layer. The composition is Tb 1
7 atm%, Fe 70 atm%, Co 13 atm%
And The film thickness was about 12 nm. An initialization layer was formed on the switch layer. TbFeCo was used for the initialization layer. The composition is Tb 23 atm%, Fe 7 atm%,
Co was set to 70 atm%. The film thickness was about 70 nm. (Recording / reproducing apparatus for magneto-optical recording medium) The recording / reproducing apparatus for the magneto-optical recording medium will be described.

This apparatus has a rotation system for a magneto-optical recording medium, a laser light source for recording and reproduction, magnetic field applying means for an initialization magnetic field, a recording magnetic field and a reproduction magnetic field, and a reproduction and signal processing system. is there. The laser light source for recording / reproducing includes a semiconductor laser having λ = 680 nm and a numerical aperture (NA) = 0.55, and an optical system having a lens and the like.

The reproducing system includes a detector such as a photodiode and an optical system for transmitting light to the detector. Then, the magneto-optical recording medium is rotated by a rotating system so that the linear velocity of the reproducing portion becomes constant, and the rotated magneto-optical recording medium is irradiated with laser light from a laser light source. (Recording method) First, an L-power laser beam and a H-power-modulated laser beam are irradiated to the magneto-optical recording medium having the above-described configuration in accordance with the recording information, and the recording information is recorded on the memory layer by an optical modulation overwriting method. I do. In this embodiment, the L power is about 5 mW and the H power is about 8 mW
And The rotation speed of the magneto-optical recording medium is 3600
rpm. (Reproduction method) Reproduce the recorded information of the recorded memory layer.

During reproduction, the magneto-optical recording medium is rotated at a linear velocity of about 9 m / s. When reproduction is performed by the reproducing apparatus, the magneto-optical recording medium is irradiated with a laser beam having a reproducing power. The reproducing power in this embodiment was set to about 2.5 mW. At this time, a magnetic field in a direction opposite to the direction in which information is recorded is applied as a reproducing magnetic field simultaneously with the irradiation of the laser beam. The applied magnetic field in this example was set to 100 Oe.

The irradiated laser light is reflected by the reproducing layer, the reflected light is made incident on a photodetector, converted into an electric signal by the photodetector, and the electric signal is differentially reproduced. As a result, in this embodiment,
Approximately 0.35 μm mark length (space is 0.35 μm)
As a result, a magneto-optical recording medium of about 46 dB was obtained.

[0032]

As described above, the magneto-optical recording medium of the present invention having the optical modulation overwrite function has a shorter mark length than the conventional one, so that a magneto-optical recording medium with a higher recording density can be obtained. In addition, since the recording layer was formed of a plurality of layers, the transfer of the recording mark to the memory layer was improved, and the recording / reproducing performance was further improved. Also, the initialization characteristics have been improved.

Therefore, the magneto-optical recording medium having an overwrite function of the present invention is capable of high-density recording and has excellent recording and reproducing performance.

Claims (7)

[Claims] 1. A disc-shaped substrate, comprising at least a memory layer, a recording layer, and an initialization layer on the substrate, wherein the recording layer records information by irradiating a laser beam to change the direction of magnetization. The memory layer transfers information recorded on the recording layer, and the initialization layer has a function of aligning the magnetization direction of the recording layer in one direction. In the medium,
A magneto-optical recording medium, wherein the recording layer is formed of a plurality of layers. 2. The magneto-optical device according to claim 1, wherein each layer of the plurality of layers is made of a rare earth metal and a transition metal, and each of the layers has a different composition of the rare earth metal and the transition metal. recoding media. 3. A layer formed on the memory layer side of the plurality of layers is a layer for promoting transfer of recording information of the recording layer to the memory layer, and is formed on the initialization layer side. 2. The magneto-optical recording medium according to claim 1, wherein the layer is a layer that promotes initialization of recording information of the recording layer. 4. The magneto-optical recording medium according to claim 1, wherein the plurality of layers include at least a layer made of a material predominant in rare earth and a layer made of a material predominant in transition metal. 5. The magneto-optical recording medium according to claim 1, wherein the plurality of layers include at least a layer made of a material predominant in rare earth and a layer made of a material predominant in transition metal. 6. The magneto-optical recording medium according to claim 1, wherein the plurality of layers include layers having at least different composition ratios of Co. 7. An overwritable magneto-optical recording medium having a recording mark having a mark length smaller than about 0.54 μm.