JP2000195115A - Magneto-optical recording medium and recording and reproducing method of magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical disk in which recording with higher density is possible while decreasing the noise during reproducing. SOLUTION: This medium consists of a light-transmitting substrate 1, a readout layer 3 formed on the substrate 1, and a recording layer 4 for magneto- optical recording of information formed on the readout layer 3. The readout layer 3 shows in-plane magnetization with dominant in-plane magnetic anisotropy at room temp. and shows transition to perpendicular magnetization with dominant perpendicular magnetic anisotropy with temp. increase. The readout layer 3 consists of GdFeCo.

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, and a method for recording / reproducing a magneto-optical recording medium applied to a magneto-optical recording apparatus.

[0002]

2. Description of the Related Art Magneto-optical disks are being researched and developed as rewritable optical disks, and some of them have already been put into practical use as external memories for computers.

A magneto-optical disk uses a perpendicular magnetization film as a recording medium and performs recording and reproduction using light. Therefore, a large recording capacity can be realized as compared with a floppy disk or a hard disk using an in-plane magnetization film.

[0004]

However, in the above-mentioned conventional configuration, the recording density of the magneto-optical disk depends on the size of the light beam used for recording and reproduction on the recording medium. There is a problem that the storage capacity cannot be increased.

In other words, when the size of the recording bit and the interval between the recording bits become smaller than the diameter of the light beam spot, a plurality of recording bits including adjacent recording bits are included in the light beam spot. Therefore, there is a problem that noise increases and it becomes impossible to separate and reproduce each recording bit.

In order to increase the recording density, means for reducing the diameter of the light beam spot include shortening the wavelength of the laser as a light source, increasing the numerical aperture (NA) of the objective lens, and reducing the angle of narrowing down the light. It is possible to increase the size.

[0007] With regard to shortening the wavelength of a laser, development of a semiconductor laser for a short wavelength has been energetically performed. However, the emission intensity is still weak and cannot be used as a light source for recording / reproducing a magneto-optical disk.

When the NA is increased, it is necessary to minimize the inclination between the objective lens for converging the light beam to the light beam spot and the surface of the magneto-optical disk.
Otherwise, the diameter of the light beam spot on the recording medium will increase. In other words, if the NA is increased, unless the assembly accuracy of the optical system of the magneto-optical disk device or the amount of warpage of the magneto-optical disk is controlled more strictly than before,
A new problem that the light beam spot diameter becomes large occurs.

For this reason, the wavelength of the semiconductor laser used in the current magneto-optical disk is 780 to 830 nm, and the NA of the objective lens is 0.45 to 0.55. Therefore, the light beam spot diameter on the recording medium is 1.7 to 2.0 μm.

In consideration of the light beam spot diameter,
The track pitch of the magneto-optical disk, that is, the recording bit interval in the radial direction of the magneto-optical disk is 1.4 to 1.6 μ.
m.

If the track pitch is made smaller than this,
At the time of reproduction, it is necessary to suppress crosstalk in which information recorded on an adjacent track leaks. For this reason, a compensation circuit for performing a special waveform processing must be provided, which causes a problem that the magneto-optical disk device becomes complicated.

Next, when performing magnetic field modulation overwriting on a magneto-optical disk, in order to obtain a sufficiently large magnetic field,
In addition to the problem that the magnetic field generating mechanism must be brought close to the magneto-optical disk, there is a problem that the magnetic field cannot be modulated at high speed.

In order to solve these problems, Japanese Patent Laid-Open Publication No. Sho 62-175948 discloses a magneto-optical recording medium having a two-layer structure including a recording layer using a perpendicular magnetization film and a recording auxiliary layer. There is proposed a light modulation overwrite method of performing overwrite by modulating light.

However, in this light modulation overwriting method, the magnetization direction of the recording auxiliary layer changes when overwriting is performed, so that it is necessary to align the magnetization direction of the recording auxiliary layer every time before overwriting. For this reason, in addition to the recording magnetic field generating mechanism, an initializing magnetic field generating mechanism is also required, which causes an increase in the size of the magneto-optical disk drive, and
There is a problem that it leads to an increase in cost.

[0015]

The magneto-optical recording medium according to the present invention has a recording layer for magneto-optically recording magnetization information, and exhibits in-plane magnetization at room temperature, but shifts to perpendicular magnetization with increasing temperature. 3. A magneto-optical recording medium according to claim 2, further comprising: a readout layer to which the magnetization of the recording layer is transferred, wherein the readout layer is GdFeCo. It is characterized by the following.

The magneto-optical recording medium according to a third aspect is characterized in that the recording layer is made of TbFeCo.

According to a fourth aspect of the present invention, in the magneto-optical recording medium, the GdFeCo is Gd _x (Fe _1-Y Co _Y ) _1-x : 0.19
<X <0.29, 0.1 <Y <0.5.

According to a fifth aspect of the present invention, there is provided a magneto-optical recording medium, comprising: a recording layer for magneto-optically recording magnetization information; And the readout layer is made of a rare earth transition metal amorphous alloy having ferrimagnetism, and has a Curie temperature of 130 ° C. or higher without a compensation temperature. The composition is set, and the film thickness is set to 10 nm or more.

According to a sixth aspect of the present invention, there is provided a magneto-optical recording medium comprising: a recording layer for magneto-optically recording magnetization information; and a recording layer which exhibits in-plane magnetization at room temperature, and shifts to perpendicular magnetization with an increase in temperature to change the magnetization of the recording layer. The readout layer is made of a rare earth transition metal alloy in which rare earth metal is predominant, and the compensation temperature is set so as not to be between room temperature and Curie temperature. The recording layer is made of a rare earth transition metal alloy in which a transition metal is predominant.

A magneto-optical recording medium according to a seventh aspect is characterized in that an intermediate layer made of an in-plane magnetic film is provided between the readout layer and the recording layer.

According to a eighth aspect of the present invention, there is provided a recording / reproducing method for a magneto-optical recording medium, wherein a recording layer made of a rare earth transition metal alloy in which a transition metal predominantly performs magneto-optical recording of magnetization information and an in-plane magnetization at room temperature, A readout layer in which the magnetization of the recording layer is transferred to perpendicular magnetization with a rise in temperature, and the readout layer is made of a rare earth transition metal alloy,
A recording / reproducing method for recording / reproducing information using a magneto-optical recording medium whose compensation temperature is set so as not to be between room temperature and the Curie temperature, and in which a rare earth metal is predominantly set, comprising: By applying a constant magnetic field for magnetizing the layer and irradiating a laser beam switched between a low first laser power and a high second laser power according to the recording signal, the magnetization direction of the recording layer is reversed. By performing recording and irradiating a laser beam having a lower laser power than the first laser power, an area smaller than the laser spot diameter of the readout layer is shifted to a perpendicular magnetization state, and The sub-lattice magnetization in the changed area is aligned in a direction stable with respect to the sub-lattice magnetization in the recording layer, and information is reproduced from the read-out layer in the perpendicular magnetization state. It is characterized in.

According to the present invention, when the light beam is irradiated to the readout layer during the reproducing operation, the temperature distribution of the irradiated portion becomes almost Gaussian distribution. Temperature rises.

As the temperature rises, the magnetization at the temperature rise site shifts from in-plane magnetization to perpendicular magnetization. At this time, the magnetization direction of the reading layer follows the magnetization direction of the recording layer due to the exchange coupling force between the two layers of the reading layer and the recording layer.

When the temperature rising portion shifts from in-plane magnetization to perpendicular magnetization, only the temperature rising portion shows the polar Kerr effect, and information is reproduced based on the reflected light from the portion.

Then, when the light beam moves to reproduce the next recording bit, the temperature of the preceding reproducing portion decreases, and the magnetization shifts from perpendicular magnetization to in-plane magnetization, so that the polar Kerr effect is not exhibited. This means that the magnetization recorded on the recording layer is masked by the in-plane magnetization of the reading layer and cannot be read. As a result, signal mixing from adjacent recording bits which causes noise and lowers the resolution of reproduction is eliminated.

As described above, since only the region heated to a predetermined temperature or higher is involved in the reproduction, it is possible to reproduce the recording bits smaller than before, and the recording density is remarkably improved.

According to the magneto-optical recording medium of the first and fourth aspects, by employing GdFeCo, which is a rare earth transition metal alloy, as the material of the readout layer, the magnetization direction can be changed from in-plane magnetization to perpendicular magnetization. A readout layer which shifts steeply to the above can be realized. Thereby, noise at the time of reproduction is reduced, so that a magneto-optical recording medium capable of performing higher-density recording can be provided.

According to the structure of the second aspect, in addition to the effect of the first aspect, the perpendicular magnetic anisotropy is reduced by employing DyFeCo as the material of the recording layer. Thereby, the external magnetic field at the time of recording can be reduced.

According to the structure of claim 3, in addition to the effect of claim 1, the perpendicular magnetic anisotropy is increased because the recording layer is made of TbFeCo. Thereby, a magneto-optical recording medium having high reproduction signal quality can be provided.

According to the fifth aspect of the present invention, the readout layer comprises:
It is made of a rare earth transition metal amorphous alloy having ferrimagnetism, and has a Curie temperature of 130 ° C. without a compensation temperature.
The composition is set so as to be as described above, and the film thickness is 10 n
Since the value is set to m or more, the quality of a reproduced signal when reading information recorded at high density is improved.

According to the configuration of claim 6, the readout layer includes:
It is made of a rare earth transition metal alloy, and its compensation temperature is set so as not to be between room temperature and the Curie temperature, and the content of the rare earth metal is set to be larger than the maximum content corresponding to the compensation composition. Therefore, a magneto-optical recording medium capable of high-density recording and reproduction can be provided.

According to the structure of claim 7, in addition to the function of claim 6, an intermediate layer made of an in-plane magnetic film is provided between the read layer and the recording layer. Can control the exchange coupling force. This increases the selection range of materials for the readout layer and the recording layer.

According to the configuration of claim 8, high-density recording and reproduction can be performed using the magneto-optical recording medium of claims 6 and 7.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the magneto-optical disk (magneto-optical recording medium) of this embodiment has a substrate 1 (base), a transparent dielectric layer 2, a readout layer 3, a recording layer 4, a protective layer 5, It has a configuration in which the overcoat layer 6 is laminated in this order.

The rare earth transition metal alloy used as the readout layer 3 has a very narrow composition range (indicated by A in the figure) showing perpendicular magnetization, as shown in the magnetic phase diagram of FIG. This is because perpendicular magnetization appears only in the vicinity of the compensation composition (indicated by P in the figure) where the moments of the rare earth metal and the transition metal balance.

The magnetic moments of the rare earth metal and the transition metal have different temperature characteristics, and at high temperatures, the magnetic moment of the transition metal becomes larger than that of the rare earth metal. For this reason, the content of the rare earth metal is set to be larger than the compensating composition at room temperature, and at room temperature, in-plane magnetization is exhibited instead of perpendicular magnetization. In this case, when the light beam is irradiated, the temperature of the irradiated portion rises, and the magnetic moment of the transition metal becomes relatively large, comes to balance with the magnetic moment of the rare earth metal, and shows perpendicular magnetization. Become.

FIGS. 3 to 6 show an example of the hysteresis characteristic of the readout layer 3. The horizontal axis indicates the readout layer 3.
Is the external magnetic field (H _ex ) applied to the film surface in the vertical direction, and the vertical axis is the polar Kerr rotation angle (θk) when light is incident from the direction also perpendicular to the film surface.

FIG. 3 shows the composition P in the magnetic phase diagram of FIG.
From the room temperature to the temperature T of the readout layer 3 of FIG. ₁Hysteria between
4 to 6 show lysis characteristics.
Temperature T₁To temperature T_TwoHysteresis characteristics up to temperature
T_TwoTo temperature T_ThreeHysteresis characteristics up to temperature T_Three
To Curie temperature T_cShowing hysteresis characteristics up to
I have.

In the temperature range from the temperature T ₁ to the temperature T ₃ , the rise of the pole Kerr rotation angle with respect to the external magnetic field shows a hysteresis characteristic which is steep, but in other temperature ranges, the pole Kerr rotation angle is almost zero. .

By using a rare earth transition metal having the above characteristics for the readout layer 3, the recording density of the magneto-optical disk can be increased. That is, it is possible to reproduce a recording bit smaller than the size of the light beam. This will be described below.

At the time of the reproducing operation, the readout layer 3 is irradiated with the reproducing light beam 7 from the side of the substrate 1 (FIG. 1) via the condenser lens 8. The temperature of the portion of the readout layer 3 irradiated with the reproduction light beam 7 is the highest near the center thereof and is higher than the temperature of the surrounding portions. This is because the reproduction light beam 7
This is because the light intensity distribution becomes a Gaussian distribution and the temperature distribution of the reproducing portion on the magneto-optical disk also becomes almost a Gaussian distribution since the light is narrowed down to the diffraction limit by the condenser lens 8.

When the intensity of the reproduction light beam 7 is set so that the temperature near the center reaches T ₁ or more and the temperature of the peripheral portion becomes T ₁ or less, only the region having the temperature of T ₁ or more is reproduced. Therefore, recording bits smaller than the diameter of the reproducing light beam 7 can be reproduced, and the recording density is significantly improved.

That is, the magnetization in the region having a temperature of T ₁ or more shifts from in-plane magnetization to perpendicular magnetization (the hysteresis characteristic of the polar Kerr rotation angle shifts from FIG. 3 to FIG. 4 or FIG. 5). At this time, the magnetization direction of the recording layer 4 is transferred to the reading layer 3 by the exchange coupling force between the two layers of the reading layer 3 and the recording layer 4. On the other hand, other than the area corresponding to the vicinity of the center of the reproducing light beam 7, because the surrounding site is the temperature T ₁ or less, in-plane magnetization state (FIG. 3) is held. As a result, the polar Kerr effect is not exhibited with respect to the reproduction light beam 7 irradiated to the film surface from the vertical direction.

As described above, when the temperature rising portion shifts from the in-plane magnetization to the perpendicular magnetization, only the vicinity of the center of the reproduction light beam 7 exhibits the polar Kerr effect, and based on the reflected light from the portion, The information recorded on the recording layer 4 is reproduced.

[0046] moving the reproducing light beam 7 (actually magneto-optical disk is rotated), when to reproduce the next recording bit, the temperature of the previous reproducing portion drops to T ₁ or less, from the perpendicular magnetization Transition to in-plane magnetization. Along with this, the portion where the temperature has decreased no longer exhibits the polar Kerr effect. Therefore, information is not reproduced from the portion where the temperature is lowered, and signal mixing from adjacent recording bits which causes noise is eliminated.

As described above, when the magneto-optical disk of the present invention is used, the recording bit smaller than the diameter of the reproducing light beam 7 can be surely reproduced, and the recording density is not affected by the adjacent recording bits. It can be significantly increased.

Next, a specific example of the magneto-optical disk of the present embodiment will be described.

The substrate 1 has a diameter of 86 mm, an inner diameter of 15 mm,
It is made of a disc-shaped glass having a thickness of 1.2 mm. Although not shown, an uneven guide track for guiding a light beam has a pitch of 1.6 μm on one surface of the substrate 1.
The groove (recess) has a width of 0.8 μm and the land (convex) has a width of 0.8 μm. That is, the width of the groove and the width of the land are formed to be 1: 1.

On the surface of the substrate 1 on which the guide tracks are formed, A1N having a thickness of 80 n is formed as the transparent dielectric layer 2.
m.

On the transparent dielectric layer 2, GdFeCo, which is a rare earth transition metal alloy thin film, is used as the readout layer 3.
It is formed with a thickness of 50 nm. The composition of GdFeCo is Gd _0.26 (Fe _0.82 Co _0.18 ) _0.74 , and its Curie temperature is about 300 ° C.

On the readout layer 3, as the recording layer 4, a rare-earth transition metal alloy thin film DyFeCo having a thickness of 50 n
m. The composition of DyFeCo is Dy _0.23
(Fe _0.78 Co _0.22 ) _0.77 , and its Curie temperature is about 200 ° C.

Due to the combination of the readout layer 3 and the recording layer 4, the magnetization direction of the readout layer 3 is almost in-plane at room temperature (that is, the layer direction of the readout layer 3).
The transition from the in-plane direction to the vertical direction occurs at a temperature of about 125 ° C.

On the recording layer 4, as a protective layer 5, A1N
Is formed with a thickness of 20 nm.

On the protective layer 5, a polyurethane acrylate-based ultraviolet-curable resin having a thickness of 5 μm is formed as the overcoat layer 6.

The above-mentioned magneto-optical disk was manufactured in the following procedure.

The guide tracks on the surface of the glass substrate 1 were formed by a reactive ion etching method.

Transparent dielectric layer 2, readout layer 3, recording layer 4
The protective layer 5 and the protective layer 5 were both formed by a sputtering method in the same sputtering apparatus without breaking vacuum. A1N of the transparent dielectric layer 2 and the protective layer 5 is obtained by setting the A1 target to N
It was formed by a reactive sputtering method in which sputtering was performed in a _two- gas atmosphere. The readout layer 3 and the recording layer 4 are made of FeC
A so-called composite target in which Gd or Dy chips are arranged on an o-alloy target, or a ternary alloy target of GdFeCo and DyFeCo, is formed by sputtering with Ar gas.

The overcoat layer 6 was formed by applying a polyurethane acrylate-based UV-curable resin with a spin coater, and then irradiating and curing the UV-ray with an ultraviolet irradiator.

Next, the results of an operation check performed using the above-described magneto-optical disk will be described.

Due to the combination of the readout layer 3 and the recording layer 4, the magnetization direction of the readout layer 3 is substantially in-plane at room temperature, and shifts from the in-plane direction to the vertical direction at a temperature of about 100 to 125 ° C. .

FIGS. 7 and 8 are graphs showing the results of actually measuring the hysteresis characteristics of the polar Kerr rotation angle at different temperatures. FIG. 7 shows the hysteresis characteristics at room temperature (25 ° C.). When the external magnetic field (H _ex ) is zero, the polar Kerr rotation angle is almost zero. This indicates that the direction of magnetization is hardly in the direction perpendicular to the film surface but in the in-plane direction. FIG. 8 shows the hysteresis characteristics at 120 ° C. It can be seen that even when the external magnetization is zero, there is a polar Kerr rotation angle of about 0.5 deg, and the state shifts to perpendicular magnetization.

The above is the confirmation of the static characteristics.
The result of dynamic measurement using an optical pickup will be described. The wavelength of the semiconductor laser of the optical pickup used for the measurement was 780 nm, and the numerical aperture (N.
A. ) Is 0.55.

First, the radius of the magneto-optical disk is 26.
A single-frequency recording bit having a length of 0.765 μm was previously recorded on a land portion at a position of 5 mm at a rotation speed of 1800 rpm (linear velocity of 5 m / sec). Recording is performed by first aligning the magnetization direction of the recording layer 4 in one direction (erased state).
The direction of the external magnetic field for recording was fixed in a direction opposite to the erasing direction, and the laser was modulated at a recording frequency (in this case, about 3.3 MHz) corresponding to a length of 0.765 μm. . The recording laser power was about 8 mW.

FIG. 9 shows the result of examining the amplitude of the reproduced signal waveform by reproducing the recorded bit string by changing the reproducing laser power. The horizontal axis is the reproduction laser power, 0.5 m
It was measured in the range of W to 3 mW. The vertical axis indicates the reproduction signal amplitude, which is normalized by the amplitude when the reproduction laser power is 0.5 mW.

In the figure, the curve indicated by A is the result for the magneto-optical disk of the present invention, and the curve B in the figure is the result for the conventional magneto-optical disk prepared for comparison and measured. is there.

In the conventional magneto-optical disk, A1N is 80 nm and DyFeCo is 2 nm on the same glass substrate 1 as described above.
The structure is such that 0 nm, A1N is 25 nm, and A1Ni is 30 nm in this order, and the same overcoat layer is provided on A1Ni.

The structure of this conventional magneto-optical disk is such that there is only one DyFeCo magnetic layer, which is a rare earth transition metal alloy, sandwiched on both sides by A1N, which is a transparent dielectric layer, and finally, A1Ni, which is a reflective film, is formed. It is a structure provided. This structure is called a reflective film structure, and is a typical configuration of a commercially available 3.5-inch size single-plate magneto-optical disk. Further, as is well known, the recording layer made of DyFeCo in a conventional magneto-optical disk has perpendicular magnetization from room temperature to high temperature.

In FIG. 9, a straight line indicated by a broken line in the figure is a straight line connecting the point 0 (origin) and the amplitude standard value at 0.5 mW. It is a straight line representing a relationship with power.

In this formula, the medium reflected light amount increases in proportion to the reproduced laser power, and can be replaced by the reproduced laser power.

The measurement result curve (B) of the conventional magneto-optical disk is below this straight line for the following reason.
That is, when the reproducing laser power is increased, the amount of reflected light from the medium increases accordingly, while the temperature of the recording medium increases. The magnetization of a magnetic material generally has the property of decreasing as the temperature rises and becoming zero at the Curie temperature.
Therefore, in the conventional magneto-optical disk, the polar Kerr rotation angle becomes smaller as the temperature rises, so that it does not follow the straight line in the figure, but is on the lower side.

On the other hand, in the measurement result curve (A) of the magneto-optical disk of the present invention, as the reproducing laser power increases, the signal amplitude sharply increases, and reaches a maximum at about 2 to 2.25 mW. Except for the value at 3 mW, all values are above the straight line, and it can be seen that an increase in the amplitude that is equal to or greater than the increase in the reproduction laser power is obtained. This result reflects the characteristic of the readout layer 3 of the present invention that the polar Kerr rotation angle hardly occurs when the temperature is low, and the magnetization rapidly shifts from in-plane magnetization to perpendicular magnetization as the temperature rises. This confirms the operation.

Although the above measurement results were obtained for the land portion, the same measurement was performed for the groove portion, and the same result was obtained.

Next, a description will be given of the result of examining the reproduction signal quality when the recording bit is made smaller. The ability to play smaller recorded bits means that
It means improvement of recording density.

FIG. 10 is a graph showing the result of measuring the reproduction signal quality (C / N) with respect to the recording bit length.
The linear velocity of the magneto-optical disk was 5 m / sec as in the previous experiment.
And recording is performed by changing the recording frequency.
/ N was measured. The optical pickup and the recording method are the same as in the previous experiment.

In the figure, the curve denoted by A is the measurement result of the magneto-optical disk of the present invention, and the reproducing laser power is 2.2.
5 mW. In the figure, the curve indicated by B is the measurement result of the conventional magneto-optical disk as in the previous experiment, and the reproducing laser power was 1 mW.

In the case of a long recording bit having a recording bit length of 0.6 μm or more, there is almost no difference in the C / N between them, but when the recording bit length becomes 0.6 μm or less, the C / N sharply increases in a conventional magneto-optical disk. It is going down. This is because as the recording bit length becomes smaller, the number (area) of recording bits existing in the irradiation diameter of the light beam increases, and it becomes impossible to identify each recording bit.

One index representing the optical resolution of the optical pickup is a cutoff spatial frequency, which is
It is determined by the wavelength of the laser as the light source and the numerical aperture of the objective lens. In the optical pickup used in this experiment, the wavelength of the laser and the numerical aperture of the objective lens (780 nm, respectively)
Using 0.55), the cutoff frequency is calculated and converted to the recording bit length, which is 780 nm / (2 × 0.55) /2=0.355 μm. In other words, the limit of the optical resolution of the optical pickup used in this experiment is 0.355 in the recording pit length.
μm. The result of the conventional magneto-optical disk described above reflects this fact, and the C / N at 0.35 μm is almost zero.

On the other hand, in the magneto-optical disk of the present invention, although the C / N decreases as the recording bit length decreases, the C / N close to 30 dB also occurs for recording bits shorter than the optical resolution of 0.355 μm. Have been obtained.

The measurement was performed for both the land and the groove, and the C / N value and tendency were almost the same.

From the above results, it was confirmed that by using the magneto-optical disk of the present invention, it was possible to reproduce recorded bits smaller than the optical analysis limit. As a result, the recording bit density can be greatly improved as compared with the conventional magneto-optical disk.

Next, a result of examining the crosstalk amount, which is another important effect, in addition to the present invention confirmed in the above experiment, will be described.

In the case of a magneto-optical disk, for example, in the case of a land specification, a guide track having a land as wide as possible and a narrow groove is formed, and only the land is used for recording and reproduction. Therefore,
Crosstalk in a land-specific magneto-optical disk refers to leakage from recording bits written on adjacent lands when an arbitrary land is reproduced. Crosstalk in a groove-specific magneto-optical disk refers to leakage from recording bits written in adjacent grooves when reproducing an arbitrary groove.

For example, according to the IS10089 standard (standard defined for the 5.25 rewritable optical disk of the ISO), a guide track having a pitch of 1.6 μm is used.
The crosstalk amount with respect to the shortest recording bit (0.765 μm) is determined to be −26 dB or less.

In the present embodiment, the crosstalk measurement method defined by the IS10089 standard is 0.76
The crosstalk amount for a recording bit of 5 μm was measured. However, in order to confirm the effect of the magneto-optical disk of the present invention, in the above-mentioned glass substrate 1 having a track pitch of 1.6 μm and the same land width and groove width of 0.8 μm, both adjacent grooves when the land portion was reproduced were used. And the amount of crosstalk from both adjacent lands when the groove portion was reproduced was measured.

FIG. 11 shows the measurement results when the land portion was reproduced. The horizontal axis is the reproduction laser power, and the vertical axis is the crosstalk amount. In the figure, the curve indicated by A is the measurement result of the magneto-optical disk of the present invention, and the curve indicated by B is the measurement result of the above-described conventional magneto-optical disk.

The conventional magneto-optical disk (B) has a large crosstalk amount of about -15 dB, while the magneto-optical disk (A) of the present invention has a crosstalk amount of about -30 dB.
A value that cleared -26 dB defined by the SO standard was obtained.

Similar results were obtained for crosstalk when the groove portion was reproduced.

FIG. 12 shows the reason why such a result was obtained.
It will be described based on.

FIG. 12 is a schematic plan view when the magneto-optical disk is viewed from directly above, in which recording bits indicated by circles (dotted lines) in the middle land portion and the adjacent group portions are recorded. The large circle (solid line) in the figure is the condensed light spot of the reproduction light beam 7, and servo is applied so that the light spot follows the land. In the figure, the land width and the group width are 0.8 μm, and the light spot diameter (light beam diameter) is 1.73 μm (= Airy disk diameter =
1.22 × 780 nm / 0.55), and the recording bit diameter is shown as 0.335 μm for convenience of explanation.

In the drawing, 7 in the reproduction light beam 7
Incoming recording bits. In the case of a conventional magneto-optical disk, each shows a perpendicular magnetization (for example, the magnetization direction of the recording bit portion is upward perpendicular to the plane of the paper, and the magnetization of the (erase portion) is downward in the region other than the recording bit). Because of the effect, the individual signals in the light beam cannot be separated. This is the reason why the C / N at 0.35 μm of the conventional magneto-optical disk is small and the crosstalk from the adjacent track is large in the above experimental results.

On the other hand, with the magneto-optical disk of the present invention,
The magnetization of the readout layer 3 becomes perpendicular in a region near the center of the reproduction light beam 7 and higher in temperature than the surroundings, and remains in-plane magnetization in other regions. Therefore, even if there are seven recording bits in the reproduction light beam 7 as shown in FIG. 3, only one located at the center of the reproduction light beam 7 contributes to the reproduction. Even with very small recording bits, a C / N of about 30 dB can be obtained. further,
Crosstalk from both adjacent tracks is also very small.

As described above, the readout layer 3
In a magneto-optical disk in which the recording layer 4 is formed on the substrate 1 having a track shape with a pitch of 1.6 μm and a land-to-groove width ratio of 1: 1 even when the value of C / N is on the land, It has been confirmed by experiments that both of them can be used for recording and reproduction without any change on the groove, and that the crosstalk is sufficiently small even when information is recorded on the recording layer 4 on the land and on the groove.

As a result, the recording density and track density in the track longitudinal direction can be increased, and both lands and grooves are used for recording and reproduction. Therefore, the recording density is greatly increased as compared with a conventional magneto-optical disk. It becomes possible.

The composition of GdFeCo in the above readout layer 3
Is Gd_0.26(Fe_0.82Co_0.18) _0.74Limited to
Not. The readout layer 3 has almost in-plane magnetization at room temperature.
At room temperature or higher, the transition from in-plane magnetization to perpendicular magnetization
Good. In rare earth transition metal alloys, rare earth and transition
By changing the metal ratio, the magnetization of rare earths and transition metals can be
The matching compensation temperature changes. GdFeCo has this compensation temperature
Gd and FeC
If the compensation temperature is changed by changing the ratio of o,
The temperature at which the transition to the perpendicular magnetization changes with this.

FIG. 13 shows Gd _X (Fe _0.82 Co _0.18 ) _1-X
2 shows the results of examining the compensation temperature and the Curie temperature when the composition of X, that is, Gd, was changed in the system No.

In the composition range where the compensation temperature is equal to or higher than room temperature (25 ° C.), as is apparent from FIG. Of these, preferably, 0.19 <X <0.29
Range. Within this range, the temperature at which the direction of magnetization moves from the in-plane to the vertical direction in a practical configuration in which the recording layer 4 is stacked on the readout layer 3 is in the range of room temperature to 200 ° C. If the temperature is too high, the laser power for reproduction becomes as high as the laser power for recording, so that recording may be performed on the recording layer 4 and the recorded information may be disturbed.

Next, in the above-mentioned GdFeCo system, F
When the ratio between e and Co is changed, that is, Gd _x (Fe
_1-Y Co _Y ) In _1-X , changes in characteristics (compensation temperature and Curie temperature) when Y is changed will be described.

FIG. 14 shows a case where Y is 0, that is, Gd
Is a diagram showing characteristics of _X Fe _1-X. In the figure, for example, when the Gd composition is X = 0.3, the compensation temperature is about 120.
In ° C., the Curie temperature is about 200 ° C.

FIG. 15 shows the case where Y is 1, ie, Gd
Is a diagram showing characteristics of _X Co _1-X. In the figure, for example, when the Gd composition is X = 0.3, the compensation temperature is about 220
In ° C., the Curie temperature is about 400 ° C.

From the above, it can be seen that, even if the Gd composition is the same, the compensation temperature and the Curie temperature increase as the Co content increases.

The higher the Curie temperature of the readout layer 3 is, the more advantageous it is because the larger the polar Kerr rotation angle at the time of reproduction is, the higher C / N can be obtained. However, not much Co
If the amount is excessively increased, the temperature at which the magnetization direction shifts from the in-plane to the perpendicular direction becomes high.

In consideration of these points, Gd _x (Fe _{1 -Y} C
o _Y ) The value of Y in _1-X is preferably in the range of 0.1 <Y <0.5.

In the readout layer 3, the characteristics such as the temperature at which the magnetization shifts from the in-plane magnetization to the perpendicular magnetization are naturally affected by the composition and thickness of the recording layer 4. this is,
This is because a magnetic exchange coupling force acts between the two layers. Therefore, the optimum composition and thickness of the readout layer 3 change depending on the material, composition and thickness of the recording layer 4.

As described above, as the material of the readout layer 3 of the magneto-optical disk of the present invention, GdFeCo which is steep from in-plane magnetization to perpendicular magnetization is optimal. However, the rare earth transition metal alloys described below can also be used.

Gd _x Fe ₁ -x has characteristics as shown in FIG. 14, and has a compensation temperature above room temperature in the range of 0.24 <X <0.35.

Gd _X Co _{1 -X} has characteristics as shown in FIG. 15, and has a compensation temperature above room temperature in the range of 0.20 <X <0.35.

When an FeCo alloy is used as the transition metal, Tb _x (Fe _Y Co _1-Y ) _1-X is 0.20 <X <
It has a compensation temperature above room temperature in the range of 0.30 (where Y is arbitrary). Dy _X (Fe _Y Co _1-Y ) _1-X is 0.2
It has a compensation temperature above room temperature in the range of 4 <X <0.33 (where Y is arbitrary). Ho _X (Fe _Y Co _1-Y )
_1-X has a compensation temperature above room temperature in the range of 0.25 <X <0.45 (where Y is arbitrary).

In addition to the above materials, when the wavelength of the semiconductor laser, which is the light source of the optical pickup, is shorter than the aforementioned 780 nm, a material having a large polar Kerr rotation angle at the wavelength is also used as the readout layer of the present invention. 3 is suitable as the material.

As described above, in an optical disk such as a magneto-optical disk, the recording density is limited by the size of the light beam, which is determined by the laser wavelength and the numerical aperture of the objective lens. Therefore, if a semiconductor laser having a shorter wavelength than now appears, the recording density of the magneto-optical disk will be improved by itself. At present, 67
Semiconductor lasers having a wavelength of 0 to 680 nm are almost at the practical level, and SHG lasers having a wavelength of 400 nm or less are being energetically studied.

The polar Kerr rotation angle of a rare-earth transition metal alloy has wavelength dependence. In general, as the wavelength becomes shorter,
The polar car rotation angle decreases. When a film having a short polarizer and a large polar Kerr rotation angle is used, the signal intensity is increased and a high-quality reproduced signal is obtained.

Nd, Pt,
By adding a trace amount of at least one element of Pr and Pd, the polar Kerr rotation angle at a short wavelength can be increased without substantially impairing the characteristics required for the readout layer 3. It is possible to provide a magneto-optical disk capable of obtaining a high-quality reproduction signal even when used.

As the readout layer 3 to which the above elements are added,
Is, specifically, for example, Nd_0.05[Gd_0.26(Fe
_0.82Co_0.18)_0.74]_0.95, Pt_0.05[Gd_0.26(Fe
_0.82Co _0.18)_0.74]_0.95, Pr_0.05[Gd_0.26(Fe
_0.82Co_0.18)_0.74]_0.95, Pd _0.05[Gd_0.26(Fe
_0.82Co_0.18)_0.74]_0.95There is.

The material of the readout layer 3 of the above-mentioned magneto-optical disk
Gd fee_0.26(Fe_0.82Co_0.18) _0.74To Nd
_0.05[Gd_0.26(Fe_0.82Co_0.18)_0.74]_0.95Instead of
When the same operation was confirmed as above, almost the same result was obtained.
was gotten.

Further, by adding at least one element of a small amount of Cr, V, Nb, Mn, Be, and Ni to the material of the readout layer 3, the environmental resistance of the readout layer 3 itself is improved. I do. That is, deterioration of characteristics due to oxidation of the material of the readout layer 3 due to moisture and oxygen penetration is reduced,
A magneto-optical disk excellent in long-term reliability can be provided.

As the readout layer 3 to which the above elements are added, specifically, for example, Cr _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 , V _0.05 [Gd _0.26 (Fe
_0.82 Co _{0. 18) 0.74] 0.95,} Nb _0.05 [Gd _0.26 (Fe
_0.82 Co _{0.18) 0.74] 0.95,} Mn _{0. 05} [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 , Be _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 , Ni _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 .

Here, an experiment performed to examine the effect of increasing the Kerr rotation angle when the above element is added to the material of the readout layer 3 will be described.

FIG. 30 shows the structure of a sample used in the experiment.

In the sample, AlN which is a transparent dielectric layer 2 was formed to a thickness of 80 nm on a glass substrate 1 and X _0.1 [Gd _0.28 (Fe _0.8 C
o _0.2 ) _0.72 ] A film having a composition of _0.9 was deposited to a thickness of 50 nm, and then
Dy _0.23 Fe _0.82 Co _0.18 ) _0.77 for the recording layer 4
It was made by depositing in nm and further coating the whole with a protective layer 5 of AlN of 20 nm. Here, X is an additional element, and is one of Nd, Pr, Pt, and Pd.

FIG. 31 shows the wavelength dependence of θK (Kerr rotation angle) measured from the glass substrate 1 side. As a comparative example,
The results for a sample containing no additive in the readout layer 3 are also shown in FIG.

In the sample containing no additive, θK is large in the long wavelength region, but is small in the short wavelength region. On the other hand, N
When d, Pr, Pt, and Pd are added, θK increases in a short wavelength range.

In general, when a magneto-optical disk is reproduced using a short-wavelength laser, the laser beam can be narrowed down as compared with the case where a magneto-optical disk is reproduced using a long-wavelength laser. The recorded bits can be reproduced. At this time, when the readout layer 3 made of a material having a short wavelength and a large θK is used, the intensity of the reproduced signal is increased, and a high-quality reproduced signal is obtained.

Therefore, according to the above experimental results, it is effective means to add the above-mentioned additional elements for recording / reproducing using a short wavelength laser. The effect of increasing θK in a short wavelength region becomes more remarkable as the amount of the additional element is increased.

X _0.1 [Gd _0.28 (Fe _0.8 C
In the composition of o _0.2 ) _0.72 ] _0.9 , the magnitude of θK in the wavelength range of 600 nm or less is such that θK (adding Pt), θK (adding Nd)> θK (adding Pd), and θK (adding Pr). (See FIG. 31). Therefore, a small amount of Pt, N
If d is added, θK can be increased. Further, the addition of Pt has an effect of improving the moisture resistance of the readout layer 3. That is, the addition of Pt has the effect of increasing θK in the short wavelength range and also has the effect of improving moisture resistance.

Xa [Gd _0.28 (Fe _0.8 Co _0.2 ) _0.72 ]
Table 1 shows the amount of addition of the material having the composition _1-a , which changes from amorphous to crystalline.

[0126]

[Table 1] Table 1 shows that Nd can be added in a larger amount than Pt. That is, when a large amount of Pt is added, the material changes from an amorphous state to a crystalline state. Therefore, noise due to crystal grain boundaries increases. However, even when a large amount of Nd is added, the material becomes amorphous. It remains and the tissue is uniform. Therefore, N
It is possible to add a large amount of d.

The addition of Pd has the effect of improving the moisture resistance of the readout layer 3 and is inexpensive because it has a greater reserve than Pt. Even if Pr is added in a large amount as in the case of Nd, the material remains amorphous and can be added in a large amount. Moreover, there is an effect of improving the moisture resistance of the readout layer 3 more than Nd.

Next, a description will be given of an experiment conducted for examining the effect of improving the moisture resistance when the above element is added to the material of the readout layer 3.

FIG. 32 shows the structure of the sample used in the experiment.

A sample was prepared by forming a transparent dielectric layer 2 of AlN on a glass substrate 1 having a group of 3.5 inches in diameter.
Is formed to a thickness of 80 nm, and X _0.1
A film having a composition of [Gd _0.28 (Fe _0.8 Co _0.2 ) _0.72 ] _0.9 was deposited to a thickness of 50 nm, and then Dy _0.23 Fe
_0.82 Co _0.18 ) _0.77 is deposited to a thickness of 50 nm, and further 20 n
m of AlN and coated with a 5 μm overcoat layer 6. Here, X is an additive element, and Pt, Pd, N
d, Pr, Ni, Mn, Be, V, Nb, or Cr.

A sample of the above-mentioned magneto-optical disk was set to 120
The sample was left in a thermostat at 2 ° C. and 2 atm (humidity: 100%), and the change over time of the C / N ratio of the reproduced signal was examined. C at the time of recording and reproducing 0.76 μm long recording bits using 780 nm light
FIG. 33 shows the time change of the / N ratio. The C / N ratio is plotted with an initial value of 0 dB. As a comparative example,
The results for a sample containing no additive in the readout layer 3 are also shown in FIG.

As is clear from the figure, Cr, V, Nb,
When Mn, Be, Ni, Pt, and Pd are added, the moisture resistance is improved. The addition of Cr is most effective in improving moisture resistance.

Table 2 shows the Kerr rotation angle (unit: degrees) of the sample of the above-mentioned magneto-optical disk, which was measured with light having a wavelength of 780 nm. As a comparative example, the Kerr rotation angle of a sample of a magneto-optical disk containing no additive in the readout layer 3 is also shown.

[0134]

[Table 2] As is clear from the table, the addition of Ni has little effect on improving the moisture resistance, but has the effect of increasing the Kerr rotation angle.

Table 3 shows that Xa [Gd _0.28 (Fe _0.8 C
o _0.2 ) _0.72 ] indicates the added amount a at which the material having the composition of _1-a changes from amorphous to crystalline.

[0136]

[Table 3] As is apparent from the table, even when a large amount of V is added, the amorphous state remains, noise due to crystal grain boundaries can be suppressed, and moisture resistance can be improved.

Table 4 shows that X _0.05 [Gd _0.28 (Fe _0.8 Co
_0.2 ) _0.72 ] The crystallization temperature Tcrys of the material having the composition of _0.95
t (temperature at which amorphous changes to crystalline, unit is ° C).

[0138]

[Table 4] As is clear from the table, the addition of Nb has the effect of increasing the crystallization temperature. Therefore, the deterioration of the readout layer 3 can be suppressed even when recording and reproduction are repeatedly performed, and the moisture resistance can be improved. Mn has a large reserve in the soil and is inexpensive.

Table 5 shows the noise level (unit: dB) of the sample of the above-mentioned magneto-optical disk. As a comparative example,
The noise level of a sample of a magneto-optical disk containing no additive in the readout layer 3 is also shown. The noise level of the sample of the comparative example was set to 0 dB.

[0140]

[Table 5] The addition of Be and Ni lowers the noise level. Be addition can improve moisture resistance more than Ni addition.

Next, deterioration of signal quality when recording and reproduction were repeatedly performed using the above sample of the magneto-optical disk was examined.

Table 6 shows the C / N ratio (unit: dB) after recording and reproducing 1 million times repeatedly at room temperature. As a comparative example,
The C / N ratio of a sample of a magneto-optical disk containing no additive in the readout layer 3 is also shown. In addition, the C / N ratio of the sample of the comparative example was set to 0 dB.

[0143]

[Table 6] Next, in the present embodiment, the thickness of the readout layer 3 is set to 50 nm, but the thickness is not limited to this. Recording and reproduction of information are performed from the readout layer 3 side, as shown in FIG. 1. However, if the thickness of the readout layer 3 is too small, the information in the recording layer 4 will be transparent. That is, the mask effect due to the in-plane magnetization of the readout layer 3 is reduced.

As described above, since the magnetic properties of the readout layer 3 are affected by the recording layer 4, the thickness of the readout layer 3 varies depending on each material and composition, but the thickness of the readout layer 3 is 20 nm. The above is necessary. The thickness is preferably 50 nm or more. If the thickness is too large, the information on the recording layer will not be transferred. Therefore, the thickness is preferably about 100 nm or less.

The readout layer 3 has a thickness of 20 nm and 30 n
34 (a) to 34 (d) show polar Kerr hysteresis loops at room temperature, measured from the substrate 1 side, by manufacturing magneto-optical disks of m, 40 nm and 50 nm (FIG. 1), respectively.

Since the composition of the recording layer 4 is adjusted to a value close to the compensation composition at room temperature, the coercive force of the recording layer 4 at room temperature is very large, but when a sufficiently large magnetic field is applied, the magnetization direction of the recording layer 4 changes. Invert. For this reason, the readout layer 3 is
Is affected by the exchange coupling force in the magnetization direction of the magnetic field, and shows a polar Kerr hysteresis loop as shown in the figure.

In all cases, the exchange coupling force acts, but when the thickness of the readout layer 3 is small (FIGS. 34A and 34B), the magnetization of the readout layer 3 is completely reduced when the applied magnetic field is zero. It can be seen that the information is oriented in the same direction as the magnetization of the recording layer 4 and the information of the recording layer 4 is not masked by the readout layer 3. On the other hand, when the thickness of the readout layer 3 is increased (FIG. 3C), the mask effect gradually appears, and in FIG. It can be seen that the mask is almost completely masked by the readout layer 3.

Next, in order to examine the degree of the mask effect when the compensation temperature was changed by changing the composition of GdFeCo of the readout layer 3 and at the same time the film thickness was also changed, a magneto-optical disk having the structure shown in FIG. 1 was manufactured. Then, the squareness ratio was determined from the polar Kerr hysteresis loop at room temperature measured from the substrate 1 side. The results are shown in FIG. The temperature in the figure indicates the compensation temperature.

The squareness ratio was calculated from squareness ratio = θkr (Kerr rotation angle at zero magnetic field) / θks (Kerr rotation angle at 15 kOe magnetic field) as shown in FIG. Squareness ratio =
When it is 1, it indicates that there is no masking effect, and when the squareness ratio = 0, it indicates that the information is completely masked.

It can be seen from the figure that the higher the compensation temperature and the greater the thickness of the readout layer 3, the greater the mask effect. When the thickness of the readout layer 3 is 100 nm or less, there is no mask effect at a compensation temperature of 100 ° C. or less. In order to obtain a mask effect, the compensation temperature needs to be 125 ° C. or higher, and preferably a compensation temperature of 150 ° C. or higher. Similarly, in order to obtain a mask effect, it is found that the thickness of the readout layer 3 needs to be 10 nm or more, preferably 20 nm or more.

Next, the composition of GdFeCo of the readout layer 3 is changed so that the magnetic properties of the rare-earth sublattice become excessive in the temperature range from room temperature to the Curie temperature, that is, the compensation temperature is reduced. To investigate the degree of the mask effect when changing the film thickness to a composition that does not have
The squareness ratio was determined. The results are shown in FIG. The temperature in the figure is
Curie temperature is shown.

From the figure, it can be seen that the higher the Curie temperature,
It can be seen that the greater the thickness of the readout layer 3, the greater the mask effect. When the thickness of the readout layer 3 is 100 nm or less, there is no mask effect at a Curie temperature of 100 ° C. or less. In order to obtain the mask effect, the Curie temperature must be 13
The temperature must be 0 ° C. or higher, and preferably a Curie temperature of 200 ° C. or higher. Similarly, in order to obtain a mask effect, it is found that the thickness of the readout layer 3 needs to be 10 nm or more, preferably 20 nm or more.

In the above, the thickness of the readout layer 3 is 1
Although the case of not more than 00 nm has been described, the readout layer 3
Even when the film thickness is 200 nm, a good mask effect can be obtained. However, in order to raise the temperature of the readout layer 3 and the recording layer 4, a very large laser power is required. Considering the performance of the semiconductor laser, the readout layer 3
Is preferably 200 nm or less, more preferably 150 nm or less. Further, the compensation temperature and the Curie temperature of the readout layer 3 are preferably 500 ° C. or less, more preferably 450 ° C. or less, from the performance of the semiconductor laser.

The material of the recording layer 4 is a material exhibiting perpendicular magnetization from room temperature to the Curie temperature, and the Curie temperature may be in a temperature range suitable for recording, that is, about 150 to 250 ° C.

In the above embodiment, the recording layer 4 is Dy
Although FeCo is used, DyFeCo is a material having a small perpendicular magnetic anisotropy, and therefore, recording can be performed even when an external magnetic field required for recording is low. This is a very advantageous point particularly in the magnetic field modulation overwrite recording method described later, and it is possible to reduce the size and power consumption of the recording external magnetic field generator.

Other than DyFeCo, TbFeCo, G
dTbFe, NdDyFeCo, GdDyFeCo, G
dTbFeCo is suitable for the recording layer 4. For example, in Tb _x (Fe _Y Co _1-Y ) _1-X, it suffices that 0.10 ≦ X ≦ 0.30 is satisfied for an arbitrary Y. More specifically, for example, Tb _0.18 (Fe _0.88 Co _0.12 )
There is _0.82 .

The material of the recording layer 4 of the magneto-optical disk was changed from Dy _0.23 (Fe _0.78 Co _0.22 ) _0.77 to Tb _0.18 (Fe
_0.88 Co _0.12 ) When the same operation as above was performed in place of _0.82 , almost the same results were obtained.

TbFeCo has a perpendicular magnetic anisotropy Ku.
Is a material as large as about 3 to 4 × 10 ⁶ erg / cc,
It is possible to supply a magneto-optical recording medium having a very high reproduction signal quality without breaking the square shape of the car loop at a high temperature.

For reference, the above TbFeCo was added to the recording layer 4.
FIG. 38 (a) shows a Kerr loop obtained with the magneto-optical disk used as the disk, and has a perpendicular magnetic anisotropy Ku of about 1 × 10 ⁶
FIG. 38B shows a Kerr loop obtained from a magneto-optical disk using DyFeCo of erg / cc as the recording layer 4.
Shown in The Kerr loop was measured at 180 ° C. from the recording layer 4 side with respect to the substrate 1 of the magneto-optical disk.

While the square shape of DyFeCo is bad, the square shape of TbFeCo indicates that the perpendicular magnetic anisotropy Ku is large. For this reason, the recording bit has a clean edge shape, and the reproduction signal quality is improved.

The material of the recording layer 4 is Cr,
By adding at least one element of V, Nb, Mn, Be, and Ni, long-term reliability can be further improved. The thickness of the recording layer 4 is determined in consideration of the material, composition, and thickness of the readout layer 3.
The thickness is preferably about 0 nm or more and 100 nm or less.

The film thickness of AlN of the transparent dielectric 2 is 80 nm.
However, the present invention is not limited to this.

The thickness of the transparent dielectric layer 2 is determined in consideration of the so-called Kerr effect enhancement, in which, when reproducing a magneto-optical disk, the polar Kerr rotation angle from the read layer 3 is increased by utilizing the interference effect of light. It is determined. In order to maximize the signal quality (C / N) during reproduction, it is necessary to increase the polar Kerr rotation angle. Therefore, the film thickness of the transparent dielectric layer 2 is the largest at the polar Kerr rotation angle. Is set to

This film thickness changes depending on the wavelength of the reproduction light and the refractive index of the transparent dielectric layer 2. In the case of this embodiment, 7
AlN with a refractive index of 2.0 for a reproduction light wavelength of 80 nm
Is used, the thickness of the AlN of the transparent dielectric layer 2 is set to 3
When the thickness is about 0 to 120 nm, the effect of the Kerr effect enhancement increases. Preferably, the thickness of the AlN of the transparent dielectric layer 2 is 70 to 100 nm, and within this range, the polar Kerr rotation angle becomes almost maximum.

In the above description, the reproduction light having a wavelength of 780 nm has been described.
For the reproduction light of m, the thickness of the transparent dielectric layer 2 may be reduced to almost half.

Further, when the refractive index of the transparent dielectric layer 2 changes due to the difference in the material of the transparent dielectric layer 2 or the manufacturing method, the value obtained by multiplying the refractive index by the film thickness (optical path length) is made equal. The thickness of the transparent dielectric layer 2 may be set.

That is, in this embodiment, the optical path length of the transparent dielectric layer 2 is 160 nm, which is obtained by multiplying the refractive index 2 of AlN of the transparent dielectric layer 2 by the film thickness of 80 nm. If is changed from 2 to 2.5, 1
What is necessary is to set the film thickness to about 60 nm / 2.5 = 64 nm.

As can be seen from the above description, the larger the refractive index of the transparent dielectric layer 2, the smaller the thickness of the transparent dielectric layer 2 is.
Also, the larger the refractive index, the greater the effect of enhancing the polar Kerr rotation angle.

AlN changes its refractive index by changing the ratio of Ar and N2, which are sputter gases at the time of sputtering, and the gas pressure. However, AlN has a relatively large refractive index of about 1.8 to 2.1. A transparent dielectric layer 2
It is suitable as a material for.

The transparent dielectric layer 2 has a role of not only enhancing the Kerr effect but also preventing oxidation of the rare-earth transition metal alloy magnetic layers of the readout layer 3 and the recording layer 4 together with the protective layer 5.

A magnetic film made of a rare earth transition metal is very easily oxidized, and particularly rare earth is easily oxidized. Therefore, unless the intrusion of oxygen and moisture from the outside is prevented as much as possible, the characteristics are significantly deteriorated by oxidation.

For this reason, in the present embodiment, a configuration is adopted in which both sides of the readout layer 3 and the recording layer 4 are sandwiched by AlN. AlN is a nitride film containing no oxygen in its component, and is a material having extremely excellent moisture resistance.

Furthermore, since AlN has a relatively large refractive index of about 2 and is transparent, and does not contain oxygen in its component, it can provide a magneto-optical disk excellent in long-term stability. In addition, it is possible to perform reactive DC (direct current) sputtering by introducing an N2 gas or a mixed gas of Ar and N2 using an A1 target, and the deposition rate is higher than that of RF (high frequency) sputtering. It is also advantageous in that it is large.

As the transparent dielectric layer 2 other than AlN, SiN, AlSiN, AlTaN,
SiAlON, TiN, TiON, BN, ZnS, Ti
O ₂ , BaTiO ₃ , SrTiO _{3 and the} like are suitable. Of these, SiN, AlSiN, AlTiN, TiN, B
N and ZnS do not contain oxygen in their components and can provide a magneto-optical disk having excellent moisture resistance.

SiN, AlSiN, AlTaN, SiA
1ON, TiN, TiON, BN, ZnS, TiO ₂ ,
BaTiO ₃ and SrTiO ₃ are formed by sputtering. AlSiN, AlTaN, TiN, TiO ₂
Is capable of performing reactive DC sputtering, and is also advantageous in that the film formation rate is higher than that of RF (high frequency) sputtering. In addition, SiN, AlSiN,
The refractive index of AlTaN, BN, and SiAlON is 1.8 to
2.1, the refractive index of TiN is 2 to 2.4, ZnS, Ti
ON has a refractive index of 2 to 2.5, TiO ₂ , BaTiO ₃ ,
SrTiO _{3 has} a refractive index of 2.2 to 2.8, and these refractive indexes vary depending on sputtering conditions.

Since SiN and AlSiN have relatively low thermal conductivity, they are suitable for high recording sensitivity magneto-optical disks.
Since AlTaN and TiN contain Ta and Ti, respectively, a magneto-optical disk having excellent corrosion resistance (pitting corrosion) can be obtained. Since BN is very hard and resistant to wear, scratches are prevented and a magneto-optical disk with excellent long-term stability can be obtained. ZnS, SiAlON, and TiON have inexpensive targets. TiO ₂ , BaTiO ₃ , SrTiO ₃ are
Since the refractive index is very large, a magneto-optical disk having excellent reproduction signal quality can be obtained.

When the same operation as above was confirmed by changing the material of the transparent dielectric layer 2 of the magneto-optical disk from AlN to SiN, almost the same results were obtained.

The thickness of AlN of the protective layer 5 is set to 20 nm in the present embodiment, but is not limited to this.
The thickness of the protective layer 5 is preferably in the range of 1 to 200 nm.

In the present embodiment, the total thickness of both the readout layer 3 and the recording layer 4 is 100 nm.
At this thickness, light incident from the optical pickup hardly passes through the magnetic layer. Therefore, the thickness of the protective layer 5 is not particularly limited, and may be any thickness as long as it is necessary to prevent the oxidation of the magnetic layer for a long time. If the material has a low oxidation preventing ability, the film thickness may be large, and if it is high, the material may be thin.

The thermal conductivity of the protective layer 5 together with the transparent dielectric layer 2 affects the recording sensitivity characteristics of the magneto-optical disk. The recording sensitivity characteristic means how much laser power is required for recording or erasing. Most of the light incident on the magneto-optical disk passes through the transparent dielectric layer 2 and is absorbed by the readout layer 3 and the recording layer 4, which are absorption films, and is converted into heat. At this time, heat of the readout layer 3 and the recording layer 4 moves to the transparent dielectric layer 2 and the protective layer 5 by heat conduction. Therefore, the thermal conductivity and heat capacity (specific heat) of the transparent dielectric layer 2 and the protective layer 5 affect the recording sensitivity.

This means that the recording sensitivity of the magneto-optical disk can be controlled to some extent by the thickness of the protective layer 5. For example, if the purpose is to increase the recording sensitivity (record and erase with a low laser power), What is necessary is just to make the film thickness of the protective layer 5 thin. Usually, in order to prolong the laser life, it is advantageous that the recording sensitivity is somewhat high, and it is better that the protective layer 5 has a small thickness.

AlN is also suitable in this sense and has excellent moisture resistance. Therefore, when used as the protective layer 5, the film thickness can be reduced and a magneto-optical disk with high recording sensitivity can be provided.

In this embodiment, a magneto-optical disk having excellent moisture resistance can be provided by using the same AlN for the protective layer 5 as the transparent dielectric layer 2, and the protective layer 5 and the transparent dielectric layer 2 are made of the same material. By forming, productivity can also be improved. As described above, AlN is a material having extremely excellent moisture resistance, and thus can be set to a relatively thin film thickness of 20 nm. The thinner is more advantageous in consideration of productivity.

As the material of the protective layer 5, in addition to AlN, in consideration of the above-mentioned objects and effects, SiN, AlSiN,
AlTaN, SiAlON, TiN, TiON, BN,
ZnS, TiO ₂ , BaTiO ₃ and SrTiO ₃ are preferred.

The use of the same material as the transparent dielectric layer 2 is also advantageous in terms of productivity.

Among these, SiN, AlSiN, Al
TaN, TiN, BN, and ZnS do not contain oxygen in their components and can provide a magneto-optical disk having excellent moisture resistance.

Examples of the material of the substrate 1 include, in addition to the above-mentioned glass, chemically strengthened glass, a glass substrate having a 2P layer formed by forming an ultraviolet-curable resin layer on these glass substrates, polycarbonate (PC), It is possible to use a substrate 1 of methyl methacrylate (PMMA), amorphous polyolefin (APO), polystyrene (PS), polychlorinated biphenyl (PVC), epoxy or the like.

When the chemically strengthened glass is used for the substrate 1, the substrate 1 has excellent mechanical properties (in the case of a magneto-optical disk, surface runout, eccentricity, warpage, inclination, etc.), and has high hardness.
It is hard to be damaged by sand and dust, it is chemically stable, it does not dissolve in various solvents, it is hard to be charged compared to plastic, so it is difficult for dust and dust to adhere, and it is chemically reinforced and it is hard to break Advantages include excellent long-term reliability of the magneto-optical recording medium, excellent optical characteristics, and high signal quality because of its excellent moisture resistance, oxidation resistance, and heat resistance. .

When the above-mentioned glass or chemically strengthened glass is used as the substrate 1, a guide track for guiding a light beam, and irregularities called prepits formed in advance on the substrate in order to obtain information such as address signals. A signal is formed on a substrate by reactive dry etching of the surface of the glass substrate. Also, 2
There is a method of irradiating an ultraviolet curable resin called a P layer to cure the resin, and then removing the stamper to form the above-described guide tracks, pre-pits and the like on the resin layer.

When a PC is used as the substrate 1, injection molding can be performed, so that the same substrate 1 can be supplied in large quantities at low cost, and the water absorption is lower than other plastics.
Improvement of long-term reliability of magneto-optical recording media, heat resistance,
Advantages include excellent impact resistance. In addition, for the materials which can be injection-molded as described below including this material, guide tracks, pre-pits, etc. are formed on the surface of the substrate 1 at the same time as molding if a stamper is attached to the surface of the molding die at the time of injection molding. Is done.

When PMMA is used for the substrate 1, injection molding can be performed, so that the same substrate 1 can be supplied in large quantities at low cost, and since it has a small birefringence as compared with other plastics, it has excellent optical characteristics. Advantages include high signal quality and excellent durability.

When APO is used for the substrate 1, injection molding can be performed, so that the same substrate 1 can be supplied in large quantities at low cost, and the water absorption is lower than other plastics.
The advantages include improved long-term reliability of the magneto-optical recording medium, low birefringence, excellent optical characteristics, high signal quality, excellent heat resistance and impact resistance. Can be

When PS is used for the substrate 1, injection molding can be performed, so that the same substrate 1 can be supplied in large quantities and at low cost, and the water absorption rate is lower than other plastics. An advantage is that the property is improved.

When PVC is used for the substrate 1, injection molding can be performed, so that the same substrate 1 can be supplied in large quantities at low cost, and the water absorption is lower than other plastics.
Advantages include improved long-term reliability of the magneto-optical recording medium, flame retardancy, and the like.

When epoxy is used for the substrate 1, the water absorption is lower than that of other plastics, so that the long-term reliability of the magneto-optical recording medium is improved. An advantage is that it is excellent.

As described above, various materials can be used for the substrate 1. When those materials are used for the substrate 1 of a magneto-optical disk, the following optical characteristics and mechanical characteristics are satisfied. It is desirable.

Refractive index: 1.44 to 1.62 Birefringence: 100 nm or less (reciprocal birefringence measured with parallel light) Transmittance: 90% or more Thickness fluctuation: ± 0.1 mm Tilt: 10 mrad or less Surface runout acceleration : 10 m / s ² or less Radial acceleration: 3 m / s ² or less Since an optical pickup for condensing a laser beam on the recording layer 4 is designed according to the refractive index of the substrate 1, the substrate 1
When the change in the refractive index of the laser beam becomes large, it becomes impossible to sufficiently focus the laser beam. When the laser light focusing state changes, the temperature distribution of the recording medium (that is, the readout layer 3 and the recording layer 4) changes, which affects recording and reproduction. In the present invention, since the temperature distribution of the recording medium at the time of reproduction becomes particularly important, it is desirable to suppress the refractive index of the substrate 1 used within the range of 1.44 to 1.62.

Further, since the laser beam is made incident through the substrate 1, if the substrate 1 has birefringence, when the laser beam passes through the substrate 1, its polarization state changes.
In the present invention, since the change in the magnetization state of the readout layer 3 is reproduced as a change in the polarization state using the Kerr effect, the reproduction cannot be performed if the polarization state changes when the light passes through the substrate 1. Therefore, it is desirable that the reciprocating birefringence of the substrate 1 when measured with parallel light is 100 nm or less.

If the transmittance of the substrate 1 is low, for example, when a light beam from the optical pickup passes through the substrate 1 during recording, the amount of light decreases. Therefore, in order to obtain the amount of light required for recording on a recording medium, a laser light source with higher output is required. In particular, in the present invention, the recording medium is composed of the recording layer 4 and the readout layer 3.
In order to raise the temperature of the recording medium as compared with the conventional single-layer recording medium (without the readout layer 3),
Since a larger amount of light is required, the transmittance of the substrate 1 is 9
Desirably, it is 0% or more.

The optical pickup for condensing the laser light on the recording medium is designed according to the thickness of the substrate 1. Therefore, when the thickness of the substrate 1 fluctuates greatly, the laser light is sufficiently condensed. You can't do that. If the state of focusing of the laser beam changes, the temperature distribution of the recording medium changes, which adversely affects recording and reproduction. In the present invention, since the temperature distribution of the recording medium at the time of reproduction becomes particularly important, the variation in the thickness of the substrate 1 used is ± 0.1 mm.
It is desirable to keep within the range.

If the substrate 1 has a tilt, the laser beam from the optical pickup is condensed on the inclined recording medium surface, and the condensing state changes according to the tilt state. As in the case where the thickness of the substrate 1 fluctuates, recording and reproduction are adversely affected. Therefore, in the present invention, the tilt of the substrate 1 is desirably 10 mrad or less, and more desirably 5 mrad or less.

When the substrate 1 moves up and down with respect to the optical pickup, the optical pickup operates to compensate for the up and down movement and focus the laser light on the recording medium surface. The compensating operation of the optical pickup becomes incomplete, and the focusing state of the laser light on the recording medium surface becomes incomplete. If the laser beam is not completely focused, the temperature distribution of the recording medium changes, which adversely affects recording and reproduction. In the present invention, since the temperature distribution of the recording medium at the time of reproduction becomes particularly important, it is desirable to suppress the surface runout acceleration of the substrate to be used to 10 m / s ² or less for the vertical movement during rotation.

The substrate 1 has 1.0 to 1.
Although guide tracks for guiding the light beam are provided at a pitch of 6 μm, if the guide tracks are eccentric, the guide tracks move in the radial direction with respect to the optical pickup during rotation. At this time, the optical pickup focuses the laser light to compensate for the movement in the radial direction and maintain a constant relationship with the guide track. However, if the movement of the guide track in the radial direction becomes too large, the compensation operation of the optical pickup is performed. It becomes imperfect, and it becomes impossible to focus the laser beam while maintaining a certain relationship with the guide track. In the present invention, since the temperature distribution of the recording medium during reproduction becomes particularly important, the radial acceleration during rotation of the substrate to be used should be suppressed to 3 m / s ² or less. Is desirable.

As a method for guiding the condensed laser light to a predetermined position on the magneto-optical disk, a spiral or
A continuous servo system using concentric guide tracks and a sample servo system using spiral or concentric pit rows are conceivable.

In the case of the continuous servo system, as shown in FIG. 16, a pitch of 1.2 to 1.6 μm and a pitch of 0.2 to 0.6 μm are used.
Groups of width are formed with a depth of about λ / (8n),
Generally, information is recorded / reproduced in a land portion. This is called a land-specific magneto-optical disk. Here, λ is the wavelength of the laser beam, and n is the refractive index of the substrate used.

It is fully possible to apply the present invention to such a general system. In the present invention, since the crosstalk due to the recording bit of the adjacent track is greatly reduced, for example, in a land type magneto-optical disk, the pitch is 0.5 to 1.2 μm and the pitch is 0.1 to 1.2 μm.
Even when a group having a width of 0.4 μm is formed, recording and reproduction can be performed without being affected by crosstalk from adjacent recording bits, and the recording density is greatly improved.

Further, as shown in FIG.
Form groups and lands of the same width at a pitch of 6 μm,
Even when recording and reproduction are performed in both the group portion and the land portion, recording and reproduction can be performed in both the group portion and the land portion without being affected by crosstalk from recording bits of an adjacent track. Density is greatly increased.

On the other hand, in the case of the sample servo system, FIG.
As shown in FIG. 8, wobble pits are formed at a pitch of 1.2 to 1.6 μm and have a depth of about (λ / (4n)), and information is recorded so that the laser beam always scans the center of the wobble pits. Regeneration is generally performed.

The present invention can be sufficiently applied to such a general system. In the present invention, since the crosstalk from the adjacent recording bits is greatly reduced, even if wobble pits are formed at a pitch of 0.5 to 1.2 μm, the crosstalk from the adjacent recording bits is affected. Recording and reproduction can be performed without being performed, and the recording density is greatly improved.

Further, as shown in FIG.
When wobble pits are formed at a pitch of 1.6 μm and information is recorded and reproduced at a position where the wobble pits have the opposite polarity, recording and reproduction can be performed without being affected by crosstalk from adjacent recording bits. It is possible, and the recording density is greatly improved.

As shown in FIG. 20, when position information of a magneto-optical disk is obtained by wobbling a groove in the continuous servo system, the wobbling state exists in an adjacent groove in a portion where the wobbling state is in an opposite phase. Although there was a problem that the crosstalk from the recording bit became large, the crosstalk from the recording bit existing in the adjacent groove occurs even in a portion where the wobbling state is in the opposite phase by applying the present invention. And good recording and reproduction can be performed.

The magneto-optical disk of the present embodiment is
It is also suitable for various recording / reproducing optical pickups as described below.

For example, when a multi-beam optical pickup using a plurality of light beams is employed, as shown in FIG. 21, the light beams at both ends of the plurality of light beams are positioned so as to scan on the guide track. Generally, a method of performing recording / reproducing with a plurality of light beams located therebetween is used. However, by using the magneto-optical head disk of the present invention, even if the interval between the light beams is narrowed, crosstalk from adjacent recording bits can be achieved. It is possible to reproduce without being affected by the above, and it is possible to shorten the pitch of the guide track, or it is possible to perform recording and reproduction with more laser beams between a pair of guide tracks, Density is greatly increased.

In the above description, it is assumed that the numerical aperture (NA) of the objective lens of the optical pickup used has a general value of 0.4 to 0.6, and the wavelength of the laser beam is The pitch of the guide track and the like are discussed assuming that the wavelength is 670 nm to 840 nm. A. Is set to be 0.6 to 0.95, the laser beam can be further narrowed down, and the pitch and width of the guide track can be further reduced by applying the magneto-optical disk of the present invention. High-density recording / reproduction becomes possible.

Further, by using an argon laser beam having a wavelength of 480 nm or a laser beam having a wavelength of 335 nm to 600 nm using an SHG element, the laser beam can be further narrowed down. By applying the present invention, the pitch of the guide track can be reduced. And the width can be further reduced, and higher-density recording and reproduction can be performed.

As for a / w, a value of 0.3 to 1.0 can be used. Where a is the optically effective diameter of the lens,
w is the radius of 1 / e2 of the center intensity when the light beam entering the lens has a Gaussian distribution.

Next, a disk format when applied to the magneto-optical disk of the present embodiment will be described.

In general, in order to maintain compatibility between different manufacturers or different magneto-optical disks, recording and reading at respective radial positions are performed on the magneto-optical disk.
The value or duty to be set for the erasing power is recorded in advance in a part of the inner and outer peripheries in a pre-pit row having a depth of about (λ / (4n)). Also,
Based on these read values, test areas in which recording and reproduction can be actually performed are provided on the inner and outer circumferences (for example, IS1
0089).

On the other hand, as for the reproduction power, information for setting a specific reproduction power is recorded in advance in a part of the inner and outer peripheries in a pre-pit string.

In the magneto-optical disk of the present invention, since the temperature distribution of the recording medium at the time of reproduction has a great effect on the reproduction characteristics, the method of setting the reproduction power is very important.

As a method of setting the reproduction power, for example, similarly to the recording power, a test area for setting the reproduction power is provided on the inner and outer circumferences, and the respective radial positions are determined from the reproduction power obtained in the test area. It is preferable to record information for optimizing the reproduction power in the pit train in a part of the inner and outer circumferences in advance.

Particularly, in a magneto-optical disk drive using the CAV method in which the number of rotations of the magneto-optical disk is always constant, the linear velocity of the magneto-optical disk changes according to the radial position. It is more preferable to change. Therefore, it is better to record information divided into as many radial areas as possible as a pre-pit string.

Similarly, as a method of setting a more optimal reproduction laser power at each radial position, the recording area is divided into a plurality of zones according to the radial position, and the recording power is set for each zone at the boundary between the zones. By optimizing the reproduction power in the test area, the temperature distribution of the recording medium during reproduction can be more accurately controlled, and good recording and reproduction can be performed.

Next, the magneto-optical disk of this embodiment is
A description will be given of the point that the present invention is applicable to various recording methods described below.

First, a recording method for a first generation magneto-optical disk that cannot be overwritten will be described.

The first generation magneto-optical disk is IS100
In accordance with the 89 standard (a standard for ISO 5.25 "rewritable optical discs), many are already on the market and overwriting is not possible, so new information is recorded where information has already been recorded. In such a case, it is necessary to perform an operation of erasing the portion once and then performing recording, which requires a minimum of two rotations of the magneto-optical disk, and has a defect that the data transfer speed is low. .

However, there is an advantage that the performance required of the magnetic film is not so high as compared with the overwritable magneto-optical disk described below.

In order to eliminate the disadvantage that overwriting cannot be performed, a method of disposing a plurality of optical heads to eliminate a rotation waiting loss and improve a data transfer speed is employed in some devices.

For example, there is a method in which two optical heads are used to erase information already recorded by a preceding optical head, and new information is recorded by an optical head following afterwards. At the time of reproduction, reproduction is performed using one of the optical heads.

In the case of recording using three optical heads, the preceding optical head erases the already recorded information, the next optical head records new information, and the remaining optical heads verify. (Check that the new information is recorded correctly).

Instead of using a plurality of optical heads, one optical head may generate a plurality of beams by using a beam splitter, and these may be used in the same manner as the plurality of optical heads.

As a result, new information can be recorded without going through the process of erasing the already recorded information.
Pseudo overwrite using a next generation magneto-optical disk can be realized.

It has been confirmed that recording, reproduction and erasing can be performed on the magneto-optical disk according to the present embodiment, as already described in the description of the experimental results, and the magneto-optical disk is applicable to this recording method. I have.

Next, the magnetic field modulation overwrite recording method will be described.

The magnetic field modulation overwrite recording method is a method of recording by modulating the magnetic field intensity according to information while irradiating a magneto-optical recording medium with a laser having a constant power, and will be described with reference to FIG. It is as follows.

FIG. 22 is a schematic diagram showing an example of a magneto-optical disk device for performing magnetic field modulation overwriting on a magneto-optical disk. A laser light source (not shown) for irradiating a laser beam during recording and reproduction, and a recording device An optical head 11 including a light receiving element (not shown) for receiving reflected light from the magneto-optical disk during reproduction, and a floating magnetic head 12 mechanically or electrically connected to the optical head 11. Have.

The flying magnetic head 12 is a flying slider 1
2a and a magnetic head 12b in which a coil is wound around a core made of MnZn ferrite or the like.
4 and floats at a constant gap of about several μm to several tens μm.

In this state, the flying magnetic head 12 and the optical head 11 are moved to a desired radial position in the recording area of the magneto-optical disk 14 so that the optical head 11 moves the recording layer of the magneto-optical disk 14 to about 2 to 10 mW. The laser beam is condensed and irradiated to raise the temperature of the recording layer 4 to near the Curie temperature (or a temperature at which the coercive force becomes almost “0”). Then, the recording layer 4 is turned upward and downward according to the information to be recorded. A reversing magnetic field is applied by the magnetic head 12b. Thus, information can be recorded by the overwrite recording method without going through the process of erasing the already recorded information.

In the present embodiment, the laser power is kept constant during magnetic field modulation overwriting. However, when the polarity of the magnetic field is switched, the laser power is reduced to a power at which no recording is performed so that recording is not performed. The recorded bit shape to be reproduced becomes more clear, and the reproduction signal quality is improved.

In magnetic field modulation overwriting, when high-speed recording is to be performed, it is necessary to modulate the magnetic field at a high speed. However, there are restrictions on the power consumption and the size of the magnetic head 12b, and an extremely large magnetic field is required. Is difficult to generate. Therefore, the magneto-optical disk 14 is required to be able to record with a relatively small magnetic field.

In the magneto-optical disk of this embodiment, the Curie temperature of the recording layer 4 is kept relatively low at 150 to 250 ° C. to facilitate recording, and DyFeCo, which is a material having small perpendicular magnetic anisotropy, is used. By adopting, the magnetic field at the time of recording can be kept lower,
The configuration is very suitable for the magnetic field modulation overwrite method.

Next, the light modulation overwrite recording method will be described.

The light modulation overwrite recording method is completely opposite to the magnetic field modulation overwrite recording method, in which a constant magnetic field intensity is applied to the magneto-optical recording medium, and the laser power is modulated according to the information for recording. Is the way. This will be described below with reference to FIGS. 23 to 27.

FIG. 24 shows the temperature dependency of the coercive force in the direction perpendicular to the film surfaces of the readout layer 3 and the recording layer 4 and the recording magnetic field H suitable for the optical modulation overwrite recording method described below.
W is shown.

The recording was performed using the recording magnetic field H_WWhile applying
Irradiate low-level and two-level modulated laser light.
And so on. That is, as shown in FIG.
When the laser beam I is irradiated, the readout layer 3 and the recording layer 3
Curie point T for both recording layers 4 _C1, T_C2Near or below
Upper temperature T_HUp to low level II laser
When light is irradiated, only the recording layer 4 has a Curie point T_C2that's all
Temperature T_LThe temperature is set to rise.

[0246] Therefore, when the laser beam of low level II is projected, since the coercive force H ₁ of the readout layer 3 is sufficiently small, the magnetization in accordance with the direction of the recording magnetic field H _W, further transferred to the recording layer 4 in the cooling process Is done. That is, the magnetization is directed upward as shown in FIG. Next, when the laser beam of high level I is projected, since beyond the compensation temperature, the magnetization direction of the readout layer 3 by the recording magnetic field H _W, opposite to the case of the laser beam of low level II, That is, it faces downward. In the cooling process, the temperature drops to the same temperature as the low-level II laser beam. However, the cooling process of the reading layer 3 and the recording layer 4 is different (the recording layer 4 is cooled faster). The temperature _TL at which the laser beam II is applied becomes the temperature _TL , and the magnetization direction of the readout layer 3 is transferred to the recording layer 4 and becomes downward. Then, down to the same temperature as the laser beam of the readout layer 3 is low II, in accordance with the direction of the recording magnetic field H _W, facing upward. At this time, since the magnetization direction of the recording layer 4 has its coercive force H ₂ sufficiently larger than the recording magnetic field H _W, it does not follow the direction of the recording magnetic field H _W has.

At the time of reproduction, when a laser beam having a laser beam intensity of level III shown in FIG. 25 is irradiated, the temperature of the readout layer 3 becomes T _R (FIG. 24), and the magnetization of the readout layer 3 changes from in-plane magnetization to perpendicular. The transition to magnetization causes the recording layer 4 and the readout layer 3
Both layers exhibit perpendicular magnetic anisotropy. At this time, the recording magnetic field H
_{Since W} is not applied or is sufficiently smaller than the coercive force H ₂ of the recording layer 4 even when it is applied, the direction of magnetization of the readout layer 3 during reproduction is changed by the exchange force acting on the interface with the recording layer 4. Matches the direction of.

Thus, information can be recorded by the overwrite recording method without going through the process of erasing already recorded information.

Incidentally, the recording may be performed by applying two types of modulated laser beams as shown in FIG. 26 or FIG. 27 while applying the recording magnetic field H _W.

That is, when a high-level laser beam of type I is irradiated, the temperature T at which the readout layer 3 and the recording layer 4 are both near or above the Curie points T _C1 and T _C2 is obtained.
When the temperature is raised to H and a low-level laser beam of type II is applied, only the recording layer 4 is heated to a temperature _TL at which the recording layer 4 has a Curie point T _C2 or higher. By doing so, the cooling process of the readout layer 3 and the recording layer 4 when the high-level laser light of type I is irradiated can be greatly different. That is, the recording layer 4 is cooled faster. For this reason, overwriting can be performed more easily.

However, after the high-level laser light of type I is irradiated, the intensity of the laser light which is irradiated for a while may be lower than the high level.

According to the recording method described above, there is an advantage that it is not necessary to apply a generally required initialization magnetic field at the time of light modulation overwriting.

The magneto-optical disk (FIG. 1) is generally called a single-sided type. In this magneto-optical disk, when the thin film portions of the transparent dielectric layer 2, the readout layer 3, the recording layer 4, and the protective layer 5 are collectively referred to as a recording medium layer, as shown in FIG. 9, the structure of the overcoat layer 6 is obtained.

On the other hand, as shown in FIG. 29, two recording medium layers 9 formed on the substrate 1 were bonded together with an adhesive layer 10 so that the recording medium layers 9.9 faced each other. The magnetic disk is called a double-sided type.

Incidentally, the material of the adhesive layer 10 is particularly preferably a polyurethane acrylate adhesive. This adhesive is a combination of three types of curing functions of ultraviolet light, heat and anaerobic, and the curing of the shadowed portion of the recording medium layer 9 through which ultraviolet light does not pass is cured by the heat and anaerobic curing function. Thus, a double-sided magneto-optical disk having extremely high moisture resistance and extremely excellent long-term stability can be provided.

The single-sided type requires only half the thickness of the magneto-optical disk as compared with the double-sided type, and is therefore advantageous for a recording / reproducing apparatus that requires a reduction in size, for example.

[0257] The double-sided type is capable of performing double-sided reproduction, and is therefore advantageous to, for example, a recording and reproducing apparatus that requires a large capacity.

Whether the single-sided type or the double-sided type is adopted depends not only on the thickness and capacity of the magneto-optical disk as described above but also on the recording method as described below.

As is well known, a light beam and a magnetic field are used for recording information on a magneto-optical disk. As shown in FIG. 22, in the magneto-optical disk device, a light beam from a light source such as a semiconductor laser is focused on the recording medium layer 9 through the substrate 1 by the condenser lens 8 and irradiated, and a position facing the light beam. A magnetic field is applied to the recording medium layer 9 by a magnetic field generator (for example, a floating magnetic head 12) such as a magnet or an electromagnet provided in the recording medium layer 9. By making the light beam intensity higher at the time of recording than at the time of reproduction, the temperature of the condensed portion of the recording medium layer 9 rises, and the coercive force of the magnetic film in that portion decreases. At this time, when a magnetic field having a magnitude larger than the coercive force is applied from the outside, the magnetization of the magnetic film is aligned in the direction of the applied magnetic field, and the recording is completed.

For example, in a magnetic field modulation overwrite system for modulating a recording magnetic field according to information, it is necessary to bring a magnetic field generator (often an electromagnet) as close to the recording medium layer 9 as possible. This is because the temperature required for recording is modulated (generally, several hundred kHz to several tens of MHz) and the magnetic field required for recording (generally, (E.g., 500e to several hundred Oe), it is necessary to approach the recording medium to about 0.2 mm or less, and in many cases to about 50 μm. For this reason,
In a double-sided magneto-optical disk, the thickness of the substrate 1 is generally around 1.2 mm and needs to be as thin as about 0.5 mm. Therefore, when an electromagnet is arranged to face the light beam, the recording magnetic field strength is insufficient. I cannot record. Therefore,
When the recording medium layer 9 suitable for the recording modulation overwrite method is employed, a single-sided type magneto-optical disk is often used.

On the other hand, in the light modulation overwrite method in which the light beam is modulated according to the information, the recording magnetic field remains in one direction or the recording magnetic field is unnecessary. Therefore, a permanent magnet having a strong generated magnetic field, for example, a permanent magnet can be used. it can. Therefore, not only a single-sided type but also a double-sided type can be adopted.

When the magneto-optical disk of the present embodiment is used as a single-sided disk, the following structural variations are possible.

The first variation is a magneto-optical disk in which a hard coat layer (not shown) is formed on the overcoat layer 6, and includes a substrate 1, a recording medium layer 9, an overcoat layer 6, and a hard coat layer. It has a structure.
As the hard coat layer, for example, an acrylate-based UV-curable hard coat resin film is formed of, for example, a polyurethane acrylate-based UV-curable resin having a thickness of about 6 μm.
On the overcoat layer 6. The thickness of the hard coat layer is, for example, 3 μm.

By forming the overcoat layer 6, deterioration of characteristics due to oxidation of the recording medium layer 9 can be prevented, and long-term reliability can be ensured. In addition, by providing a hard coat film, even if a recording magnet comes into contact with the disc, the hard coat film, which has high hardness and excellent abrasion resistance, makes it hard to be scratched. In addition, even if a scratch occurs, it can be prevented from reaching the recording medium layer 9.

It is needless to say that the function of the hard coat layer may be added to the overcoat layer 6 so that only the overcoat layer 6 may be used.

A second variation is a light in which a hard coat layer is formed on the overcoat layer 6 and a hard coat layer (not shown) is formed on the surface of the substrate 1 opposite to the recording medium layer 9. A magnetic disk, a hard coat layer / substrate 1 / recording medium layer 9 / overcoat layer 6 /
It has the structure of a hard coat layer.

As a material of the substrate 1 for a magneto-optical disk,
PC and other plastics are often used,
These materials are much softer than glass and can be scratched by rubbing with your nails. If the scratches are severe when recording and reproducing with a light beam, servo jumps may occur, making it impossible to record and reproduce information.

In the magneto-optical disk of the present embodiment, since reproduction is performed using only the vicinity of the center of the light beam, the influence of defects such as scratches on the surface of the substrate 1 on the reproduction is smaller than that of the conventional magneto-optical disk. Will also be large. For this reason, by providing the hard coat layer on the surface of the substrate 1 on the side opposite to the recording medium layer 9, the present configuration in which the generation of scratches can be prevented is very effective.

It is apparent that the same effect can be obtained in the double-sided type by providing a hard coat layer on the surface of each of the substrates 1 of the magneto-optical disk.

The third variation is the first and second variations.
On the overcoat layer 6 in a variation of
This is a magneto-optical disk in which an antistatic coat layer (not shown) or a layer having an added antistatic function is further formed on the hard coat layer.

If dust or dust adheres to the surface of the substrate 1, it may be impossible to record and reproduce information as in the case of scratches. Further, when dust is formed on the overcoat film 6, in the case of the magnetic field modulation overwrite method, the magnet is used as a floating magnetic head 12 (FIG. 22) to cover the overcoat film 6 by several μm.
In such a case, dust and dirt cause damage to the flying magnetic head 12 and the recording medium layer 9.

If a structure having an antistatic function is provided on the surface on the substrate 1 side or the surface on the recording medium layer 9 side as in this structure, dust and dirt in the air can be removed from the surface of the substrate 1 or the surface of the recording medium layer 9. Adhesion on the overcoat layer 6 can be prevented.

In the magneto-optical disk of the present embodiment, since reproduction is performed using only the vicinity of the center of the light beam, the effect of defects such as dust and dust on the surface of the substrate 1 on the reproduction is the same as that of the conventional magneto-optical disk. This configuration is extremely effective because it is larger than a disk.

As the antistatic layer, for example, an acrylic hard coat resin mixed with a conductive filler can be used, and its film thickness is suitably about 2 to 3 μm.

The antistatic layer is provided for the purpose of lowering the surface resistivity and making it difficult for dirt, dust and the like to be formed on both the plastic substrate 1 and the glass substrate 1.

In addition, as a matter of course, an antistatic effect may be added to the overcoat layer 6 or the hard coat layer.

It is apparent that this configuration can be applied to the surface of each substrate 1 of the magneto-optical disk also in the double-sided type.

The fourth variation is a magneto-optical disk in which a lubricating layer (not shown) is formed on the overcoat layer 6, and the structure of the substrate 1, the recording medium layer 9, the overcoat layer 6, and the lubricating layer is changed. Have. As the lubrication layer,
For example, a fluorine-based resin can be used, and its film thickness is suitably about 2.

By providing the lubricating layer, when the floating magnetic head 12 is used by the magnetic field modulation overwrite method, the lubricity between the floating magnetic head 12 and the magneto-optical disk can be improved.

That is, the floating magnetic head 12 is arranged to record information while maintaining a gap of several μm to several tens μm on the recording medium layer 9. The levitation type magnetic head 12 generated by the air pressure due to the high speed rotation of the magneto-optical disk and the pressure by the suspension 13 acting to press the layer 9.
The above-mentioned gap is maintained by balancing the levitation force acting to separate the recording medium from the recording medium layer 9.

With the use of such a floating magnetic head 12, the time required to start rotation of the magneto-optical disk and reach a predetermined number of rotations, and at the end of rotation the time required to stop the rotation from the predetermined number of rotations to stop. (Contact-Start-St) where the magnetic head 12 contacts the magneto-optical disk
op) method, the floating magnetic head 12
When the magneto-optical disk is attracted, the flying magnetic head 12 may be damaged when the magneto-optical disk starts rotating. However, according to the magneto-optical disk of the present embodiment, since the lubricating film is provided on the overcoat layer 6, the lubricity between the floating magnetic head 12 and the magneto-optical disk is improved, and the floating type by suction is improved. Damage to the magnetic head 12 can be prevented.

As a matter of course, it is not necessary to separately provide the overcoat layer 6 and the lubricating layer as long as the material prevents the deterioration of the recording medium layer 9 and also has the moisture protection property.

According to a fifth variation, a moisture-permeable layer (not shown) and a second overcoat layer (not shown) are laminated on the surface of the substrate 1 opposite to the recording medium layer 9. This is a magneto-optical disk and has a structure of overcoat layer / moisture-permeable layer / substrate 1 / recording medium layer 9 / overcoat layer 6.

The moisture permeation preventing layers include, for example, A1N, A1S
iN, SiN, A1TaN, SiO, ZnS, TiO ₂
Or the like, and a film thickness of about 5 nm is appropriate. The second overcoat layer is particularly effective when a highly hygroscopic plastic such as PC is used for the substrate 1.

The moisture permeation preventing layer has an effect of suppressing a change in warpage of the magneto-optical disk due to a change in environmental humidity. This will be described below.

In the case where the moisture permeation preventing film is not provided on the light incident side of the substrate 1, for example, when the environmental humidity is greatly changed, the plastic substrate is provided only from the side without the recording medium layer 9, that is, from the incident light side of the substrate 1. First, moisture is absorbed or released. Due to this moisture absorption and release, the plastic substrate 1 locally changes in volume, and the plastic substrate 1 is warped.

[0287] The warpage of the magneto-optical disk is caused by the substrate 1 with respect to the optical axis of the light beam used for reproducing and recording information.
Is tilted, so that the servo deviates and the signal quality deteriorates, or in severe cases, the servo jump occurs.

If the substrate 1 has a tilt, the laser beam from the optical head 11 (FIG. 22) is condensed on the inclined surface of the recording medium layer 9 and condensed according to the state of the tilt. The state changes, which adversely affects recording and reproduction.

Further, when the substrate 1 moves up and down with respect to the optical head 11, the optical head 11 operates to compensate for the up and down movement and focus the laser beam on the surface of the recording medium layer 9. Becomes too large, the compensating operation of the optical head 11 becomes incomplete, and the focusing state of the laser light on the surface of the recording medium layer 9 becomes incomplete. If the laser beam is not completely focused, the temperature distribution of the recording medium layer 9 changes, which affects recording and reproduction. In the present embodiment, since the temperature distribution of the recording medium layer 9 at the time of reproduction becomes particularly important, it is necessary to suppress the warpage of the substrate 1 and the warp change due to the environment as much as possible.

In the case of the magneto-optical disk of this configuration, the presence of the moisture permeation preventing layer eliminates the absorption and release of moisture on the surface side of the substrate 1, so that the warpage of the substrate 1 when the environment changes can be suppressed significantly. As described above, the configuration is particularly suitable for the magneto-optical disk of the present invention.

The second overcoat layer on the moisture permeation preventing layer is provided for the purpose of preventing scratches on the moisture permeation preventing layer, protecting the surface of the substrate 1, and the like. Medium layer 9
It may be the same as the overcoat layer 6 above.

Further, in addition to this structure, for example, the above-mentioned hard coat layer or antistatic layer may be provided instead of or on the second overcoat layer.

In the above embodiment, a groove having a pitch of 1.6 μm was formed on the substrate 1. However, it was confirmed that even a groove having a pitch of 1.2 μm could provide recording / reproducing characteristics having no practical problem.

Thus, for example, when the laser wavelength is 78
A short-wavelength laser shorter than 0 nm is used. A. If the spot diameter of the reproduction light beam 7 is reduced by using the condenser lens 8 having a diameter larger than 0.55, even if the groove has a pitch of 1.2 μm or less (for example, a pitch of 0.8 μm), there is a practical problem. Recording and playback without any problems are possible.

The land width and the groove width need to take into account an error of at least ± 0.05 μm in manufacturing.

The ratio of the land width to the groove width is:
It is preferable that the C / N on the land and the C / N on the groove are set to be substantially the same. Therefore, the ratio may be slightly shifted from 1: 1 in consideration of the groove depth.

In a magneto-optical disk drive that performs recording and reproduction with one light beam, in order to switch the tracking servo from a track on a land to a track on a groove, it is necessary to switch the polarity of the tracking servo.

As a recording method, first, recording is performed on tracks on lands, and after recording is performed on tracks on all lands, the polarity of tracking servo is switched to perform recording on tracks on grooves. Also, the track is divided into logical areas in the radial direction of the magneto-optical disk,
First, recording is performed on a track on a land of a certain logical division area, and after recording is performed on tracks on all lands of the logical division area, recording is performed on a track on a groove of the logical division area. Then, the access speed improves.

In a magneto-optical disk drive which uses two or more light beams and applies tracking servo to tracks on lands and tracks on grooves, it is not necessary to switch the polarity of tracking servo. Moreover, high-speed data transfer becomes possible. Note that it is necessary to separate a plurality of light beams to some extent so that the shape of the recording bit is not disturbed by thermal interference during recording.

The second embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as the members shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The magneto-optical disk of the present embodiment is shown in FIG.
As shown in the figure, the substrate 1, the transparent dielectric layer 2, the readout layer 3, the recording layer 4, the heat radiation layer 20, and the overcoat layer 6 are laminated in this order.

For example, Al can be used for the heat radiation layer 20, and its film thickness is suitably about 100 nm. Substrate 1,
For the transparent dielectric layer 2, the readout layer 3, the recording layer 4, and the overcoat layer 6, the same materials as those in the above embodiment can be used.

[0303] Since the heat radiation layer 20 is provided on the recording layer 4, there is an effect of sharpening the recording bit shape at the time of recording. This is for the following reason.

Most of the light beam incident from the incident surface side is absorbed by the readout layer 3 and the recording layer 4 and converted into heat. At this time, the heat is conducted in the thickness direction of the readout layer 3 and the recording layer 4 and also conducted in the layer direction, that is, in the lateral direction. If the amount of heat conduction in the lateral direction is large and the speed of heat conduction is low, for example, when recording is to be performed at a higher speed and with a higher recording density, heat is applied to the next recording bit to be recorded. Adverse effects. For this reason, the recording bit becomes longer than a predetermined length, or a recording bit spread in a lateral direction with respect to the guide track is formed. When the recording bits spread in the horizontal direction, the amount of crosstalk increases, and good recording and reproduction cannot be performed.

In this embodiment, since the heat radiation layer 20 made of Al having high heat conductivity is formed on the recording layer 4, the spread of heat in the lateral direction is released to the heat radiation layer 20 side, that is, in the thickness direction. As a result, the spread of heat in the lateral direction as described above can be reduced. Therefore, it is possible to perform recording without thermal interference under a higher density and higher speed recording condition.

Further, the provision of the heat radiation layer 20 is advantageous also in light modulation overwrite recording as described below.

The presence of the heat radiation layer 20 makes it possible to more clearly differentiate the temperature change between the readout layer 3 and the recording layer 4 when the region once heated by the light beam is cooled in the recording process. Can be provided. This effect is because the cooling process of the readout layer 3 and the recording layer 4 when a high-level laser beam is irradiated can be greatly different (the recording layer 4 is cooled faster).
Overwriting can be performed more easily.

Al, which is a material for the heat radiation layer 20, has a higher thermal conductivity than the rare earth transition metal alloy film used for the readout layer 3 and the recording layer 4, and is a material suitable for the heat radiation layer 20. In addition, when AlN is used for the transparent dielectric layer 2, this AlN is formed by reactively sputtering an Al target with Ar and N2 gases, so that the same AN is used.
The heat radiation layer 20 can be easily formed by sputtering the target with Ar gas. Al is also a very inexpensive material.

The material of the heat radiation layer 20 is Au, A in addition to Al.
Any material such as g, Cu, SUS, Ta, Cr or the like having a higher thermal conductivity than the readout layer 3 and the recording layer 4 may be used.

[0310] When Au, Ag, and Cu are used for the heat radiation layer, the oxidation resistance, the moisture resistance, and the pitting corrosion resistance are excellent, so that the long-term reliability is improved.

[0311] When SUS, Ta, or Cr is used for the heat radiation layer, long-term reliability is improved because of excellent oxidation resistance, moisture resistance, and pitting corrosion resistance.

In this embodiment, the thickness of the heat radiation layer 20 is set to 100 nm. However, the heat radiation effect increases as the thickness increases, and the long-term reliability also improves. However, as already described, since it also affects the recording sensitivity of the magneto-optical disk, it is necessary to set the film thickness in accordance with the thermal conductivity and specific heat of the material, and the range of 5 to 200 nm is preferable. In particular, 10 to 100 nm is preferable. If the material has relatively high thermal conductivity and excellent corrosion resistance, the film thickness is 10 to 10
It can be made as thin as about 0 nm, and the time required for film formation at the time of manufacturing can be shortened.

Also, a dielectric layer (not shown) may be inserted between the recording layer 4 and the heat radiation layer 20. The same material as the transparent dielectric layer 2 may be used for the dielectric layer.
The materials described in the first embodiment such as A1N, SiN, and A1SiN can be used. In particular, A1N, SiN, A1Si
If a nitride film containing no oxygen is used for components such as N, TiN, A1TaN, ZnS, and BN, a magneto-optical disk with more excellent long-term reliability can be provided. The thickness of the dielectric layer is preferably in the range of 10 to 100 nm.

The third embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as the members shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The magneto-optical disk of this embodiment is similar to that shown in FIG.
As shown in the figure, the substrate 1, the transparent dielectric layer 2, the readout layer 3, the recording layer 4, the transparent dielectric layer 21, the reflective layer 22, and the overcoat layer 6 are laminated in this order.

For example, AlN can be used for the transparent dielectric layer 21, and its thickness is suitably about 30 nm. For example, Al can be used for the reflective layer 22, and its thickness is suitably about 30 nm. The same material as in the above embodiment can be used for the substrate 1, the transparent dielectric layer 2, the readout layer 3, the recording layer 4, and the overcoat layer 6. However, the thickness of the readout layer 3 is set to 15 nm, which is half the thickness of the first embodiment, and the thickness of the recording layer 4 is set to 15 nm, which is half the thickness of the first embodiment. It has a thickness.

That is, in the magneto-optical disk of the present embodiment, a part of the incident light beam passes through the readout layer 3 and the recording layer 4, passes through the transparent dielectric layer 21, and passes through the reflection layer 22. It is designed to be reflected.

Thus, the light reflected on the surface of the readout layer 3 and the light reflected by the reflective layer 22 and transmitted again through the recording layer 4 and the readout layer 3 interfere with each other, and the magneto-optical effect is enhanced, and The rotation angle increases. Therefore, information can be reproduced with higher accuracy, and the quality of a reproduced signal is improved.

In this structure, in order to enhance the enhancement effect, the thickness of the transparent dielectric layer 2 should be 70 to 100 n.
m is optimal, and at this time, the thickness of the transparent dielectric layer 21 is 15 to
50 nm is preferred.

The thickness of the transparent dielectric layer 2 is set to 70 to 100 nm.
The reason for this is that, as already described in the first embodiment, the enhancement effect of the polar car rotation angle becomes the largest.

As the thickness of the transparent dielectric layer 21 increases, the polar Kerr rotation angle increases as the thickness increases, but the reflectivity decreases. If the reflectance is too small, the signal for applying servo to the guide track becomes small, and stable servo cannot be applied. For this reason,
The thickness of the transparent dielectric layer 21 is preferably about 15 to 50 nm.

If the refractive index of the transparent dielectric layer 21 is made larger than the refractive index of the transparent dielectric layer 2, the enhancement effect can be further enhanced.

Since the readout layer 3 and the recording layer 4 are both layers made of a rare-earth transition metal alloy and have a high light absorptivity, when the combined film thickness is 50 nm or more, almost no light is transmitted. , The enhancement effect cannot be obtained. Therefore, the combined film thickness of these two layers is 10 to 5
0 nm is preferred.

If the thickness of the reflective layer 22 is too small, light is transmitted through the reflective layer 22 and the enhancement effect is reduced. Therefore, at least about 20 nm is required.
On the other hand, if the thickness is too large, the laser power required for recording, reproduction and the like becomes high, and the recording sensitivity of the magneto-optical disk is reduced. Therefore, the preferred film thickness for the reflective layer 22 is in the range of 20 to 100 nm.

The reason for using Al as the material of the reflection layer 22 is that the reflectance is about 80% in the wavelength range of the semiconductor laser.
And the fact that it is possible to use an Al target common to the AlN of the transparent dielectric layer 2 during formation by sputtering. As mentioned above, A
When forming 1N, reactive sputtering is performed using a mixed gas of Ar and N ₂ or N ₂ gas, and when forming A1 of the reflective layer 22, Ar gas is introduced to perform sputtering.

As the reflection layer other than A1, Au, Pt,
Any material, such as Co, Ni, Ag, Cu, SUS, Ta, and Cr, having a reflectance of 50% or more at the wavelength of the light beam may be used.

When Au, Pt, Cu, and Co are used for the reflection layer 22, the long-term reliability is improved because of excellent oxidation resistance, moisture resistance, and pitting resistance.

When Ni is used for the reflective layer 22, the magneto-optical disk has high recording sensitivity because of its low thermal conductivity.
It has excellent oxidation resistance, moisture resistance, and pitting resistance, so that long-term reliability is improved.

When Ag is used for the reflective layer 22, the long-term reliability is improved because of excellent oxidation resistance, moisture resistance and pitting resistance. Moreover, Ag targets are inexpensive.

[0330] When SUS, Ta, or Cr is used for the reflective layer 22, the magneto-optical disk can be provided with more excellent long-term reliability because it is extremely excellent in oxidation resistance, moisture resistance, and pitting corrosion resistance. .

A fourth embodiment of the present invention will be described with reference to FIGS.
2 will be described below. For convenience of explanation, members having the same functions as the members shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The magneto-optical disk of this embodiment is similar to that shown in FIG.
As shown in the figure, the substrate 1, the transparent dielectric layer 2, the readout layer 3, the recording layer 4, the protective layer 5, and the overcoat layer 6 are laminated in this order. Although the structure is similar to the structure of the magneto-optical disk of the first embodiment, the magnetic characteristics of the readout layer 3 are different as described in detail below.

The readout layer 3 is made of a rare earth transition metal alloy, and is a ferrimagnetic material in which the sublattice magnetic moment of the rare earth metal and the sublattice magnetic moment of the transition metal are in opposite directions. The temperature characteristics of these sublattice magnetic moments are different from each other. At a high temperature, the magnetic moment of the transition metal becomes relatively larger than the magnetic moment of the rare earth metal.

The content of the rare earth metal is made larger than the compensating composition at room temperature so that the readout layer 3 is in an in-plane magnetization state at room temperature. When the light beam is irradiated, the temperature of that portion rises, and the sublattice magnetic moment of the transition metal becomes relatively large. Therefore, the magnetization as a whole becomes smaller, and shows a perpendicular magnetization.

That is, the temperature characteristics of the coercive force shown in FIG.
As described above, the readout layer 3 is at room temperature (T _ROOM) At magnetization
Is the in-plane magnetization state facing the in-plane direction of the film, and TP1
At the above temperature, the magnetization is oriented perpendicular to the film surface.
It becomes a magnetized state and the reading temperature (T_READVertical at
It becomes a magnetized film.

Therefore, the readout layer 3 of this embodiment is
R at room temperature containing more rare earth metal than compensating composition
It has an E-rich composition. Further, the readout layer 3 must always have an RE-rich composition from room temperature to the Curie temperature. Here, RE-rich refers to a composition in which the content of the rare earth metal is larger than the compensation composition,
M-rich is a composition in which the transition metal content is higher than the compensation composition.

The recording layer 4 is made of a rare earth transition metal alloy composed of a perpendicular magnetization film, and has a coercive force H at room temperature for stably storing information recorded as a magnetization direction.
C2 (see FIG. 42) needs to be sufficiently high. When a disturbance such as an external magnetic field is considered, a coercive force of about 100 kA / m is sufficient, but preferably a coercive force of 400 kA / m or more is desirable.

Next, light modulation overwriting in the above-described magneto-optical disk will be described.

When the light beam is irradiated and the temperature of the recording layer 4 rises to near the Curie temperature T _C2 at which recording is performed, the magnetization direction of the recording layer 4 is aligned with the direction of the recording magnetic field. It is determined by the balance between the magnetostatic coupling force to be made and the exchange coupling force to make the directions of the sublattice magnetic moments of the readout layer 3 and the recording layer 4 uniform. for that reason,
In the vicinity of the Curie temperature T _{C2 at which} recording is performed, the direction of the force exerted on the recording layer 4 by the magnetostatic coupling force and the exchange coupling force needs to be opposite. That is, since the readout layer 3 is RE-rich near the Curie temperature T _{C2 of} the recording layer 4, the recording layer 4 needs to be TM-rich.

When the temperature of the recording layer 4 rises to near its Curie temperature T _C2 (T _{L in} FIG. 42) by irradiating the magneto-optical disk with a light beam having a relatively low first power. The magnetization of the readout layer 3 is oriented in the direction of the recording magnetic field because the magnetization of the readout layer 3 becomes very small or disappears. Further, the temperature of the readout layer 3 on the light incident side is
, That is, T ₁₁ (average temperature of the readout layer 3)> T ₂₂ (average temperature of the recording layer 4). When the exchange coupling force acting on the recording layer 4 from the readout layer 3 is compared with the magnetostatic coupling force exerted on the recording layer 4 by the recording magnetic field, the recording magnetic field exerts a static The magnetic coupling force becomes relatively strong. As a result, the magnetization direction of the recording layer 4 can be directed to a direction determined by the magnetostatic coupling force exerted on the recording layer 4 by the recording magnetic field.

Next, when the temperature of the recording layer 4 rises to the Curie temperature T _C2 or higher (T _{H in} FIG. 42) by irradiating the magneto-optical disk with a light beam of a relatively high second power, The temperature rises through a similar process, but the temperature difference in the film thickness direction is eliminated in the process of decreasing the temperature, and when the temperature drops to near the Curie temperature of the recording layer 4, T
₁₁ = it is possible to realize the state of the T _22. At this time,
Since the magnetization of the recording layer 4 becomes very small or disappears, the magnetization direction of the reading layer 3 is directed to the direction of the recording magnetic field.

In this case, the exchange coupling force acting on the recording layer 4 from the readout layer 3 becomes relatively strong as compared with the case where the light beam of the first power is relatively low. As a result, the magnetization direction of the recording layer 4 can be directed to a direction determined by the exchange coupling force from the readout layer 3.

As described above, the magnetization direction of the recording layer 4 is changed between when the light beam having the relatively low first power is irradiated and when the light beam having the relatively high second power is irradiated. It becomes possible. That is, light modulation overwriting becomes possible.

When reading the recorded magnetization direction of the recording layer 4, a light beam having a lower power than the first power is irradiated. Since the intensity of the irradiated light beam generally has a Gaussian distribution, the temperature distribution of the readout layer 3 also has a Gaussian distribution. Therefore, it is possible to bring the readout layer 3 only in the central portion smaller than the light beam diameter into the perpendicular magnetization state.

The magnetization direction of the readout layer 3 is determined by exchange coupling with the recording layer 4 so that the directions of the sublattice magnetic moments of the readout layer 3 and the recording layer 4 are aligned. Therefore, it is possible to read out the magnetization direction of the recording layer 4 only in a range smaller than the light beam diameter at the central portion of the light beam.

When the recording layer 4 is RE-rich near the Curie temperature TC2, light modulation overwriting cannot be performed, but information recorded by a recording method such as magnetic field modulation overwriting can be read. It is.

In the above description, the readout layer 3 is at room temperature (T
_ROOM ) is an in-plane magnetization state in which the magnetization is in the in-plane direction of the film, and it is necessary to be in a perpendicular magnetization state in which the magnetization is in a direction perpendicular to the film surface at a temperature of T _P1 or more with a rise in temperature. It was determined that the film had to be a perpendicular magnetization film at the reading temperature (T _READ ). However, the read output at the time of reading depends on the inclination of the magnetization of the read layer 3, so that the read layer 3 has a complete in-plane magnetization state at room temperature, and does not need to have a complete perpendicular magnetization state at the read temperature.

That is, at room temperature and reading temperature,
If the state of the magnetization inclination of the readout layer 3 is different, the effect of reading out the magnetization direction of the recording layer 4 only in a range smaller than the light beam diameter at the center of the light beam at the time of reading can be obtained.

Next, a specific example of the above-mentioned magneto-optical disk and a method of manufacturing the same, a light modulation overwrite using this magneto-optical disk, and a reproduction test thereof will be described.

A1, consisting of Gd, Dy, Fe and Co
In sputtering apparatus having the original target, and disposed to face the substrate 1 made of polycarbonate having pre-grooves and pre-pits on the target, after evacuating the inside sputtering device to 1 × 10 ^-6 Torr, argon and nitrogen And a power is supplied to the target of A1, and a gas pressure of 4 × 10 ⁻³ Torr, 12 nm / mi
At a sputtering speed of n, a transparent dielectric layer 2 of A1N having a thickness of 80 nm was formed.

Next, after evacuating again to 1 × 10 ⁻⁶ Torr, argon gas was introduced, and Gd, Fe, Co
To the target at a gas pressure of 4 × 10 ⁻³ Torr and a sputtering speed of 15 nm / min.
A readout layer 3 made of FeCo and having a thickness of 50 nm was formed. The readout layer 3 was RE-rich, had no compensation temperature, and had a Curie temperature T _C1 of 300 ° C. G
The composition of dFeCo is Gd _0.26 (Fe _0.82 Co _0.18 )
It was _0.74 .

Next, the power supplied to Gd is stopped,
Power is supplied to the Dy target, and DyFe
A recording layer 4 made of Co and having a thickness of 50 nm was formed. The recording layer 4 is TM-rich at room temperature and has a coercive force H _C2 of 80.
The temperature was 0 kA / m, no compensation temperature was present, and the Curie temperature T _C2 was 150 ° C. The composition of DyFeCo was Dy _0.23 (Fe _0.82 Co _0.18 ) _0.77 .

Next, a mixed gas of argon and nitrogen was introduced, power was supplied to the target of A1, and a gas pressure of 4 × 1 was applied.
A protective layer 5 of A1N having a thickness of 20 nm was formed at a gas pressure of 0 ^-3 Torr and a sputtering speed of 12 nm / min. The thickness of the protective layer 5 may be determined so that the readout layer 3 and the recording layer 4 can be protected from corrosion such as oxidation.

Next, an ultraviolet curable resin was applied by spin coating, and an ultraviolet ray was applied to form an overcoat layer 6.

Here, the thickness of each of the readout layer 3 and the recording layer 4 was set to 50 nm.
Was set to 100 nm, it was possible to more effectively utilize the temperature difference in the film thickness direction.

The above-mentioned magneto-optical disk was mounted on a magneto-optical disk device, and rotated at a laser beam irradiation position so that the linear velocity of the magneto-optical disk became 10 m / s.
With the recording magnetic field of 25 kA / m applied, the first laser power was set to 6 mW, and the second laser power was set to 10 mW.
When recording was performed by modulating the laser power at a frequency of 5 MHz with mW, 1
Inverted magnetic domains having a length of μm could be formed.

When information was reproduced with a laser power of 2 mW, a magneto-optical signal of 5 MHz could be obtained from the readout layer 3 in accordance with the inverted magnetic domains formed in the readout layer 3.

Next, when overwriting was performed by modulating the laser power at a frequency of 10 MHz on the inverted magnetic domain formed at 5 MHz, the inverted magnetic domain formed at 5 MHz disappeared. , Newly 1μm
Inverted magnetic domains having a length of 0.5 μm could be formed periodically.

When the information was reproduced again with the laser power set to 2 mW, only the 10 MHz magneto-optical signal having the same magnitude as the 5 MHz magneto-optical signal was generated according to the inverted magnetic domain formed in the recording layer 4. It could be obtained from the readout layer 3. This means that in the readout layer 3,
This means that the magnetization state of the readout layer 3 is reproduced only in the portion where the temperature has risen and the magnetization state is perpendicular.

The fifth embodiment of the present invention will be described below with reference to FIG. For convenience of explanation, members having the same functions as the members shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The magneto-optical disk of this embodiment is similar to that shown in FIG.
As shown in FIG. 1, the substrate 1, the transparent dielectric layer 2, the readout layer 3, the intermediate layer 29 composed of an in-plane magnetized film, the recording layer 4, the protective film 5, and the overcoat layer 6 are laminated in this order. ing. That is, an intermediate layer 29 made of an in-plane magnetic film is provided between the read layer 3 and the recording layer 4 of the magneto-optical disk of the fourth embodiment.

The light modulation overwriting and reproduction are performed in the same manner as in the fourth embodiment, except that the exchange coupling force between the readout layer 3 and the recording layer 4 is provided by providing the intermediate layer 29 made of an in-plane magnetized film. Can be controlled, and the degree of freedom in film design is improved.

The intermediate layer 29 need only be in an in-plane magnetization state up to the Curie temperature of the intermediate layer 29 at all times. However, when the temperature of the intermediate layer 29 becomes equal to or higher than the Curie temperature, the exchange coupling between the readout layer 3 and the recording layer 4 is released, and in order to realize more reliable light modulation overwriting, the intermediate layer 29 is required.
Is preferably about the same as the Curie temperature T _C2 of the recording layer 4, that is, 150 to 250 ° C.

The intermediate layer 29 is specifically formed of, for example, Dy
An in-plane magnetized film made of FeCo is used. DyFeC
o, TbFeCo, GdTbFe, NdDyF
eCo is preferred. In addition, Cr, V,
Long-term reliability can be improved by adding at least one element of Nb, Mn, Be, and Ni. The thickness of the intermediate layer 29 is determined in consideration of the material, composition, and thickness of the readout layer 3; Middle layer 2
9 is continuously formed in the same sputtering apparatus together with the readout layer 3 and the recording layer 4.

A magneto-optical disk having an intermediate layer 29 made of DyFeCo was prototyped using the same sputtering apparatus as in the above embodiment. Other configurations are the same as those of the above embodiment. The Curie temperature of the intermediate layer 29 was set to 150 ° C., the same as that of the recording layer 4.

This magneto-optical disk was mounted on a magneto-optical disk device and subjected to the same recording and reproduction test as in the above embodiment. As a result, good overwrite characteristics and reproduction characteristics were obtained. However, in the present embodiment, the intermediate layer 9 controls the exchange coupling between the readout layer 3 and the recording layer 4, and the exchange coupling force is weak. Therefore, the optimum magnitude of the recording magnetic field is 22 kA / m, which is different from the above embodiment.

A reference example of the present invention will be described below with reference to FIGS. 44 to 46. For convenience of explanation, members having the same functions as the members shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 44, the magneto-optical disk of this reference example has a substrate 1, a transparent dielectric layer 2, a readout layer 3, an intermediate layer 30 made of a nonmagnetic film, a recording layer 4, a protective film 5, It has a configuration in which the coat layers 6 are stacked in this order.

At the time of recording, if the intermediate layer 30 made of a non-magnetic film does not exist, a strong exchange coupling force acts from the readout layer 3 to the recording layer 4, thereby deteriorating the recording characteristics. Therefore, stable recording can be performed by providing the intermediate layer 30 made of the nonmagnetic film of the present embodiment and releasing the exchange coupling.

As the intermediate layer 30, specifically, for example,
AlN with a thickness of 5 nm is used. Since the intermediate layer 30 is formed so that exchange coupling between the recording layer 4 and the readout layer 3 does not work, it is sufficient that AlN is formed between the recording layer 4 and the readout layer 3 as a monolayer or more. If the intermediate layer 30 is too thick, the magnetic field generated from the recording layer 4 for aligning the magnetization of the readout layer 3 becomes weak. Therefore, the thickness of the intermediate layer 30 is suitably equal to or less than 50 nm.

In the magneto-optical disk of the present embodiment, specifically, the substrate 1 has a diameter of 86 mm, an inner diameter of 15 mm, and a thickness of 1.0 mm.
It is made of 2 mm disk-shaped glass. Although not shown, an uneven guide track for guiding a light beam is provided on one surface of the substrate 1 at a pitch of 1.6 μm, a groove (recess) width of 0.8 μm, and a land (convex portion). The width is 0.
It is formed at 8 μm. That is, the width of the groove and the width of the land are formed to be 1: 1.

On the surface of the substrate 1 on which the guide tracks are formed, A1N having a thickness of 80 n is formed as the transparent dielectric layer 2.
m.

On the transparent dielectric layer 2, as the readout layer 3, a rare-earth transition metal alloy thin film GdFeCo is formed with a thickness of 50 nm. The composition of GdFeCo is
_{Gd 0. 26 (Fe 0.82 Co 0.18} ) _0.74, the Curie temperature is about 300 ° C..

Due to the combination of the readout layer 3 and the recording layer 4, the magnetization direction of the readout layer 3 is almost in-plane at room temperature (that is, the layer direction of the readout layer 3).
The transition from the in-plane direction to the vertical direction occurs at a temperature of about 125 ° C.

On the readout layer 3, as the intermediate layer 30, A
1N is formed with a thickness of 5 nm.

On the intermediate layer 30, as the recording layer 4, a rare earth
The transition metal alloy thin film DyFeCo has a thickness of 50 nm.
It is formed with. The composition of DyFeCo is Dy
_0.23(Fe _0.78Co_0.22)_0.77And that Curie Wen
The degree is about 200 ° C.

On the recording layer 4, as a protective layer 5, A1N
Is formed with a thickness of 20 nm.

On the protective layer 5, a polyurethane acrylate-based ultraviolet curable resin having a thickness of 5 μm is formed as the overcoat layer 6.

This magneto-optical disk is a read-out layer 3 of the magneto-optical disk shown as a specific example in the first embodiment.
An intermediate layer 30 was provided between the recording layer 4 and the recording layer 4. When the same operation as in the first embodiment was confirmed, almost the same result was obtained.

As a material of the intermediate layer 30 other than AlN,
SiN, AlSiN, AlTaN, SiAlON, Ti
N, TiON, BN, ZnS, TiO ₂ , BaTiO ₃ ,
A dielectric material such as SrTiO ₃ can be used.

Further, Al, Si, Ta, Ti, Cu, A
Non-magnetic metal materials such as u, Ag, and Pt, or alloys thereof can be used.

As a variation of the above-described magneto-optical disk, as shown in FIG. 45, a substrate 1, a transparent dielectric layer 2,
There is a magneto-optical disk in which a readout layer 3, an intermediate layer 30 made of a nonmagnetic film, a recording layer 4, a heat radiation layer 20, and an overcoat layer 6 are laminated in this order. The heat radiation layer 20 is as described in detail in the first embodiment.

As another variation of the above-described magneto-optical disk, as shown in FIG. 46, a substrate 1, a transparent dielectric layer 2, a readout layer 3, an intermediate layer 30 made of a non-magnetic film, a recording layer 4, and a second transparent layer. There is a magneto-optical disk in which a dielectric layer 21, a reflection layer 22, and an overcoat layer 6 are laminated in this order.
This magneto-optical disk is composed of the recording layer 4 of the magneto-optical disk.
And a second transparent dielectric layer 21 and a reflective layer 22 provided between the first transparent dielectric layer 21 and the overcoat layer 6.
1 and the reflective layer 22 are as described in detail in the first embodiment.

In the first to fifth embodiments and the reference example described above, the magneto-optical disk is used as the magneto-optical recording medium. However, the present invention can be applied to a magneto-optical card and a magneto-optical tape. In the case of a magneto-optical tape, the rigid substrate 1
Instead, a flexible tape base (substrate), for example, a tape base made of polyethylene terephthalate may be used.

[0385]

According to the first and fourth aspects of the present invention, it is possible to reproduce recorded bits smaller than before, and the recording density is significantly improved. Moreover, GdFeCo
The readout layer 3 in which the magnetization direction changes very steeply from in-plane magnetization to perpendicular magnetization can be realized. Thereby, noise at the time of reproduction is reduced, so that a magneto-optical recording medium capable of performing higher-density recording can be provided.

According to the invention of claim 2, in addition to the above effects, the perpendicular magnetic anomaly of the recording layer is reduced. Thereby, the external magnetic field at the time of recording can be reduced.

According to the third aspect of the invention, in addition to the above effects, the perpendicular magnetic direction of the recording layer is increased. Thereby, a magneto-optical recording medium having high reproduction signal quality can be provided.

According to the fifth aspect of the present invention, the quality of a reproduced signal when reading information recorded at high density is improved.

According to the invention of claim 6, a magneto-optical recording medium capable of high-density recording and reproduction can be provided.

According to the seventh aspect of the present invention, the selection range of materials for the readout layer and the recording layer is increased.

According to the eighth aspect of the present invention, high-density recording and reproduction can be performed using the magneto-optical recording medium according to the sixth and seventh aspects of the present invention.

[Brief description of the drawings]

FIG. 1, showing a first embodiment of the present invention, is an explanatory diagram showing a schematic configuration of a magneto-optical disk and a reproducing operation.

FIG. 2 is an explanatory diagram of a magnetic state showing magnetic characteristics of a readout layer of the magneto-optical disk of FIG.

FIG. 3 is an explanatory diagram showing a relationship between an externally applied magnetic field applied to a readout layer and a polar Kerr rotation angle from room temperature to temperature T ₁ in FIG. 2;

FIG. 4 is an explanatory diagram showing a relationship between an externally applied magnetic field applied to a readout layer and a polar Kerr rotation angle from a temperature T ₁ to a temperature T ₂ in FIG. 2;

In Figure 5 a temperature T ₃ from the temperature T ₂ in FIG. 2 is an explanatory diagram showing the relationship between the externally applied magnetic field and polar Kerr rotation angle to be applied to the readout layer.

FIG. 6 is an explanatory diagram showing a relationship between an externally applied magnetic field applied to a readout layer and a polar Kerr rotation angle at a temperature T ₃ Curie temperature T _c in FIG. 2;

FIG. 7 is a graph showing the results of actually measuring the dependence of the polar Kerr rotation angle of the readout layer of the magneto-optical disk of FIG. 1 at room temperature on the externally applied magnetic field.

FIG. 8 shows a reading layer of the magneto-optical disk shown in FIG.
6 is a graph showing the results of actually measuring the externally applied magnetic field dependency of the polar Kerr rotation angle in FIG.

FIG. 9 is a graph in which the reproduction signal amplitude of the magneto-optical disk of FIG. 1 is plotted against the reproduction laser power.

FIG. 10 shows the reproduction signal quality (C / C) of the magneto-optical disk shown in FIG.
9 is a graph in which N) is plotted against the recording bit length.

FIG. 11 is a graph showing a result of measuring crosstalk of the magneto-optical disk of FIG.

FIG. 12 is an explanatory diagram showing an effect of the magneto-optical disk of FIG. 1;

FIG. 13 is a graph showing the composition dependence of the Curie temperature (T _c ) and the compensation temperature (T _comp ) of Gd _x (Fe _0.82 Co _0.18 ) _{1 -X} .

FIG. 14 is a graph showing the composition dependence of the Curie temperature (T _c ) and the compensation temperature (T _comp ) of Gd _X Fe _{1 -X} .

FIG. 15 is a graph showing the composition dependence of the Curie temperature (T _c ) and the compensation temperature (T _comp ) of Gd _X Co _{1 -X} .

16 is an explanatory diagram showing an example of land and group shapes formed on the substrate of the magneto-optical disk of FIG.

FIG. 17 is an explanatory diagram showing another example of the land and group shapes formed on the substrate of the magneto-optical disk of FIG. 1;

18 is an explanatory diagram showing an example of an arrangement of wobble pits formed on a substrate of the magneto-optical disk of FIG.

19 is an explanatory diagram showing another example of the arrangement of wobble pits formed on the substrate of the magneto-optical disk of FIG.

20 is an explanatory diagram showing an example of a wobble ring groove formed on a substrate of the magneto-optical disk of FIG.

FIG. 21 is an explanatory diagram showing a recording / reproducing method when a plurality of light beams are used in the magneto-optical disk of FIG.

FIG. 22 is an explanatory diagram showing a magnetic field modulation overwrite recording method using the magneto-optical disk of FIG. 1;

FIG. 23 is an explanatory diagram showing an optical modulation overwrite recording method using the magneto-optical disk of FIG. 1 and showing a method of magnetizing the readout layer and the recording layer.

24 is an explanatory diagram showing a light modulation overwrite recording method using the magneto-optical disk of FIG. 1 and showing the temperature dependence of the coercive force of the readout layer and the recording layer.

FIG. 25 is an explanatory diagram showing an example of the intensity of a light beam applied to the magneto-optical disk of FIG. 1 at the time of light modulation overwriting and at the time of reproduction.

FIG. 26 is an explanatory diagram showing another example of the intensity of the light beam applied to the magneto-optical disk of FIG. 1 at the time of light modulation overwriting and at the time of reproduction.

FIG. 27 is an explanatory diagram showing another example of the intensity of the light beam applied to the magneto-optical disk of FIG. 1 at the time of light modulation overwriting and at the time of reproduction.

FIG. 28 is an explanatory diagram showing a single-sided type of the magneto-optical disk of FIG. 1;

FIG. 29 is an explanatory diagram showing a double-sided type of the magneto-optical disk of FIG. 1;

30 is an explanatory diagram showing a schematic configuration of a sample for examining the effect of increasing the Kerr rotation angle when an element is added to the readout layer of the magneto-optical disk of FIG. 1;

FIG. 31 is a graph showing the wavelength dependence of the Kerr rotation angle of the sample of FIG. 30.

FIG. 32 is an explanatory diagram showing a schematic configuration of a sample for examining the effect of improving moisture resistance when an element is added to the readout layer of the magneto-optical disk of FIG. 1;

FIG. 33 is a graph showing the time change of the C / N ratio of the sample of FIG. 32;

34 is a graph showing a Kerr hysteresis loop measured by changing the thickness of the readout layer of the magneto-optical disk shown in FIG. 1, and (a) to (d) of FIG.
Kerr hysteresis obtained at 30, 40, 50 nm
It is a graph which shows a loop.

FIG. 35 is a graph in which the squareness ratio of the readout layer of the magneto-optical disk of FIG. 1 is plotted against the film thickness for each compensation temperature.

FIG. 36 is an explanatory diagram showing a calculation method for obtaining a squareness ratio from FIG. 29;

FIG. 37 is a graph in which the squareness ratio of the readout layer of the magneto-optical disk of FIG. 1 is plotted against the film thickness at each Curie temperature.

FIGS. 38A and 38B are graphs showing Kerr loops obtained on the magneto-optical disk of FIG. 1, wherein FIGS. is there.

FIG. 39 shows a second embodiment of the present invention,
FIG. 2 is a schematic configuration diagram of a magneto-optical disk.

FIG. 40 shows a third embodiment of the present invention;
FIG. 2 is a schematic configuration diagram of a magneto-optical disk.

FIG. 41 shows a fourth embodiment of the present invention,
FIG. 2 is a schematic configuration diagram of a magneto-optical disk.

FIG. 42 is an explanatory diagram showing temperature characteristics of coercive force of the readout layer and the recording layer of FIG. 41.

FIG. 43 shows a fifth embodiment of the present invention;
FIG. 2 is a schematic configuration diagram of a magneto-optical disk.

FIG. 44 shows a reference example of the present invention, and is a schematic configuration diagram of a magneto-optical disk.

FIG. 45 shows a variation of the magneto-optical disk of FIG. 44, and is a schematic configuration diagram of a magneto-optical disk having a heat dissipation layer.

FIG. 46 shows a variation of the magneto-optical disk of FIG. 44 and is a schematic configuration diagram of a magneto-optical disk having a reflective layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 1 (base) 2 Transparent dielectric layer 3 Readout layer 4 Recording layer 5 Protective layer 6 Overcoat layer 9 Recording medium layer 10 Adhesive layer 20 Heat dissipation layer 21 Transparent dielectric layer (second transparent dielectric layer) 22 Reflective layer 29 Intermediate layer 30 Intermediate layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichiro Nakayama 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Junsaku Nakajima 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Co., Ltd. (72) Inventor Akira Takahashi 22-22, Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Co., Ltd. (72) Inventor Kenji 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Co., Ltd. (72) Inventor Naoyasu Ikeya 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka

Claims (8)

[Claims] 1. A recording layer for magneto-optically recording magnetization information, and a readout layer which shows in-plane magnetization at room temperature, shifts to perpendicular magnetization with a rise in temperature, and transfers the magnetization of the recording layer. A magneto-optical recording medium, wherein the readout layer is GdFeCo. 2. The magneto-optical recording medium according to claim 1, wherein said recording layer is made of DyFeCo. 3. The magneto-optical recording medium according to claim 1, wherein said recording layer is made of TbFeCo. 4. The above-mentioned GdFeCo: Gd _x (Fe _1-Y Co _Y ) _1-x : 0.19 <X <0.29,
2. The method according to claim 1, wherein 0.1 <Y <0.5 is satisfied.
The magneto-optical recording medium according to the above. 5. A recording layer for magneto-optically recording magnetization information, and a readout layer which shows in-plane magnetization at room temperature, shifts to perpendicular magnetization with a rise in temperature, and transfers the magnetization of the recording layer. The readout layer is made of a rare earth transition metal amorphous alloy having ferrimagnetism, the composition is set such that the Curie temperature is 130 ° C. or higher without a compensation temperature,
A magneto-optical recording medium having a thickness set to 10 nm or more. 6. A recording layer for magneto-optically recording magnetization information, and a readout layer which shows in-plane magnetization at room temperature, shifts to perpendicular magnetization with a rise in temperature, and transfers the magnetization of the recording layer. The readout layer is made of a rare earth transition metal alloy in which rare earth metal is predominant, and its compensation temperature is set so as not to be between room temperature and the Curie temperature. A magneto-optical recording medium comprising a rare earth transition metal alloy. 7. The magneto-optical recording medium according to claim 9, wherein an intermediate layer made of an in-plane magnetic film is provided between the readout layer and the recording layer. 8. A recording layer made of a rare earth transition metal alloy in which a transition metal predominantly performs magneto-optical recording of magnetization information, and a recording layer which exhibits in-plane magnetization at room temperature, transitions to perpendicular magnetization with a rise in temperature, A readout layer to which magnetization is transferred, wherein the readout layer is made of a rare earth transition metal alloy, the compensation temperature of which is set so as not to be between room temperature and the Curie temperature, and the rare earth metal is A method of recording and reproducing information on a magneto-optical recording medium using a predominantly set magneto-optical recording medium for recording and reproducing information, the method comprising: applying a constant magnetic field for magnetizing a readout layer; By irradiating a laser beam switched between the first laser power and the high second laser power, the recording direction is reversed and the recording is performed.
By irradiating laser light with a laser power even lower than the laser power of the above, the area smaller than the laser spot diameter of the readout layer is shifted to the perpendicular magnetization state,
In addition, the sub-lattice magnetization of the region of the readout layer in the perpendicular magnetization state is aligned in a direction stable with respect to the sub-lattice magnetization of the recording layer,
A method for recording / reproducing information on / from a magneto-optical recording medium, wherein information is reproduced from a region of the readout layer in a perpendicular magnetization state.