JPH06150414A - Magneto-optical recording medium - Google Patents

Abstract

(57) [Summary] [Structure] The substrate 1 having a light-transmitting property and the in-plane magnetization formed on the substrate 1 and having the superior in-plane magnetic anisotropy at room temperature, while the perpendicular magnetic anisotropy increases with temperature A read layer 3 that shifts to a perpendicular magnetization that is dominant in directionality, and is formed on the read layer 3,
It has a recording layer 4 for magneto-optically recording information and a reflective layer 6 formed on the recording layer 4, and the reflective layer 6 is made of AlN.
A magneto-optical recording medium which is any one of i, AlTi, AlTa, and AlSi. [Effect] Therefore, it becomes possible to reproduce a recording bit smaller than the conventional one, and the recording density is remarkably improved. Moreover, it is possible to provide a magneto-optical disk having excellent reproduction signal quality, high recording density, and excellent moisture resistance.

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

[0002]

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

Since a magneto-optical disk uses a perpendicular magnetization film as a recording medium and performs recording and reproduction by using light, 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 conventional structure, the recording density of the magneto-optical disk depends on the size of the light beam used for recording / reproducing on the recording medium. In addition, there is a problem that the storage capacity cannot be increased.

That is, when the recording bit size and the recording bit interval become smaller than the light beam spot diameter, a plurality of recording bits including adjacent recording bits enter the light beam spot. Therefore, there is a problem in that noise increases and it becomes impossible to reproduce each recorded bit separately.

[0006]

In order to solve the above-mentioned problems, a magneto-optical recording medium according to the invention of claim 1 is provided with a translucent substrate and an in-plane magnetism formed at room temperature at room temperature. A reading layer that exhibits in-plane magnetization in which anisotropy is dominant, and shifts to perpendicular magnetization in which perpendicular magnetic anisotropy is dominant with a rise in temperature, and a recording layer that is formed on the reading layer and magneto-optically records information. It has a reflective layer formed on the recording layer, and the reflective layer is any one of AlNi, AlTi, AlTa, and AlSi.

A magneto-optical recording medium according to the invention of claim 2 is
In order to solve the above-mentioned problems, a translucent substrate and an in-plane magnetization formed on the substrate, in which the in-plane magnetic anisotropy is dominant, at room temperature, the perpendicular magnetic anisotropy increases as the temperature rises. Has a read layer that shifts to the dominant perpendicular magnetization, a recording layer formed on the read layer for magneto-optically recording information, and a heat dissipation layer formed on the recording layer. ,
It is characterized by being any one of AlTi, AlTa, and AlSi.

[0008]

According to the structure of claim 1, when the reading layer is irradiated with the light beam during the reproducing operation, the temperature distribution of the irradiated portion becomes almost Gaussian distribution. The temperature rises only in the vicinity area.

Along with this temperature rise, the magnetization of the temperature rise portion 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 the in-plane magnetization to the perpendicular magnetization, only the temperature rising portion exhibits the polar Kerr effect, and the 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 previous reproducing portion decreases and the perpendicular magnetization changes to the in-plane magnetization, so that the polar Kerr effect is not exhibited. This means that the magnetization recorded in the recording layer is masked by the in-plane magnetization of the read layer and cannot be read. This eliminates signal mixing from adjacent recorded bits that causes noise and reduces reproduction resolution.

As described above, since only the area heated to a predetermined temperature or higher is involved in the reproduction, it becomes possible to reproduce a recording bit smaller than in the conventional case, and the recording density is remarkably improved.

Moreover, AlNi and AlT are formed on the recording layer.
Since the reflective layer made of i, AlTa, or AlSi is provided, it is possible to provide a magneto-optical recording medium having excellent reproduction signal quality, high recording density, and excellent moisture resistance.

According to the second aspect of the present invention, the heat dissipation layer made of any of AlNi, AlTi, AlTa, and AlSi is provided in place of the reflection layer, so that the recording bit shape becomes clean and the reproduction signal quality is improved. A magneto-optical recording medium having excellent moisture resistance can be provided.

[0015]

DETAILED 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 read layer 3, a recording layer 4, and a transparent dielectric layer 5. The reflective layer 6 and the overcoat layer 7 are laminated in this order.

As shown in the magnetic phase diagram of FIG. 2, 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. This is because the perpendicular magnetization appears only near the compensating composition (indicated by P in the figure) in which the moments of the rare earth metal and the transition metal are balanced.

The magnetic moments of the rare earth metal and the transition metal have different temperature characteristics, and the magnetic moment of the transition metal becomes larger than that of the rare earth metal at high temperatures. Therefore, the content of the rare earth metal is set to be larger than that of the compensating composition at room temperature so that the in-plane magnetization does not appear at room temperature but the perpendicular magnetization does. In this case, when the temperature of the irradiation site rises due to the irradiation of the light beam, the magnetic moment of the transition metal becomes relatively large and becomes balanced with the magnetic moment of the rare earth metal, so that the perpendicular magnetization is exhibited. Become.

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

FIG. 3 shows the composition P in the magnetic phase diagram of FIG.
4 shows the hysteresis characteristics of the readout layer 3 from room temperature to the temperature T _1. FIGS. 4 to 6 show the hysteresis characteristics from the temperature T ₁ to the temperature T ₂ and the temperatures T ₂ to the temperature T _{3, respectively.} hysteresis characteristic up, and shows the hysteresis characteristic from the temperature T ₃ to the Curie temperature Tc.

In the temperature range from temperature T ₁ to temperature T ₃ , the polar Kerr rotation angle exhibits a steep rise with respect to the external magnetic field, but in other temperature ranges, the polar Kerr rotation angle is almost zero. .

The use of the rare earth transition metal having the above characteristics in the read layer 3 increases the recording density of the magneto-optical disk. That is, it is possible to reproduce recorded bits smaller than the size of the light beam. This will be described below.

During the reproducing operation, the reproducing light beam 8 is applied to the readout layer 3 from the substrate 1 (FIG. 1) side through the condenser lens 9. The temperature of the part of the readout layer 3 irradiated with the reproduction light beam 8 is the highest in the vicinity of the central part thereof and is higher than the temperature of the peripheral part. This is because the reproduction light beam 8
Since the light is condensed to the diffraction limit by the condenser lens 9, its light intensity distribution has a Gaussian distribution, and the temperature distribution of the reproducing portion on the magneto-optical disk also has a Gaussian distribution.

When the intensity of the reproduction light beam 8 is set so that the temperature in the vicinity of the center reaches T ₁ or higher and the temperature in the peripheral portion becomes T ₁ or lower, only the region having the temperature of T ₁ or higher is reproduced. Therefore, the recording bit smaller than the diameter of the reproduction light beam 8 can be reproduced, and the recording density is remarkably improved.

That is, the magnetization of the region having a temperature of T ₁ or higher shifts from in-plane magnetization to vertical 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, since the temperature is T ₁ or less in the peripheral region other than the region corresponding to the vicinity of the center of the reproduction light beam 8, the in-plane magnetization state (FIG. 3) is maintained. As a result, the polar Kerr effect is not exhibited with respect to the reproduction light beam 8 irradiated on the film surface in the vertical direction.

In this way, 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 8 exhibits the polar Kerr effect, and based on the reflected light from the portion, The information recorded on the recording layer 4 is reproduced.

When the reproducing light beam 8 moves (actually, the magneto-optical disk rotates) to reproduce the next recording bit, the temperature of the previous reproducing portion drops to T ₁ or less, and the perpendicular magnetization is lost. Transition to in-plane magnetization. Along with this, the region where the temperature is lowered does not exhibit the polar Kerr effect. Therefore, the information is not reproduced from the portion where the temperature is lowered, and the signal mixture from the adjacent recording bit, which is a cause of 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 reproduction light beam 8 can be surely reproduced, and the adjacent recording bits are not affected, so that the recording density can be improved. It can be significantly increased.

Next, a specific example of the magneto-optical disk of this embodiment will be shown.

The substrate 1 is made of disk-shaped glass having a diameter of 86 mm, an inner diameter of 15 mm and a thickness of 1.2 mm. Although not shown in the drawings, a concave-convex guide track for guiding the light beam has a pitch of 1.6 μm, a groove (concave) width of 0.8 μm, and a land (convex) on one surface of the substrate 1. The width is 0.8 μm.

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

GdFeCo, which is a rare-earth transition metal alloy thin film, is used as the readout layer 3 on the transparent dielectric layer 2.
It is formed with a thickness of 15 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 read-out layer 3, as a recording layer 4, a rare earth-transition metal alloy thin film DyFeCo having a thickness of 15 n was formed.
It is formed by 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 read layer 3 and the recording layer 4, the magnetization direction of the read layer 3 is substantially in-plane (that is, the layer direction of the read layer 3) at room temperature,
The temperature shifts from the in-plane direction to the vertical direction at a temperature of about 125 ° C.

On the recording layer 4, a transparent dielectric layer 5 is formed.
A1N is formed with a thickness of 30 nm.

On the transparent dielectric layer 5, a reflective layer 6 is formed.
A1Ni is formed with a thickness of 30 nm. The content of Ni in A1Ni is 5 atm%.

On the reflection layer 6, a polyurethane acrylate-based UV curable resin is formed as an overcoat layer 7 with a thickness of 5 μm.

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

The guide track on the surface of the glass substrate 1 was formed by the reactive ion etching method.

The transparent dielectric layer 2, the read layer 3, the recording layer 4, the transparent dielectric layer 5 and the reflective layer 6 were all formed by the sputtering method in the same sputtering apparatus without breaking the vacuum. A1N of the transparent dielectric layers 2.5 was formed by a reactive sputtering method in which an A1 target was sputtered in an N ₂ gas atmosphere. Readout layer 3 and recording layer 4
Is a so-called composite target in which Gd or Dy chips are arranged on a FeCo alloy target, or Gd.
It was formed by sputtering with Ar gas using a ternary alloy target of FeCo and DyFeCo.

The reflective layer 6 was formed by sputtering an Ar gas using an AlNi alloy target.
Instead of the AlNi alloy target, a composite target in which Ni pieces are arranged on the Al target may be used.

The overcoat layer 7 was formed by applying a polyurethane acrylate-based UV-curable resin with a spin coater, and then irradiating it with UV rays with an UV irradiator to cure it.

In the above magneto-optical disk, the read layer 3
The total thickness of the recording layer 4 and the recording layer 4 is 30 nm, which is set to a very small thickness. Therefore, the reproduction light beam 8 incident from the substrate 1 side passes through the reading layer 3 and the recording layer 4, is reflected by the reflecting layer 6, and is incident on the recording layer 4 and the reading layer 3 again. As a result, the reproduction light beam 8 enters from the substrate 1 side and is reflected by the readout layer 3 and the light reflected by the reflection layer 6 interfere with each other, and the magneto-optical effect is enhanced. That is, the polar car rotation angle becomes large.
Therefore, the information can be reproduced with higher accuracy and the quality of the reproduced signal is improved.

Since AlNi has a high reflectance, the light transmitted through the read layer 3 and the recording layer 4 can be efficiently reflected. Therefore, it is suitable as a material for the reflective layer 6.

Since AlNi has a relatively low thermal conductivity, the laser power required for recording and reproduction can be set low. In other words, the magneto-optical disk has high sensitivity. Thereby, the life of the semiconductor laser as the light source of the magneto-optical disk device can be extended.

When the laser power required for recording was examined using the above-mentioned magneto-optical disk, it was confirmed that recording can be performed with a laser power lower than 0.5 mW as compared with the magneto-optical disk in which only the reflective layer 6 is replaced with pure Al. did it.

It was also confirmed that the optimum laser power during reproduction was lower than that of the magneto-optical disk in which only the reflective layer 6 was replaced with pure Al.

Further, AlNi is extremely excellent in moisture resistance and can provide a magneto-optical recording medium excellent in long-term reliability.

The results of the moisture resistance test of the above magneto-optical disk will be described below.

The magneto-optical disk was left under the environmental conditions of 80 ° C. and 90% RH for 1000 hours, and the change in its characteristics was examined. For comparison, a magneto-optical disk having the same structure as above except that the reflective layer 6 was replaced with pure Al was also examined in the same manner.

As a result, in the magneto-optical disk using pure Al for the reflective layer 6, many pinholes were generated in the reflective layer 6 for Al. Due to this pinhole, the noise measured in the recording / reproducing experiment was increased, and the reproduced signal quality (C / N) was deteriorated by 10 dB as compared with the initial stage.

On the other hand, in the magneto-optical disk of this embodiment, the number of pinholes in the reflective layer 6 was very small, about several. Therefore, there was no increase in noise, and the characteristics that were the same as those at the initial stage were obtained even after being left under the above environmental conditions.

The content of Ni in AlNi is 0-10.
Atm% is preferred. If the Ni content becomes too large, the reflectance decreases as the Ni content increases, and the reproduction signal quality (C / N) deteriorates. When the amount of Ni is up to 10 atm%, the deterioration of C / N is not so remarkable and a practical value can be obtained. Further, even if the Ni content is as small as about 0.5 atm%, the recording sensitivity is improved and the moisture resistance is remarkably improved as compared with Al.

As the material of the reflective layer 6, AlTi, AlT
a and AlSi are also suitable.

Since these materials also have high reflectance, the light transmitted through the read layer 3 and the recording layer 4 can be efficiently reflected, and a magneto-optical disk with excellent reproduction signal quality can be provided. it can.

Since these materials also have relatively low thermal conductivity, the laser power required for recording / reproducing can be set low, and the life of the semiconductor laser in the magneto-optical disk device can be extended.

Magneto-optical disk having AlTi reflective layer 6 containing 1.5 atm% of Ti, A containing 1.5 atm% of Ta
Magneto-optical disk with 1Ta reflective layer 6, 10at Si
As for the magneto-optical disk having the AlSi reflective layer 6 containing m%, the laser power required for recording and reproducing was obtained and the moisture resistance test was conducted in the same manner as above, and the same result as above was obtained. .

Ti content in AlTi and Al
The Ta content in Ta is preferably 0 to 10 atm%. If the content of these elements becomes too large, the reflectance decreases as Ti or Ta increases, and the reproduction signal quality (C / N) deteriorates. When the content is up to 10 atm%, the deterioration of C / N is not so remarkable and a practical value can be obtained. Even if the content is as small as about 0.5 atm%, the recording sensitivity is improved and the moisture resistance is remarkably improved as compared with Al.

The content of Si in AlSi is 0 to 50.
Atm% is preferred. If the content of these elements becomes too large, the reflectance decreases as the content of Si increases, and the reproduction signal quality (C / N) deteriorates. When the content is up to 50 atm%, the deterioration of C / N is not so remarkable and a practical value can be obtained. Even if the content is as small as about 0.5 atm%, the recording sensitivity is improved and the moisture resistance is remarkably improved as compared with Al.

The use of AlTa for the reflective layer 6 has the following advantages.

The AlTa reflective layer 6 is formed by sputtering an AlTa alloy target or a composite target in which Ta pieces are arranged on an Al target with Ar gas.

[0062] Incidentally, AlTa alloy target or a composite target which arranged Ta pieces on Al target N ₂ gas, or, when sputtered in a mixed gas of Ar gas and N ₂ gas, by reactive sputtering, Al
TaN is formed. Since AlTaN is transparent and has a large refractive index of around 2, the transparent dielectric layer 2.5
It can be used as a material.

Therefore, the transparent dielectric layers 2.5 and the reflective layer 6 can be formed using the same target. For this reason,
The sputter device can be downsized, and the manufacturing cost of the magneto-optical disk can be significantly reduced.

Even when AlSi is used for the reflective layer 6, A
There are similar advantages to the case of using 1Ta for the reflective layer 6.

That is, the AlSi reflective layer 6 is made of AlS.
Si on i alloy target or Al target
It is formed by sputtering a composite target in which pieces are arranged with Ar gas. AlSi alloy target or a composite target which arranged Si pieces on Al target N ₂ gas, or, when sputtered in a mixed gas of Ar gas and N ₂ gas, by reactive sputtering, Al
SiN is formed.

Since AlSiN is transparent and has a large refractive index of around 2, it can be used as a material for the transparent dielectric layers 2.5.

Therefore, the transparent dielectric layers 2.5 and the reflective layer 6 can be formed using the same target. For this reason,
The sputter device can be downsized, and the manufacturing cost of the magneto-optical disk can be significantly reduced.

Next, the film thickness of the reflective layer 6 will be described.

If the thickness of the reflective layer 6 is too thin, light will pass through the reflective layer 6 and the enhancement effect will decrease. Therefore, the film thickness should be at least about 20 nm. On the other hand, if the film thickness is too large, the laser power required for recording, reproduction, etc. will increase, and the recording sensitivity of the magneto-optical disk will decrease. For this reason, it is necessary to set the film thickness in accordance with the thermal conductivity and the specific heat of the material of the reflective layer 6, but usually 100 nm or less is preferable. Therefore, the preferable film thickness of the reflective layer 6 is in the range of 20 to 100 nm.

The above-mentioned AlNi, AlTi, AlT
Since a and AlSi are materials having extremely excellent moisture resistance, it is possible to provide a magneto-optical recording medium having excellent long-term reliability even when the film thickness is as thin as about 30 nm or less.

In the magneto-optical disk of this embodiment, the thickness of the transparent dielectric layer 2 is optimally 70 to 100 nm for enhancement of the magneto-optical effect. Is preferably 15 to 50 nm.

By setting the film thickness of the transparent dielectric layer 2 as described above, the polar Kerr rotation angle of the reflected light from the readout layer 3 can be increased by the light interference effect. In order to increase the signal quality (C / N) during reproduction as much as possible, it is necessary to increase the polar Kerr rotation angle. Therefore, the film thickness of the transparent dielectric layer 2 is such that the polar Kerr rotation angle is the largest. 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 the above-mentioned first embodiment, A having a refractive index of 2.0 with respect to the reproduction light wavelength of 780 nm
Since 1N is used, if the film thickness of AlN of the transparent derivative layer 2 is set to about 30 to 1200 nm, the Kerr effect enhancement effect becomes large. In addition, preferably, the film thickness of AlN of the transparent dielectric layer 2 is 70 to 100 nm, and the polar Kerr rotation angle is maximized in this range.

Although the above description is for the reproduction light of wavelength 780 nm, for example, for the reproduction light of wavelength 400 nm which is half the wavelength, if the film thickness of the transparent dielectric layer 2 is also halved. good.

Furthermore, 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 transparent product is transparent so that the value (optical path length) obtained by multiplying the refractive index and the film thickness becomes the same. The film thickness of the dielectric layer 2 may be set.

That is, for example, Al of the transparent dielectric layer 2
The optical path length of the transparent dielectric layer 2 is 160 nm, which is obtained by multiplying the refractive index 2 of N by the film thickness of 80 nm, but when the refractive index of this AlN changes from 2 to 2.5, 160 nm / 2.5 = 64 nm It suffices to set the film thickness to some extent.

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

As for the film thickness of the transparent dielectric layer 5, the polar Kerr rotation angle increases as the film thickness increases, but the reflectance decreases. If the reflectance is too small, the signal for applying servo to the guide track becomes small, and stable servo cannot be applied. Therefore, the film thickness of the transparent dielectric layer 5 is preferably about 15 to 50 nm.

If the refractive index of the transparent dielectric layer 5 is made larger than that of the transparent dielectric layer 2, the enhancement effect can be further enhanced.

The material of the transparent dielectric layers 2 and 5 is A
1N is preferred.

AlN is a material having a relatively large refractive index of about 1.8 to 2.1, although its refractive index changes by changing the ratio of Ar to N ₂ which is a sputtering gas at the time of sputtering and the gas pressure. It is possible to provide a magneto-optical disk having a large enhancement effect of the magneto-optical effect and excellent reproduction signal quality.

The transparent dielectric layer 2 not only has the role of Kerr effect enhancement as described above,
The transparent dielectric layer 5 and the read layer 3 and the recording layer 4 also have a role of preventing the magnetic material made of a rare earth transition metal alloy from being oxidized.

The readout layer 3 and the recording layer 4 made of a rare earth transition metal are very easily oxidized, and especially the rare earth is easily oxidized. For this reason, if the invasion of oxygen and moisture from the outside is not prevented as much as possible, the characteristics will be significantly deteriorated by oxidation.

Therefore, in this embodiment, the read layer 3 and the recording layer 4 are sandwiched on both sides by AlN. AlN is a nitride that does not contain oxygen as its component, and is a material having extremely excellent moisture resistance.

AlTaN and AlSiN are also suitable as the material of the transparent dielectric layer 2 or 5.

In addition, SiN, SiAlON, TiN, TiON,
BN, ZnS, TiO ₂ , BaTiO ₃ , SrTiO _{3 and the} like are also suitable.

Among these, particularly, SiN, TiN, BN, Zn
S 2 does not contain oxygen as a component and can provide a magneto-optical disk having excellent moisture resistance.

Further, since the readout layer 3 and the recording layer 4 made of a rare earth transition metal alloy absorb light well, when the total thickness of these layers is 50 nm or more, almost no light is transmitted and the Kerr effect enhancement is achieved. Will not be able to.
Therefore, the total thickness of these two layers is preferably 10 to 50 nm.

The composition of GdFeCo in the readout layer 3 is Gd
It is not limited to _0.26 (Fe _0.82 Co _0.18 ) _0.74 . The readout layer 3 has almost in-plane magnetization at room temperature, and the in-plane magnetization may be changed to the perpendicular magnetization at room temperature or higher. In rare earth-transition metal alloys, changing the ratio of rare earth to transition metal changes the compensation temperature at which the magnetizations of the rare earth and transition metal are balanced. Since GdFeCo is a material system that exhibits perpendicular magnetization near this compensation temperature, if the compensation temperature is changed by changing the ratio of Gd and FeCo, the temperature at which in-plane magnetization changes to perpendicular magnetization also changes accordingly.

FIG. 7 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 of Gd _X (Fe _0.82 Co _0.18 ) _1-X .

In the composition range in which the compensation temperature is room temperature (25 ° C.) or higher, X is 0.18 or higher, as is apparent from FIG.
Of these, the range of 0.19 <X <0.29 is preferable.
Within this range, the temperature at which the direction of magnetization shifts from the in-plane direction to the perpendicular direction is in the range of room temperature to 200 ° C. in the actually used configuration in which the recording layer 4 is laminated on the read layer 3. If this temperature is too high, the laser power for reproduction will be 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 GdFeCo system, the characteristics (compensation temperature) when the ratio of Fe and Co was changed, that is, when Y was changed in GdX _X (Fe _{1 -Y} Co _Y ) _{1 -X} . And the change in Curie temperature).

FIG. 8 shows that when Co is zero, that is, Gd _X
It is a figure which shows the characteristic of Fe1 _-X . In the figure, for example,
When the Gd composition is X = 0.3, the compensation temperature is about 120 ° C and the Curie temperature is about 200 ° C.

FIG. 9 shows that when Fe is zero, that is, Gd _X
It is a figure which shows the characteristic of Co1 _-X . In the figure, for example,
When the Gd composition is X = 0.3, the compensation temperature is about 220 ° C and 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 rise as the amount of Co increases.

Since a higher C / N can be obtained when the polar Kerr rotation angle during reproduction is as large as possible, a higher Curie temperature of the read layer 3 is advantageous. However, it should be noted that if the Co content is increased too much, the temperature at which the magnetization direction shifts perpendicularly from the surface also increases.

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

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

As described above, GdFeCo, which is steep from in-plane magnetization to perpendicular magnetization, is the most suitable material for the read layer 3 of the magneto-optical disk of the present invention. The same effect can be obtained.

Gd _x Fe _1-X has the characteristics shown in FIG. 8 and has a compensation temperature above room temperature in the range of 0.24 <X <0.35.

Gd _x Co _1-X has the characteristics shown in FIG. 9, and has a compensation temperature above room temperature in the range of 0.20 <X <0.35.

When a FeCo alloy is used as the transition metal, Tb _X (Fe _Y Co _1-Y ) _1-X has a compensation temperature above room temperature in the range of 0.20 <X <0.30 (where Y is arbitrary). Have.
Dy _X (Fe _Y Co _1-Y ) _1-X is 0.24 <X <0.33 (At this time,
Y has a compensation temperature at room temperature or higher in any range. Ho _X
(Fe _Y Co _1-Y ) _1-X has a compensation temperature at room temperature or higher 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, becomes shorter than the above-mentioned 780 nm, a material having a large polar Kerr rotation angle at that wavelength can be read by the present invention. It is suitable as a material for the layer 3.

As already described, 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 wavelength shorter than that of the present time appears, the recording density of the magneto-optical disk is improved by itself. Now, already 670
Semiconductor lasers with wavelengths up to 680 nm are almost at the practical level, and SHG lasers with wavelengths below 400 nm are being actively researched.

The polar Kerr rotation angle of a rare earth-transition metal alloy has wavelength dependence, and generally, when the wavelength becomes shorter,
The polar car rotation angle will decrease. If a film with a short wavelength and a large polar Kerr rotation angle is used, the signal strength is increased and a high quality reproduction signal is obtained.

Nd, Pt, Pr and Pd are used as the material of the above-mentioned readout layer 3.
By adding a trace amount of at least one of these elements,
Provided is a magneto-optical disk capable of increasing a polar Kerr rotation angle at a short wavelength with almost no loss of characteristics required for the readout layer 3 and obtaining a high quality reproduction signal even when a short wavelength laser is used. it can.

The read layer 3 to which the above element is added is specifically, for example, Nd _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 , Pt _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 , Pr _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 , Pd _0.05 [Gd _0.26 (Fe
_0.82 Co _0.18 ) _0.74 ] _0.95 .

Further, the environment resistance of the readout layer 3 itself is improved by adding a trace amount of at least one element of Cr, V, Nb, Mn, Be and Ni to the material of the readout layer 3 described above. To do. That is, it is possible to provide a magneto-optical disk excellent in long-term reliability by suppressing deterioration of characteristics due to oxidation of the material of the read layer 3 due to invasion of water and oxygen.

The read layer 3 to which the above element is added is, 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 .

The material of the recording layer 4 is a material developed and used in the conventional magneto-optical disk, that is, a material exhibiting perpendicular magnetization from room temperature to the Curie temperature, and the Curie temperature is in a temperature range suitable for recording, that is, It may be about 150 to 250 ° C. Although DyFeCo is used as the recording layer 4 in the above-described embodiment, DyFeCo is a material having a small perpendicular magnetic anisotropy, and therefore recording can be performed even when the 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, GdTbFe, NdDyFe
Co, GdDyFeCo and GdTbFeCo are suitable for the recording layer 4. As an example, in Tb _X (Fe _Y Co _1-Y ) _1-X ,
It suffices that 0.10 ≦ X ≦ 0.30 is satisfied for any Y. More specifically, for example, Tb _0.18 (Fe
_0.88 Co _0.12 ) _0.82 .

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

Further, as the material of the recording layer 4 described above, Cr, V, N
By adding at least one element of b, Mn, Be, and Ni, the long-term reliability can be improved.

As the material of the substrate 1, in addition to the above-mentioned glass, chemically strengthened glass, a so-called 2P-layered glass substrate having a UV-curable resin layer formed on these glass substrates, polycarbonate (PC), poly It is possible to use the substrate 1 made of methyl methacrylate (PMMA), amorphous polyolefin (APO), polystyrene (PS), polychlorinated biphenyl (PVC), epoxy, or the like.

When chemically strengthened glass is used for the substrate 1, it has excellent mechanical properties (in the case of a magneto-optical disk, surface wobbling, eccentricity, warpage, inclination, etc.), a large hardness,
Hard to be scratched by sand and dust, chemically stable so it does not dissolve in various solvents, less likely to be charged as compared to plastic, so dust and dirt do not adhere, and chemically strengthened so it is hard to break In addition, since it has excellent moisture resistance, oxidation resistance, and heat resistance, long-term reliability of the magneto-optical recording medium is improved, optical characteristics are excellent, and high signal quality can be obtained. .

When the above-mentioned glass or chemically strengthened glass is used as the substrate 1, a guide track for guiding a light beam and unevenness called pre-pits formed in advance on the substrate to obtain information such as an address signal. As a method of forming a signal on a substrate, the surface of these glass substrates is formed by reactive dry etching. Also, 2
After applying an ultraviolet curable resin called P layer on the glass substrate 1, a mold called a stamper is pressed against this resin layer, and the resin is cured by irradiating with ultraviolet rays, and then the stamper is peeled off to form a resin layer on the resin layer. There is a method of forming the above-mentioned guide track, pre-pit, and the like.

When a PC is used for the substrate 1, injection molding is possible, so that the same substrate 1 can be supplied in a large amount at a low cost, and since the water absorption rate is lower than other plastics,
Improved long-term reliability of magneto-optical recording media, heat resistance,
The advantage is that it has excellent impact resistance. For materials that can be injection-molded as described below, including this material, guide tracks, pre-pits, etc. can be formed on the surface of the substrate 1 simultaneously with molding if a stamper is attached to the surface of the molding die during injection molding. To be done.

When PMMA is adopted for the substrate 1, injection molding is possible, so that a large amount of the same substrate 1 can be supplied at low cost, and since the birefringence is smaller than other plastics, it has excellent optical characteristics. The advantages include high signal quality and excellent durability.

When APO is used for the substrate 1, injection molding is possible, so that a large amount of the same substrate 1 can be supplied at low cost, and the water absorption rate is lower than other plastics.
The advantages are that the long-term reliability of the magneto-optical recording medium is improved, the birefringence is small, the optical characteristics are excellent, the high signal quality is obtained, and the heat resistance and the impact resistance are excellent. To be

When PS is used as the substrate 1, injection molding is possible, so that the same substrate 1 can be supplied in large quantities at low cost, and since the water absorption rate is lower than other plastics, long-term reliability of the magneto-optical recording medium is obtained. The advantage is that the property is improved.

When PVC is used for the substrate 1, injection molding is possible, so that a large amount of the same substrate 1 can be supplied at low cost, and its water absorption rate is lower than other plastics.
The advantages are that the long-term reliability of the magneto-optical recording medium is improved and that it is flame-retardant.

When epoxy is used for the substrate 1, the water absorption rate is lower than that of other plastics, so that the long-term reliability of the magneto-optical recording medium is improved, and the thermosetting resin is excellent in heat resistance. The advantage is that it is excellent.

As described above, various materials can be used as the substrate 1, but when these materials are used as the substrate 1 of the magneto-optical disk, the following optical characteristics and mechanical characteristics are satisfied. Is desirable.

Refractive index: 1.44 to 1.62 Birefringence: 100 nm or less (reciprocal birefringence measured by parallel light) Transmittance: 90% or more Thickness variation: ± 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 The optical pickup for converging the laser light on the recording medium is designed according to the refractive index of the substrate 1.
If the variation in the refractive index of the laser becomes large, the laser light cannot be collected sufficiently. When the focused state of the laser light changes, the temperature distribution of the recording medium (that is, the read layer 3 and the recording layer 4) changes, which affects recording and reproduction. In the present invention, the temperature distribution of the recording medium during reproduction becomes particularly important, so 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 light is made incident through the substrate 1, if the substrate 1 has birefringence, the polarization state of the laser light changes when the laser light passes through the substrate 1.
Since the present invention reproduces the change in the magnetization state of the readout layer 3 as the change in the polarization state by using the Kerr effect, if the polarization state changes when passing through the substrate 1, the reproduction cannot be performed. Therefore, it is desirable that the reciprocal birefringence of the substrate 1 when measured with parallel light is 100 nm or less.

Further, if the transmittance of the substrate 1 becomes low, for example, at the time of recording, when the light beam from the optical pickup passes through the substrate 1, the amount of light will decrease. Therefore, in order to obtain the amount of light required for recording on the recording medium, a laser light source with higher output is required. Particularly in the present invention, the recording medium is a recording layer 4 and a reading layer 3
In order to raise the temperature of the recording medium as compared with the conventional single-layer (without the reading layer 3) recording medium,
Since a larger amount of light is required, the transmittance of the substrate 1 is 9
It is preferably 0% or more.

Since the optical pickup for focusing the laser light on the recording medium is designed according to the thickness of the substrate 1, the laser light is sufficiently focused when the thickness of the substrate 1 fluctuates greatly. Can not do. When the focused state of the laser light changes, the temperature distribution of the recording medium changes, which adversely affects recording and reproduction. In the present invention, the temperature distribution of the recording medium during reproduction is particularly important, so it is desirable to suppress the thickness variation of the substrate 1 used within ± 0.1 mm.

When the substrate 1 is tilted, the laser light from the optical pickup is focused on the tilted recording medium surface, and the focused state changes depending on the tilted state. As in the case where the thickness of the substrate 1 changes, recording and reproduction are adversely affected. Therefore, in the present invention, the tilt of the substrate 1 is preferably 10 mrad or less, more preferably 5 mrad or less.

When the substrate 1 moves up and down with respect to the optical pickup, the optical pickup operates so as to compensate the vertical movement and focus the laser light on the surface of the recording medium, but if the vertical movement becomes too large. The compensation operation of the optical pickup becomes incomplete, and the condensed state of the laser light on the surface of the recording medium becomes incomplete. If the focused state of the laser light is incomplete, 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 during reproduction becomes particularly important, it is desirable to suppress the surface wobbling acceleration to 10 m / s ² or less when the substrate used is moved up and down during rotation.

In addition, 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 have an eccentricity, the guide tracks move in the radial direction with respect to the optical pickup during rotation. At this time, the optical pickup collects the laser light in order to compensate the movement in the radial direction and maintain a constant relationship with the guide track, but if the movement of the guide track in the radial direction becomes too large, the compensating operation of the optical pickup will occur. It becomes incomplete, and it becomes impossible to focus the laser beam in a state where the guide track is kept in a constant relationship. In the present invention, the temperature distribution of the recording medium during reproduction is particularly important. Therefore, with respect to the radial movement of the substrate used during rotation, the radial acceleration should be suppressed to 3 m / s ² or less. Is desirable.

As a method of guiding the focused laser light to a predetermined position of the magneto-optical disk, spiral or
A continuous servo method using a concentric guide track and a sample servo method using a spiral or concentric pit row can be considered.

In the case of the continuous servo system, as shown in FIG. 10, the pitch is 1.2 to 1.6 μm and the pitch is 0.2 to 0.6 μm.
Width groups are formed with a depth of about λ / (8n),
Information is generally recorded and reproduced at the land portion. This is called a land specification magneto-optical disk. Where λ is the wavelength of the laser beam and n is the refractive index of the substrate used.

The present invention can be sufficiently applied to such a general system. In the present invention, the crosstalk due to the recording bits of the adjacent tracks is significantly reduced.
Even when a group having a width of 0.4 μm is formed, recording / reproduction can be performed without being affected by crosstalk from adjacent recording bits, and the recording density is significantly improved.

Further, as shown in FIG. 11, 0.8-1.
Forming groups and lands of the same width at a pitch of 6 μm,
Even when recording / reproducing is performed on both the group portion and the land portion, recording / reproducing can be performed on both the group portion and the land portion without being affected by crosstalk from the recording bits of adjacent tracks. The density is greatly improved.

On the other hand, in the case of the sample servo system, FIG.
2, wobble pits are formed with a depth of about (λ / (4n)) at a pitch of 1.2 to 1.6 μm, and information is recorded so that the laser beam always scans the center of the wobble pits. Regeneration is generally performed.
It is quite possible to apply the present invention to such a general system. In the present invention, by significantly reducing the crosstalk from the adjacent recording bits,
Even when the wobble pits are formed with a pitch of 0.5 to 1.2 μm, recording and reproduction can be performed without being affected by crosstalk from adjacent recording bits.
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 / reproduced at positions where the wobble pits have opposite polarities, recording / reproduction can be performed without being affected by crosstalk from adjacent recording bits. It becomes possible and the recording density is greatly improved.

Further, as shown in FIG. 14, in the continuous servo system, when the position information of the magneto-optical disk is obtained by wobbling the groove, the wobbling state exists in the adjacent groove in the opposite phase portion. Although there has been a problem that crosstalk from recording bits becomes large, by applying the present invention, crosstalk from recording bits existing in an adjacent groove may occur even in a portion where the wobbling state has an opposite phase. Therefore, it is possible to perform good recording and reproduction.

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

For example, when employing a plurality of optical pickups or a multi-beam type optical pickup in which a plurality of light beams are produced from one light source, as shown in FIG. 15, the light beams at both ends of the plurality of light beams are guided. A method is generally used in which positioning is performed so that scanning is performed on a track, and recording and reproduction are performed with a plurality of light beams positioned between them. However, it is possible to reproduce without being affected by the crosstalk from the adjacent recording bits, and it is possible to shorten the pitch of the guide tracks or to use more laser beams between the pair of guide tracks. It becomes possible to record and reproduce, and the recording density is greatly improved.

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 light is The guide track pitch and the like are discussed as being 670 nm to 840 nm. A. Is further increased to 0.6 to 0.95, the laser beam is further narrowed down, and by applying the magneto-optical disk of the present invention, the pitch and width of the guide track can be further narrowed. High-density recording / reproducing is 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 is further narrowed down, and by applying the present invention, the pitch of the guide track is reduced. Also, the width can be further narrowed, and recording and reproduction with higher density can be performed.

Regarding a / w, those of 0.3 to 1.0 can be used. Where a is the optically effective diameter of the lens,
w is the diameter of the light beam entering the lens, and is the radius of 1 / e ² of the central intensity when the Gaussian distribution is used.

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

Generally, in a magneto-optical disk, in order to maintain compatibility between different manufacturers or between different magneto-optical disk disks, what value or duty the recording and erasing powers at the respective radial positions are set. Whether to set to (λ / (4n))
It is pre-recorded in a pre-pit row with a depth. Further, based on those read values, a test area in which recording and reproduction can be actually performed is provided on the inner and outer circumferences (for example, refer to IS10089 standard).

On the other hand, regarding the reproducing power, information for setting a specific reproducing power is recorded in advance in a part of the inner and outer circumferences in a prepit row.

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

As a reproducing power setting method, for example, with respect to the reproducing power as well as the recording power, a test area for setting the reproducing power is provided on the inner and outer circumferences, and each radial position is determined from the reproducing power obtained in the test area. It is desirable to previously record information for optimizing the reproduction power in the pit row in a part of the inner and outer circumferences.

Particularly in a magneto-optical disk drive using the CAV system in which the number of revolutions of the magneto-optical disk is always constant, the linear velocity of the magneto-optical disk changes depending on the radial position. Therefore, the reproducing laser power depends on 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 prepit row.

Similarly, as a method of setting a more optimum reproducing 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. Also, by optimizing the reproduction power in the test area, the temperature distribution of the recording medium during reproduction can be controlled more accurately, and good recording / reproduction can be performed.

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

First, the recording method of the first generation magneto-optical disk which cannot be overwritten will be described.

The first generation magneto-optical disk is IS10089.
In accordance with the standard (standard of ISO 5.25 "rewritable optical disc), many are already on the market,
Since overwriting cannot be performed, when newly recording information at a place where information has already been recorded, it is necessary to perform an operation of once erasing that portion and then recording. Therefore, it is necessary to rotate the magneto-optical disk at least twice, and there is a defect that the data transfer rate is slow.

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 drawback that overwriting is not possible, a method of arranging a plurality of optical heads to eliminate the loss of waiting for rotation and improve the data transfer speed is adopted in some devices.

For example, it is a method of using two optical heads to erase the information already recorded by the preceding optical head and record new information by the optical head chasing afterwards. When reproducing, either one of the optical heads is used for reproduction.

When recording is performed 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 perform verification. (Check that the new information is recorded correctly).

Further, instead of using a plurality of optical heads, a plurality of beams may be produced by using a single optical head with a beam splitter, and this may be used in the same manner as the plurality of optical heads.

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

The magneto-optical disk of the present embodiment has been confirmed to be capable of recording, reproducing and erasing as already described in the explanation of the experimental results, and is a magneto-optical disk applicable to this recording system. .

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. For example,

FIG. 16 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 laser light at the time of recording and reproducing, and recording. And an optical head 11 incorporating a light receiving element (not shown) for receiving the reflected light from the magneto-optical disk during reproduction, and a floating magnetic head 12 mechanically or electrically connected to the optical head 11. I have it.

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.
It is pressed by 4 and is levitated with a constant gap of about several μm to several tens of μm.

In this state, the floating 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, and the recording layer of the magneto-optical disk 14 is moved from the optical head 11 to about 2 to 10 mW. Laser light is focused and irradiated to raise the temperature of the recording layer 4 to near the Curie temperature (or the temperature at which the coercive force becomes almost “0”), and then, upward or downward depending on the information to be recorded. A magnetic field to be reversed is applied by the magnetic head 12b. As a result, information can be recorded by the overwrite recording method without passing through the process of erasing the already recorded information.

In this embodiment, the laser power was kept constant at the time of magnetic field modulation overwriting. However, when the polarity of the magnetic field is switched, the laser power is lowered to a non-recording power so that recording is not performed. The recorded bit shape becomes clearer and the reproduction signal quality is improved.

In the magnetic field modulation overwrite, in order to perform high-speed recording, it is necessary to modulate the magnetic field at high speed, but there is a restriction in terms of power consumption and size of the magnetic head 12b, and a very large magnetic field. 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 adopted. By doing so, the magnetic field at the time of recording can be suppressed to a lower level, and the configuration is very suitable for the magnetic field modulation overwrite method.

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

The optical modulation overwrite recording method is completely opposite to the magnetic field modulation overwrite recording method, in which a constant magnetic field strength 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. 17 to 21.

FIG. 18 shows the temperature dependence of the coercive force in the direction perpendicular to the film surfaces of the read layer 3 and the recording layer 4 and the recording magnetic field H suitable for the optical modulation overwrite recording method described below.
_{Shows W.}

Recording is performed by applying a recording magnetic field H _W and irradiating laser light whose intensity is modulated into two levels, high and low. That is, as shown in FIG. 19, when a high-level I laser beam is irradiated, both the reading layer 3 and the recording layer 4 are heated to a temperature T _H near or above the Curie points T _C1 , T _C2. When the laser light of low level II is irradiated, only the recording layer 4 is set to be heated up to the temperature T _L which becomes the Curie point T _C2 or more.

Therefore, when the low-level II laser beam is irradiated, the coercive force H ₁ of the reading layer 3 is sufficiently small, and the magnetization is transferred to the recording layer 4 in the cooling process according to the direction of the recording magnetic field H _W. To be done. That is, as shown in FIG. 17, the magnetization is upward.

Next, when the high-level I laser beam is irradiated, since the compensation temperature is exceeded, the magnetization direction of the readout layer 3 is different from that of the low-level II laser beam due to the recording magnetic field H _W. The opposite direction, that is, the downward direction. In the cooling process, the temperature drops to the same temperature as the low level II laser light,
The reading layer 3 and the recording layer 4 have different cooling processes (the recording layer 4
Therefore, first, only the recording layer 4 becomes the temperature _TL at which the low-level II laser beam is irradiated, and the magnetization direction of the read layer 3 is transferred to the recording layer 4 and becomes downward. After that, the reading layer 3 is lowered to the same temperature as the low-level II laser beam, and is turned upward according to the direction of the recording magnetic field H _W. At this time, the magnetization direction of the recording layer 4 is the coercive force H ₂ is sufficiently larger than the recording magnetic field H _W, recording magnetic field H _W
I do not follow the direction.

When the intensity of the laser beam at the time of reproduction, that is, the level III laser beam of FIG. 19 is irradiated, the temperature of the read layer 3 becomes T _R (FIG. 18), and the magnetization of the read layer 3 is perpendicular to the in-plane magnetization. The recording layer 4 and the read layer 3 are switched to the magnetization.
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, the magnetization direction of the read layer 3 at the time of reproduction matches the direction of the recording layer 4 due to the exchange force acting on the interface with the recording layer 4.

As a result, it is possible to record information by the overwrite recording method without going through the process of erasing the already recorded information.

The recording may be performed by applying the modulated two types of laser light as shown in FIG. 20 or 21 while applying the recording magnetic field H _W.

That is, when the type I high-level laser beam is irradiated, the temperature T at which both the reading layer 3 and the recording layer 4 reach the Curie points T _C1 , T _C2 or higher.
_{When the} temperature is raised to _H and the low-level type II laser beam is irradiated, only the recording layer 4 is set to the temperature T _L at which the Curie point T _C2 or higher is reached. By doing so, the cooling process of the read layer 3 and the recording layer 4 can be greatly different particularly when irradiated with a high level type I laser beam. That is, the recording layer 4 is cooled faster. Therefore, overwriting can be performed more easily.

However, the intensity of the laser light that is irradiated for a while after being irradiated with the high level laser light of type I may be equal to or lower than the high level.

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

The magneto-optical disk (FIG. 1) is generally called a single-sided type. This magneto-optical disk comprises a transparent dielectric layer 2, a reading layer 3, a recording layer 4, a transparent dielectric layer 5,
When the thin film portion of the reflective layer 6 is generally referred to as a recording medium layer, as shown in FIG. 22, the substrate 1 and the recording medium layer 1 are
9, the structure of the overcoat layer 7 is obtained.

On the other hand, as shown in FIG. 23, two pieces of the recording medium layer 19 formed on the substrate 1 are bonded by the adhesive layer 10 so that the recording medium layers 19 and 19 face each other. The magnetic disk is called a double-sided type.

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 rays, heat and anaerobic, and the curing of the shadowed portion of the recording medium layer 19 that does not transmit ultraviolet rays is cured by the heat and anaerobic curing functions. Thus, it is possible to provide a double-sided magneto-optical disk having extremely high humidity resistance and extremely excellent long-term stability.

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 miniaturization, for example.

Since the double-sided type allows double-sided reproduction, it is advantageous for a recording / reproducing apparatus which requires a large capacity, for example.

Whether to adopt the single-sided type or the double-sided type depends largely on the recording system as described below, in addition to considering the thickness and capacity of the magneto-optical disk as described above.

As is well known, a light beam and a magnetic field are used for recording information on the magneto-optical disk. In the magneto-optical disk device (see FIG. 16), a light beam from a light source such as a semiconductor laser is condensed by a condenser lens on the recording medium layer 19 through the substrate 1 and irradiated, and the light beam is provided at a position opposite to this. Magnetic field generator such as a magnet, electromagnet, etc. (for example,
A magnetic field is applied to the recording medium layer 19 by the floating magnetic head 12). By making the light beam intensity higher during recording than during reproduction, the temperature of the recording medium layer 19 in the focused portion rises, and the coercive force of the magnetic film in that portion decreases. At this time, if a magnetic field having a magnitude larger than the coercive force is applied from the outside, the magnetization of the magnetic film follows the direction of the applied magnetic field and the recording is completed.

For example, in the magnetic field modulation overwrite system that modulates the recording magnetic field according to information, it is necessary to bring the magnetic field generator (mostly an electromagnet) as close to the recording medium layer 19 as possible. This is modulated by the frequency required for recording (generally several hundred kHz to several tens MHz) due to heat generation of the coil of the electromagnet, device power consumption, size, etc., and the magnetic field required for recording (generally 500e to several hundreds of Oe), the recording medium is about 0.2 mm or less, and in most cases 50 μ.
It is necessary to bring them closer to about m. Therefore, in the double-sided type magneto-optical disk, the thickness of the substrate 1 is generally 1.2.
Since it is about mm and needs to be about 0.5 mm even if it is thin, when the electromagnet is arranged so as to face the light beam, the recording magnetic field strength becomes insufficient and recording cannot be performed. Therefore, when the recording medium layer 19 suitable for the recording modulation overwrite system is adopted, 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, it is possible to use, for example, a permanent magnet having a strong generated magnetic field, and to dispose it by a few mm from the recording medium layer 19 without arranging it as close as possible to the recording medium layer 19 as in the magnetic field modulation overwrite method. it can. Therefore, not only the single-sided type but also the double-sided type can be adopted.

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

The first variation is a magneto-optical disk in which a hard coat layer (not shown) is formed on the overcoat layer 7, and the substrate 1 / recording medium layer 19 / overcoat layer 7 / hard coat layer is formed. It has a structure. As the hard coat layer, for example, an acrylate-based UV-curable hard coat resin film, which is made of, for example, a polyurethane acrylate-based UV-curable resin and has a film thickness of about 6
It is formed on the overcoat layer 7 of μm. The film thickness of the hard coat layer is, for example, 3 μm.

By forming the overcoat layer 7, it is possible to prevent characteristic deterioration due to oxidation of the recording medium layer 19 and ensure long-term reliability. In addition to this, by providing a hard coat film, even if a recording magnet comes into contact with the disc, for example, the hard coat film with high hardness and excellent abrasion resistance makes it difficult to scratch. Further, even if a scratch is generated, it can be prevented from reaching the recording medium layer 19.

Further, as a matter of course, the function of the hard coat layer may be added to the overcoat layer 7, and only the overcoat layer 7 may be used.

The second variation is a light in which a hard coat layer is formed on the overcoat layer 7 and a hard coat layer (not shown) is formed on the surface of the substrate 1 opposite to the recording medium layer 19. It is a magnetic disk and has a structure of hard coat layer / substrate 1 / recording medium layer 19 / overcoat layer 7 / hard coat layer.

As the material of the substrate 1 for the magneto-optical disk,
Many plastics such as PC are used,
These materials are much softer than glass and can be scratched just by rubbing them with your nails. In the worst case, when the recording / reproducing is performed with a light beam, this flaw may cause servo skipping, which makes it impossible to record / reproduce information.

In the magneto-optical disk of this embodiment, since reproduction is carried out only in 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 greater than that in the conventional magneto-optical disk. It gets bigger. Therefore, by providing the hard coat layer on the surface of the substrate 1 on the side opposite to the recording medium layer 19, the present structure capable of preventing the occurrence of scratches is very effective.

Also in the double-sided type, it is apparent that the same effect can be obtained by providing a hard coat layer on the surface of each substrate 1.1 of the magneto-optical disk.

The third variation is the above first and second variations.
On the overcoat layer 7 of the variation of
It is a magneto-optical disk in which an antistatic coating layer (not shown) or a layer having an antistatic function is further formed on the hard coat layer.

If the surface of the substrate 1 is dusty or dusty, it may be impossible to record / reproduce information as with scratches. Further, if dust is present on the overcoat film 6, in the case of the magnetic field modulation overwriting method, the magnet is used as the floating magnetic head 12 (FIG. 16), and the overcoat film 6 is covered by several μm.
In the case where they are arranged with a gap of 1, the dust and the dust cause damage to the floating magnetic head 12 and the recording medium layer 19.

With this construction, if a layer having an antistatic function is provided on the surface of the substrate 1 side or the surface of the recording medium layer 19 side, dust, dust, etc. in the air will be generated on the surface of the substrate 1 or It is possible to prevent the adhesion on the overcoat layer 7.

In the magneto-optical disk of the present embodiment, since reproduction is carried out only in the vicinity of the center of the light beam, the influence of defects such as dust and dust on the surface of the substrate 1 on reproduction is affected by the conventional magneto-optical disk. Since this is larger than the above, this configuration is extremely effective.

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

The antistatic layer is provided for the purpose of lowering the surface resistivity and making dust and dirt less likely to occur, regardless of whether it is the plastic substrate 1 or the glass substrate 1.

Further, as a matter of course, an antistatic effect may be added to the overcoat layer 7 or the hard coat layer.

Also in the double-sided type, it is obvious that this structure can be applied to the surface of each of the substrates 1 and 1 of the magneto-optical disk.

The fourth variation is a magneto-optical disk in which a lubricating layer (not shown) is formed on the overcoat layer 7, and has a structure of substrate 1 / recording medium layer 19 / overcoat layer 7 / lubrication layer. Have As the lubricating layer, for example, a fluorine-based resin can be used, and its film thickness is appropriately about 2 μm.

By providing the lubricating layer, when the floating magnetic head 12 is used in 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 on the recording medium layer 19 while maintaining a gap of several μm to several tens μm. The suspension 13 acting to press against the layer 19 balances the levitation force acting to separate the levitation type magnetic head 12 from the recording medium layer 19 generated by the air flow due to the high-speed rotation of the magneto-optical disk, and the above gap is maintained. To be kept.

By using the floating magnetic head 12 as described above, the floating of the magneto-optical disk is started at the start of rotation, until the rotation speed reaches the predetermined rotation speed, and at the end of the rotation until the rotation stops from the predetermined rotation speed. When the CSS (Contact-Start-Stop) method in which the magnetic head 12 and the magneto-optical disk are in contact is adopted, if the floating magnetic head 12 and the magneto-optical disk are attracted to each other, the magneto-optical disk is floated at the start of rotation. The magnetic head 12 may be damaged. However,
According to the magneto-optical disk of the present embodiment, since the lubricating film is provided on the overcoat layer 7, the lubricity between the floating magnetic head 12 and the magneto-optical disk is improved, and the floating magnetic head 12 due to the attraction. Can be prevented from being damaged.

Naturally, it is not necessary to separately provide the overcoat layer 7 and the lubricating layer as long as they are materials that also have a moisture-proof protection performance for preventing the deterioration of the recording medium layer 19.

In a fifth variation, a moisture permeation preventive 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 19. It is a magneto-optical disk and has a structure of overcoat layer / moisture permeation preventive layer / substrate / recording medium layer 19 / overcoat layer 7.

For the moisture permeation preventive layer, for example, A1N, A1SiN, Si
A transparent dielectric material such as N, A1TaN, SiO, ZnS, TiO ₂ can be used, and its film thickness is preferably about 5 nm. The second overcoat layer is particularly effective when a highly hygroscopic plastic such as PC is used as the substrate 1 for the substrate 1.

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

If this moisture permeation preventive film is not provided on the light incident side of the substrate 1, the plastic substrate is formed only from the side where the recording medium layer 19 is absent, that is, from the incident light side of the substrate 1 when the environmental humidity changes greatly. Water is absorbed or released in 1). By this moisture absorption and desorption, the plastic substrate 1
Causes a local volume change, and the plastic substrate 1 is warped.

The warp 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, the servo is deviated, the signal quality is deteriorated, and in severe cases, servo skipping occurs.

When the substrate 1 is tilted, the laser light from the optical head 11 (FIG. 16) is focused on the inclined surface of the recording medium layer 19, and the laser light is focused according to the tilted state. The state will change, 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 so as to compensate for the up and down movement and focus the laser beam on the surface of the recording medium layer 19, but the up and down movement. Is too large, the compensation operation of the optical head 11 becomes incomplete, and the condensing state of the laser light on the surface of the recording medium layer 19 becomes incomplete. If the focused state of the laser light is incomplete, the temperature distribution of the recording medium layer 19 changes, which affects recording and reproduction. In the present embodiment, the temperature distribution of the recording medium layer 19 during reproduction is particularly important, so it is necessary to suppress the warp of the substrate 1 and the warp change due to the environment as much as possible.

In the magneto-optical disk of this structure, the moisture permeation preventive layer prevents moisture absorption and release of water on the front surface side of the substrate 1, so that the warpage of the substrate 1 when the environment changes can be suppressed significantly. Therefore, as described above, the structure is particularly suitable for the magneto-optical disk of the present invention.

The second overcoat layer on the moisture permeation preventive layer is provided for the purpose of preventing damage to the moisture permeation preventive layer, protecting the surface of the substrate 1, and the like. Medium layer 1
It may be the same as the overcoat layer 7 on 9.

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

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 those of the members shown in the drawings of the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the magneto-optical disk of this example, as shown in FIG. 24, a substrate 1, a transparent dielectric layer 2, a reading layer 3, a recording layer 4, a heat dissipation layer 20, and an overcoat layer 7 were laminated in this order. Have a configuration.

The substrate 1 is made of disk-shaped glass having a diameter of 86 mm, an inner diameter of 15 mm and a thickness of 1.2 mm. Although not shown, an uneven guide track for guiding the light beam is formed on the surface of one side of the substrate 1 with a pitch of 1.6 μm, a groove width of 0.8 μm, and a land width of 0.8 μm. Has been done.

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

On the transparent dielectric layer 2, GdFeCo, which is a rare-earth transition metal alloy thin film, is used as the read-out 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 a recording layer 4, a rare earth-transition metal alloy thin film DyFeCo having a thickness of 50 n was formed.
It is formed by 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 reading layer 3 and the recording layer 4, the magnetization direction of the reading layer 3 is substantially in-plane (that is, the layer direction of the reading layer 3) at room temperature,
The temperature shifts from the in-plane direction to the vertical direction at a temperature of about 125 ° C.

As the heat dissipation layer 20, A1 is formed on the recording layer 4.
Ni is formed to have a thickness of 100 nm. The content of Ni in A1Ni is 5 atm%.

On the heat dissipation layer 20, a polyurethane acrylate type ultraviolet curing resin is formed as the overcoat layer 7 with a thickness of 5 μm. The heat dissipation layer 20 is AlN
It was formed by sputtering with Ar gas using an i alloy target. Instead of the AlNi alloy target, a composite target in which Ni pieces are arranged on the Al target may be used.

On the heat dissipation layer 20, a polyurethane acrylate type ultraviolet curable resin is formed as the overcoat layer 7 with a thickness of 5 μm.

Substrate 1, transparent dielectric layer 2, readout layer 3,
The recording layer 4 and the overcoat layer 7 can be made of the same material as in the above embodiment.

Since the heat dissipation layer 20 is provided on the recording layer 4, there is an effect that the shape of the recording bit can be made clearer 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 reading layer 3 and the recording layer 4 and converted into heat. At this time, heat is conducted not only in the thickness direction of the read layer 3 and the recording layer 4 but also in the layer, that is, in the lateral direction. When the amount of heat conduction in the lateral direction is large and the speed of heat conduction is slow, for example, when recording is performed at higher speed and higher recording density, heat is applied to the recording bit to be recorded next. Have a negative impact. For this reason, the recording bit becomes longer than the predetermined length, or the recording bit spreading in the lateral direction with respect to the guide track is formed. If 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 dissipation layer 20 made of AlNi having high heat conductivity is formed on the recording layer 4, it is necessary to allow the heat spread in the lateral direction to escape to the heat dissipation layer 20 side, that is, the thickness direction. It is possible to reduce the spread of heat in the lateral direction as described above. Therefore, it becomes possible to perform recording without thermal interference under a recording condition of higher density and higher speed.

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

Due to the presence of the heat dissipation layer 20, when a region whose temperature has been once raised by irradiation with a light beam is cooled in the course of recording, a clearer difference in temperature change between each of the reading layer 3 and the recording layer 4 can be obtained. Can have This effect can greatly differ the cooling process of the read layer 3 and the recording layer 4 when irradiated with a high level laser light (the recording layer 4 is cooled faster).
Overwriting can be performed more easily.

AlNi, which is the material of the heat dissipation layer 20, has a higher thermal conductivity than the rare earth transition metal alloy films used for the read layer 3 and the recording layer 4, and is a material suitable for the heat dissipation layer 20.

Recording was performed using the above magneto-optical disk, and the linear velocity of the magneto-optical disk was set to 5 m / sec to obtain 0.7.
Playback signal quality (C /
As a result of measuring N), C / N of 50 dB was obtained. Also for a magneto-optical disk on which the heat dissipation layer 20 is not formed, C
As a result of measuring / N, C / N is 3 dB due to the heat dissipation layer 20.
It has been found that the above is improved.

Further, the amount of crosstalk was also measured using the magneto-optical disk of the present example by a measuring method in conformity with the IS10089 standard (standard defined for ISO 5.25 "rewritable optical disk). In the magneto-optical disk of this example, the amount of crosstalk was about -33 dB, and it was found that the amount of crosstalk was reduced by 3 dB or more as compared with the case where the heat dissipation layer 20 was not formed.

Further, AlNi is extremely excellent in moisture resistance and can provide a magneto-optical disk having excellent long-term reliability.

The results of the humidity resistance test of the above magneto-optical disk will be described below.

The magneto-optical disk was left for 1000 hours under the environmental conditions of 80 ° C. and 90% RH, and the change in its characteristics was examined. For comparison, a magneto-optical disk having the same structure as the above except that the heat dissipation layer 20 was replaced with pure Al was also examined in the same manner.

As a result, in the magneto-optical disk using the heat dissipation layer 20 of pure Al, many pinholes were generated in the heat dissipation layer 20 of Al. Due to this, many pinholes were generated in the recording layer 4 and the reading layer 3. On the other hand, in the magneto-optical disk of the present example, the pinholes were extremely small, about several. Therefore, the C / N and the amount of crosstalk were the same as the initial values even after being left under the above environmental conditions.

The content of Ni in AlNi is preferably 0-10 atm%. If the Ni content becomes too large, the thermal conductivity will decrease, and the read layer 3 and the recording layer 4 will be used during recording.
The heat generated in 2 becomes difficult to escape to the heat dissipation layer 20. Therefore, the reproduction signal quality (C / N) is deteriorated. When the Ni content is up to 10 atm%, the C / N deterioration is not so remarkable and a practical value can be obtained. Moreover, even if the Ni content is as small as about 0.5 atm%, the moisture resistance is remarkably improved as compared with Al.

As the material of the heat dissipation layer 20, AlTi, AlTa, Al
Si is also suitable.

A magneto-optical disk having a heat dissipation layer 20 of AlTi containing 1.5 atm% of Ti, a magneto-optical disk having a heat dissipation layer 20 of AlTa containing 1.5 atm% of Ta, and 10 atm% of Si.
Also for the magneto-optical disk having the AlSi heat dissipation layer 20,
When the dynamic characteristic measurement and the moisture resistance test were performed in the same manner as above, the same results as above were obtained.

The content of Ti in AlTi and the content of Ta in AlTa are preferably 0 to 10 atm%. If the content of these elements is too large, the thermal conductivity decreases, and the heat generated in the reading layer 3 and the recording layer 4 during recording becomes difficult to escape to the heat dissipation layer 20. Therefore, the playback signal quality (C
/ N) will be deteriorated. When the amount of Ti or Ta is up to 10 atm%, the deterioration of C / N is not so remarkable and a practical value can be obtained. Further, even if the Ni or Ta content is as small as about 0.5 atm%, the moisture resistance is remarkably improved as compared with Al.

The content of Si in AlSi is preferably 0 to 50 atm%. If the content of these elements is too large, the thermal conductivity decreases, and the heat generated in the reading layer 3 and the recording layer 4 during recording becomes difficult to escape to the heat dissipation layer 20.
Therefore, the reproduction signal quality (C / N) is deteriorated. Si
When the amount is up to 50 atm%, the deterioration of C / N is not so remarkable and a practical value can be obtained. Also, the Si content is 0.5a
Even with a very small amount of about tm%, the moisture resistance is significantly improved compared to Al.

The use of AlTa for the heat dissipation layer 20 has the following advantages.

The heat dissipation layer 20 of AlTa is formed by sputtering an AlTa alloy target or a composite target in which Ta pieces are arranged on an Al target with Ar gas.

By the way, an AlTa alloy target or a composite target obtained by arranging Ta pieces on an Al target is used.
_When sputtering is performed with ₂ gas or a mixed gas of Ar gas and N ₂ gas, AlTaN 3 is formed by reactive sputtering. AlTaN is transparent and has a large refractive index of about 2 and can be used as a material for the transparent dielectric layer 2.

Therefore, the transparent dielectric layer 2 and the heat dissipation layer 20 are
And can be formed using the same target. Therefore, the sputtering apparatus can be downsized, and the manufacturing cost of the magneto-optical disk can be significantly reduced.

Even when AlSi is used for the heat dissipation layer 20, AlTa
There is the same advantage as when the heat dissipation layer 20 is used.

That is, the AlSi heat dissipation layer 20 is formed by sputtering an AlSi alloy target or a composite target in which Si pieces are arranged on an Al target with Ar gas. AlSi alloy target or a composite target which arranged Si pieces on Al target N ₂ gas or, when sputtered in a mixed gas of Ar gas and N ₂ gas, by reactive sputtering, AlSiN is formed. Al
SiN is transparent and has a large refractive index of about 2 and can be used as a material for the transparent dielectric layer 2.

Therefore, the transparent dielectric layer 2 and the heat dissipation layer 20 are
And can be formed using the same target. Therefore, the sputtering apparatus can be downsized, and the manufacturing cost of the magneto-optical disk can be significantly reduced.

Next, the film thickness of the heat dissipation layer 20 will be described.

The larger the thickness of the heat dissipation layer 20, the higher the heat dissipation effect and the longer-term reliability. However, if the thickness of the heat dissipation layer 20 is too large, the recording sensitivity of the magneto-optical disk will be reduced. It is necessary to set the film thickness according to the thermal conductivity and the specific heat of the material of the heat dissipation layer 20, but normally 5 to 200 nm is preferable, and 10 to 100 nm is more preferable. If the material has a relatively high thermal conductivity and excellent corrosion resistance, the film thickness of the heat dissipation layer 20 may be 10 to 100 nm, so that the film formation time can be shortened.

In the above magneto-optical disk, the recording layer 4
Forming the protective layer of the embodiment between the heat dissipation layer 20 and the heat dissipation layer 20 has the following advantages.

That is, the rare earth-transition metal alloys of the read layer 3 and the recording layer 4 are very likely to be oxidized, and the characteristics thereof are easily deteriorated by the penetration of moisture from the outside. for that reason,
A material having excellent moisture resistance was used for the heat dissipation layer 20.
If a protective layer is further formed between the heat dissipation layer 20 and the heat dissipation layer 20, a magneto-optical disk having more excellent moisture resistance can be provided.

As the material for the protective layer, AlN used in the transparent dielectric layer 2 is suitable, and it is advantageous in manufacturing if the protective layer and the transparent dielectric layer 2 are made of the same material.

The thickness of the protective layer is preferably 10 to 100 nm. The material of the protective layer is SiN, AlSiN, Ti
Oxygen-free nitrides such as N, AlTaN, ZnS, and BN are suitable.

The variation of the magneto-optical disk of this embodiment is the same as that of the above-mentioned embodiment, and the description thereof will be omitted.

In the above-mentioned first and second embodiments, the magneto-optical disk is taken as an example of the magneto-optical recording medium, but the present invention can be applied to a magneto-optical card and a magneto-optical tape. In the case of a magneto-optical tape, a flexible tape base (base), for example, a tape base made of polyethylene terephthalate may be used instead of the rigid substrate 1.

A magneto-optical disk according to the invention of claim 1 is a substrate 1 having a light-transmitting property, and is formed on the substrate 1 and exhibits in-plane magnetization with in-plane magnetic anisotropy predominant at room temperature. A read layer 3 that shifts to a perpendicular magnetization in which the perpendicular magnetic anisotropy is dominant as the temperature rises, a recording layer 4 formed on the read layer 3 for magneto-optically recording information, and a reflection formed on the recording layer 4. The reflective layer 6 has a layer 6, and the reflective layer 6 is made of AlNi, AlT.
i, AlTa, or AlSi.

Therefore, it becomes possible to reproduce the recording bit smaller than the conventional one, and the recording density is remarkably improved. Moreover, AlNi, AlTi, Al on the recording layer 4
Since the reflective layer 6 made of Ta or AlSi is provided, it is possible to provide a magneto-optical disk having excellent reproduction signal quality, high recording density, and excellent moisture resistance.

As described above, the magneto-optical disk according to the invention of claim 2 is a substrate 1 having a light-transmitting property, and is formed on the substrate 1 and has an in-plane magnetic anisotropy which is superior at room temperature. On the recording layer 4, a read layer 3 that exhibits magnetization and changes to perpendicular magnetization in which the perpendicular magnetic anisotropy is dominant as the temperature rises, and a recording layer 4 that is formed on the read layer 3 and magneto-optically records information. Has a heat dissipation layer 20 formed in
It is one of AlNi, AlTi, AlTa, and AlSi.

Therefore, it becomes possible to reproduce the recording bit smaller than the conventional one, and the recording density is remarkably improved. AlNi, AlTi, AlTa, A on the recording layer 4
Since the heat dissipation layer 20 made of any of 1Si is provided, it is possible to provide a magneto-optical recording medium having a clean recording bit shape, excellent reproduction signal quality, and excellent moisture resistance.

[0266]

As described above, the magneto-optical recording medium according to the first aspect of the present invention has a substrate having a light-transmitting property and an in-plane in which the in-plane magnetic anisotropy is superior at room temperature. Formed on the read layer, which shows magnetization, and which shifts to perpendicular magnetization in which perpendicular magnetic anisotropy is dominant with temperature rise, and which is formed on the read layer and magneto-optically records information. Since the reflective layer is provided, it is possible to reproduce recorded bits smaller than conventional ones, and the recording density is remarkably improved.
Moreover, AlNi, AlTi, AlTa,
Since the reflective layer made of any of AlSi is provided, it is possible to provide a magneto-optical recording medium having excellent reproduction signal quality, high recording density, and excellent moisture resistance.

The magneto-optical recording medium according to the invention of claim 2 is
As described above, a light-transmissive substrate and an in-plane magnetization that is formed on the substrate and has an in-plane magnetic anisotropy that is dominant at room temperature, while a perpendicular magnetic anisotropy that is dominant as the temperature rises. Since it has a read layer that shifts to magnetization, a recording layer that is formed on the read layer and magneto-optically records information, and a heat dissipation layer that is formed on the recording layer, reproduction of recorded bits smaller than conventional is performed. This makes it possible to significantly improve the recording density.
Moreover, AlNi, AlTi, AlTa,
Since the heat dissipation layer made of any of AlSi is provided, it is possible to provide a magneto-optical recording medium having a clean recording bit shape, excellent reproduction signal quality, and excellent moisture resistance.

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention and 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 read 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 the read layer and a polar Kerr rotation angle from room temperature to temperature T ₁ in FIG.

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

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

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

FIG. 7 is a graph showing composition dependence of Curie temperature (Tc) and compensation temperature (Tcomp) of Gd _X (Fe _0.82 Co _0.18 ) _1-X .

Fig. 8 Curie temperature (Tc) and compensation temperature (Tco of Gd _X Fe _1-X
3 is a graph showing the composition dependence of mp).

FIG. 9: Curie temperature (Tc) and compensation temperature (Tco) of Gd _X Co _1-X
3 is a graph showing the composition dependence of mp).

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

11 is an explanatory diagram showing another example of the shapes of lands and groups formed on the substrate of the magneto-optical disc of FIG.

12 is an explanatory diagram showing an example of the arrangement of wobble pits formed on the substrate of the magneto-optical disc of FIG.

FIG. 13 is an explanatory diagram showing another example of the arrangement of wobble pits formed on the substrate of the magneto-optical disc of FIG.

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

15 is an explanatory diagram showing a recording / reproducing method in the magneto-optical disk of FIG. 1 when a plurality of light beams are used.

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

17 is an explanatory diagram showing a light modulation overwrite recording method using the magneto-optical disk of FIG. 1 and a magnetization method of a read layer and a recording layer.

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

19 is an explanatory diagram showing an example of the intensity of a light beam with which the magneto-optical disk of FIG. 1 is irradiated at the time of optical modulation overwrite and at the time of reproduction.

FIG. 20 is an explanatory diagram showing another example of the intensity of the light beam with which the magneto-optical disk of FIG. 1 is irradiated at the time of optical modulation overwrite and at the time of reproduction.

FIG. 21 is an explanatory diagram showing another example of the intensity of the light beam with which the magneto-optical disk of FIG. 1 is irradiated during optical modulation overwrite and during reproduction.

22 is an explanatory diagram showing a single-sided type of the magneto-optical disc of FIG. 1. FIG.

23 is an explanatory diagram showing a double-sided type of the magneto-optical disc shown in FIG. 1. FIG.

FIG. 24 shows a second embodiment of the present invention and is a schematic configuration diagram of a magneto-optical disk.

[Explanation of symbols]

 1 Substrate (Substrate) 2 Transparent Dielectric Layer 3 Readout Layer 4 Recording Layer 5 Transparent Dielectric Layer 6 Reflective Layer 7 Overcoat Layer 10 Adhesive Layer 19 Recording Medium Layer 20 Heat Dissipation Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Zenteru Murakami 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Akira Takahashi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Kenji Ota 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture

Claims (2)

[Claims] 1. A transparent substrate and a substrate formed on the substrate,
At room temperature, the in-plane magnetic anisotropy is dominant, while the in-plane magnetization shifts to the perpendicular magnetization where the perpendicular magnetic anisotropy is dominant as the temperature rises. It has a recording layer for recording and a reflective layer formed on the recording layer, and the reflective layer is AlNi, AlTi, AlTa, AlS.
A magneto-optical recording medium which is any one of i. 2. A transparent substrate and a substrate formed on the substrate,
At room temperature, the in-plane magnetic anisotropy is dominant, while the in-plane magnetization shifts to the perpendicular magnetization where the perpendicular magnetic anisotropy is dominant as the temperature rises. It has a recording layer for recording and a heat dissipation layer formed on the recording layer, and the heat dissipation layer is AlNi, AlTi, AlTa, AlS.
A magneto-optical recording medium which is any one of i.