JP2981063B2 - Magneto-optical disk and magneto-optical reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk and a magneto- optical reproducing apparatus applied to a magneto- optical reproducing apparatus .

[0002]

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

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

[0004]

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

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

[0006]

According to a first aspect of the present invention, there is provided a magneto-optical disk comprising: a recording layer for magneto-optically recording information; an in-plane magnetization at room temperature;
A magneto-optical disk having a readout layer on which the magnetization direction of the recording layer is transferred by transition to perpendicular magnetization with a rise in temperature, wherein a test area for optimizing a reproduction laser power is provided.
Are provided in a part of the inner and outer circumferences , and optimization information for optimizing the reproducing laser power at each radial position from the reproducing laser power obtained in the test area.
There is characterized that you have been pre-recorded.

The magneto-optical disk according to the invention of claim 2 is:
In order to solve the above-mentioned problems, a recording layer for recording information magneto-optically and a read-out in which the magnetization direction of the recording layer is transferred while exhibiting in-plane magnetization at room temperature, transitioning to perpendicular magnetization with increasing temperature, A recording area divided into a plurality of zones corresponding to radial positions, and a test area for optimizing a reproduction laser power is formed for each zone. .

[0008] A magneto-optical reproducing apparatus according to a third aspect of the present invention comprises:
In order to solve the above problem, a magneto-optical device according to claim 2 is provided.
A magneto-optical reproducing apparatus for reproducing disks, wherein each zone is
Optimal reproduction laser power in the test area
Is characterized by

According to a fourth aspect of the present invention, there is provided a magneto-optical reproducing apparatus.
2. A magneto-optical reproducing apparatus for reproducing a magneto-optical disk according to claim 1 , wherein said optimizing method comprises:
Information and the reproduction laser obtained in the above test area
The reproduction laser power is changed according to the radial position of the magneto-optical disk based on the power.

[0010]

According to the first aspect of the present invention, when the light beam is irradiated to the readout layer during the reproducing operation, the temperature distribution of the irradiated portion becomes substantially Gaussian distribution, so that the center is smaller than the diameter of the light beam. The temperature in only the vicinity increases.

As the temperature rises, the magnetization at the temperature rising portion shifts from in-plane magnetization to perpendicular magnetization, and the magnetization of the recording layer
The direction of the magnetization of the readout layer follows the direction of.

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

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

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

In addition, a test area for optimizing the reproduction laser power is provided in a part of the inner and outer circumferences .
To optimize the reproducing laser power at each radial position from the reproducing laser power obtained in the test area.
Since the optimization information is recorded in advance , it is possible to more accurately control the temperature distribution of the magneto-optical disk during reproduction, and it is possible to provide a magneto-optical disk capable of excellent reproduction.

According to the second aspect of the present invention, the recording area has a radius
It is divided into multiple zones according to the location, and each zone
A test area is formed to optimize the playback laser power
The temperature distribution of the magneto-optical disk during playback.
Control can be performed more accurately, and good reproduction is possible.
Can be provided.

According to the third aspect of the present invention, the magneto-optical device of the second aspect is provided.
Using a magnetic disk, the test area
To optimize the playback laser power during playback.
More precise control of temperature distribution of magneto-optical disk
Magneto-optical reproducing device that enables good reproduction
Can be provided.

According to the fourth aspect of the present invention, a magneto-optical element to be reproduced is provided.
The playback laser power is changed according to the radial position of the disc.
The temperature distribution of the magneto-optical disk during playback.
Control can be performed more accurately, and good reproduction is possible.
The magneto-optical reproducing device can be provided.

[0019]

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

As shown in FIG. 1, the magneto-optical disk of this embodiment has a substrate 1 (base), a transparent dielectric layer 2, a readout layer 3, a recording layer 4, a transparent dielectric layer 5, a reflective layer 6, It has a configuration in which the coat layers 7 are stacked in this order.

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

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

FIGS. 3 to 6 show an example of the hysteresis characteristic of the readout layer 3, and the horizontal axis indicates 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 also incident from the direction perpendicular to the film surface.

FIG. 3 shows the composition P in the magnetic phase diagram of FIG.
Of the readout layer 3 shows the hysteresis characteristic between from room temperature to temperatures T _1, 4 to 6, respectively, the temperature T ₃ hysteresis characteristic from temperatures T ₁ to temperature T _2, the temperature T ₂ hysteresis characteristic up, and shows the hysteresis characteristic from the temperature T ₃ to the Curie temperature Tc.

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

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

At the time of the reproducing operation, the readout layer 3 is irradiated with the reproducing light beam 8 from the side of the substrate 1 (FIG. 1) via the condenser lens 9. The temperature of the portion of the readout layer 3 irradiated with the reproduction light beam 8 rises most in the vicinity of the central portion thereof, and becomes higher than the temperature of the peripheral portion. This is because the reproduction light beam 8
This is because the light intensity distribution becomes a Gaussian distribution and the temperature distribution at the reproducing portion on the magneto-optical disk also becomes almost a Gaussian distribution because the light is narrowed down to the diffraction limit by the condenser lens 9.

The temperature near the center is above T ₁ is reached, when the intensity of the reproducing light beam 8 so that the temperature of the surrounding site is T ₁ or less is set, playback only area having above T ₁ temperature Therefore, recording bits smaller than the diameter of the reproducing light beam 8 can be reproduced, and the recording density is significantly improved.

That is, the magnetization in the region having a temperature equal to or higher than T ₁ shifts from in-plane magnetization to perpendicular magnetization (the hysteresis characteristic of the polar Kerr rotation angle shifts from FIG. 3 to FIG. 4 or FIG. 5). At this time, the magnetization direction of the recording layer 4 is transferred to the reading layer 3 by the exchange coupling force between the two layers of the reading layer 3 and the recording layer 4. On the other hand, other than the area corresponding to the vicinity of the center of the reproducing light beam 8, because the surrounding site is the temperature T ₁ or less, in-plane magnetization state (FIG. 3) is held. As a result, the reproduction light beam 8 irradiated to the film surface from the vertical direction does not exhibit the polar Kerr effect.

As described above, when the temperature rising portion shifts from the in-plane magnetization to the perpendicular magnetization, only the vicinity of the center of the reproduction light beam 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.

[0031] moving the reproducing light beam 8 (actually magneto-optical disk is rotated), when to reproduce the next recording bit, the temperature of the previous reproducing portion drops to T ₁ or less, from the perpendicular magnetization Transition to in-plane magnetization. Along with this, the portion where the temperature has decreased no longer exhibits the polar Kerr effect. Therefore, information is not reproduced from the portion where the temperature is lowered, and signal mixing from adjacent recording bits which causes noise is eliminated.

As described above, when the magneto-optical disk of the present invention is used, recording bits smaller than the diameter of the reproducing light beam 8 can be surely reproduced, and the recording density is not affected by the adjacent recording bits. It can be significantly increased.

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

The substrate 1 is made of a disc-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 a light beam is provided on one surface of the substrate 1 at a pitch of 1.6 μm, a groove (recess) width of 0.8 μm, and a land (convex portion). The width is 0.8 μm.

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

On the transparent dielectric layer 2, GdFeCo, which is a rare earth transition metal alloy thin film, is used as the readout layer 3.
It is formed with a thickness of 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 readout layer 3, as the recording layer 4, a rare-earth transition metal alloy thin film DyFeCo having a thickness of 15 n
m. The composition of DyFeCo is Dy _0.23
(Fe _0.78 Co _0.22 ) _0.77 , and its Curie temperature is about 200 ° C.

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

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

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

On the reflective layer 6, a polyurethane acrylate-based ultraviolet curable resin having a thickness of 5 μm is formed as the overcoat layer 7.

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

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

The transparent dielectric layer 2, the readout layer 3, the recording layer 4, the transparent dielectric layer 5, and the reflective layer 6 were all formed by a sputtering method in the same sputtering apparatus without breaking vacuum. A1N of the transparent dielectric layers 2 and 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 reflection layer 6 was formed by sputtering with an Ar gas using an AlNi alloy target.
Note that, instead of the AlNi alloy target, a composite target in which Ni pieces are arranged on an Al target may be used.

The overcoat layer 7 was formed by applying a polyurethane acrylate-based UV-curable resin using a spin coater, and then irradiating and curing the UV-ray with an ultraviolet irradiator.

In the above-described magneto-optical disk, the read layer 3
And the total thickness of 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 readout layer 3 and the recording layer 4, is reflected by the reflection layer 6, and enters the recording layer 4 and the readout layer 3 again. As a result, the light reflected by the readout layer 3 when the reproduction light beam 8 enters from the substrate 1 side and the light reflected by the reflection layer 6 interfere with each other, so that the magneto-optical effect is enhanced. That is, the polar car rotation angle increases.
For this reason, information can be reproduced with higher accuracy, and the reproduction signal quality is improved.

Since AlNi has a high reflectance, light transmitted through the readout layer 3 and the recording layer 4 can be efficiently reflected. For this reason, 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. As a result, 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-described magneto-optical disk, it was confirmed that recording could be performed with a laser power lower by 0.5 mW or more than that of a magneto-optical disk in which only the reflective layer 6 was replaced with pure Al. did it.

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

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

Hereinafter, the results of the moisture resistance test of the magneto-optical disk will be described.

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 configuration as above except that the reflective layer 6 was changed to pure Al was also examined.

As a result, in the magneto-optical disk using pure Al for the reflective layer 6, many pinholes were generated in the Al of the reflective layer 6. Due to this pinhole, the noise measured in the recording / reproduction experiment increased, and the reproduction signal quality (C / N) 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 reflection layer 6 was extremely small, about several. For this reason, there was no increase in noise, and the same characteristics as those at the initial stage were obtained even after being left under the above environmental conditions.

The content of Ni in AlNi is from 0 to 10
atm% is preferred. If the Ni content is too high, the reflectivity decreases as the Ni content increases, leading to deterioration of the reproduction signal quality (C / N). If the Ni content 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 a material of the reflection layer 6, AlTi, AlT
a and AlSi are also suitable.

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

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

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

Ti content and Al content in AlTi
The content of Ta in Ta is preferably 0 to 10 atm%. If these contents are too large, the reflectivity 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. Further, 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 from 0 to 50.
atm% is preferred. If these contents are too large, the reflectivity decreases as the Si content increases, leading to a deterioration in the reproduction signal quality (C / N). If the content is up to 50 atm%, the deterioration of C / N is not so remarkable, and a practical value can be obtained. Further, 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 reflection layer 6 of AlTa is formed by sputtering an AlTa alloy target or a composite target having a Ta piece disposed on an Al target with Ar gas.

[0066] 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 about 2, the transparent dielectric layers 2.5
It can be used as a material.

Therefore, the transparent dielectric layers 2 and 5 and the reflection 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.

When AlSi is used for the reflection layer 6, A
There is the same advantage as the case where lTa is used for the reflective layer 6.

That is, the reflection layer 6 of AlSi is made of AlS
Si alloy target or Al target on Si
It is formed by sputtering a composite target on 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. AlSiN is transparent and has a large refractive index of about 2, so that the transparent dielectric layers 2.5
It can be used as a material.

Therefore, the transparent dielectric layers 2 and 5 and the reflection 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 thickness of the reflection layer 6 will be described.

If the thickness of the reflective layer 6 is too small, light will pass through the reflective layer 6 and the enhancement effect will be reduced. For this reason, the film thickness must 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, it is preferably 100 nm or less. Therefore, the preferred film thickness for the reflective layer 6 is in the range of 20 to 100 nm.

The above AlNi, AlTi, AlT
Since a and AlSi are materials having extremely excellent moisture resistance, a magneto-optical disk having excellent long-term reliability can be provided even if the film thickness is as thin as about 30 nm or less.

In the magneto-optical disk of the present embodiment, for enhancing the magneto-optical effect, the thickness of the transparent dielectric layer 2 is optimally 70 to 100 nm, and at this time, the thickness of the transparent dielectric layer 5 is 15-50 nm is preferred.

When the thickness of the transparent dielectric layer 2 is set 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 set so that the polar Kerr rotation angle is maximized. 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 first embodiment, the A of the refractive index is 2.0 with respect to the reproduction light wavelength of 780 nm.
Since 1N is used, when the thickness of AlN of the transparent dielectric layer 2 is set to about 30 to 1200 nm, the effect of the Kerr effect enhancement is increased. Preferably, the AlN film thickness of the transparent dielectric layer 2 is 70 to 100 nm, and within this range, the polar Kerr rotation angle is almost maximum.

Although the above description has been made with respect to reproduction light having a wavelength of 780 nm, for example, with respect to reproduction light having a wavelength of 400 nm, which is half the wavelength, the thickness of the transparent dielectric layer 2 may be reduced to approximately half.

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

That is, for example, the Al of the transparent dielectric layer 2
The optical path length of the transparent dielectric layer 2 is 160 nm obtained by multiplying the refractive index 2 of N by the film thickness of 80 nm. When the refractive index of AlN changes from 2 to 2.5, it becomes about 160 nm / 2.5 = 64 nm. What is necessary is just to set the film thickness.

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

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

As the material of the transparent dielectric layers 2 and 5, 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 is changed by changing the ratio of Ar and N ₂ , which are sputter gases at the time of sputtering, and the gas pressure. In addition, a magneto-optical disk having a large enhancement effect of the magneto-optical effect and excellent in reproduction signal quality can be provided.

The transparent dielectric layer 2 not only has the role of the Kerr effect enhancement as described above, but also
In addition to the transparent dielectric layer 5, it also has a role of preventing oxidation of the magnetic material composed of the rare earth transition metal alloy of the readout layer 3 and the recording layer 4.

The readout layer 3 and the recording layer 4 made of a rare earth transition metal are very easily oxidized, and particularly rare earths are easily oxidized. Therefore, unless the intrusion of oxygen and moisture from the outside is prevented as much as possible, the characteristics are significantly deteriorated by oxidation.

Therefore, in the present embodiment, a configuration is adopted in which both sides of the readout layer 3 and the recording layer 4 are sandwiched by AlN. AlN is a nitride that does not contain oxygen in its component, and is a material having extremely excellent moisture resistance.

Further, 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.

In particular, SiN, TiN, BN, Zn
S 2 does not contain oxygen in its component and can provide a magneto-optical disk having excellent moisture resistance.

The readout layer 3 and the recording layer 4 made of a rare-earth transition metal alloy absorb light well, and when the combined thickness is 50 nm or more, almost no light is transmitted, and the enhancement of the Kerr effect is enhanced. Can not be.
Therefore, the combined film thickness of these two layers is preferably 10 to 50 nm.

The composition of GdFeCo in the readout layer 3 is GdFeCo.
It is not limited to _0.26 (Fe _0.82 Co _0.18 ) _0.74 . The readout layer 3 has substantially in-plane magnetization at room temperature, and may shift from in-plane magnetization to perpendicular magnetization at a temperature equal to or higher than room temperature. In the rare earth transition metal alloy, if the ratio of the rare earth and the transition metal is changed, the compensation temperature at which the magnetization of the rare earth and the transition metal is balanced changes. 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 to FeCo, the temperature at which the in-plane magnetization shifts 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, ie, Gd, was changed in the system of Gd _X (Fe _0.82 Co _0.18 ) _{1 -X} .

In the composition range where the compensation temperature is equal to or higher than room temperature (25 ° C.), X is 0.18 or higher as is apparent from FIG.
Of these, the range is preferably 0.19 <X <0.29.
Within this range, the temperature at which the direction of magnetization moves from the in-plane to the vertical direction in a practical configuration in which the recording layer 4 is stacked on the readout layer 3 is in the range of room temperature to 200 ° C. If the temperature is too high, the laser power for reproduction becomes as high as the laser power for recording, so that recording may be performed on the recording layer 4 and recorded information may be disturbed.

Next, in the above-mentioned GdFeCo system, the characteristics (compensation temperature) when the ratio of Fe and Co is changed, that is, when Y is changed in GdX _X (Fe _{1 -Y} Co _Y ) _{1 -X} And Curie temperature) will be described.

FIG. 8 shows the case where Co is zero, that is, Gd _X
FIG. 3 is a view showing characteristics of Fe _1-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 the case where Fe is zero, that is, Gd _X
FIG. 3 is a view showing characteristics of Co _1-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 Co content increases.

The higher the Curie temperature of the readout layer 3 is, the more advantageous the higher the Curie temperature of the readout layer 3 is. However, it should be noted that if the amount of Co is excessively increased, the temperature at which the magnetization direction shifts perpendicularly from the in-plane becomes high.

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

As described above, the material of the readout layer 3 of the magneto-optical disk of the present invention is optimally GdFeCo, which has a steep transition from in-plane magnetization to perpendicular magnetization. Similar effects can be obtained.

Gd _x Fe _{1 -X} has characteristics as 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 characteristics as shown in FIG. 9 and has a compensation temperature above room temperature in the range of 0.20 <X <0.35.

When an FeCo alloy is used as the transition metal, Tb _X (Fe _Y Co _1-Y ) _1-X can be adjusted at room temperature or higher within a range of 0.20 <X <0.30 (where Y is arbitrary). Having.
Dy _X (Fe _Y Co _1-Y ) _1-X is 0.24 <X <0.33 (at this time,
(Y is arbitrary) and has a compensation temperature at room temperature or higher. Ho _{X
(Fe Y Co 1-Y)} 1-X is, 0.25 <X <0.45 (this time, Y is optional) has a compensation temperature above room temperature in the range of.

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

As described above, in an optical disk such as a magneto-optical disk, the recording density is limited by the size of the light beam, which is determined by the laser wavelength and the numerical aperture of the objective lens. Therefore, if a semiconductor laser having a shorter wavelength than now appears, the recording density of the magneto-optical disk will be improved by itself. At present, it is already 670
Semiconductor lasers with wavelengths of up to 680 nm are almost at the practical level, and SHG lasers with wavelengths of 400 nm or less are being vigorously studied.

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

Nd, Pt, Pr, Pd are used for the material of the readout layer 3 described above.
By adding a small amount of at least one of the elements,
Provided is a magneto-optical disk capable of increasing the polar Kerr rotation angle at a short wavelength without substantially impairing the characteristics required for the readout layer 3 and obtaining a high-quality reproduction signal even when a short-wavelength laser is used. it can.

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

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

The material of the recording layer 4 is a material developed and used in a conventional magneto-optical disk, that is, a material exhibiting perpendicular magnetization from room temperature to the Curie temperature. A temperature of about 150 to 250 ° C. is sufficient. In the above embodiment, DyFeCo is used for the recording layer 4. However, DyFeCo is a material having a small perpendicular magnetic anisotropy. Therefore, recording can be performed even when an external magnetic field required for recording is low. This is a very advantageous point particularly in the magnetic field modulation overwrite recording method described later, and it is possible to reduce the size and power consumption of the recording external magnetic field generator.

Other than DyFeCo, TbFeCo, 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 is sufficient that 0.10 ≦ X ≦ 0.30 is satisfied for any Y. More specifically, for example, Tb _0.18 (Fe
_0.88 Co _0.12 ) There is _0.82 .

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

Further, the material of the recording layer 4 is Cr, V, N
Addition of at least one of b, Mn, Be, and Ni can further improve long-term reliability.

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

When chemically strengthened glass is employed for the substrate 1, the substrate 1 is excellent in mechanical properties (in the case of a magneto-optical disk, surface runout, eccentricity, warpage, inclination, etc.), and has high hardness.
It is hard to be damaged by sand and dust, it is chemically stable, it does not dissolve in various solvents, it is hard to charge compared to plastic, so it is difficult for dust and dust to adhere, and it is chemically reinforced and it is hard to break It has excellent moisture resistance, oxidation resistance, and heat resistance, so that the long-term reliability of the magneto-optical disk is improved, the 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 irregularities called prepits formed in advance on the substrate in order to obtain information such as address signals and the like. A signal is formed on a substrate by reactive dry etching of the surface of the glass substrate. Also, 2
After applying an ultraviolet curable resin called a P layer on a glass substrate 1, a mold called a stamper is pressed against the resin layer, and the resin is cured by irradiating ultraviolet rays. Then, the stamper is peeled off and the resin layer is removed. There is a method of forming the above-mentioned guide tracks, pre-pits and the like.

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

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

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

[0122] When employing the PS to the substrate 1, since it is injection molded, a mass-production of the same substrate 1, can be supplied at low cost, compared with other plastic, because of the low water absorption, light
An advantage is that the long-term reliability of the magnetic disk is improved.

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

When epoxy is used for the substrate 1, the long-term reliability of the magneto-optical disk is improved since the water absorption is lower than that of other plastics. And the like.

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

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

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

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

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

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

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

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

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

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

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

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

On the other hand, in the case of the sample servo system, FIG.
As shown in FIG. 2, wobble pits are formed at a pitch of 1.2 to 1.6 μm and have a depth of about (λ / (4n)), and information is recorded so that the laser beam always scans the center of the wobble pit. Regeneration is generally performed.

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

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

Further, as shown in FIG. 14, when the position information of the magneto-optical disk is obtained by wobbling the groove in the continuous servo system, the wobbling state exists in the adjacent groove at a portion where the phase is reversed. Although there was a problem that the crosstalk from the recording bit became large, the crosstalk from the recording bit existing in the adjacent groove occurs even in a portion where the wobbling state is in the opposite phase by applying the present invention. And good recording and reproduction can be performed.

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

For example, when a multi-beam optical pickup in which a plurality of optical pickups or a single light source produces a plurality of light beams is employed, as shown in FIG. 15, the light beams at both ends of the plurality of light beams are guided. In general, a method of performing positioning on a track and performing recording / reproducing with a plurality of light beams positioned therebetween is used. However, by using the magneto-optical head disk of the present invention, the interval between the light beams is reduced. It is possible to reproduce even without being affected by crosstalk from adjacent recording bits, and it is possible to shorten the pitch of the guide track, or to use more laser beams between a pair of guide tracks. Recording and reproduction can be performed, 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 beam is The pitch of the guide track and the like are discussed assuming that the wavelength is 670 nm to 840 nm. A. Is set to be 0.6 to 0.95, the laser beam can be further narrowed down, and the pitch and width of the guide track can be further reduced by applying the magneto-optical disk of the present invention. High-density recording / reproduction becomes possible.

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

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

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

In general, in order to maintain compatibility between different manufacturers or different magneto-optical disks, recording and reading at respective radial positions are performed on the magneto-optical disk.
The value or duty to be set for the erasing power is recorded in advance in a part of the inner and outer peripheries in a pre-pit row having a depth of about (λ / (4n)). Also,
Based on those read values, test areas in which recording and reproduction can be actually performed are provided on the inner and outer circumferences (for example, IS1008
9 See standards).

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

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

Therefore, as a method of setting the reproducing power, for example, similarly to the recording power, the reproducing power is provided with test areas for setting the reproducing power on the inner and outer peripheries. Information for optimizing the playback power at the radial position (optimization
It is preferable to record the information in advance in a part of the inner and outer circumferences in a pit row.

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

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

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

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

The first generation magneto-optical disk is IS10089
Many products are already commercially available in accordance with the standards (standards defined for the 5.25 "rewritable optical disc of ISO)
Since overwriting cannot be performed, when new information is to be recorded in a place where information has already been recorded, it is necessary to perform an operation of first erasing the portion and then recording. Therefore, at least two rotations of the magneto-optical disk are required, and the data transfer speed is low.

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

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

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

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

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

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

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

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 a magnetic field intensity according to information while irradiating a laser of a constant power to a magneto-optical recording medium, and will be described with reference to FIG. It is as follows.

FIG. 16 is a schematic view showing an example of a magneto-optical disk apparatus for performing magnetic field modulation overwriting on a magneto-optical disk. A laser light source (not shown) for irradiating a laser beam during recording and reproduction, and a recording medium An optical head 11 including a light receiving element (not shown) for receiving reflected light from the magneto-optical disk during reproduction, and a floating magnetic head 12 mechanically or electrically connected to the optical head 11. Have.

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

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

In this embodiment, the laser power is fixed at the time of magnetic field modulation overwriting. However, when the polarity of the magnetic field is switched, the laser power is reduced to a power at which no recording is performed so that the recording is not performed. The recording bit shape becomes clearer, and the reproduction signal quality is improved.

In magnetic field modulation overwriting, when high-speed recording is to be performed, it is necessary to modulate the magnetic field at a high speed. However, there are restrictions on the power consumption and size of the magnetic head 12b. 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 the present 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 employed. By doing so, the magnetic field at the time of recording can be suppressed lower, and the configuration is very suitable for the magnetic field modulation overwrite method.

Next, the light 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 intensity is applied to the magneto-optical recording medium, and the laser power is modulated according to the information for recording. Is the way. This will be described below with reference to FIGS. 17 to 21.

FIG. 18 shows the temperature dependence of the coercive force in the direction perpendicular to the film surfaces of the readout layer 3 and the recording layer 4 and the recording magnetic field H suitable for the optical modulation overwrite recording method described below.
_W is shown.

[0174] recording is performed while applying a recording magnetic field H _W, height, by irradiating the two levels of intensity modulated laser beam. That is, as shown in FIG. 19, when the laser light of the high level I is irradiated, both the readout layer 3 and the recording layer 4 are heated to a temperature T _H near or above the Curie points T _C1 and T _C2. When the low-level II laser light is irradiated, only the recording layer 4 is set to rise to a temperature _TL at which the Curie point T _C2 or more is reached.

[0175] Therefore, when the laser beam of low level II is projected, since the coercive force H ₁ of the readout layer 3 is sufficiently small, the magnetization in accordance with the direction of the recording magnetic field H _W, further transferred to the recording layer 4 in the cooling process Is done. That is, as shown in FIG. 17, the magnetization is directed upward.

Next, when the high-level I laser beam is irradiated, the temperature exceeds the compensation temperature. Therefore, the magnetization direction of the readout layer 3 depends on the recording magnetic field HW and _{differs from the case} of the low-level II laser beam. In the opposite direction, that is, downward. In the process of cooling, the temperature drops to the same temperature as the low-level II laser light,
The cooling processes of the readout layer 3 and the recording layer 4 are different (recording layer 4
Is cooled faster), so that only the recording layer 4 first reaches the temperature _TL at which the low-level II laser beam is irradiated, and the magnetization direction of the readout layer 3 is transferred to the recording layer 4 and becomes downward. Then, down to the same temperature as the laser beam of the readout layer 3 is low II, in accordance with the direction of the recording magnetic field H _W, facing upward. At this time, 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
Does not follow the direction of

When the laser beam intensity at the time of reproduction is irradiated with the laser beam of level III in FIG. 19, the temperature of the readout layer 3 becomes T _R (FIG. 18), and the magnetization of the readout layer 3 changes from the in-plane magnetization to the perpendicular. The transition to magnetization causes the recording layer 4 and the readout layer 3
Both layers exhibit perpendicular magnetic anisotropy. At this time, the recording magnetic field H
Since _W is either not applied sufficiently smaller than the coercive force of H ₂ recording layer 4, the magnetization direction of the readout layer 3 at the time of reproduction is consistent with the orientation of the recording layer 4 by the exchange force acting on the interface between the recording layer 4.

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

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

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

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

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

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

On the other hand, as shown in FIG. 23, two optical recording medium layers 19 formed on the substrate 1 are bonded together by the adhesive layer 10 so that the recording medium layers 19 are opposed to 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 light, heat and anaerobic, and the curing of the shadowed portion of the recording medium layer 19 through which ultraviolet light does not pass is cured by the heat and anaerobic curing function. Thus, a double-sided magneto-optical disk having extremely high moisture resistance and extremely excellent long-term stability can be provided.

The single-sided type requires only half the thickness of the magneto-optical disk as compared with the double-sided type.

The double-sided type is capable of performing double-sided reproduction, and is therefore advantageous for a recording / reproducing apparatus requiring a large capacity, for example.

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

As is well known, a light beam and a magnetic field are used for recording information on a magneto-optical disk. In the magneto-optical disk device (see FIG. 16), a light beam from a light source such as a semiconductor laser is condensed on the recording medium layer 19 through the substrate 1 by the condensing lens, and is radiated. Magnetic field generators such as magnets and electromagnets (for example,
A magnetic field is applied to the recording medium layer 19 by the flying magnetic head 12). By making the light beam intensity higher at the time of recording than at the time of reproduction, the temperature of the recording medium layer 19 at the converged portion increases, and the coercive force of the magnetic film at that portion decreases. At this time, when a magnetic field having a magnitude larger than the coercive force is applied from the outside, the magnetization of the magnetic film is aligned in the direction of the applied magnetic field, and the recording is completed.

For example, in a magnetic field modulation overwrite system in which a recording magnetic field is modulated according to information, it is necessary to bring a magnetic field generator (often an electromagnet) as close to the recording medium layer 19 as possible. This is because the frequency required for recording is modulated (generally hundreds of kHz to several tens of MHz) due to the heat generated by the coil of the electromagnet, the power consumption of the device, the size, and the like, and the magnetic field required for recording (generally, (E.g., about 500e to several hundred Oe), the recording medium has a thickness of about 0.2 mm or less, often 50 μm.
m needs to be approached. For this reason, in a double-sided magneto-optical disk, the thickness of the substrate 1 is generally less than 1.2.
Since it is about mm and a thickness of at least about 0.5 mm is required, when an electromagnet is arranged so as to face the light beam, the recording magnetic field intensity is insufficient and recording cannot be performed. Therefore, when the recording medium layer 19 suitable for the recording modulation overwrite method 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, a permanent magnet having a strong generated magnetic field, for example, a permanent magnet can be used. Even if the magnetic field modulation overwrite method is not used, as close to the recording medium layer 19 as possible, the recording medium layer 19 can be arranged at a distance of several mm from the recording medium layer 19. it can. Therefore, not only a single-sided type but also a double-sided type can be adopted.

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

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

By forming the overcoat layer 7, deterioration in characteristics due to oxidation of the recording medium layer 19 can be prevented, and long-term reliability can be ensured. In addition, by providing a hard coat film, even if a recording magnet comes into contact with the disc, the hard coat film, which has high hardness and excellent abrasion resistance, makes it hard to be scratched. In addition, even if a flaw occurs, it can be prevented from reaching the recording medium layer 19.

Naturally, the function of the hard coat layer may be added to the overcoat layer 7 so that only the overcoat layer 7 is sufficient.

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

In the magneto-optical disk of this embodiment, reproduction is performed using only the vicinity of the center of the light beam. Therefore, the influence of defects such as scratches on the surface of the substrate 1 on the reproduction is greater than in the conventional magneto-optical disk. It gets bigger. For this reason, by providing the hard coat layer on the surface of the substrate 1 on the side opposite to the recording medium layer 19, this configuration in which the generation of scratches can be prevented is very effective.

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

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

If dust or dust adheres to the surface of the substrate 1, it may not be possible to record and reproduce information as in the case of scratches. Further, when dust is deposited on the overcoat film 6, in the case of the magnetic field modulation overwrite method, the magnet is used as a floating magnetic head 12 (FIG. 16) to cover the overcoat film 6 by several μm.
In such a case, dust and dirt cause damage to the flying magnetic head 12 and the recording medium layer 19.

If a layer having an antistatic function is provided on the surface on the substrate 1 side or the surface on the recording medium layer 19 side as in this configuration, dust and dirt in the air can be removed from the surface of the substrate 1 or the surface thereof. Adhesion on the overcoat layer 7 can be prevented.

In the magneto-optical disk of the present embodiment, since reproduction is performed using only the vicinity of the center of the light beam, the influence of defects such as dust and dust on the surface of the substrate 1 on the reproduction is not affected by the conventional magneto-optical disk. 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 suitably about 2 to 3 μm.

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

It is needless to say that an antistatic effect may be added to the overcoat layer 7 or the hard coat layer.

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

The fourth variation is a magneto-optical disk in which a lubricating layer (not shown) is formed on the overcoat layer 7, and the structure of the substrate 1, the recording medium layer 19, the overcoat layer 7, and the lubricating layer is changed. Have. As the lubricating layer, for example, a fluorine-based resin can be used, and its thickness is suitably 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 type magnetic head 12 is disposed on the recording medium layer 19 for recording information while maintaining a gap of several μm to several tens μm. The gap between the pressure by the suspension 13 acting to press against the layer 19 and the levitation force generated by the airflow due to the high-speed rotation of the magneto-optical disk and acting to separate the flying magnetic head 12 from the recording medium layer 19 is balanced. Will be kept.

By using such a floating magnetic head 12, the time required to start the rotation of the magneto-optical disk and reach a predetermined number of rotations, and at the end of the rotation until the rotation stops from the predetermined number of rotations and stops. (Contact-Start-Stop) system, in which the magnetic head 12 and the magneto-optical disk are in contact with each other, when the floating magnetic head 12 and the magneto-optical disk are attracted to each other, the magnetic head 12 rises when the magneto-optical disk starts rotating. The type magnetic head 12 may be damaged. However,
According to the magneto-optical disk of this 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 Can be prevented from being damaged.

As a matter of course, it is not necessary to separately provide the overcoat layer 7 and the lubricating layer as long as the material prevents the deterioration of the recording medium layer 19 and also has the moisture resistance protection performance.

In a fifth variation, a moisture-permeable layer (not shown) and a second overcoat layer (not shown) are laminated on the surface of the substrate 1 opposite to the recording medium layer 19. It is a magneto-optical disk and has a structure of overcoat layer / moisture-permeable preventing layer / substrate 1 / recording medium layer 19 / overcoat layer 7.

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

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

In the case where the moisture permeation preventing film is not provided on the light incident side of the substrate 1, for example, when the environmental humidity changes greatly, the plastic substrate is formed only from the side where the recording medium layer 19 is not provided, that is, from the incident light side of the substrate 1. First, moisture is absorbed or released. This moisture absorption and release allows the plastic substrate 1
Causes a local change in volume, and the plastic substrate 1 is warped.

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

If the substrate 1 has a tilt, the laser light from the optical head 11 (FIG. 16) is condensed on the inclined surface of the recording medium layer 19, and is condensed according to the state of the tilt. The state changes, which adversely affects recording and reproduction.

Further, when the substrate 1 moves up and down with respect to the optical head 11, the optical head 11 operates to compensate for the up and down movement and focus the laser beam on the surface of the recording medium layer 19. Becomes too large, the compensating operation of the optical head 11 becomes incomplete, and the condensing state of the laser beam on the surface of the recording medium layer 19 becomes incomplete. If the laser beam is not completely focused, the temperature distribution of the recording medium layer 19 changes, which affects recording and reproduction. In the present embodiment, since the temperature distribution of the recording medium layer 19 during reproduction becomes particularly important, it is necessary to suppress the warpage of the substrate 1 and the warp change due to the environment as much as possible.

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

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

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

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 shown in the drawings of the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the magneto-optical disk of this embodiment, as shown in FIG. 24, a substrate 1, a transparent dielectric layer 2, a readout layer 3, a recording layer 4, a heat radiation layer 20, and an overcoat layer 7 are laminated in this order. It has a configuration.

The substrate 1 is made of a disc-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 a light beam is formed on one surface 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. Have been.

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

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

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

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

On the recording layer 4, as a heat radiation layer 20, A1
Ni is formed with a thickness of 100 nm. The content of Ni in A1Ni is 5 atm%.

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

On the heat radiation layer 20, a polyurethane acrylate-based ultraviolet curable resin having a thickness of 5 μm is formed as the overcoat layer 7.

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

Since the heat radiating layer 20 is provided on the recording layer 4, there is an effect that the recording bit shape is made clearer during recording. This is for the following reason.

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

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

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

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

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

Using the above-mentioned magneto-optical disk, recording was performed, and the linear velocity of the magneto-optical disk was set to 5 m / sec, and recording was performed for 0.7 minutes.
Reproduction signal quality of a recording bit length of 65 μm (C /
As a result of measuring N), a C / N of 50 dB was obtained. Regarding the magneto-optical disk having no heat radiation layer 20, C
As a result of measuring / N, C / N was 3 dB by the heat dissipation layer 20.
It was found that the above was improved.

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

Furthermore, AlNi is very excellent in moisture resistance, and can provide a magneto-optical disk excellent in long-term reliability.

Hereinafter, the results of the moisture resistance test of the above-described magneto-optical disk will be described.

The magneto-optical disk was allowed to stand for 1000 hours under the environmental conditions of 80 ° C. and 90% RH, and changes in its characteristics were examined. For comparison, a magneto-optical disk having the same configuration as above except that the heat radiation layer 20 was replaced with pure Al was also examined.

As a result, in the magneto-optical disk using the heat radiation layer 20 made of pure Al, a large number of pinholes were generated in Al of the heat radiation layer 20. Due to this, many pinholes were also generated in the recording layer 4 and the readout layer 3. On the other hand, in the magneto-optical disk of this example, the number of pinholes was extremely small, about several. For this reason, the C / N and the amount of crosstalk obtained characteristics which were not different from the initial state even after being left under the above environmental conditions.

The Ni content in AlNi is preferably from 0 to 10 atm%. If the Ni content is too high, the thermal conductivity decreases, and the readout layer 3 and the recording layer 4
It is difficult for the heat generated in the step to escape to the heat radiation layer 20. Therefore, the reproduction signal quality (C / N) is degraded. If the Ni content is up to 10 atm%, the deterioration of C / N is not so remarkable, and a practical value can be obtained. Further, even when the Ni content is as small as about 0.5 atm%, the moisture resistance is remarkably improved as compared with Al.

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

A magneto-optical disk having a heat radiation layer 20 of AlTi containing 1.5 atm% of Ti, a magneto-optical disk having a heat radiation layer 20 of AlTa containing 1.5 atm% of Ta, and containing 10 atm% of Si
Regarding the magneto-optical disk having the heat radiation layer 20 of AlSi,
When the dynamic characteristics 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 these contents are too large, the thermal conductivity decreases, and it becomes difficult for the heat generated in the reading layer 3 and the recording layer 4 to escape to the heat radiation layer 20 during recording. Therefore, the reproduction signal quality (C
/ N). When the Ti amount or the Ta amount 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 of Ni or Ta 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 from 0 to 50 atm%. If these contents are too large, the thermal conductivity decreases, and it becomes difficult for the heat generated in the reading layer 3 and the recording layer 4 to escape to the heat radiation layer 20 during recording.
For this reason, the reproduction signal quality (C / N) is degraded. Si amount is 50a
Up to tm%, the deterioration of C / N is not so remarkable, and a practical value can be obtained. Also, the Si content is 0.5atm%
Even to a small extent, 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 radiation layer 20 of AlTa is formed by sputtering an AlTa alloy target or a composite target having a Ta piece disposed on an Al target with Ar gas.

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

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

In the case where AlSi is used for the heat dissipation layer 20, the AlTa
Has the same advantage as the case where is used for the heat radiation layer 20.

That is, the heat radiation layer 20 of AlSi 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
Since SiN is transparent and has a large refractive index of around 2, it can be used as a material for the transparent dielectric layer 2.

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

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

As the thickness of the heat radiation layer 20 increases, the heat radiation effect increases and the long-term reliability improves. However, if the thickness of the heat radiation layer 20 is too large, the recording sensitivity of the magneto-optical disk is reduced. Although it is necessary to set the film thickness in accordance with the thermal conductivity and specific heat of the material of the heat radiation layer 20, it is usually preferably from 5 to 200 nm, more preferably from 10 to 100 nm. If the material has relatively high thermal conductivity and excellent corrosion resistance, the film thickness of the heat radiation layer 20 can 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 above embodiment between the heat dissipation layer 20 and the heat radiation layer 20 has the following advantages.

That is, the rare earth transition metal alloys of the readout layer 3 and the recording layer 4 are very easily oxidized, and their characteristics are easily deteriorated by the invasion of moisture from the outside. for that reason,
Although a material having excellent moisture resistance was used for the heat radiation layer 20, the recording layer 4
When a protective layer is further formed between the magnetic disk and the heat radiation layer 20, a magneto-optical disk having more excellent moisture resistance can be provided.

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

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

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

Although the first and second embodiments have been described with reference to a magneto-optical disk as a magneto-optical recording medium , 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 (substrate), for example, a tape base made of polyethylene terephthalate may be used instead of the rigid substrate 1.

The magneto-optical disk according to the first aspect of the present invention has a recording layer 4 for recording information magneto-optically, and exhibits in-plane magnetization at room temperature, but shifts to perpendicular magnetization as the temperature rises, and And a readout layer 3 to which the magnetization direction of 4 is transferred, and a test area for optimizing the reproduction laser power is provided.
Together provided in a part of the inner and outer circumference, optimization information for optimizing the reproducing laser power at each radial position from the reproducing laser power obtained in the test area
Is a configuration recorded in advance.

Therefore, it is possible to reproduce recording bits smaller than in the conventional case, and the recording density is remarkably improved. In addition, a test area for optimizing the reproduction laser power is provided in a part of the inner and outer circumferences , and an optimum for optimizing the reproduction laser power at each radial position from the reproduction laser power obtained in the test area. because of information <br/> paper is recorded in advance, it is possible to control the temperature distribution of the magneto-optical disk during reproduction more correctly, can provide a magneto-optical disk that enables a good reproduction.

The magneto-optical disk according to the second aspect of the present invention has a recording layer 4 for magneto-optically recording information,
A readout layer 3 which shows in-plane magnetization at room temperature, shifts to perpendicular magnetization with an increase in temperature, and transfers the magnetization direction of the recording layer 4, and the recording area is plural in accordance with the radial position. And a test area for optimizing the reproduction laser power is formed for each zone.

Therefore, it is possible to reproduce recording bits smaller than before, and the recording density is remarkably improved. Moreover, the recording area has a plurality of zones corresponding to the radial positions.
The reproduction laser power is
The test area to be optimized is
More precise control of magnetic disk temperature distribution
To provide a magneto-optical disk that can perform good reproduction.
Can be provided.

A magneto-optical reproducing apparatus according to the third aspect of the present invention.
Is a magneto-optical disk according to claim 2 as described above.
A magneto-optical reproducing apparatus for reproducing data in each zone.
Optimizing the playback laser power in the test area
You.

Therefore, the magneto-optical disk of claim 2 can be
And the reproduction rate in the test area for each zone.
Optimizes the laser power, so that
Temperature distribution can be controlled more accurately,
It is possible to provide a magneto-optical reproducing device capable of excellent reproduction.

[0272] The magneto-optical reproducing device corresponding to the invention of claim 4, as described above, a magneto-optical reproducing apparatus for reproducing the magneto-optical disc corresponding to claim 1, said optimization information
And the reproduction laser power obtained in the test area.
And the reproducing laser power is changed according to the radial position of the magneto-optical disk.

Accordingly, half of the magneto-optical disk to be reproduced is
Changing the playback laser power according to the diameter position
Control the temperature distribution of the magneto-optical disk during playback more accurately.
Magneto-optical device that can control
An energy regeneration device can be provided.

[0274]

As described above, the magneto-optical disk according to the first aspect of the present invention has a recording layer for magneto-optically recording information and exhibits in-plane magnetization at room temperature, but shifts to perpendicular magnetization as the temperature rises. In addition, since the recording layer has the readout layer to which the magnetization direction of the recording layer is transferred, it is possible to reproduce the recording bit smaller than before, and the recording density is remarkably improved.
Moreover, there is a test area to optimize the reproduction laser power.
Together provided in a part of the inner and outer circumference, optimization information for optimizing the reproducing laser power at each radial position from the reproducing laser power obtained in the test area
There is an effect that pre-recorded have Runode, it becomes possible to more accurately control the temperature distribution of the magneto-optical disk during reproduction, it is possible to provide a magneto-optical disk that enables a good reproduction.

The magneto-optical disk according to the second aspect of the present invention
As described above, the recording layer that magneto-optically records information and the readout layer that shows in-plane magnetization at room temperature, transitions to perpendicular magnetization as the temperature rises, and transfers the magnetization direction of the recording layer are provided. Therefore, it is possible to reproduce recording bits smaller than before, and the recording density is remarkably improved. In addition, the recording area is divided into a plurality of zones according to the radial position, and a test area for optimizing the reproduction laser power is formed for each zone, so that the temperature distribution of the magneto-optical disk during reproduction can be more accurate. This makes it possible to provide a magneto-optical disk capable of excellent reproduction.

The magneto-optical reproducing device according to the third aspect of the present invention
As described above, using the magneto-optical disk of claim 2,
For each zone, the reproduction laser power in the test area
Optimization, the temperature of the magneto-optical disk during
Cloth can be controlled more accurately, and good reproduction
The effect of being able to provide a magneto-optical reproducing device
Play.

The magneto-optical reproducing apparatus according to the fourth aspect of the present invention
As described above, the magneto-optical disk of claim 1 is reproduced.
The optimization information and the test area
Since the reproducing laser power is changed according to the radial position of the magneto-optical disk based on the obtained reproducing laser power, the temperature distribution of the magneto-optical disk during reproduction can be more accurately controlled, which is favorable. This provides an effect that a magneto-optical reproducing device capable of performing accurate reproduction can be provided.

[Brief description of the drawings]

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

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

In Figure 3 temperatures T ₁ from room temperature 2 is an explanatory diagram showing the relationship between the externally applied magnetic field and polar Kerr rotation angle to be applied to the readout layer.

In Figure 4 temperature T ₂ from the temperature T ₁ of the 2 is an explanatory diagram showing the relationship between the externally applied magnetic field and polar Kerr rotation angle to be applied to the readout layer.

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

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

FIG. 7 is a graph showing the composition dependence of the Curie temperature (Tc) and the 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 dependency of mp).

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

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

FIG. 11 is an explanatory view showing another example of the land and group shapes formed on the substrate of the magneto-optical disk of FIG. 1;

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

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

FIG. 14 is an explanatory diagram showing an example of a wobble ring groove formed on a substrate of the magneto-optical disk of FIG. 1;

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

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

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

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

FIG. 19 is an explanatory diagram showing an example of the intensity of a light beam applied to the magneto-optical disk of FIG. 1 at the time of light modulation overwriting and at the time of reproduction.

FIG. 20 is an explanatory diagram showing another example of the intensity of the light beam applied to the magneto-optical disk of FIG. 1 at the time of light modulation overwriting and at the time of reproduction.

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

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

FIG. 23 is an explanatory diagram showing a double-sided type of the magneto-optical disk of FIG. 1;

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate (base) 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

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 11/10 581 G11B 11/10 581B 586 586C (72) Inventor Yoshiteru Murakami 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Inside (72) Inventor Akira Takahashi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Kenji 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) JP-A-5-205336 (JP, A) JP-A-6-124500 (JP, A) JP-A-60-125937 (JP, A) JP-A-2-5221 (JP, A) JP-A-6-12521 −28675 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 11/10 506 G11B 11/10 511 G11B 7/00

Claims (4)

(57) [Claims] 1. A recording layer for magneto-optically recording information, and a readout layer which exhibits in-plane magnetization at room temperature, shifts to perpendicular magnetization with an increase in temperature, and transfers the magnetization direction of the recording layer. a magneto-optical disk, a test area to optimize the reproduction laser power is within the outer periphery of the
A part of which is provided to optimize the reproduction laser power at each radial position from the reproduction laser power obtained in the test area.
Optimization information, the magneto-optical disk, characterized that you have been pre-recorded. 2. A recording layer for magneto-optically recording information, and a readout layer which shows in-plane magnetization at room temperature, shifts to perpendicular magnetization with an increase in temperature, and transfers the magnetization direction of the recording layer. A magneto-optical disk, wherein a recording area is divided into a plurality of zones corresponding to radial positions, and a test area for optimizing a reproduction laser power is formed for each zone. 3. A magneto-optical reproducing apparatus for reproducing a magneto-optical disk according to claim 2, wherein a reproducing laser power is optimized in said test area for each zone. 4. A magneto-optical reproducing apparatus for reproducing a magneto-optical disk according to claim 1 , wherein said optimization information and the reproduction information obtained in said test area are reproduced.
A magneto-optical reproducing apparatus characterized in that a reproducing laser power is changed according to a radial position of a magneto-optical disk based on raw laser power .