JP2914544B2 - Magneto-optical storage element - 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 storage device such as a magneto-optical disk, a magneto-optical tape, and a magneto-optical card.

[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 to practical use as external memories for computers.

In a magneto-optical disk using a perpendicular magnetic film as a recording medium, recording and reproduction are performed using light, so that a large recording capacity can be realized as compared with a floppy disk or a hard disk using an in-plane magnetic film.

In order to further increase the recording density of a magneto-optical disk, the diameter of a light beam spot on a recording medium may be reduced. As a method of reducing the light beam spot diameter, there is a method of shortening the wavelength of the light beam.

[0005]

However, since it is difficult at present to shorten the oscillation wavelength of a semiconductor laser as a light source, there is a problem that the recording density of a magneto-optical disk cannot be further increased. .

[0006]

According to a first aspect of the present invention, there is provided a magneto-optical memory device, wherein a groove for guiding a light beam is formed on one surface of a transparent substrate. On the other hand, at the room temperature, the in-plane magnetic anisotropy shows the in-plane magnetization where the in-plane magnetic anisotropy is dominant, while the perpendicular magnetic anisotropy shifts to the dominant perpendicular magnetization as the temperature rises, and the recording layer for recording information Are formed in this order. The depth of the groove is set so that the readout layer and the recording layer on the groove and the readout layer and the recording layer on the land between the grooves are almost vertically divided , and the reproduction is performed. Sometimes the readout layer
In, the temperature of the light beam
Only the area near the center smaller than the spot diameter has the polar Kerr effect.
It is characterized by showing .

The magneto-optical memory device according to the second aspect of the present invention
In order to solve the above problem, the depth of the groove is 130 to 280 nm.

[0008]

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, and is smaller than the diameter of the light beam spot. The temperature in the region near the center rises more than the temperature in the surrounding region.

As the temperature rises, the magnetization at the temperature rise site shifts from in-plane magnetization to perpendicular magnetization. At this time, followed by the magnetization direction of the readout layer in the direction of magnetization of the record layer.

When the temperature rising portion shifts from in-plane magnetization to perpendicular magnetization, only the temperature rising portion shows the polar Kerr effect, and information is reproduced based on 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 area near the center smaller than the diameter of the light beam spot heated to a predetermined temperature or higher is involved in the reproduction, it is possible to reproduce the recording bits smaller than the conventional one. The density is significantly improved.

Further, the depth of the groove is set so that the readout layer and the recording layer on the groove and the readout layer and the recording layer on the land between the grooves are substantially vertically separated, so that the groove is formed at the time of recording. Recording bits are less likely to spread to adjacent tracks.

As a result, crosstalk is reduced during reproduction, so that the track pitch can be made smaller, and higher density recording can be performed.

According to the structure of claim 2, since the depth of the groove is set to 130 to 280 nm, a strong tracking error signal is obtained in addition to the effect of claim 1. This enables stable tracking even during high-density recording.

[0016]

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

As shown in FIG. 1, the magneto-optical disk (magneto-optical storage element) of this embodiment has a substrate 1 (base), a transparent dielectric layer 2, a readout layer 3, a recording layer 4, a protective layer 5, It has a configuration in which the coat layers 6 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. 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 pole Kerr rotation angle shows a hysteresis characteristic in which the rise of the pole Kerr rotation angle is steep with respect to the external magnetic field, but in other temperature ranges, the pole Kerr rotation angle is almost zero. .

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

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

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

That is, the magnetization in the region having a temperature 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 7, because the surrounding site is the temperature T ₁ or less, in-plane magnetization state (FIG. 3) is held. As a result, the polar Kerr effect is not exhibited with respect to the reproduction light beam 7 irradiated to the film surface from the vertical direction.

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

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

As described above, when the magneto-optical disk of this embodiment is used, the recording bit smaller than the diameter of the reproducing light beam 7 can be surely reproduced, and the recording density is not affected by the adjacent recording bit. 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. Groove depth is 200
nm.

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.

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

On the readout layer 3, as the recording layer 4, a rare earth transition metal alloy thin film DyFeCo is
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 substantially in-plane at room temperature (that is, the layer direction of the readout layer 3).
The transition from the in-plane direction to the vertical direction occurs at a temperature of about 125 ° C.

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

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

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

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

Transparent dielectric layer 2, readout layer 3, recording layer 4
The protective layer 5 and the protective layer 5 were both formed by a sputtering method in the same sputtering apparatus without breaking vacuum. A1N of the transparent dielectric layer 2 and the protective layer 5 is obtained by setting the A1 target to N1.
It was formed by a reactive sputtering method in which sputtering was performed in a _two- gas atmosphere. The readout layer 3 and the recording layer 4 are made of FeC
A so-called composite target in which Gd or Dy chips are arranged on an o-alloy target, or a ternary alloy target of GdFeCo and DyFeCo, is formed by sputtering with Ar gas.

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

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

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

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

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

First, the radius of the magneto-optical disk is 26.
A rotation speed of 1800 rpm (linear velocity 5
m / sec), a single frequency recording bit 0.765 μm long was pre-recorded. In the recording, first, the direction of magnetization of the recording layer 4 is aligned in one direction (erasing state), and then the direction of the external magnetic field for recording is fixed in the direction opposite to the erasing direction. The recording was performed by modulating the laser at a recording frequency corresponding to the above (in this case, about 3.3 MHz). The recording laser power was about 8 mW.

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

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

In the conventional magneto-optical disk, an A1N film having a thickness of 80 nm and a DyFeC
o 20 nm, A1N 25 nm, A1Ni 30 nm
Are laminated in this order, and the same overcoat layer as described above is provided on A1Ni.

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

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

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

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

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

Next, a description will be given of the result of examining the reproduction signal quality when the recording bit is made smaller.

The linear velocity of the magneto-optical disk was set at 5 m / sec as in the previous experiment, recording was performed while changing the recording frequency, and the C / N was measured. The optical pickup and the recording method are the same as in the previous experiment. The reproducing laser power was 2.25 mW. For comparison, the C / N was measured for a conventional magneto-optical disk as in the previous experiment. The reproducing laser power at this time was 1 mW.

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

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

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

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

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

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

For example, according to the ISO 10089 standard (the standard defined for the 5.25 "rewritable optical disk of the ISO), a guide track having a 1.6 μm pitch
The crosstalk amount with respect to the shortest recording bit (0.765 μm) is determined to be −26 dB or less.

In this embodiment, 0.765 μm is measured based on the crosstalk measurement method defined in the ISO10089 standard.
The amount of crosstalk with respect to m recording bits was measured. However, in order to confirm the effect of the magneto-optical disk of the present embodiment, in the above-described glass substrate 1 having a track pitch of 1.6 μm and the same land width and groove width of 0.8 μm, the depth of the groove was set to 200 nm. The amount of crosstalk from both adjacent grooves when the land portion was reproduced was measured and compared between the magneto-optical disk of No. 1 and a magneto-optical disk having a groove depth of 70 nm.

As a result of the measurement, in the magneto-optical disk of the present embodiment, the crosstalk amount was improved by 3 dB or more as compared with the conventional magneto-optical disk.

The depth of the groove is from 70 nm to 200 nm.
The reason why the amount of crosstalk was reduced,
A description will be given with reference to FIGS.

In a magneto-optical disk having a groove depth of 200 nm, the read layer 3 and the recording layer 4 on the groove and the read layer 3 and the recording layer 4 on the land between the grooves are formed as shown in FIG. It is almost vertically divided. Therefore, heat is hardly conducted between the readout layer 3 and the recording layer 4 on the groove and the readout layer 3 and the recording layer 4 on the land between the grooves. That is, heat is not easily conducted to the adjacent track.

Therefore, when information is recorded on a track on a land, as shown in FIG. 12A, the recording bit spreads along the land but does not spread to the adjacent groove.

On the other hand, in a magneto-optical disk having a groove depth of 70 nm, as shown in FIG. 11, the readout layer 3 and the recording layer 4 on the groove and the readout layer 3 and the recording layer 4 on the land between the grooves. Is almost not divided up and down. Therefore, heat is easily conducted between the readout layer 3 and the recording layer 4 on the groove and the readout layer 3 and the recording layer 4 on the land between the grooves. That is, heat is easily conducted to the adjacent track. Therefore, FIG.
As shown in (1), the recording bit spreads along the land and also spreads to the adjacent groove.

As a result, the amount of crosstalk is smaller in a magneto-optical disk having a groove depth of 200 nm than in a magneto-optical disk having a groove depth of 70 nm.

By the way, the intensity of the tracking error signal becomes maximum when the depth of the groove is set so as to satisfy the following equation.

D = λ (2k−1) / (8n) where d is the depth of the groove, λ is the wavelength of the light beam, n
Is the refractive index of the transparent substrate, and k is a natural number (1, 2, 3,
...).

Assuming that k = 2, in this embodiment, d ≒ 1
90 nm. At this time, the intensity of the tracking error signal becomes maximum, and stable tracking becomes possible.

Λ = 670-830 nm, n = 1.4
In the case of 4 to 1.55, 160 nm ≦ d ≦ 215 nm. At this time, the intensity of the tracking error signal becomes maximum, and stable tracking becomes possible.

That is, when setting the depth of the groove,
It is sufficient that the readout layer 3 and the recording layer 4 on the groove and the readout layer 3 and the recording layer 4 on the land between the grooves can be substantially vertically separated, and that the intensity of the tracking error signal increases. In consideration of this, it is preferable to set the groove depth so that 130 nm ≦ d ≦ 280 nm.

The degree of the above-mentioned division varies depending on the thickness of each of the transparent dielectric layer 2, the readout layer 3, and the recording layer 4. Therefore, when setting the depth of the groove, this is also taken into consideration. Is preferred.

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. 13 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 the recorded information may be disturbed.

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

FIG. 14 shows a case where Y is 0, 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. 15 shows the case where Y is 1, ie, 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.

A higher C / N can be obtained when the polar Kerr rotation angle at the time of reproduction is as large as possible. Therefore, a higher Curie temperature of the readout layer 3 is advantageous. 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 thickness of the recording layer 4. this is,
This is because a magnetic exchange coupling force acts between the two layers. Therefore, the optimum composition and thickness of the readout layer 3 change depending on the material, composition and thickness of the recording layer 4.

As described above, as the material of the readout layer 3 of the magneto-optical disk of this embodiment, GdFeCo, which has a steep transition from in-plane magnetization to perpendicular magnetization, is optimal, but rare earth transition metal alloys described below are also suitable. The same effect can be obtained.

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

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

When an FeCo alloy is used as the transition metal, Tb _X (Fe _Y Co _1-Y ) _1-X is not less than room temperature within the 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 the 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 on the level of practical use, and SHG lasers with wavelengths of 400 nm or less are being studied energetically.

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
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.

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 reading layer 3, the environmental resistance of the reading 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.

Next, in this embodiment, the readout layer 3
Was 50 nm, but the film thickness is not limited to this. As shown in FIG.
From the side, if the thickness of the readout layer 3 is too thin,
The information in the recording layer 4 becomes transparent. That is, the mask effect due to the in-plane magnetization of the readout layer 3 is reduced.

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

The material of the recording layer 4 is a material exhibiting perpendicular magnetization from room temperature to the Curie temperature, and the Curie temperature may be in a temperature range suitable for recording, that is, about 150 to 250 ° C. In this 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. In addition, Cr, V, Nb, Mn, Be, Ni
If at least one element is added, the long-term reliability can be further improved. The thickness of the recording layer 4 is determined depending on the material, composition, and thickness of the readout layer 3, and is preferably about 20 nm or more and 100 nm or less.

The film thickness of AlN of the transparent dielectric 2 is not limited to 80 nm.

The thickness of the transparent dielectric layer 2 is determined in consideration of the so-called Kerr effect enhancement, in which, when reproducing a magneto-optical disk, the polar Kerr rotation angle from the readout layer 3 is increased by utilizing the interference effect of light. It is determined. Signal quality during playback
In order to increase (C / N) 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. You.

This film thickness changes depending on the wavelength of the reproduction light and the refractive index of the transparent dielectric layer 2. In the case of this embodiment, 780 nm
Since AlN having a refractive index of 2.0 is used with respect to the reproduction light wavelength, when the thickness of AlN of the transparent dielectric layer 2 is set to about 30 to 120 nm, the effect of the Kerr effect enhancement is increased. Preferably, the film thickness of AlN of the transparent dielectric layer 2 is 70 to 100 nm, and within this range, the polar Kerr rotation angle becomes almost maximum.

The above description has been made with respect to reproduction light having a wavelength of 780 nm. However, for 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 changes due to the difference in the material of the transparent dielectric layer 2 or the manufacturing method, the value obtained by multiplying the refractive index by the film thickness (optical path length) is made the same. The thickness of the transparent dielectric layer 2 may be set.

That is, in the present embodiment, the multiplication of the refractive index 2 of AlN of the transparent dielectric layer 2 and the film thickness of 80 nm, 160 nm
Is the optical path length of the transparent dielectric layer 2. If the refractive index of AlN changes from 2 to 2.5, the film thickness may be set to about 160 nm / 2.5 = 64 nm.

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

AlN can be obtained by changing the ratio of Ar and N ₂ , which are sputter gases at the time of sputtering, and the gas pressure.
Although the refractive index changes, it is a material having a relatively large refractive index of about 1.8 to 2.1, and is suitable as a material for the transparent dielectric layer 2.

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

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

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

Further, since AlN has a relatively large refractive index of about 2 and is transparent, and does not contain oxygen in its component, it can provide a magneto-optical disk having excellent long-term stability.
In addition, by using the A1 target, and N ₂ gas or Ar
Reactive DC (direct current) sputtering can be performed by introducing a mixed gas of N ₂ , which is advantageous in that the film formation rate is higher than that of RF (high frequency) sputtering.

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

The thickness of the AlN film of the protective layer 5 is set in this embodiment.
Although it was set to 20 nm, it is not limited to this. Protective layer 5
The range of the film thickness is preferably 1 to 200 nm.

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

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

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

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

In this embodiment, the protective layer 5 is formed of the transparent dielectric layer 2
By using the same AlN as that described above, a magneto-optical disk having excellent moisture resistance can be provided, and productivity can be improved by forming the protective layer 5 and the transparent dielectric layer 2 from the same material. As described above, AlN is a material having extremely excellent moisture resistance, and can be set to a relatively thin film thickness of 20 nm. The thinner is more advantageous in consideration of productivity.
In addition to AlN, the material of the protective layer 5 is SiN, AlSiN, AlTa, which is used as the material of the transparent dielectric layer 2 in consideration of the above objects and effects.
N, SiAlON, TiN, TiON, BN, ZnS,
TiO ₂ , BaTiO ₃ and SrTiO ₃ are preferred.

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

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

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

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

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

When a PC is used 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.
Improvement of long-term reliability of magneto-optical recording media, heat resistance,
Advantages include excellent impact resistance. In addition, for the materials which can be injection-molded as described below including this material, guide tracks, pre-pits, etc. are formed on the surface of the substrate 1 at the same time as molding if a stamper is attached to the surface of the molding die at the time of injection molding. Is done.

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

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

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

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

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

As described above, various materials can be used for the substrate 1. When these 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 : 10 m / s ² or less Radial acceleration: 3 m / s ² or less An optical pickup for condensing laser light on the recording layer 4 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, so that 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 this embodiment, it is desirable that the tilt of the substrate 1 be 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 this embodiment, since the temperature distribution of the recording medium during reproduction becomes particularly important, the radial acceleration of the substrate to be used in the radial direction during rotation is suppressed to 3 m / s ² or less. It is desirable.

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

In the case of the continuous servo system, as shown in FIG. 16, a pitch of 1.2 to 1.6 μm and a pitch of 0.2 to 0.6 μm are used.
A groove having a width of about λ / (8n) is formed;
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 groove 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.
Grooves and lands of the same width are formed at a pitch of 6 μm,
Even when recording and reproduction are performed in both the groove portion and the land portion, recording and reproduction can be performed in both the groove portion and the land portion without being affected by crosstalk from recording bits of an adjacent track. Density is greatly increased.

On the other hand, in the case of the sample servo system, FIG.
As shown in FIG. 8, wobble pits are formed at a pitch of 1.2 to 1.6 μm and have a depth of about (λ / (4n)), and information is recorded so that the laser beam always scans the center of the wobble pits. Regeneration is generally performed.
It is quite possible to apply the present invention to such a general system. In the present invention, by greatly reducing crosstalk from adjacent recording bits,
Even when wobble pits are formed at a pitch of 0.5 to 1.2 μm, recording and reproduction can be performed without being affected by crosstalk from adjacent recording bits.
The recording density is greatly improved.

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

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

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

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

In the above description, it is assumed that the numerical aperture (NA) of the objective lens of the optical pickup to be 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.

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 these read values, test areas in which recording and reproduction can be actually performed are provided on the inner and outer circumferences (for example, ISO
10089 standard).

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

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

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

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

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

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

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

The first generation magneto-optical disk is an ISO 10
In accordance with the 089 standard (a standard for ISO 5.25 "rewritable optical discs), many are already on the market and overwriting is not possible, so new information is recorded where information has already been recorded. In such a case, it is necessary to perform an operation of erasing the portion once and then performing recording, which requires a minimum of two rotations of the magneto-optical disk, and has a defect that the data transfer speed is low. .

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

In order to eliminate the disadvantage that overwriting cannot be performed, for example, a method of arranging 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 of erasing information already recorded by a preceding optical head using two optical heads and recording new information by an optical head chasing later. At the time of reproduction, reproduction is performed using one of the optical heads.

When recording is performed using three optical heads, the preceding optical head erases the already recorded information, the next optical head records new information, and the remaining optical heads 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 this 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 the magnetic field intensity according to information while irradiating a magneto-optical recording medium with a laser having a constant power, and will be described with reference to FIG. It is as follows.

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

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

In this state, the flying magnetic head 12 and the optical head 11 are moved to a desired radial position in the recording area of the magneto-optical disk 14, and 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 lowered 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 performing high-speed recording, 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, and the magnetic head 12b has a very large magnetic field. Is difficult to generate. Therefore, the magneto-optical disk 14 is required to be able to record with a relatively small magnetic field.

In the magneto-optical disk of this embodiment, DyFeCo, which is a material having a low perpendicular magnetic anisotropy, is employed in which the Curie temperature of the recording layer 4 is kept relatively low at 150 to 250 ° C. to facilitate recording. 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, and applies a constant magnetic field intensity to the magneto-optical recording medium and modulates the laser power according to the information for recording. Is the way. This will be described below with reference to FIGS. 23 to 27.

FIG. 24 shows the temperature 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.

[0177] 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. 25, when the laser light of 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.

[0178] Therefore, when the laser beam of low level II is projected, since the coercive force H ₁ of the readout layer 3 is sufficiently small, the magnetization in accordance with the direction of the recording magnetic field H _W, further transferred to the recording layer 4 in the cooling process Is done. That is, the magnetization is directed upward as shown in FIG.

[0179] Next, when the laser beam of high level I is projected, since beyond the compensation temperature, the magnetization direction of the readout layer 3 by the recording magnetic field H _W, as in the laser beam of low level II is 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 the level III in FIG. 25, the temperature of the readout layer 3 becomes T _R (FIG. 24), 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, the information can be recorded by the overwrite recording method without going through the process of erasing the already recorded information.

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

That is, when a high-level laser beam of type I is irradiated, the temperature T at which the readout layer 3 and the recording layer 4 are both near or above the Curie points T _C1 and T _C2 is obtained.
_{When the} temperature is raised to _H and a low-level 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 which is irradiated for a while may be lower than the high level.

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

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

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

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

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

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

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

For example, in the magnetic field modulation overwrite system that modulates a recording magnetic field according to information, it is necessary to bring a magnetic field generator (often an electromagnet) as close to the recording medium layer 9 as possible. This is because the 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, (Approximately 50 Oe to hundreds of Oe) is generated on the recording medium, which is 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.
mm and a thickness of about 0.5 mm is required, so if an electromagnet is placed facing the light beam, the recording magnetic field strength will be insufficient and recording will not be possible. Therefore, it is suitable for the recording modulation overwrite method. When the recording medium layer 9 is adopted, a single-sided type magneto-optical disk is often used.

On the other hand, in the light modulation overwrite method in which the light beam is modulated according to the information, the recording magnetic field remains in one direction, or the recording magnetic field is unnecessary. Therefore, it is possible to use a permanent magnet having a strong generated magnetic field, for example, a permanent magnet, and to dispose the recording medium layer 9 at a distance of several mm from the recording medium layer 9 without disposing the recording medium layer 9 as close as possible as in the magnetic field modulation overwrite method. 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 6, and includes a substrate 1 / recording medium layer 9 / overcoat layer 6 / hard coat layer. It has a structure.
As the hard coat layer, for example, an acrylate-based UV-curable hard coat resin film is formed of, for example, a polyurethane acrylate-based UV-curable resin having a thickness of about 6 μm.
On the overcoat layer 6. The thickness of the hard coat layer is, for example, 3 μm.

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

[0198] Naturally, the function of the hard coat layer may be added to the overcoat layer 6 so that only the overcoat layer 6 is sufficient.

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

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

In the magneto-optical disk of the present embodiment, since reproduction is performed using only the vicinity of the center of the light beam, the influence of defects such as scratches on the surface of the substrate 1 on the reproduction is 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 9, the present configuration in which the generation of scratches can be prevented is very effective.

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

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

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

If a layer having an antistatic function is provided on the surface on the substrate 1 side or the surface on the recording medium layer 9 side as in the present 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 6 can be prevented.

In the magneto-optical disk of this 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 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 dust and the like to adhere, regardless of the plastic substrate 1 or the glass substrate 1.

[0209] Naturally, an antistatic effect may be added to the overcoat layer 6 or the hard coat layer.

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

The fourth variation is a magneto-optical disk in which a lubricating layer (not shown) is formed on the overcoat layer 6, and the structure of the substrate 1, the recording medium layer 9, the overcoat layer 6, and the lubricating layer is changed. Have. As the lubrication layer,
For example, a fluorine-based resin can be used, and its 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 magnetic head 12 is arranged to record information on the recording medium layer 9 while maintaining a gap of several μm to several tens μm. The levitation type magnetic head 12 generated by the air pressure due to the high speed rotation of the magneto-optical disk and the pressure by the suspension 13 acting to press the layer 9.
The above-mentioned gap is maintained by balancing the levitation force acting to separate the recording medium from the recording medium layer 9.

By using such a floating magnetic head 12, the time required for the magneto-optical disk to start rotating and to reach a predetermined number of revolutions, and to end the rotation and to stop the rotation from the predetermined number of revolutions to stop. (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 6, 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 6 and the lubricating layer as long as the material prevents moisture in the recording medium layer 9 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 9. This is a magneto-optical disk and has a structure of overcoat layer / moisture-permeable layer / substrate 1 / recording medium layer 9 / overcoat layer 6.

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 9 is not provided, that is, from the incident light side of the substrate 1. First, moisture is absorbed or released. Due to this moisture absorption and release, the plastic substrate 1 locally changes in volume, and the plastic substrate 1 is warped.

The warping 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 a tilt is present on the substrate 1, the laser light from the optical head 11 (FIG. 22) is condensed on the inclined surface of the recording medium layer 9, 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 so as to compensate for the vertical movement and focus the laser beam on the surface of the recording medium layer 9. Becomes too large, the compensating operation of the optical head 11 becomes incomplete, and the focusing state of the laser light on the surface of the recording medium layer 9 becomes incomplete. If the laser beam is not completely focused, the temperature distribution of the recording medium layer 9 changes, which affects recording and reproduction. In the present embodiment, since the temperature distribution of the recording medium layer 9 during reproduction becomes particularly important, it is necessary to minimize the warpage of the substrate 1 and the change in warpage due to the environment.

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 greatly 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 9
It may be the same as the overcoat layer 6 above.

Further, in addition to the present 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. 30, a substrate 1, a transparent dielectric layer 2, a read layer 3, a recording layer 4, a heat radiation layer 20, and an overcoat layer 6 are laminated in this order. It has a configuration.

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

A groove is formed on the substrate 1, and the depth of the groove is set in the same manner as in the above embodiment.

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

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

In this embodiment, since the heat radiation layer 20 made of Al having high heat conductivity is formed on the recording layer 4, the 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.

Further, the readout layer 3 and the recording layer 4 on the groove and the readout layer 3 and the recording layer 4 on the land are
Since it is almost vertically divided, heat is not easily conducted to adjacent tracks. As a result, the recording bit does not spread to the adjacent track, and crosstalk is reduced.

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 obtain a clearer difference in the temperature change between the readout layer 3 and the recording layer 4 when the area once heated by the light beam cooling in the recording process is cooled. Can be provided. This effect is because the cooling process of the readout layer 3 and the recording layer 4 when a high-level laser beam is irradiated can be greatly different (the recording layer 4 is cooled faster).
Overwriting can be performed more easily.

Al, which is a material 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. In addition, when AlN is used for the transparent dielectric layer 2, since this AlN is formed by reactively sputtering an Al target with Ar and N ₂ gas, heat is radiated by sputtering the same Al target with Ar gas. The layer 20 can be easily formed. Al is also a very inexpensive material.

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

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

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

In this embodiment, the thickness of the heat radiation layer 20 is set to 10
Although it is set to 0 nm, the thicker the thickness, the higher the heat radiation effect, and also the longer-term reliability is improved. However, as described above, it also affects the recording sensitivity of the magneto-optical disk, so it is necessary to set the film thickness in accordance with the thermal conductivity and specific heat of the material, and the range of 5 to 200 nm is good. Above all, 10-100nm
Is preferred. If the material has a relatively high thermal conductivity and excellent corrosion resistance, the film thickness can be as thin as about 10 to 100 nm, and the time required for film formation at the time of manufacturing can be shortened.

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

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

In the magneto-optical disk according to the present invention, the in-plane magnetic anisotropy is superior at room temperature to the groove-side surface of the transparent substrate 1 on which the groove for guiding the light beam is formed on one surface. A readout layer 3 which exhibits a strong in-plane magnetization, but shifts to a perpendicular magnetization in which the perpendicular magnetic anisotropy is dominant as the temperature rises;
Since the recording layer 4 for recording information is formed in this order, it is possible to reproduce recording bits smaller than before, and the recording density is remarkably improved. In addition, since the depth of the groove is set so that the readout layer 3 and the recording layer 4 on the groove and the readout layer 3 and the recording layer 4 on the land between the grooves are substantially vertically separated, the groove is formed during recording. This makes it difficult for the recorded bits to spread to adjacent tracks. Therefore, crosstalk during reproduction is reduced. Therefore, the track pitch can be further reduced, and higher density recording can be performed.

In the magneto-optical disk according to the second aspect of the present invention, as described above, the depth of the groove is set to 130 to 2
Since the thickness is set to 80 nm, a strong tracking error signal can be obtained in addition to the above-mentioned effects. This enables stable tracking even during high-density recording.

[0245]

As described above, the magneto-optical memory element according to the first aspect of the present invention has an in-plane surface at room temperature on the groove side of the transparent substrate having the groove for guiding the light beam formed on one side. A readout layer which shifts to a perpendicular magnetization in which the perpendicular magnetic anisotropy is dominant as the temperature rises while an in-plane magnetization in which the magnetic anisotropy is dominant, and a recording layer for recording information are formed in this order. Therefore, it is possible to reproduce the recording bit smaller than before, and the recording density is remarkably improved. Moreover,
Since the depth of the groove is set so that the readout layer and the recording layer on the groove and the readout layer and the recording layer on the land between the grooves are almost vertically separated,
It becomes difficult for recording bits formed during recording to spread to adjacent tracks. Therefore, crosstalk during reproduction is reduced. Therefore, the track pitch can be further reduced, and an effect that higher density recording can be performed can be achieved.

The magneto-optical memory device according to the second aspect of the present invention
As described above, the depth of the groove is set to 130 to 280.
Since nm is set, in addition to the effect of the first aspect, a strong tracking error signal can be obtained. Thereby, there is an effect that stable tracking can be performed even during high-density recording.

[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.

[6] In the Curie temperature Tc from the temperature T ₃ 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. 7 is a graph showing the results of actually measuring the dependence of the polar Kerr rotation angle of the readout layer of the magneto-optical disk of FIG. 1 at room temperature on the externally applied magnetic field.

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

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

FIG. 10 is an explanatory diagram showing a sectional structure of the magneto-optical disk of FIG. 1;

FIG. 11 is an explanatory diagram showing a cross-sectional structure of a magneto-optical disk according to a comparative example.

FIG. 12 is an explanatory diagram showing the spread of recording bits;
(A) corresponds to the magneto-optical disk of FIG. 10, and (b) corresponds to the magneto-optical disk of the comparative example of FIG.

FIG. 13: Curie temperature (Tc) of Gd _X (Fe _0.82 Co _0.18 ) _1-X
4 is a graph showing the composition dependence of the compensation temperature (Tcomp).

FIG. 14 shows the Curie temperature (Tc) and compensation temperature (Tc) of Gd _X Fe _1-X
9 is a graph showing the composition dependency of (comp).

FIG. 15 shows Curie temperature (Tc) and compensation temperature (Tc) of Gd _X Co _1-X
9 is a graph showing the composition dependency of (comp).

FIG. 16 is an explanatory diagram showing an example of land and groove shapes formed on the substrate of the magneto-optical disk of FIG. 1;

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

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

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

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

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

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

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

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

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

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

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

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

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

FIG. 30 shows a second embodiment of the present invention, and 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 Protective layer 6 Overcoat layer 9 Recording medium layer 10 Adhesive layer 20 Heat dissipation layer

──────────────────────────────────────────────────続 き Continued on the front page (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 Sharp Corporation (56) References JP-A-5-205336 (JP, A) JP-A-4-13253 (JP, A) JP-A-1-213842 (JP, A) JP-A-1-189039 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 11/10 506

Claims (2)

(57) [Claims] An in-plane magnetic anisotropy with in-plane magnetic anisotropy is predominant at room temperature on a groove-side surface of a transparent substrate in which a groove for guiding a light beam is formed on one surface. A readout layer that shifts to perpendicular magnetization in which perpendicular magnetic anisotropy is dominant, and a recording layer for recording information are formed in this order, and a readout layer and a recording layer on a groove, and a readout on a land between the grooves. as is the layer and the recording layer are substantially separated vertically, the depth of the groove is set, playback
In the readout layer, the temperature is increased by a light beam.
Area near the center smaller than the spot diameter of the light beam
A magneto-optical storage element characterized in that only the region shows the polar Kerr effect . 2. The magneto-optical storage element according to claim 1, wherein the depth of the groove is 130 to 280 nm.