JPH05290430A - Magneto-optical recording method and magneto-optical recording medium and device to be used therein - Google Patents

Abstract

PURPOSE:To improve reproduced output without changing the recording characteristics of the magneto-optical recording medium. CONSTITUTION:A reproducing layer 5 which can transfer the information recorded on an information storage layer 3 and exhibits the higher magneto- optical effect than the magneto-optical effect of the information storage layer 3 is provided. A reproduction control layer 6 is provided between this reproducing layer 5 and the information storage layer 3. The reproducing layer 5 and the information storage layer 3 are magnetically coupled at the reproduction temp. The reproducing layer 5 and the information storage layer 3 are magnetically shut off at the recording temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention records information by irradiating a recording medium having an information storage layer with light to raise its temperature, thereby changing the magnetization state of the information storage layer to record information. The present invention relates to a magneto-optical recording method for irradiating a medium with light to reproduce information recorded in the information storage layer by utilizing a magneto-optical effect, and a magneto-optical recording medium and apparatus used therefor.

[0002]

2. Description of the Related Art A conventional general magneto-optical recording medium has, for example, a sectional structure shown in FIG. In this magneto-optical recording medium, a dielectric layer 52 (thickness: about 90 nm) made of silicon nitride (SiN _x ) and TbFeCo are formed on a transparent substrate 51 made of glass or the like having a guide groove for tracking.
An information storage layer 53 (having a thickness of about 100 nm) and the like, and a protective layer 54 (having a thickness of about 200 nm) made of silicon nitride and the like are sequentially laminated. The dielectric layer 52 is the substrate 5
The laser light incident from the 1 side is multiply reflected inside,
It serves to increase the rotation angle (Kerr rotation angle) of the polarization plane of the reflected light generated in the information storage layer 53. The protective layer 54 functions to protect the information storage layer 53 from corrosion such as oxidation.

The coercive force of the information storage layer 53 has a temperature characteristic shown in FIG. That is, it becomes large at room temperature TR, becomes infinite at compensation temperature Tcomp, and becomes small near Curie temperature Tc.

The principle of recording / reproducing information on / from this magneto-optical recording medium is as follows.

First, an external magnetic field is applied to this recording medium,
The magnetization of the information storage layer 53 is aligned in one direction. And
When recording information, the recording medium is irradiated with a pulsed laser beam while applying a recording magnetic field Hrec having a magnitude shown in FIG. 14 (opposite direction to the external magnetic field). The temperature of the recording medium at that location rises due to the irradiation of the laser beam, and
When the recording temperature Tw shown in FIG.
The coercive force of 3 is smaller than the recording magnetic field Hrec. Therefore, the magnetization of the information storage layer 53 is inverted in the direction of the recording magnetic field Hrec to form a recording magnetic domain.

When erasing the information thus recorded, the external magnetic field is reversed and the recording medium is continuously irradiated with laser light.

When reproducing information, the recording magnetic domain formed as described above is irradiated with laser light having a lower power than during recording and erasing, and the Kerr rotation angle of the polarization plane of the reflected light is detected. .. The Kerr rotation angle differs depending on the presence or absence of the recording magnetic domain, the shape, or the size, and the information is reproduced based on this.

The above-mentioned magneto-optical recording medium cannot be overwritten. For this reason, conventionally, an overwritable magneto-optical recording medium having, for example, a sectional structure shown in FIG. 15 has been proposed. In this magneto-optical recording medium, a dielectric layer 5 made of silicon nitride or the like is provided on a transparent substrate 51 such as glass provided with a guide groove for tracking.
2 (thickness about 90 nm) is formed and TbFeC is formed on it.
a memory layer 53a (thickness: about 40 nm) made of o and T
The recording layer 53b made of bDyFeCo (thickness of about 100 n
m) are laminated and formed. Two layers, the memory layer 53a and the recording layer 53b, become the information storage layer 53. Recording layer 53
A protective layer 54 (thickness of about 200 n
m) is formed.

Since the film thickness of the memory layer 53a is about 40 nm, the reproducing laser light emitted through the substrate 51 reaches the recording layer 53b only slightly. Therefore, the polarization plane of the reflected light rotates mainly reflecting the magnetization state of the memory layer 53a. The recording layer 53b is magnetically exchange-coupled with the memory layer 53a for storing information, and is used for performing single beam overwrite.

Next, the principle of overwriting of this magneto-optical recording medium will be described with reference to FIGS. Figure 1
6 is a graph showing the coercive force versus temperature characteristics of the memory layer 53a and the recording layer 53b, and FIG. 17 is an explanatory diagram showing changes in the magnetization of the memory layer 53a and the recording layer 53b at the time of overwriting.

As shown in FIG. 16, the Curie temperature Tcm of the memory layer 53a is lower than the Curie temperature Tcr of the recording layer 53b, and at room temperature TR, the coercive force of the recording layer 53b is smaller than that of the memory layer 53a. I am doing it. Therefore, if the initialization magnetic field Hini having the magnitude shown in FIG. 16 is applied by a permanent magnet or the like at room temperature TR, as shown in FIG.
As shown in (b), the magnetization of the recording layer 53b can be aligned in one direction without changing the magnetization direction (information) of the memory layer 53a.

This recording medium in which the magnetization direction of the recording layer 53b is aligned by the initializing magnetic field Hini is irradiated with a laser beam having a relatively small intensity (low level) to raise the temperature to near the Curie temperature Tcm of the memory layer 53a. And the memory layer 5
The coercive force of 3a disappears completely or almost. At this time, since the Curie temperature Tcr of the recording layer 53b is higher than the Curie temperature Tcm of the memory layer 53a, the magnetization direction of the recording layer 53b does not change (FIG. 17C).

When the temperature of the recording medium is lowered after the irradiation of the laser beam is finished, the magnetization of the memory layer 53a appears, and the magnetization at this time has the same direction as the magnetization of the recording layer 53b due to the exchange coupling force (FIG. 17 ( e)). This state does not change even if the temperature further decreases to room temperature TR. This is erasure.

On the other hand, a relatively high intensity (high level) laser beam is applied to this recording medium while applying a recording magnetic field Hrec of the magnitude shown in FIG. 16, and the temperature rises to near the Curie temperature Tcr of the recording layer 53b. Then, the memory layer 53a
Completely disappears, and the coercive force of the recording layer 53b also completely or almost completely disappears (FIG. 17 (d)).

When the temperature of the recording medium is lowered a little after the irradiation of the laser beam is finished, the magnetization of the recording layer 53b first appears. At this time, the magnetization direction of the recording layer 53b is reversed and becomes the same as the recording magnetic field Hrec. (FIG. 17 (f)). When the temperature further decreases and becomes lower than the Curie temperature Tcm of the memory layer 53a, the magnetization of the memory layer 53a appears, but the direction of the magnetization at this time is the direction of the magnetization of the recording layer 32 (recording magnetic field Hrec due to the exchange coupling force). (Same direction as) (FIG. 17 (g)). This state does not change even at room temperature TR. This is a record.

As described above, according to the magneto-optical recording medium shown in FIG. 15, the direction of magnetization (information) of the memory layer 53a is arbitrarily adjusted by modulating the laser light intensity between the high level and the low level. Can be changed. That is, single beam overwrite is possible. This method is disclosed, for example, in JP-A-62-175948.

[0017]

In the conventional overwritable magneto-optical recording medium shown in FIG. 15, the memory layer 5 is used.
Since the Curie temperature Tcm of 3a is low and the film thickness is thin, the Kerr rotation angle of the reflected light is small, and the S / N that can be satisfied during reproduction
There is a problem that can not be obtained.

Therefore, in order to increase the S / N at the time of reproduction, it has been proposed to add a reproduction layer (transfer layer) capable of obtaining a large Kerr rotation angle to this conventional magneto-optical recording medium (for example, (See JP-A-63-64651). However, in that case, if the film thickness of the reproducing layer is increased, there is a problem that overwrite cannot be performed properly due to the influence of the magnetization of the reproducing layer.

Therefore, an object of the present invention is to provide a magneto-optical recording method capable of obtaining a larger S / N than the conventional one at the time of reproduction without deteriorating the recording characteristics of information, and a magneto-optical recording medium and an apparatus used therefor. To provide.

[0020]

[Means for Solving the Problems]

(1) In the magneto-optical recording method of the present invention, by irradiating a recording medium having an information storage layer with light to raise its temperature, the magnetization state of the information storage layer is changed to record information. In a magneto-optical recording method of irradiating a recording medium with light to reproduce the information recorded in the information storage layer by utilizing a magneto-optical effect, it is possible to transfer the information recorded in the information storage layer. And a reproducing layer that exhibits a larger magneto-optical effect than the information storage layer is provided, and the reproducing layer and the information storage layer are magnetically coupled at a reproducing temperature,
At the recording temperature, the reproducing layer and the information storage layer are magnetically cut off from each other.

The magnetic coupling and interruption of the reproduction layer and the information storage layer are preferably performed by a reproduction control layer composed of a magnetic layer having a Curie point lower than the recording temperature and higher than the reproduction temperature.

Further, it is preferable to irradiate light having an intensity which does not change the magnetization state of the information storage layer while changing the magnetization state of the reproduction layer during reproduction. This improves the resolution during reproduction and enables high density reading.

(2) In the magneto-optical recording medium of the present invention, an information storage layer that records information by changing the magnetization state by irradiating light to raise the temperature, and information recorded in the information storage layer. And a reproducing layer capable of transferring a magnetic field and exhibiting a larger magneto-optical effect than the information storing layer, magnetically couple the reproducing layer and the information storing layer at the reproducing temperature, and form the reproducing layer at the recording temperature. A reproduction control layer for magnetically blocking the information storage layer is provided.

The thickness of the reproducing layer is 15 nm or more, 60
nm or less, preferably 20 nm or more, 50 nm
The following is more preferable. If it is less than 15 nm,
Since light reaches the reproduction control layer and the information storage layer through the reproduction layer, the light does not sufficiently interact with the reproduction layer, and as a result, a sufficient Kerr rotation angle cannot be obtained.
If it exceeds 60 nm, the magnetic domain shape of the information storage layer may be disturbed by the magnetization of the reproduction layer. If it is 20 nm or more, a sufficient Kerr rotation angle is obtained, and if it is 50 nm or less, it does not affect the magnetic domain shape of the information storage layer.

The reproducing layer is sufficient if it exhibits a larger magneto-optical effect than the information storage layer. For example, there are alloys of rare earth metals such as Gd, Tb, Nd, Dy, Pr and Sm and transition metals such as Fe, Co, Ni and Cr.
In order to improve the corrosion resistance, Nb, Ti,
You may add Pt, Cr, Ta, Ni, etc. Also, P
A superlattice film such as t / Co or Pd / Co can also be used, and in these films, the light wavelength is 200 nm to 600 n.
In the range of m, the Kerr rotation angle is particularly large, and good reproduction characteristics can be obtained.

The coercive force and the magnetization of the reproducing layer are preferably small enough to faithfully reflect the magnetic domain shape of the information storage layer and not disturb the magnetic domain shape. Magnetic materials having such characteristics include Gd-Fe-Co-based materials and Gd-Tb-based materials.
-Fe-Co system, Gd-Dy-Fe-Co system, Nd-D
y-Fe-Co type, Nd-Tb-Fe-Co type, P
There are t / Co multilayer films and the like.

The thickness of the reproduction control layer is 2 nm or more and 2
It is preferably 0 nm or less, and 5 nm or more and 10 nm
The following is more preferable. If it is less than 2 nm, the reproducing layer cannot be accurately controlled, and it is too thin to raise the effective Curie temperature. When it exceeds 20 nm, the recording sensitivity is deteriorated due to being too thick, and the information transfer performance of the information storage layer is deteriorated. Furthermore, there is a risk of disturbing the magnetic domain shape of the memory layer. Within the range of 5 to 10 nm, there are no such difficulties, and switching between magnetic coupling and interruption is smoothly performed.

The reproduction control layer is preferably formed of a magnetic layer having a Curie temperature lower than the recording temperature and higher than the reproduction temperature. Examples of such a magnetic layer include alloys of rare earth metals such as Gd, Tb, Nd, Dy, Pr, and Sm and transition metals such as Fe, Co, Ni, and Cr. In order to improve the corrosion resistance, Nb, T
You may add i, Pt, Cr, Ta, Ni, etc.

The information storage layer includes a recording layer having a small coercive force at room temperature which is initialized by an initializing magnetic field, and a memory layer having a large coercive force at room temperature for storing information. It is preferably provided in contact with the reproduction control layer.

When the memory layer and the storage layer are provided, a magnetic layer for aligning and initializing the magnetization of the recording layer in one direction can be provided together. In this case, it is not necessary to separately provide magnetic field applying means for aligning and magnetizing the recording layer in one direction.

The initializing magnetic layer magnetically couples the initializing layer whose magnetization is not reversed during the recording operation, the initializing layer and the recording layer at the reproducing temperature, and the initializing layer at the recording temperature. It is preferable to include an initialization control layer that magnetically shields the storage layer from the recording layer.

The initialization control layer may have the same composition and thickness as the reproduction control layer. As the initialization layer, a magnetic film (for example, TbCo) capable of generating a magnetic field equivalent to the initialization magnetic field applied by the external magnet is sufficient.

The information storage layer (including the memory layer and the recording layer) is preferably formed of the same alloy of rare earth metal and transition metal as the reproducing layer.

(3) The magneto-optical recording apparatus of the present invention is characterized by comprising the magneto-optical recording medium of the above (2).

In this magneto-optical recording apparatus, at the time of reproduction, the magnetization state of the reproducing layer of the magneto-optical recording medium is changed, and the magneto-optical recording medium is irradiated with light having an intensity that does not change the magnetization state of the information storage layer. It is preferable to have means. This improves the resolution during reproduction and enables high density reading.

[0036]

In the magneto-optical recording method, the magneto-optical recording medium and the device of the present invention, the reproducing layer and the information storage layer are magnetically coupled at the time of reproduction, so that the reproducing layer exhibiting a large magneto-optical effect is the information storage layer. Reflects the magnetization state of. Therefore, a high level reproduction signal can be obtained by utilizing the large magneto-optical effect of the reproduction layer.

At the time of recording, since the reproducing layer and the information storage layer are magnetically cut off, the reproducing layer does not affect the recording operation. Therefore, the same recording characteristics as when there is no reproducing layer can be obtained.

Therefore, it is possible to reproduce information with a higher S / N than before while maintaining the same recording characteristics as before.

[0039]

Embodiments of the present invention will be described below with reference to FIGS.

[Opto-Magnetic Recording Medium] (Structure of First Embodiment) FIG. 1 is a sectional view showing the structure of the first embodiment of the magneto-optical recording medium of the present invention.

In this magneto-optical recording medium, a dielectric layer 2 made of SiN _x is formed on a transparent substrate 1 (having a diameter of 5.25 inches) made of glass or the like and provided with a guide groove for tracking.
(Thickness 70 nm) is formed, on which a reproducing layer 5 (thickness 30 nm) made of a transition metal-rich Gd ₁₈ Tb ₄ Fe ₆₀ Co ₁₈ amorphous alloy thin film and a Dy ₂₅ Fe ₇₅ amorphous alloy are formed. A reproduction control layer 6 (thickness: 5 nm) made of a thin film is laminated and formed. A memory layer 3a (thickness: 20 nm) made of a transition metal-rich Tb ₂₁ Fe ₆₁ Co ₁₈ amorphous alloy thin film and a rare earth-rich Tb ₁₆ Dy ₁₆ are formed on the reproduction control layer 6.
An information storage layer 3 including a recording layer 3b (thickness 70 nm) including a Fe ₆₀ Co ₈ amorphous alloy thin film is laminated and formed. The reproduction layer 5, the reproduction control layer 6, the memory layer 3a, and the recording layer 3b thus stacked are magnetically exchange-coupled to each other. A protective layer 4 (thickness: 100 nm) made of SiN _x is further formed on the recording layer 3b.

(Manufacturing Method of First Embodiment) The magneto-optical recording medium having the above-mentioned structure is manufactured as follows.

First, the transparent substrate 1 was loaded into a high frequency magnetron sputtering apparatus, and after evacuating to 0.1 mPa or less, a mixed gas of Ar and N ₂ was introduced, and Si was used as a target at a gas pressure of 1.3 Pa. Reactive sputtering was performed to form SiN _x (thickness 70 nm) as the dielectric layer 2.

After that, sputtering was performed using a GdTbFeCo alloy target at an Ar gas pressure of 0.7 Pa,
A transition metal rich Gd ₁₈ Tb ₄ Fe ₆₀ C is used as the reproducing layer 5.
An o ₁₈ amorphous alloy thin film (thickness 30 nm) was formed on the dielectric layer 2.

Next, a DyFe alloy target was used to perform sputtering at an Ar gas pressure of 0.7 Pa, and a Dy ₂₅ Fe ₇₅ amorphous alloy thin film (thickness: 5 n
m) was formed on the reproduction layer 5.

Next, using a TbFeCo alloy target, sputtering is also performed at an Ar gas pressure of 0.7 Pa,
Tb ₂₁ Fe ₆₁ Co rich in transition metal is used as the memory layer 3a.
_{An 18} amorphous alloy thin film (thickness: 20 nm) was formed on the reproduction control layer 6.

Next, a TbDyFeCo alloy target was used to sputter at an Ar gas pressure of 0.7 Pa, and the rare earth-rich Tb ₁₆ Dy ₁₆ Fe ₆₀ Co was used as the recording layer 3b.
_{8 An} amorphous alloy thin film (thickness 70 nm) was formed on the memory layer 3a.

Finally, the inside of the apparatus was again evacuated to 0.1 mPa or less, a mixed gas of Ar gas and N ₂ gas was introduced, and reactive sputtering was performed with Si as a target at a gas pressure of 1.3 Pa. As protective layer 4, SiN _x (thickness 10
0 nm) was formed.

(Test Results of First Example) With respect to the magneto-optical recording medium having the above-mentioned structure, the magnetic characteristics versus temperature characteristics of the memory layer 3a and the recording layer 3b were measured, and the characteristics shown in FIG. 2 were obtained. From FIG. 2, at room temperature TR (25 ° C.), the coercive force of the recording layer 3b is 3 kOe, and the coercive force of the memory layer 3a is 2.
It was 0 kOe. Also, the Curie temperature Tcp of the reproduction layer 5
Is 450 ° C. and the Curie temperature Tcc of the reproduction control layer 6 is 75
Was ° C.

When the recording temperature and the erasing temperature of the recording medium were examined by overwriting with the recording magnetic field = 0.4 kOe and the recording laser light intensity (recording power) = 10 mW, the recording temperature was about 250 ° C. and the erasing temperature was It was about 125 ° C. Therefore, during recording and erasing, the magnetization of the reproduction control layer 6 disappears and the magnetization of the reproduction layer 5 remains. Therefore, the reproducing layer 5 and the memory layer 3a storing information are magnetically cut off, and the reproducing layer 5 does not affect the overwrite operation.

On the other hand, if the intensity of the reproducing laser beam (reproducing power) is adjusted so that the reproducing temperature of the recording medium is lower than the Curie temperature Tcc (75 ° C.) of the reproducing control layer 6, the reproducing operation is performed. Sometimes the reproducing layer 5 and the memory layer 3a are magnetically coupled. Therefore, a high level reproduction signal can be obtained by utilizing the large magneto-optical effect of the reproduction layer 5.

Next, the magneto-optical recording medium was used to perform overwriting, and the recording / reproducing characteristics were examined. The initialization magnetic field Hini was set to 5 kOe and was applied by a Sm-Co based permanent magnet. Recording mark length is 5μm, playback power is 1.2
It was set to mW.

FIG. 3 shows the recording / reproducing characteristics of this magneto-optical recording medium during overwriting. The conventional magneto-optical recording medium is also shown. The conventional magneto-optical recording medium used here is the same as the magneto-optical recording medium of the first embodiment except for the reproducing layer 5 and the reproducing control layer 6.

As shown in FIG. 3, in the magneto-optical recording medium of the present invention, when the recording power is 10 mW, C of 62 dB is obtained.
/ N is obtained. On the other hand, the conventional magneto-optical recording medium achieves only 59 dB. Therefore, it is understood that the magneto-optical recording medium of the present invention can obtain a C / N higher than the conventional one by 3 dB. This corresponds to the fact that the Kerr rotation angle is effectively improved to about 1.4 times.

As can be seen from FIG. 3, the overwrite characteristic has a sensitivity slightly lower than that of the conventional one due to the presence of the reproduction layer 5 and the reproduction control layer 6 (a larger recording power is required). Except that it is the same as the conventional one.

An overwrite repetition test was conducted using the magneto-optical recording medium of the first embodiment. The result is shown in FIG. As can be seen from FIG. 4, there is almost no change in C / N even after overwriting 10 ⁷ times. This is also the same as the conventional one.

Further, regarding the magneto-optical recording medium of the first embodiment, the thickness of the reproducing layer 5 was changed and the change of C / N was examined. The result is shown in FIG. The thickness of the reproducing layer 5 is 15 nm
When it is less than the above, the addition effect of the reproducing layer 5 is small and a sufficiently large Kerr rotation angle cannot be obtained, so that the C / N is not large. When the thickness of the reproducing layer 5 exceeds 60 nm, C / N
However, according to the microscopic observation, it was found that this was due to the magnetic domain of the memory layer 3a being disturbed by the reproducing layer 5. Therefore, the film thickness of the reproducing layer 5 is
The range of 15 nm to 60 nm is preferable, and 20 nm to 50 nm
The range of nm is more preferable.

FIG. 5 also shows the C / N change of a magneto-optical recording medium manufactured in the same manner as in the first embodiment except for the reproduction control layer 6. Comparing the two, in the case where the reproduction control layer 6 is not provided, the disorder of the shape of the magnetic domain of the memory layer 3a due to the addition of the reproduction layer 5 appears remarkably. It can be seen that is hardly improved.

(Structure of Second Embodiment) FIG. 6 is a cross-sectional view of the essential parts showing the structure of the second embodiment of the magneto-optical recording medium of the present invention. The second embodiment is different from the first embodiment in that the information storage layer 3 is composed of one layer.

The magneto-optical recording medium of the second embodiment is a transparent substrate 1 made of glass or the like provided with a guide groove for tracking.
(Diameter 5.25 inches), a dielectric layer 2 made of SiN _x (thickness 70 nm), and a transition metal rich Gd ₁₈ T.
A reproduction layer 5 (thickness 30 nm) made of a b ₄ Fe ₆₀ Co ₁₈ amorphous alloy thin film and a reproduction control layer 6 (thickness 5 nm) made of a Dy ₂₅ Fe ₇₅ amorphous alloy thin film are formed. These configurations are the same as those in the first embodiment.

On the reproduction control layer 6, a rare earth rich T
An information storage layer 3 made of a b ₂₄ Fe ₆₈ Co ₈ amorphous alloy thin film (thickness: 80 nm) is formed. The reproduction layer 5, the reproduction control layer 6, and the information storage layer 3 thus laminated are magnetically exchange-coupled with each other.

A protective layer 5 (thickness: 100 nm) made of SiN _x is formed on the information storage layer 3 as in the first embodiment.

(Manufacturing Method of Second Embodiment) The magneto-optical recording medium of the second embodiment having the above structure is manufactured as follows.

First, the transparent substrate 1 was loaded into a high frequency magnetron sputtering apparatus, and the SiN _x thin film (thickness 70 nm) to be the dielectric layer 2 and the reproducing layer 5 were formed in the same manner as in the first embodiment.
A transition metal-rich Gd ₁₈ Tb ₄ Fe ₆₀ Co ₁₈ amorphous alloy thin film (thickness 30 nm) and a Dy ₂₅ Fe ₇₅ amorphous alloy thin film (thickness 5 nm) to be the reproduction control layer 6 are sequentially stacked. Formed.

Next, sputtering was performed using a TbFeCo alloy target at an Ar gas pressure of 0.7 Pa, and rare earth-rich Tb as an information storage layer 3 was formed on the reproduction control layer 6.
_{A 24} Fe ₆₈ Co ₈ amorphous alloy thin film (thickness: 80 nm) was formed.

Finally, a SiN _x thin film (thickness 100 nm) to be the protective layer 5 was formed in the same manner as in the first embodiment.

(Test Results of Second Example) With respect to the magneto-optical recording medium of the second example, the coercive force versus temperature characteristic of each layer was measured. As a result, the compensation temperature of the information storage layer 3 was 80 ° C and its Curie temperature was 220 ° C. Since the reproduction layer 5 and the reproduction control layer 6 have the same structure as that of the first embodiment, the Curie temperatures thereof are the same as those of the first embodiment and are 450 ° C. and 75 ° C., respectively.

Further, as in the first embodiment, the recording magnetic field =
Information was recorded and erased at 0.4 kOe and a recording power of 10 mW, and the recording temperature and the erasing temperature were examined. As a result, both were about 180 ° C. Therefore, during recording and erasing, the magnetization of the reproduction control layer 6 disappears and the magnetization of the reproduction layer 5 remains. Therefore, the reproducing layer 5 and the information storage layer 3 are magnetically shielded from each other, and the reproducing layer 5 does not affect the recording and erasing operations.

On the other hand, if the reproducing power is adjusted so that the temperature during reproducing becomes lower than the Curie temperature Tcc (75 ° C.) of the reproducing controlling layer 6, the reproducing layer 5 and the information storage layer 3 during reproducing. And are magnetically coupled. Therefore, a high level reproduction signal can be obtained by utilizing the large magneto-optical effect of the reproduction layer 5.

Next, the recording / reproducing characteristics were examined using the magneto-optical recording medium of the second embodiment. Recording mark length is 5μ
m, and the reproducing power was 1 mW. Since this magneto-optical recording medium cannot be overwritten, the laser beam of 10 mW power was continuously applied to the medium at the time of erasing by reversing the direction of the recording magnetic field.

FIG. 7 shows the recording / reproducing characteristics. The conventional magneto-optical recording medium is also shown. The conventional magneto-optical recording medium used here is the same as the magneto-optical recording medium of the second embodiment except for the reproducing layer 5 and the reproducing control layer 6.

As shown in FIG. 7, in the magneto-optical recording medium of the present invention, when the recording power is 10 mW, C of 62 dB is obtained.
/ N is obtained. On the other hand, in the conventional magneto-optical recording medium, only 60 dB is obtained. Therefore, it is understood that the magneto-optical recording medium of the present invention can obtain C / N higher by 2 dB than the conventional one. This corresponds to an increase in the Kerr rotation angle of about 1.2 times.

As can be seen from FIG. 7, the recording / erasing characteristics have the sensitivity lowered to some extent as compared with the conventional one due to the presence of the reproducing layer 5 and the reproducing control layer 6 (the larger recording power is It is the same as the conventional one except that it is necessary).

A recording / erasing repetition test was conducted using the magneto-optical recording medium of the second embodiment. The result is shown in FIG. As can be seen from FIG. 8, there is almost no change in C / N even after 10 ⁷ recording / erasing operations. This is also the same as the conventional one.

(Third Embodiment) FIG. 9 is a cross-sectional view of the essential parts showing the structure of the third embodiment of the magneto-optical recording medium of the present invention.
In the third embodiment, an initialization layer 7 and an initialization control layer 8 are provided between the recording layer 3b and the protective layer 4 of the first embodiment. In this embodiment, the recording layer 3 is formed by the initialization layer 7.
Since the initialization magnetic field is applied to b, there is an advantage that it is not necessary to provide an initialization magnet outside.

In the magneto-optical recording medium of the third embodiment, the initialization control layer 8 formed on the recording layer 3b is the reproduction control layer 6
Performs the same action as. That is, at the recording temperature and the erasing temperature, the magnetization of the initialization control layer 8 disappears and the recording layer 3b and the initialization layer 7 are magnetically cut off from each other. At the reproducing temperature, the magnetization of the initialization control layer 8 remains, the recording layer 3b and the initialization layer 7 are magnetically coupled, and the magnetization direction of the recording layer 3b becomes the same as that of the initialization layer 7. That is, it is initialized. Therefore, the initialization control layer 8 is the same magnetic layer as the reproduction control layer 6, for example, the same D as the reproduction control layer 6 of the first embodiment.
It can be formed from a y ₂₅ Fe ₇₅ amorphous alloy thin film (thickness 5 nm).

Since the initialization layer 7 formed on the initialization control layer 8 provides a magnetic field for initializing the recording layer 3b, it has a large coercive force at room temperature TR and a high Curie temperature. Can be arbitrarily formed by a magnetic layer whose magnetization direction does not reverse through the recording / erasing operation. For example, it can be formed of a TbFe amorphous alloy thin film.

The manufacturing method of the third embodiment is almost the same as that of the first embodiment, and after the recording layer 3b is formed, the initialization control layer 8 and the initialization layer 7 are laminated and formed, and then the protective layer is formed. Four
Should be formed. The initialization control layer 8 may be formed by the same method as the reproduction control layer 6, and the initialization layer 7 may be formed by the same method.

[Opto-Magnetic Recording Method] Using the magneto-optical recording medium of the first embodiment, information was recorded by changing the recording power with a recording mark length of 0.4 μm. Also, the reproduction power is 1.0
Set in the range of up to 4.0 mW and play the information,
N was measured. The result is shown in FIG.

As can be seen from FIG. 10, the maximum C / N value is about 35 dB when the reproduction is performed at the same reproduction power of 1.2 mW as the test of the first embodiment. The obtained value is very low as compared with the value (62 dB) obtained in the above test. This is because the recording mark length is shorter than the spot diameter of the reproducing laser beam, so that the adjacent recording marks cannot be sufficiently decomposed.

However, as can be seen from FIG. 10, when the reproducing power was increased from 1.2 mW, the C / N sharply increased around 2.5 mW and reached the maximum at 3.5 mW. On the other hand, if you increase the playback power to 4.0 mW,
On the contrary, the C / N is decreasing. Therefore, in this case, if the reproducing power is set in the range of approximately 2.5 to 3.5 mW, even a recording magnetic domain having a recording mark length of 0.4 μm can be sufficiently decomposed and reproduced. This phenomenon is based on the following reasons.

When the magneto-optical recording medium of the first embodiment is irradiated with laser light with a reproduction power within the above range, the magnetization of the reproduction layer 5 is in the same direction as the magnetization of the memory layer 3a in front of the laser light spot. However, behind the laser beam spot, the temperature of the reproducing layer 5 rises due to heating and the coercive force of the reproducing layer 5 decreases, and the recording magnetic field Hrec causes the direction of magnetization of the reproducing layer 5 to be the recording magnetic field Hrec. Aligned in the same direction. That is, in the rear of the laser beam spot, the magnetization direction of the reproducing layer 5 is the same regardless of the presence or absence of the recording mark. Therefore, it is equivalent to no light hitting the rear of the reproduction spot, in other words, equivalent to irradiating the laser light of a small spot only in front of the laser light spot. In this way, the resolution of the laser beam is increased, resulting in a high C / N even with a recording mark as small as 0.4 μ.
It is thought to be reproducible in.

The magnetization of the reproduction layer 5 aligned in the direction of the recording magnetic field Hrec during reproduction is affected by the exchange control of the reproduction control layer 6, the memory layer 3a and the recording layer 3b as the temperature decreases thereafter. Receive and return.

The reproducing power at this time is the recording magnetic field H
The magnetization direction of the reproducing layer 5 changes depending on rec, but the magnetization direction of the memory layer 3a for storing information is set to a range in which it does not change. Further, it is sufficient that the magnetization direction of the reproducing layer 5 is aligned in one direction by the recording magnetic field Hrec, and the temperature of the reproducing layer 5 does not have to rise to near the Curie temperature.

FIG. 11 shows changes in C / N with respect to the recording mark length of the magneto-optical recording medium of the first embodiment. The conventional magneto-optical recording medium used in the test of the first embodiment is also shown. The recording power was 8 mW and the reproducing power was 3.5 mW. It can be seen from FIG. 11 that the magneto-optical recording medium of the present invention can realize a resolution about twice that of the conventional one.

The magneto-optical recording method described here is the same as the above second method.
It can also be applied to the magneto-optical recording medium of the embodiment.
In the magneto-optical recording medium of the second embodiment, the reproducing power changes the magnetization direction of the reproducing layer 5 depending on the recording magnetic field Hrec.
The magnetization direction of the information storage layer 3 is set within a range that does not change.

[Opto-Magnetic Recording Device] FIG. 12 is a block diagram showing an embodiment of the magneto-optical recording device of the present invention.

This magneto-optical recording device comprises the magneto-optical recording medium 12 of the first embodiment described above. The magneto-optical recording medium 12 is rotationally driven by a driving device (not shown). In the vicinity of the magneto-optical recording medium 12, there are provided an initialization magnet 10 for applying an initialization magnetic field for preliminarily aligning the magnetization of the recording layer 3b in one direction before recording, and a recording magnet 11 for applying the recording magnetic field. ing.

The recording control system 17 controls the laser light source drive circuit 16 at the time of recording, and modulates the power of the laser light between a high level and a low level according to the recording information. The modulated laser light emitted from the laser light source 15 is introduced into the beam splitter 14 by the lens 13, and further the lens 1
The light is focused on the magneto-optical recording medium 12 by 3 to form a recording magnetic domain there.

The laser light emitted from the laser light source 15 during reproduction is condensed on the magneto-optical recording medium 12 via the lens 13, the beam splitter 14 and the lens 13.
The reflected light is reflected by the lens 13 and the beam splitter 14.
Is introduced into the reproduction optical system 18, converted into an electric signal by the reproduction system 19, and then sent to the reproduction power control system 20.

The reproduction power control system 20 controls the laser light source drive circuit 16 during reproduction, and sets the reproduction power to a power capable of high resolution reproduction (for example, about 3 mW). Preferably, the reproduction power is controlled so that the reproduction output becomes maximum when recording is performed with the shortest recording mark length.

This device is capable of performing single beam overwrite in the same manner as described in the section of the prior art with reference to FIGS.

In this apparatus, if the magneto-optical recording medium of the third embodiment is used as the magneto-optical recording medium 12, the initialization magnet 10 can be omitted.

[0094]

According to the magneto-optical recording method, the magneto-optical recording medium and the apparatus thereof of the present invention, a larger S / N than that of the conventional one can be obtained at the time of reproduction without deteriorating the recording characteristics of information.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a first embodiment of a magneto-optical recording medium of the present invention.

FIG. 2 is a graph showing the temperature dependence of the coercive force of the magneto-optical recording medium of the first embodiment.

FIG. 3 is a graph showing the recording power dependence of C / N of the magneto-optical recording medium of the first example.

FIG. 4 is a graph showing changes in C / N with respect to the number of overwrites of the magneto-optical recording medium of the first embodiment.

FIG. 5 is a graph showing the dependence of C / N on the reproducing layer thickness of the magneto-optical recording medium of the first example.

FIG. 6 is a cross-sectional view of essential parts of a second embodiment of the magneto-optical recording medium of the present invention.

FIG. 7 is a graph showing the recording power dependence of C / N of the magneto-optical recording medium of the second example.

FIG. 8 is a graph showing changes in C / N with respect to the number of recording / erasing of the magneto-optical recording medium of the second embodiment.

FIG. 9 is a cross-sectional view of essential parts of a third embodiment of the magneto-optical recording medium of the present invention.

FIG. 10 shows C / C for the magneto-optical recording medium of the first embodiment.
7 is a graph showing a change in recording power dependency of N with respect to reproduction power.

FIG. 11 shows C / C for the magneto-optical recording medium of the first embodiment.
7 is a graph showing the dependency of N on the recording mark length.

FIG. 12 is a schematic block diagram showing an embodiment of a magneto-optical recording apparatus of the present invention.

FIG. 13 is a cross-sectional view of essential parts showing a general structure of a conventional magneto-optical recording medium.

14 is a graph showing the temperature dependence of the coercive force of the magneto-optical recording medium of FIG.

FIG. 15 is a cross-sectional view of essential parts showing an example of a conventional overwritable magneto-optical recording medium.

16 is a graph showing the temperature dependence of the coercive force of the conventional magneto-optical recording medium of FIG.

FIG. 17 is an explanatory diagram for explaining an overwrite operation of the conventional magneto-optical recording medium of FIG.

[Explanation of symbols]

 1 Transparent Substrate 2 Dielectric Layer 3 Information Storage Layer 3a Memory Layer 3b Recording Layer 4 Protective Layer 5 Reproducing Layer 6 Reproducing Control Layer 7 Initializing Layer 8 Initializing Control Layer 10 Initializing Magnet 11 Recording Magnet 12 Magneto-Optical Recording Medium 13 Lens 14 Beam Splitter 15 Laser Light Source 16 Laser Light Source Driving Circuit 17 Recording Control System 18 Reproducing Optical System 19 Reproducing System 20 Reproducing Power Control System

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Keikichi Ando 1-280, Higashi Koikeku, Kokubunji, Tokyo Metropolitan Research Center, Hitachi, Ltd. (72) Inventor Masahiro Ojima 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory

Claims (12)

[Claims] 1. A recording medium having an information storage layer is irradiated with light to raise its temperature, thereby changing the magnetization state of the information storage layer to record information, and irradiating the recording medium with light. In the magneto-optical recording method for reproducing the information recorded in the information storage layer by utilizing a magneto-optical effect, the information recorded in the information storage layer can be transferred, and more than the information storage layer. Providing a reproducing layer exhibiting a large magneto-optical effect, magnetically coupling the reproducing layer and the information storage layer at a reproducing temperature, and magnetically disconnecting the reproducing layer and the information storage layer at a recording temperature. And a magneto-optical recording method. 2. The reproduction control layer, which is a magnetic layer having a Curie point lower than the recording temperature and higher than the reproduction temperature, magnetically connects and disconnects the reproduction layer and the information storage layer. 1. The magneto-optical recording method described in 1. 3. The magneto-optical recording method according to claim 1, wherein at the time of reproduction, the recording medium is irradiated with light having an intensity that does not change the magnetization state of the information storage layer while changing the magnetization state of the reproduction layer. .. 4. An information storage layer for recording information by irradiating light to raise the temperature to change the magnetization state, and the information recorded in the information storage layer can be transferred, and the information storage. Layer, which exhibits a magneto-optical effect greater than that of the layer, and the reproducing layer and the information storage layer are magnetically coupled at the reproducing temperature, and the reproducing layer and the information storage layer are magnetically cut off at the recording temperature. A reproduction control layer for controlling a magneto-optical recording medium. 5. The thickness of the reproduction layer is 15 nm or more and 60.
The magneto-optical recording medium according to claim 4, which is in the range of nm or less. 6. The thickness of the reproduction control layer is 2 nm or more, 2
The magneto-optical recording medium according to claim 4, which is in a range of 0 nm or less. 7. The magneto-optical recording medium according to claim 4, wherein the reproduction control layer is a magnetic layer having a Curie temperature lower than the recording temperature and higher than the reproduction temperature. 8. The information storage layer includes a recording layer having a small coercive force at room temperature which is initialized by an initializing magnetic field, and a memory layer having a large coercive force at room temperature for storing information. The magneto-optical recording medium according to claim 4, wherein a layer is provided in contact with the reproduction control layer. 9. The magneto-optical recording medium according to claim 8, further comprising a magnetic layer that initializes the magnetization of the recording layer by aligning the magnetization in one direction. 10. The initializing magnetic layer magnetically couples the initializing layer and the recording layer at the reproducing temperature with the initializing layer whose magnetization is not reversed during the recording operation, and at the recording temperature. The magneto-optical recording medium according to claim 9, further comprising an initialization control layer that magnetically blocks the initialization layer and the recording layer. 11. A magneto-optical recording apparatus comprising the magneto-optical recording medium according to claim 4. 12. A means for irradiating the magneto-optical recording medium with light having an intensity that does not change the magnetization state of the information storage layer during reproduction and changes the direction of magnetization of the reproduction layer. The magneto-optical recording device described in.