JPH07262632A - Magneto-optical recording medium and rproducing method for same - Google Patents

Abstract

PURPOSE:To obtain a magnetically super resolution type magneto-optical recording medium producing a super-resolving effect without using a reproducing magnetic field and more effective in attaining stability of magnetic bits over a long-period of time and in reducing the size of a drive as compared with a conventional super-resolving medium and to provide a reproducing method for the magneto-optical recording medium. CONSTITUTION:A reproducing layer 1 consisting of at least rare earth metals and transition metals, a cutting layer 2, a bias layer 3 and a recording layer 4 are disposed on a substrate as magnetic layers exchange-coupled to one another. When the magnetic layers are heated with reproducing light, the exchange coupling force between the recording layer 4 and the reproducing layer 1 is reduced or eliminated and the sub-lattice magnetization of the reproducing layer 1 is reversed in the high temp. part to the direction at low temp.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magneto-optical recording medium.

[0002]

2. Description of the Related Art Magneto-optical recording media have been put to practical use as high-density, low-cost rewritable information recording media. Particularly, a medium using a recording layer of an amorphous alloy of a rare earth metal and a transition metal shows very excellent characteristics.

The magneto-optical disk is a recording medium having a very large capacity, and it is desired to further increase the capacity as the amount of information in society increases. If the recording density of the optical disk is normal,
It depends on the size of the spot of the reproduction light. The size of the spot can be made smaller as the wavelength of the laser becomes shorter. Therefore, a study on making the wavelength of the laser shorter is under way, but it is very difficult.

On the other hand, attempts of so-called super-resolution technology have been made in recent years to obtain various resolutions higher than those determined by the wavelength of laser by various means. One of them is a magnetically induced super resolution, which uses a magneto-optical disk and exchange coupling force between multilayer films.
(Hereinafter referred to as MSR) has been reported. One form of this system uses a medium composed of three layers, which are exchange-coupled with each other, a reproducing layer having a small coercive force, a cutting layer having a low Curie temperature, and a recording layer having a high Curie temperature and a high coercive force.

When heated by reproducing light while applying a reproducing magnetic field, exchange coupling is broken at a high temperature portion of the medium. Since the reproducing layer has a small coercive force by itself, the magnetization is uniformly oriented in the reproducing magnetic field in the high temperature portion to erase the recorded bit. As a result, only the low temperature portion is reproduced, and the reproduction range is narrowed as a result. Therefore, the same effect as when the reproduction light is narrowed down can be obtained, and high density recording bits can be reproduced.

The erased recording bit is restored by being transferred from the recording layer when the medium temperature is lowered and the exchange coupling is restored. In this method, the signal is detected in the front part of the reproduction light spot, and therefore, front aperture detection (FA
Called D). A drawback of the FAD method is that a reproducing magnetic field (Hr) is required during reproduction. The reproducing magnetic field is usually 2
A magnetic field of 4000 A / m or more is required, and there is a drawback that the bits recorded in the recording layer are likely to become unstable by reproducing while applying a reproducing magnetic field.

Further, there is a possibility that a magnetic field larger than the magnetic field required for recording may be required for reproduction, which is a big problem in downsizing the magnetic head and simplifying the apparatus.
Particularly in magnetic field modulation recording, the recording magnetic field is often 10000 A / m or less, and the application of the reproducing magnetic field imposes a heavy burden on the magnetic head.

[0008]

On the other hand, in the previous application, as in the case of FAD, the temperature increased and the exchange coupling was broken while using the three exchange-coupled magnetic layers of the recording layer, the cutting layer and the reproducing layer. At this time, due to the magnetostatic coupling between the recording layer and the reproducing layer, the sub-lattice magnetization of the reproducing layer is inverted as compared with the case where the exchange coupling is strong, which enables super-resolution reproduction. The type showed super-resolution.

With this method, super-resolution is possible in the absence of a reproducing magnetic field or in a very low reproducing magnetic field. In this method, the recording layer needs to have a considerably large magnetization in order to invert the reproducing layer with a static magnetic field. However, when the magnetization is large, the perpendicular magnetic anisotropy of the recording layer is lowered and the direction of the magnetization becomes oblique, or a minute inversion region is generated inside the recording mark. Therefore, the recording layer is required to have contradictory properties such as generation of a large static magnetic field and high perpendicular magnetic anisotropy, and both cannot be sufficiently satisfied.

[0010]

According to the present invention, by reversing the magnetization of a high temperature portion at the time of reproduction, a bias layer is formed in contact with a recording layer in a medium which can obtain a super-resolution effect by a method different from the conventional principle using a mask. It is possible to obtain excellent reproduction characteristics by providing The gist of the present invention is to provide a magnetic layer, which is composed of at least a reproducing layer made of a rare earth and a transition metal, a cutting layer, a bias layer, and a recording layer, which are exchange-coupled with each other, on a substrate. Curie temperatures of the recording layer and the recording layer are Tc1 and Tc, respectively.
c2, Tc3, Tc4 and coercive force are Hc1, Hc2, Hc3 and Hc4 respectively
And Tc1, Tc2, Tc3 and Tc4 are 50 ° C. or higher, and

[0011]

[Equation 2] Tc1> Tc2, Tc3> Tc2, Tc4> Tc2, and the magnetic layer is exchanged between the recording layer and the reproducing layer when heated by the reproducing light to a temperature near Tc2 or higher. In a magneto-optical recording medium in which the coupling force decreases or disappears, and as a result, the sub-lattice magnetization of the reproducing layer at the high temperature portion is reversed with respect to the direction at the time of low temperature, the bias layer is It exists in a magneto-optical recording medium characterized by having a large volume magnetic susceptibility.

The reason for setting Tc1, Tc2, Tc3, and Tc4 to 50 ° C. or higher is that the ambient temperature of the medium is usually 50 ° C. or lower. When recording on such media,
First, while applying a magnetic field in a fixed direction, continuous light is irradiated to align the magnetization in one direction (erasing). Next, while applying a magnetic field in the opposite direction, pulsed light corresponding to information is irradiated to generate a magnetic domain due to magnetization in the opposite direction to erasing (recording).

Apart from this, a magnetic field modulation system for applying a modulation to the recording magnetic field according to information can also be used. In the three-layer structure of the reproducing layer 1, the cutting layer 2, and the recording layer 3 as shown in FIG. 2 which we have previously shown, the dominant sublattice magnetizations of the reproducing layer 1 and the recording layer 3 are different, and the cutting layer 2 When the exchange coupling force 5 below the Curie temperature Tc2 is strong, the mutual magnetization is stable because the exchange coupling force 5 is directed in the opposite direction.

When such a medium is heated by reproducing light, the exchange coupling force 5 between the recording layer 3 and the reproducing layer 1 becomes small or disappears in the vicinity of Tc2. At this time, the main force acting on the magnetization of the reproducing layer 1 is the force due to the magnetostatic coupling force 6 between the magnetizations of the recording layer 3 and the reproducing layer 1. Since the magnetostatic coupling force 6 acts in the opposite direction to the exchange coupling force 5, the sublattice magnetization of the reproducing layer 1 is inverted with respect to the state at the low temperature.

In order to cause the magnetization reversal by the magnetostatic coupling force 5 in such a structure, it is necessary that the predominant sublattice magnetizations of the recording layer 3 and the reproducing layer 1 are different from each other at Tc2. That is, if the recording layer 3 is the rare earth metal dominant, the reproducing layer 1 is the transition metal dominant, and if the recording layer 3 is the transition metal dominant, the reproducing layer 1 is the rare earth metal dominant. In the case of normal reproduction, when the distance between the recording magnetic domains 7 is shortened, the signals in the recording direction and the erasing direction cancel each other out, so that the signals cannot be distinguished and the signal level is lowered.

On the other hand, in the above method, since the sublattice magnetization of the high temperature portion 8 being reproduced is inverted as shown in FIG. 3, the signal due to the Kerr rotation obtained from that portion also has the opposite polarity. Become. Therefore, when the high temperature portion 8 is in the recording direction, the signal has the same polarity as the signal from the surrounding erasing portion, and the two signals are added, so that a large signal level can be obtained even if the recording magnetic domain 7 has a high density.

When the high temperature portion 8 is in the erasing direction, the signal has the same polarity as the signal from the surrounding recording portion, and a large signal level can be obtained. Further, in the method of the present invention, the magnetization reversal occurs only in the high temperature portion 8 of the reproduction spot 9, so that a sharp reproduction signal having a very narrow width is obtained as compared with the conventional method in which the entire reproduction spot 9 is involved in the signal. Therefore, even fine recording can be easily reproduced.

In order to cause stable magnetization reversal by magnetostatic coupling in the magnetostatic coupling type super-resolution as described above,
In the vicinity of Tc2, both the recording layer and the reproducing layer must have opposite polarities and have a considerable amount of magnetization. However, as the magnetization of the recording layer is increased, the perpendicular magnetic anisotropy decreases, and the magnetization does not stand vertically, or minute magnetization reversal occurs.

For the recording layer, a magnetic layer having a large magnetization capable of obtaining a sufficient static magnetic field and a magnetic layer having a sufficient perpendicular magnetic anisotropy must be selected, and there is no recording layer that sufficiently satisfies both. . In particular, when the recording layer has a composition in which the rare earth metal is dominant at Tc2, the magnetic susceptibility near room temperature is Tc2.
Since it is larger than that, good characteristics cannot be obtained.

Therefore, the recording layer had to have a composition in which the transition metal was dominant. For this reason, in the present invention, the bias layer 3 is provided in contact with the recording layer 4 to generate the static magnetic field 6 for reversal as shown in FIG. The recording layer 4 and the bias layer 3 have an exchange coupling force of 5
Thus, the cutting layers 2 are bonded even when the Curie temperature Tc2 is exceeded. A film having a small magnetic susceptibility and a high perpendicular magnetic anisotropy is used for the recording layer 4, while the bias layer 3 is used for the recording layer 4.
A film having a larger magnetic susceptibility is provided to generate a large static magnetic field 6.

In this way, the recording layer 4 generates perpendicular magnetic anisotropy, and the bias layer 3 plays a role of generating a static magnetic field, whereby a large composition margin can be obtained and at the same time the bias layer 3 is generated. It is possible to obtain better signal characteristics by the strong static magnetic field 6. Further, since the bias layers 3 and the recording layers 4 can adopt different polarities, the range of selection of the recording layers 4 is greatly expanded.

Even if the bias layer has a large magnetic susceptibility at room temperature and the magnetization direction is not completely perpendicular, if the recording layer is perpendicularly magnetized, the magnetic susceptibility of the bias layer decreases near Tc2. Good characteristics can be obtained when is vertical. The configuration in which the bias layer is not vertical at a low temperature and is vertical at a high temperature is a preferable configuration because the signal level from the low temperature portion becomes small and crosstalk is reduced.

When the bias layer is Tc2 and transition metal-dominant composition, the reproducing layer is Tc2 and rare earth metal-dominant composition. At this time, similarly to the reason described above, it is preferable that the magnetization of the reproducing layer is not perfectly perpendicular at low temperature. Each layer will be described in more detail below. Since the reproducing layer is required to cause stable magnetization reversal, the coercive force H of the reproducing layer is
c must be small to some extent.

However, if it is too small, the reproduction signal is deteriorated. Therefore, at Tc2, Hc is preferably 2000 A / m or more and 40,000 A / m or less. Further, it is preferable to reduce the perpendicular magnetic anisotropy of the reproducing layer in order to reduce the increase in the energy of the domain wall due to the magnetization reversal, but if it is too small, the reproduction signal deteriorates.
Perpendicular magnetic anisotropy is 2 × 10 ⁵ erg / cc or more, 8 ×
It is preferably 10 ⁶ erg / cc or less, particularly preferably 5 × 10 ⁵
It is erg / cc or more and 6 × 10 ⁶ erg / cc or less.

The perpendicular magnetic anisotropy can be changed by adjusting the film stress by the gas pressure or the like during film formation, and it is 5 × 10 ⁸ dyne / cm ² or more and 5 × 10 ⁹ dyne / cm ² The following are preferred. The material used for the reproducing layer is GdFe
Co, GdCo, GdFe, GdDyFe, GdDyC
o, GdDyFeCo, GdTbFe, GdTbCo,
GdTbFeCo, DyFeCo, DyCo, TbC
Alloys of rare earths and transition metals such as o, TbFeCo, TbDyFeCo, and TbDyCo are preferably used.

Among them, it is preferable to use an alloy containing Gd from the viewpoint of Curie temperature and coercive force. Especially GdFe
It is preferable to use an alloy containing Co as a main component. The Curie temperature is preferably 250 ° C. or higher. P
A magnetic substance such as tCo or a superlattice of Pt and Co may be used alone or as a reproducing layer by laminating an alloy of a rare earth and a transition metal.

In order to increase the perpendicular magnetic anisotropy of the reproducing layer, it is preferable that the magnetic layer be given a certain amount of film stress to generate anisotropy due to the inverse magnetostriction effect. If the film stress is too large, it will adversely affect the durability of the film, so 1 × 10 ⁹ erg / c
It is preferably c or more and 5 × 10 ⁹ erg / cc or less. The smaller the thickness of the reproducing layer is, the larger the magnetic force is, which is preferable.

However, if it is too thin, the reproduction signal becomes small, so that it is preferably 8 nm or more and 500 nm or less. More preferably, it is 12 nm or more and 350 nm or less.
On the other hand, the force received by the reproducing layer also affects the magnetization of the reproducing layer itself. Therefore, it is preferable that the reproducing layer also has a certain degree of magnetization at Tc2. The volume susceptibility of the reproducing layer at Tc2 is preferably 150 emu / cc or more, more preferably 200 emu / cc or more.

On the other hand, if the magnetization is too large at room temperature, the perpendicular magnetic anisotropy decreases, and the magnetization of the recording layer exchange-coupled with the reproducing layer does not stand perpendicularly. Therefore, the reproducing magnetization at room temperature is 500 emu / cc or less. Is preferred, and more preferably 450 emu / cc or less. The room temperature referred to here is a temperature of use environment, but is typically about 25 ° C.

The cutting layer needs to have a Curie temperature lower than that of the reproducing layer or the recording layer. The Curie temperature of the cutting layer is preferably about 100 to 180 ° C. It is preferable that the cutting layer has a high perpendicular magnetic anisotropy and generates a strong force in the magnetization of the reproducing layer.

The material used for the cutting layer is TbF.
e, TbFeCo, DyFeCo, DyFe, TbDy
Alloys of rare earths and transition metals such as FeCo are preferred. The thickness of the cutting layer is preferably 2 nm or more and 30 nm or less. The bias layer needs to have at least a larger magnetization than the reproducing layer in order to generate a magnetic field that reverses the reproducing layer.

The volume susceptibility of the bias layer is 1 at Tc2.
It is preferably 50 emu / cc or more, more preferably 200 emu / cc or more. However, if it is too large, the magnetization is not perpendicular at Tc2 and the signal characteristics deteriorate, so
It is preferably 500 emu / cc or less. The Curie temperature of the bias layer is preferably 250 ° C. or higher. The film thickness is preferably 2 nm or more and 50 nm or less.

The material used for the bias layer is G
dFeCo, GdCo, GdFe, GdDyFe, Gd
DyCo, GdDyFeCo, GdTbFe, GdTb
Co, GdTbFeCo, DyFeCo, DyCo, T
bCo, TbFeCo, TbDyFeCo, TbDyC
An alloy of a rare earth element such as o and a transition metal is preferably used.

Above all, it is preferable to use an alloy containing Gd. It is particularly preferable to use GdFeCo. Since the recording layer is a layer in which recording is stably stored, it is necessary that the recording layer has a Curie temperature that is not deteriorated by a reproducing beam. The Curie temperature of the recording layer is 200 to 280 ° C.
A degree is preferable.

If the Curie temperature of the recording layer is too high, the laser power required for recording will be too high.
The recording layer also needs to have a high perpendicular magnetic anisotropy in order to give a strong force to the magnetization of the reproducing layer. TbFeCo, TbCo, DyFe are used as the material forming the recording layer.
Co, TbDyFeCo, GdTbFe, GdTbFe
An alloy of a rare earth element such as Co and a transition metal is preferably used.

It is particularly preferable to use an alloy containing Tb in order to obtain a high perpendicular magnetic anisotropy. Among them, TbFeC
o is preferred. The thickness of the recording layer is 10 nm or more and 50 nm
The following is preferable. The magnetization of the recording layer is smaller than that of the bias layer at Tc2, and is 150em at Tc2.
It is preferably u / cc or less.

Further, in order to store the magnetization stably in the recording layer, it is preferable that the recording layer has at least a coercive force larger than that of the reproducing layer. A preferable coercive force is 240 kA / m or more. The perpendicular magnetic anisotropy is preferably 2 × 10 ⁶ erg / cc or more. When the alloy of rare earth metal and transition metal is used for the above magnetic layer, it is very easy to oxidize, so it is preferable to adopt a mode in which protective films are provided on both sides of the magnetic layer.

As the protective film, simple substances such as Si oxide, Al oxide, Ta oxide, Ti oxide, Si nitride, Al nitride and Si carbide, or a mixture thereof are preferably used.
The thickness of the protective film is preferably about 50 nm to 150 nm.
After forming a protective film on the substrate side, that is, a protective film between the substrate and the magnetic layer, plasma etching the surface of the protective film to improve the magnetic anisotropy of the magnetic layer provided next on the protective film. You can

Providing a high heat-conducting substance made of a simple substance such as Al, Cu, Au, Ag or the like or an alloy mainly composed of Al, Cu, Au, Ag or the like as a heat dissipation layer on the recording layer side of the magnetic layer directly or through a protective layer This is a desirable structure for stabilizing the heat distribution during use. The thickness of the heat dissipation layer is 10 nm to 100
About nm is preferable.

[0040]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist. Example 1 A polycarbonate substrate having a guide groove with a track pitch of 1.4 μm was introduced into a sputtering apparatus, and 5 × 10
Evacuation was performed to a vacuum degree of ^-5 Pa or less.

After that, as the protective layer, 80 nm oxide Ta was formed on the substrate by reactive sputtering. Next, on the oxidized Ta, a 30 nm reproducing layer made of Gd ₃₄ (Fe ₈₀ Co ₂₀ ) ₆₆ (numerical value is atomic%), a 15 nm cutting layer made of Tb ₂₀ Fe ₈₀ , and a Gd ₁₈ (Fe ₇₀ Co ₃₀ ) ₈₂ A 20 nm bias layer and a 40 nm recording layer of Tb ₂₃ (Fe ₈₀ Co ₂₀ ) ₇₇ .

Finally, an 80 nm protective layer made of SiN was provided. The Curie temperatures of the reproducing layer, the cutting layer, the bias layer, and the recording layer were measured. The reproducing layer was 300 ° C. or higher, the cutting layer was 120 ° C., the bias layer was 300 ° C. or higher, and the recording layer was 2 ° C.
It was 40 ° C. The magnetization of the rare earth metal was dominant in the reproducing layer at room temperature, and the compensation temperature was 190 ° C.

The magnetization of the transition metal was predominant in the cutting layer and the bias layer at room temperature. In addition, the room temperature (25
Coercive force at ℃) is almost zero and Kerr rotation angle θk1 is 0.2
4 deg. , The volume magnetic susceptibility is 380 emu / cc, 120
The coercive force is 10,000 A / m and the Kerr rotation angle θk2 is 0.34 deg. , Volume susceptibility is 250emu / cc
Met.

The volume magnetic susceptibility of the bias layer at 120 ° C. was 390 emu / cc. The disc thus produced was evaluated for CN ratio using an evaluator having a wavelength of 780 nm and a numerical aperture of 0.55. The recording conditions are a linear velocity of 7 m / s and a frequency of 9 MHz (mark length 0.39 μm) 30%.
After recording, measurement was performed while changing the reproducing power Pr without applying a reproducing magnetic field. When Pr was 2.0 mW or more, the signal phase was completely reversed and the high CN The ratio (narrowband signal-to-noise ratio) was obtained, and when Pr = 2.4 mW, a CN ratio of 46.5 dB was obtained. Furthermore, when recording was performed at 2 MHz on an adjacent track and crosstalk was measured, a low value of -36 dB was obtained.

Example 2 A polycarbonate substrate having a guide groove with a track pitch of 1.4 μm was introduced into a sputtering apparatus, and 5 × 10 5 was used.
Evacuation was performed to a vacuum degree of ^-5 Pa or less.

After that, as the protective layer, 80 nm oxide Ta was formed on the substrate by reactive sputtering. Next, on the oxidized Ta, 30 including Gd ₁₉ (Fe ₈₀ Co ₂₀ ) ₈₁ is formed.
nm reproduction layer, a 15 nm cutting layer made of Tb ₂₀ Fe ₈₀ , a ₂₀ nm bias layer made of Gd ₃₅ (Fe ₇₀ Co ₃₀ ) ₆₅ , and a 40 nm recording layer made of Tb ₂₃ (Fe ₈₀ Co ₂₀ ) ₇₇ . .

Finally, an 80 nm protective layer made of SiN was provided. The composition x of the recording layer was changed as shown in Table 2.
The Curie temperatures of the reproducing layer, the cutting layer, the bias layer and the recording layer were measured.
The temperature was 0 ° C., the bias layer was 300 ° C. or higher, and the recording layer was 240 ° C.

The Curie temperature of the recording layer was about 240 ° C., although it varied slightly depending on the composition. At room temperature (25 ° C.), the bias layer was dominated by the magnetization of the rare earth metal, and the compensation temperature was 200 ° C. The magnetization of the transition metal was dominant in the reproducing layer and the cutting layer at room temperature. The coercive force of the reproducing layer at room temperature is 2200 A / m, and the Kerr rotation angle θk1 is 0.1.
8 deg. , The volume magnetic susceptibility is 420 emu / cc, and 120
The coercive force at 1 ° C is 1600 A / m, and the Kerr rotation angle θk2 is 0.34 deg. The volume susceptibility was 330 emu / cc.

The volume magnetic susceptibility of the bias layer at 120 ° C. was 380 emu / cc. The disc thus produced was evaluated for CN ratio using an evaluator having a wavelength of 780 nm and a numerical aperture of 0.55. Recording conditions are a linear velocity of 7 m / s, a frequency of 9 MHz, a recording power of 9 mW, and a recording duty of 30%.

After recording, measurement was performed while changing the reproducing power Pr without applying a reproducing magnetic field. When Pr was 2.0 mW or more, it was found that the signal phase was completely inverted when the Pr was 2.0 mW or less. High CN ratio at the same time, P
At r = 2.4 mW, a CN ratio of 47.3 dB was obtained.
Furthermore, when recording was performed at 2 MHz on an adjacent track and crosstalk was measured, a low value of -39 dB was obtained.

Comparative Example 1 A disk was produced in the same manner as in Example 1 except that the bias layer was not provided. The CN ratio was 43.2 dB when the CN ratio was measured under the same conditions as in Example 1 without applying the reproducing magnetic field and with the reproducing power Pr = 2.4 mW. Comparative Example 2 A disk was produced in the same manner as in Example 1 except that the reproducing layer was composed of Gd ₂₆ (Fe ₈₀ Co ₂₀ ) ₇₄ and no bias layer was provided.

The Curie temperature of the reproducing layer was 300 ° C. or higher. The rare earth metal was dominant at room temperature, and the compensation temperature was 90 ° C. The coercive force of the reproducing layer at room temperature is 560
Kerr rotation angle θk1 = 0.33 at 00 A / m, coercive force at 120 ° C. is 48000 A / m, Kerr rotation angle θk2 =
It was 0.34.

After that, when the reproducing magnetic field was not applied under the same conditions as in Example 1 and the CN ratio was measured with the reproducing power Pr = 2.0 mW, it was 28 dB. A reproducing magnetic field of 400 in the erasing direction
When reproduction was performed by applying 00 A / m, 46.1 dB was obtained. No reversal of signal polarity was observed. Further, Example 1 was performed with a reproducing magnetic field of 40000 A / m applied.
Crosstalk was measured in the same manner as in -23.
It was dB.

Comparative Example 3 Using the same substrate as that used in Example 1, 90 nm Ta oxide was used as a protective layer and Tb ₂₁ (Fe ₉₃ C) was used as a recording layer.
o ₇ ) ₇₉ is 28 nm, SiN is 30 nm as an intermediate layer,
A disk having Al of 40 nm as a reflective layer was prepared. Then, the CN ratio was measured under the same conditions as in Example 1 without applying a reproducing magnetic field and at a reproducing power Pr = 2.0 mW.
It was 6 dB. No signal phase reversal was observed. Furthermore, when the crosstalk was measured in the same manner as in Example 1, it was -25 dB.

[0055]

By providing a bias layer for generating a magnetic field in a super-resolution magneto-optical recording medium using magnetic domain inversion by magnetostatic coupling, a super-resolution effect superior to the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of a mechanism of a magneto-optical recording / reproducing system of the present invention.

FIG. 2 is an explanatory diagram of a mechanism of a conventional magnetostatic coupling type super-resolution magneto-optical recording medium.

FIG. 3 is an explanatory plan view of a magnetostatic coupling type super-resolution magneto-optical recording medium.

[Explanation of symbols]

 1 reproducing layer 2 cutting layer 3 bias layer 4 recording layer 5 exchange coupling force 6 magnetostatic coupling force 7 recording magnetic domain 8 high temperature part (reversal part) 9 reproducing spot 10 reproducing spot moving direction 11 track

Claims (3)

[Claims] 1. A magnetic layer, which is composed of at least a reproducing layer, a cutting layer, a bias layer, and a recording layer, which are composed of at least a rare earth metal and a transition metal, and which are exchange-coupled to each other, is provided on a substrate. When the Curie temperatures of the bias layer and the recording layer are Tc1, Tc2, Tc3, and Tc4, respectively, Tc1, Tc2,
Tc3 and Tc4 are 50 ° C. or higher, and the following relationships are satisfied: Tc1> Tc2, Tc3> Tc2, Tc4> Tc2, and the magnetic layer is heated to a temperature near Tc2 or higher by heating with reproducing light. At this time, in the magneto-optical recording medium, the exchange coupling force between the recording layer and the reproducing layer decreases or disappears, and as a result, the sub-lattice magnetization of the reproducing layer in the high temperature portion is reversed with respect to the direction of the low temperature portion. The magneto-optical recording medium is characterized in that the bias layer is exchange-coupled with the recording layer at Tc2 and has a larger volume magnetic susceptibility than the recording layer. 2. At Tc2, when the recording layer is predominantly magnetized by a rare earth metal, the bias layer is predominantly magnetized by a transition metal, and when the reproducing layer is predominantly magnetized by a transition metal, the bias layer is The magneto-optical recording medium according to claim 1, wherein the rare earth metal is predominantly magnetized. 3. The magneto-optical recording medium according to claim 1, which is irradiated with reproducing light having an intensity at which the sub-lattice magnetization of at least a part of the reproducing layer of the reproducing portion is inverted to generate a reproducing magnetic field of 16000 A / m or less. A reproducing method for a magneto-optical recording medium, which is characterized in that reproduction is carried out with or without applying a reproducing magnetic field.