JPH06259827A - Magneto-optical recording medium and magneto-optical reproducing device - Google Patents

Abstract

PURPOSE:To provide the magneto-optical disk with which high-quality signals are obtainable even if the line speed of a disk is slow. CONSTITUTION:A specified magnetic field is impressed to the periphery of an irradiation spot 6 at the time of reproducing previously recorded information. The information 9 of a recording layer 2 is transferred to a reproducing layer 1 only in the transfer region 10 which is a part within an irradiated spot 6 heated up to a high temp. by this irradiated spot 6 and the magnetization 3 of the reproducing layer faces one direction exclusive of the transfer region 10. As a result, the length in the major axis direction of the transfer region 1 0 does not increase even if the line speed of the disk falls and, therefore, the resolution of detection is not degraded and consequently, the reproduced signals having the high quality are obtd. even under the slow line speed condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly to an optical card and an optical disk for reading information by using a laser beam and a magneto-optical reproducing apparatus using the optical card.

[0002]

2. Description of the Related Art The beam diameter of an optical disk on a disk is given by about λ / NA, where λ is the wavelength of laser light and NA is the numerical aperture of an objective lens. If there are two or more recording marks in the beam spot, these marks cannot be detected separately. Therefore, the shortest reproducible mark length of the optical disc is λ / (2NA), which is 1/2 of the irradiation spot diameter.

In recent years, a super-resolution magneto-optical disk using an exchange coupling film composed of a recording layer and a reproducing layer has been proposed as a method of reading a recording mark smaller than this value.

As disclosed in Japanese Patent Laid-Open No. 3-93058, this system uses an initializing magnet to align the magnetization of the reproducing layer in one direction before reproducing, and the temperature distribution generated in the irradiation spot during reproducing. The magnetization of the recording layer is transferred to the reproducing layer when the exchange coupling film reaches a certain temperature or higher.

The reproducing principle will be described below with reference to FIGS. 3A and 3B which are a sectional view and a plan view, respectively.

First, as in the case of an ordinary magneto-optical disk, a laser beam having a power higher than that at the time of reproducing is irradiated and the power of the laser beam or the direction of a magnetic field applied at the time of recording is modulated to the recording layer 2. A magnetic domain having a length corresponding to the recording information (hereinafter referred to as a mark) is recorded. At this point, the magnetization 3 of the reproducing layer is aligned in the direction of the magnetization of the mark of the recording layer by exchange coupling.

Next, the magnetization 3 of the reproducing layer 1 is aligned in one direction by the initialization magnet 5 regardless of the magnetization 4 of the recording layer 2. When passing through the irradiation spot 6, the temperature of a part of the irradiation spot of the reproducing layer 1 rises, and when the temperature exceeds a certain temperature, the magnetization direction of the recording layer 2 is transferred to the reproducing layer 1.

Therefore, the transfer of magnetization is performed by the irradiation spot 6
Will happen in part. As a result, only the information of the transferred area 10 can be detected, and the information of the recording mark 9 that is ½ or less of the irradiation spot diameter can be read.

[0009]

Although the above magneto-optical recording medium is an epoch-making technology, research has revealed that the signal quality (C / N) deteriorates when the disk linear velocity decreases. .

Normally, the linear velocity of the disk performing the above super-resolution reproduction is 7 m / s or more. On the other hand, in the case of digital audio information or digital image information that has been subjected to image compression processing, it is 0.6 to 4.0 m / s, which is about a fraction of the conventional example. (Data transfer rate: 1.5-10 Mbp
s, shortest mark length: 0.4 μm) An object of the present invention is to provide a magneto-optical recording medium and a magneto-optical recording medium which can obtain a high-quality signal even under a low linear velocity condition such as a disc linear velocity of 4 m / s or less. It is to provide a reproducing apparatus.

[0011]

In order to achieve the above object, a recording layer for recording information and a reproduction layer for reading information are provided, and an irradiation spot for reproduction is formed at the time of reproduction. In the magneto-optical recording medium to which a reproducing magnetic field is applied in the vicinity including the irradiation spot, Hr is the reproducing magnetic field strength,
When Hc is the coercive force of the reproducing layer and Hexc is the exchange coupling force acting on the reproducing layer due to the interaction between the recording layer and the reproducing layer, in a part of the irradiation spot,

[0012]

[Formula 1] Hr + Hc <Hexc There is a region where the formula 1 holds, and in the part other than the irradiation spot, Hr> Hexc + Hc. The information of the recording layer is transferred to the reproducing layer, and the magnetization of the reproducing layer is in a fixed direction in the portion other than the irradiation spot.

Further, in the magneto-optical reproducing apparatus for reproducing information from the magneto-optical recording medium, a spot forming means for forming an irradiation spot for producing a high temperature portion on the recording medium during reproduction and the irradiation spot are provided. Magnetic field applying means for applying the reproducing magnetic field in the vicinity including the information reading means for reading the information recorded in the irradiation spot,
In the area to which the reproducing magnetic field is applied, the information of the recording layer is transferred to the reproducing layer in a region within the irradiation spot where the equation 1 is satisfied, and in the portion other than the irradiation spot, the magnetization of the reproducing layer is in a constant direction. It was decided to be.

[0014]

Before explaining the principle of the present invention, the cause of the problems in the above-mentioned prior art will be described.

FIG. 2 shows the positional relationship between the irradiation spot and the temperature distribution at the time of laser irradiation, and the effective information read area (aperture: information from the recording layer to the reproducing layer in the irradiation spot) when the disk linear velocity is low and when it is high. FIG. 3 is a diagram schematically showing a region in which is transferred.

When the disk is rotating at a low linear velocity, the center 11 of the irradiation spot almost coincides with the highest temperature part 12. However, as the disc linear velocity increases, the highest temperature part 12 shifts to the rear of the irradiation spot, and the deviation between the irradiation spot center 11 and the highest temperature part 12 increases.

This is because (1) the temperature behind the irradiation spot is higher than that in front of the irradiation spot because of the effect of heat remaining, and (2) when the disk linear velocity increases, the heat influences further toward the rear. Because it does.

Further, in the conventional super-resolution magneto-optical recording medium,
Once the recording mark is transferred from the recording layer to the reproducing layer,
The recording mark remains transferred to that portion until the reproducing layer is initialized again.

Therefore, as shown in FIG. 2, the distance in the major axis direction of the aperture with respect to the irradiation spot diameter becomes shorter as the disc linear velocity increases, and becomes longer as the disc linear velocity decreases.

That is, as the disk linear velocity decreases, the mark detection resolution deteriorates. This is the cause of the decrease in C / N at low linear velocity.

The basis of the present invention is to realize a magnetic film having magnetic characteristics such that the distance in the major axis direction of the aperture does not become long even if the linear velocity of the disk decreases.

Differences between the conventional system and the super-resolution magneto-optical reproducing system of the present invention will be described below.

In the conventional method, before the reproduction, an initialization magnetic field opposite to the reproduction magnetic field is applied to align the magnetization of the reproduction layer in one direction. Then, during reproduction, a reproducing magnetic field is applied to transfer the magnetization of the recording layer to the reproducing layer. On the other hand, in the magneto-optical reproducing method of the present invention, only the reproducing magnetic field is applied around the reproducing portion. (Therefore, the reproducing magnetic field is applied to the medium not only when the medium is being irradiated with the laser, but also before and after the irradiation.) In the conventional method shown in FIG. 3, the recording mark 9 is once transferred from the recording layer 2 to the reproducing layer 1.
When the recording mark 9 is transferred to the reproducing layer 1, the recording mark 9 remains transferred to the reproducing layer 1 until it is initialized by the initializing magnet 5, whereas in the super-resolution magneto-optical reproducing method of the present invention shown in FIG. It is at the point of being initialized again by the applied reproducing magnetic field 8.

As a result, as shown in FIG. 4, only the high temperature portion becomes the aperture, so that the distance in the major axis direction of the aperture hardly changes even if the disk linear velocity decreases.
Therefore, the detection resolution does not deteriorate.

Next, the conditions of the medium required to obtain the super-resolution magneto-optical recording medium of the present invention will be shown.

In the magneto-optical recording medium of the present invention, a two-layer magnetic film of a recording layer and a reproducing layer is used as a film for recording information.

First, a mark is recorded on the recording layer by the same method as the conventional method. That is, a laser power stronger than the reproduction power is irradiated while being modulated according to the information to be recorded, and the temperature of the recording layer is raised to near the Curie temperature of the recording layer. At this time, a magnetic field in a fixed direction is applied around the laser spot. Since the coercive force of the recording layer decreases near the Curie temperature, the magnetization is inverted by the applied magnetic field to record the mark.

In order to realize the super-resolution magneto-optical reproducing system of the present invention, first, the magnetization 3 of the reproducing layer is aligned in one direction regardless of the direction of the magnetization of the recording layer (initialization) before reproducing. A magnetic field generated in the reproducing layer by the recording layer is called an exchange coupling magnetic field Hexc.

Further, the magnetic film originally has a property to keep the magnetization direction as it is, and contrary to this property, the magnetic field for reversing the magnetization corresponds to the coercive force Hc. Therefore, the magnetic field Ha for changing the magnetic field of the reproducing layer can be expressed by the sum of the exchange coupling magnetic field and the coercive force of the reproducing layer, and when the reproducing magnetic field Hr is larger than Ha, initialization by the reproducing magnetic field becomes possible. . Also, due to the reproducing magnetic field,
The recording marks on the recording layer must not be inverted. Therefore, magnetic properties satisfying the following conditions are required.

[0030]

## EQU00002 ## Hexc (record) + Hc (record)> Hr number 2

[0031]

## EQU00003 ## Hr> Hexc (reproduction) + Hc (reproduction) Formula 3 Here, Hc (recording) and Hc (reproduction) are coercive forces of the recording layer and the reproducing layer, respectively, and Hexc (recording) and Hexc.
(Reproduction) is the magnitude of the exchange coupling magnetic field acting on the recording layer and the reproduction layer, respectively. Further, the mathematical expression 2 represents the condition that the magnetization of the recording layer is not reversed, and the mathematical expression 3 represents the condition that the magnetization of the reproducing layer is reversed. Since the expression 2 is a condition for holding the information of the recording layer, it must be always satisfied except at the time of recording, and will be omitted hereinafter.

Next, the conditions necessary for irradiating the reproducing light will be shown.
Upon irradiation with reproducing light, the magnetization direction of the reproducing layer is returned to the original state. For that purpose, it is necessary to satisfy the following conditions at the regeneration temperature or higher.

[0033]

## EQU00004 ## Hr <Hexc (reproduction) -Hc (reproduction) Expression 4 Here, the sign of Hc (reproduction) is opposite to that of Expression 1, which means that the reproduction layer is initialized by the reproduction magnetic field. Therefore, the relative relationship between the reproducing magnetic field and the magnetization direction of the reproducing layer is
This is the opposite of the case.

As described above, it is possible to obtain a magneto-optical disk and a magneto-optical reproducing device in which the resolution is not lowered and the signal quality is not deteriorated even at a low linear velocity.

[0035]

FIG. 7 shows a detailed structure of a magneto-optical disk (optical recording medium) according to the present invention. The disc includes a substrate 16, an interference layer 17, a reproducing layer 1, a recording layer 2, a thermal diffusion film 18, and a protective film 1.
It consists of 9. The substrate 16 is made of polycarbonate and has a tracking groove as in the conventional magneto-optical disk.

The interference layer 17 and the protective layer 19 are made of silicon nitride, and the thermal diffusion layer 18 is made of an Al alloy, and they are formed by sputtering.

Next, the conditions of the medium required to obtain the super-resolution magneto-optical recording medium will be shown.

In the magneto-optical recording medium of this embodiment, two layers of magnetic films, a recording layer and a reproducing layer, are used as a film for recording information. FIG. 8 shows an example of temperature change of coercive force of the reproducing layer and the recording layer used in the present invention. First, for the reproducing layer, a rare earth metal-transition metal (RE-TM) alloy having a RE rich composition having a compensation point at room temperature or higher (this point is different from the conventional technique), for example, a rare earth metal magnetic moment is dominant is used. To do. In the recording layer, TM in which the transition metal magnetic moment is dominant
The RE-TM alloy having the rich composition or the RE-TM alloy having the RE-rich composition may be used, but here, the case where the RE-TM alloy having the TM-rich composition is used will be described.

First, a mark is recorded on the recording layer by the same method as the conventional method. That is, a laser power stronger than the reproduction power is irradiated while being modulated according to the information to be recorded, and the temperature of the recording layer is raised to near the Curie temperature of the recording layer. At this time, a magnetic field in a fixed direction is applied around the laser spot. Since the coercive force of the recording layer decreases near the Curie temperature, the magnetization is inverted by the applied magnetic field to record the mark.

Although the reproducing layer has an RE-rich composition at room temperature, it has a TM-rich composition near the Curie temperature of the recording layer. Therefore, at the time of laser irradiation of the recording power, both the recording layer and the reproducing layer are TM rich. As a result, due to the recording, the directions of the transition metal magnetic moments in the recording layer and the reproducing layer become the same. Then, when the temperature drops to around room temperature, the reproducing layer has a RE-rich composition, and therefore the magnetization of the reproducing layer has a direction opposite to the transition metal moment of the reproducing layer.

At this time, there are two kinds of magnetization states A and B shown in FIG. Here, the large arrows 3 and 4 represent the overall magnetization, that is, the direction of magnetization obtained by combining the transition metal magnetic moment and the rare earth metal magnetic moment, and the small arrows 14 and 15 represent the direction of the transition metal magnetic moment. (By the way, in this case, the arrow indicating the direction of magnetization in FIG. 3 corresponds to the direction of the transition metal magnetic moment.) In order to realize the super-resolution magneto-optical reproduction method of the present invention, first, prior to reproduction, The magnetization 3 of the reproducing layer is aligned in one direction regardless of the magnetization direction of the recording layer (initialization).
Therefore, only the magnetization 3 of the reproducing layer in the B magnetized state is reversed by the reproducing magnetic field Hr to the B'magnetized state. Then, during reproduction, a part of the irradiation spot is changed from the state of B ′ to A
By returning to the state of, super-resolution reproduction is achieved.

What should be noted here is that the direction of the transition metal magnetic moment 1 of the reproducing layer of B'is opposite to the direction of the transition metal magnetic moment 2 of the recording layer.

Usually, a magnetic film formed by continuously laminating two layers is exchange-coupled between the two layers. This bond is a bond that tries to align the directions of the transition metal magnetic moments of the two layers in the same direction. Therefore, when the directions of the transition metal magnetic moments of the adjacent magnetic films are the same, the energy state becomes the most stable.

On the other hand, if the transition metal magnetic moments of the adjacent magnetic films are directed in opposite directions, a domain wall is created between the two layers, resulting in an unstable energy state. However, this unstable state can exist stably under a certain applied magnetic field. This applied magnetic field is called an exchange coupling magnetic field Hexc.

In addition, the magnetic film originally has a property to keep the direction of magnetization as it is, and contrary to this property, the magnetic field for reversing the magnetization corresponds to the coercive force Hc. Therefore, the magnetic field Ha for changing from the state B to the state B ′ can be expressed by the sum of the exchange coupling magnetic field and the coercive force of the reproducing layer, and can be initialized by the reproducing magnetic field when the reproducing magnetic field Hr is larger than Ha. Becomes Also, the recording mark on the recording layer must not be inverted by the reproducing magnetic field. Therefore, magnetic characteristics satisfying the conditions of the above equations 2 and 3 are required.

In Equations 2 and 3, Hc (recording) and Hc (reproduction) are the coercive forces of the recording layer and the reproducing layer, respectively, and Hexc (recording) and Hexc (reproducing) are the recording layer and the reproducing layer, respectively. Is the magnitude of the exchange coupling magnetic field that acts on.
Further, the mathematical expression 2 represents the condition that the magnetization of the recording layer is not reversed, and the mathematical expression 3 represents the condition that the magnetization of the reproducing layer is reversed. Formula 2 is a condition for holding information in the recording layer, and therefore must be always satisfied except during recording.

Next, the conditions necessary for irradiating the reproducing light will be shown.
When the reproducing light is irradiated, the magnetization direction of the reproducing layer in the state B ′ is returned to the original state B again. For that purpose, it is necessary to satisfy the condition of the above-mentioned mathematical expression 4 at the reproduction temperature or higher.

FIG. 6 schematically shows an example of magnetic characteristics satisfying the relationships of the above expressions 3 and 4. Room temperature R.I. T. 3 is satisfied, and above the regeneration temperature Tr, expression 4 is satisfied.
The conditions of are met. Therefore, in order to obtain the super-resolution magneto-optical disk according to the present invention, at least a medium having magnetic characteristics as shown in FIG. 6 is required.

Also, even if the temperature of the medium once rises above the reproduction temperature Tr and then drops to the reproduction temperature Tr as the irradiation spot passes, the condition of equation 3 is not satisfied immediately.
Here, when the temperature at which the condition of Equation 3 is satisfied again is called the initialization temperature Tini, in order to transfer the magnetization of the recording layer to the reproducing layer only within the irradiation spot, the medium temperature outside the irradiation spot is equal to or lower than Tini. Must be

The above-mentioned magnetic characteristics are the compensation temperature Tco of the reproducing layer.
This is achieved by setting mp near the regeneration temperature.
The reason for this will be described below.

The exchange coupling magnetic field Hexc can be expressed by the following equation.

Hexc = σw / (2Ms × t) where σw is the domain wall energy stored in the domain wall per unit area when a domain wall exists between the recording layer and the reproducing layer, and Ms is the saturation magnetization of the reproducing layer. , T are the thickness of the reproducing layer.

Σw monotonically decreases with increasing temperature,
Ms theoretically becomes zero near the compensation temperature. Naturally, t does not change. Therefore, Hexc is theoretically infinite near the compensation temperature Tcomp.

Hc also becomes infinite at the compensation temperature, but He
It is experimentally known that not only xc + Hc but also Hexc-Hc diverges to infinity.

Therefore, the magnetic characteristics as shown in FIG. 6 can be obtained, and as a result, the magneto-optical reproducing system according to the present invention can be realized.

FIG. 8 shows temperature changes of the coercive force 21 of the reproducing layer and the coercive force 20 of the recording layer. It is desirable that the recording layer has a sufficiently large coercive force near room temperature and a Curie temperature Tc lower than that of the reproducing layer. In this example, an amorphous alloy film of Tb-Fe-Co was used. This film has a TM-rich composition in which the magnetization of the transition metal (TM) is dominant at room temperature and has a Curie temperature Tc.
Is about 200 ° C., and the coercive force Hc at room temperature is about 10 kOe.

On the other hand, it is desirable that the reproducing layer has a small coercive force 21 at room temperature and a Curie temperature higher than that of the reproducing layer.
In this example, an amorphous alloy film of Gd-Fe-Co was used. The higher the Gd content, the higher the compensation temperature. Therefore, the content is increased, and in the present invention, the compensation temperature is set higher than room temperature, in contrast to the conventional example where the compensation temperature is lower than room temperature. This film has an RE-rich composition in which the magnetization of rare earth metal (RE) is dominant at room temperature, and the compensation temperature is about 110 ° C. The Curie temperature is about 30.
The coercive force at 0 ° C. and room temperature is about 0.5 kOe. The two-layer magnetic film was continuously formed by magnetron sputtering in the same chamber.

FIG. 9 shows the recording mark pitch dependency of C / N of the super-resolution magneto-optical disk (disk A) prepared as described above. The recording / reproducing apparatus used at this time is provided with a semiconductor laser having a wavelength of 830 nm, a lens for lens focusing with a numerical aperture of 0.55, and a permanent magnet of 2 kOe on the opposite side of the lens. The disk linear velocity at the time of measurement was set to 3.2 m / s.

In the conventional detection method that does not use the super-resolution phenomenon, the mark pitch at the detection limit is λ / (2NA) = 0.
Given at 75 μm. The C / N of the conventional structure disk (disk B) which does not show the super-resolution phenomenon is 0.75 which is the diffraction limit.
Below μm, it is below 20 dB. On the other hand, in the disc according to the present invention, a signal having a C / N of 40 dB or more is obtained from a mark having a mark pitch less than the detection limit. Therefore, super-resolution detection has been achieved.

Next, the disk linear velocity dependence of C / N of the conventional super-resolution magneto-optical disk (disk C) and the above-mentioned super-resolution magneto-optical disk (disk A) according to the present invention is shown. When measuring the disk C, a reproducing magnetic field of 0.3 kOe was applied to the opposite side of the lens, and a magnetic field of 2 kOe was applied as an initializing magnetic field in a direction opposite to the reproducing magnetic field at a position that does not affect this magnetic field. . The laser power during reproduction was 2 mW and the recording mark pitch was 0.9 μm in both disc measurements.

The results are shown in FIG. For both disks A and B, a sufficient signal level is obtained when the linear velocity is 8 m / s. It can be seen that the reproduction signal level of the disc B decreases as the disc linear velocity decreases, but the reproduction signal level of the disc A hardly decreases.

When the magneto-optical reproducing method of the present invention is used, a problem is that the magnetization retained in the recording layer is transferred to the reproducing layer, that is, the size and shape of the aperture fluctuates at room temperature, and the optical system is changed. Laser output fluctuation due to contamination of the
Furthermore, it is a point that changes sensitively to changes in the disk linear velocity.

For example, when the room temperature rises, the temperature of the medium also rises accordingly, so that the temperature of the highest temperature portion may reach the re-reversal temperature Trt or higher and the initialization condition may be satisfied again. At temperatures higher than the compensation temperature Tcomp, He is
This is because xc + Hc drops sharply. Further, the size of the aperture is expanded even if it is not initialized. As the size of the aperture increases, the detection resolution decreases and the signal quality deteriorates.

On the contrary, when the size of the aperture is reduced, the effect of super-resolution is increased, but the signal amplitude is reduced, which is not preferable.

Therefore, it becomes necessary to properly control the size and shape of the aperture. As a method of doing this, it is preferable to judge the size and shape of the aperture from the detected reproduction signal pattern and adjust the reproduction power to control it.

For example, when it is determined from the reproduction signal pattern that the aperture size is larger than an appropriate value, the laser power is reduced to reduce the aperture size.

Next, an embodiment in which the size of the aperture is controlled will be shown. Table 1 below shows reproduction signal output values of the disk A with the disk ambient temperature Td as a parameter.

[0068]

[Table 1]

According to this table, a good reproduction signal is obtained at Td of 25 ° C., but at 50 ° C., the signal output level rises and the signal amplitude becomes small. This is because the medium temperature during reproduction rises due to the increase in Td, and as a result, the aperture is expanded. When the aperture is enlarged, a wide range of recording marks are detected, so that the output level of the reproduction signal is raised overall, and the resolution of the recording marks is lowered, so that the signal amplitude is narrowed.

The reason why the reproduction signal level is lowered when Td is 5 ° C. is that the aperture is reduced in contrast to the case where Td is 50 ° C. That is, the medium temperature at the time of reproduction is lowered as Td is lowered, and as a result, the aperture is reduced. When the aperture is reduced, the resolution of the recording mark is improved, but since only a part of the recording mark is detected, the reproduction signal level is lowered as a whole.

As described above, the reproduction signal level and the size of the aperture are related. Therefore, the aperture adjusting circuit shown in the block diagram of FIG. 11 is provided. The magneto-optical reproducing apparatus according to the present invention has an optical head 23, an aperture adjusting circuit, and a magnetic head driving circuit 27 (not shown in FIG. 11). The information recorded on the magneto-optical disk 22 is detected by the optical head 23 (spot forming means and information reading means), and the aperture adjusting circuit 24 (area determining means and area control) is provided between the optical head 23 and the RF signal detecting circuit 25. Means). Then, the difference between the reproduction signal level and the proper level is obtained by the aperture adjustment circuit 24, and a signal corresponding to this difference is transmitted to the semiconductor laser drive circuit 26.
Here, the reproduction laser power is increased when the reproduction signal level is high, and the reproduction laser power is decreased when the reproduction signal level is low. The results are shown in Table 2 below.

[0072]

[Table 2]

Despite the change in Td as shown in this table, it was possible to obtain almost the same reproduced signal as when Td was 25 ° C.

Even when the reproducing magnetic field is changed instead of adjusting the reproducing laser power, the same result as when Td is 25 ° C. can be obtained. In this case, as shown in the block diagram of FIG. 12, the signal from the aperture adjusting circuit is transmitted to the magnetic head drive circuit 27 (magnetic field applying means), and the reproduction magnetic field by the magnetic head 28 is increased when the reproduction signal level is high. It was set high, and it was set low when the playback signal level was low.

[0075]

As described above, by using the magneto-optical recording medium and the magneto-optical reproducing apparatus according to the present invention, for example, even under a low linear velocity condition such that the disc linear velocity is 4 m / s or less. Since the detection resolution does not decrease, a high quality signal can be obtained.

[Brief description of drawings]

FIG. 1 is a principle diagram of a conventional technique.

FIG. 2 is an explanatory diagram showing a relationship between a disc linear velocity and an aperture.

FIG. 3 is a principle view of the present invention.

FIG. 4 is an illustration of an aperture according to the present invention.

FIG. 5 is an explanatory diagram showing magnetization of a reproducing layer and a recording layer.

FIG. 6 is an explanatory diagram showing the temperature dependence of each reversal magnetic field.

FIG. 7 is a block diagram of a magneto-optical recording medium according to the present invention.

FIG. 8 is an explanatory diagram showing temperature characteristics of coercive force of a reproducing layer and a recording layer.

FIG. 9 is an explanatory diagram showing the mark pitch dependency of C / N.

FIG. 10 is an explanatory diagram showing the disc linear velocity dependence of C / N.

FIG. 11 is a block diagram of a magneto-optical reproducing device that adjusts an aperture.

FIG. 12 is a block diagram of a magneto-optical reproducing device that adjusts an aperture.

[Explanation of symbols]

1 ... Reproducing layer, 2 ... Recording layer, 3 ... Reproducing layer magnetization, 4 ... Recording layer magnetization, 5 ... Initializing magnet, 6 ... Irradiation spot, 7 ... Lens, 8 ... Reproducing magnet, 9 ... Recording mark, 10 ... Transfer area, 11 ... Irradiation spot center, 12 ... Highest temperature part, 13 ...
Aperture, 14 ... Transition metal magnetic moment of reproducing layer,
15 ... Transition metal magnetic moment of recording layer, 16 ... Substrate,
17 ... Interference layer, 18 ... Thermal diffusion layer, 19 ... Protective layer, 20 ...
Coercive force of recording layer, 21 ... Coercive force of reproducing layer, 22 ... Magneto-optical recording medium of the present invention, 23 ... Optical head, 24 ... Aperture adjusting circuit of the present invention, 25 ... RF signal detecting circuit, 26 ... Semiconductor laser drive Circuit, 27 ... Magnetic head drive circuit, 28
... magnetic head, Hr ... reproducing magnetic field, Hc ... coercive force, R.
T. ... room temperature, Tr ... regeneration temperature, Tini ... initialization temperature,
Trt ... Re-inversion temperature, Tcomp compensation temperature, Tc ... Curie temperature, Td ... Disk ambient temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Video Media Research Laboratory, Hitachi, Ltd. (72) Inventor Kuniichi Onishi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Address Company Inside the Hitachi Media Visual Media Laboratory (72) Inventor Toru Sasaki 292 Yoshida-cho, Totsuka-ku, Yokohama City, Kanagawa Prefecture Inside the Hitachi Image Media Research Center (72) Inventor Nakajima Yoshida Totsuka-ku, Yokohama City, Kanagawa Prefecture 292, Machi Incorporated company Hitachi, Ltd. Visual Media Research Center

Claims (6)

[Claims] 1. A recording layer for recording information and a reproducing layer for reading information, wherein an irradiation spot for reproduction is formed at the time of reproduction, and a reproducing magnetic field is applied to the vicinity including the irradiation spot. In the magneto-optical recording medium, Hr is the intensity of the reproducing magnetic field, Hc is the coercive force of the reproducing layer, and Hc is
When exc is a magnetic field that acts on the reproducing layer due to the interaction between the recording layer and the reproducing layer, a part of the irradiation spot has a region where Hr + Hc <Hexc 1 and In the part other than the irradiation spot, Hr> Hexc + Hc, and in the region where the reproducing magnetic field is applied, the information of the recording layer is transferred to the reproducing layer in the region where the above expression 1 is satisfied, and in the part other than the irradiation spot, A magneto-optical recording medium, wherein the magnetization of the reproducing layer is in a fixed direction. 2. The magneto-optical recording medium according to claim 1, wherein the recording layer of the magneto-optical recording medium is a rare earth metal-transition metal (RE-TM) alloy amorphous thin film. recoding media. 3. The magneto-optical recording medium according to claim 1 or 2, wherein the magnetization of the reproducing layer of the magneto-optical recording medium has a compensation temperature in the vicinity of a reached temperature when irradiated with an irradiation spot during reproduction. A characteristic magneto-optical recording medium. 4. A magneto-optical reproducing apparatus for reproducing information from the magneto-optical recording medium according to claim 1, 2 or 3, wherein an irradiation spot for forming a high temperature portion is formed on the recording medium during reproduction. The spot forming means, the magnetic field applying means for applying the reproducing magnetic field in the vicinity including the irradiation spot, and the information reading means for reading the information recorded in the irradiation spot, and the range to which the reproducing magnetic field is applied. Of the magneto-optical recording medium, the information of the recording layer is transferred to the reproducing layer in the region of the irradiation spot where the equation 1 is satisfied, and the magnetization of the reproducing layer is in a constant direction in the portion other than the irradiation spot. Playback device. 5. The magneto-optical reproducing apparatus according to claim 4, wherein the area determining means for determining the size of the transferred area based on the reproduction signal and the laser power of the reproducing light or the magnitude of the magnetic field applied at the time of reproduction are used. A magneto-optical reproducing apparatus comprising: a region control unit that controls the size of the transfer region by adjusting. 6. A magneto-optical reproducing method for reproducing information from the magneto-optical recording medium according to claim 1, wherein an irradiation spot for forming a high temperature portion is formed on the recording medium during reproduction. And applying the reproduction magnetic field in the vicinity including the irradiation spot, and reading the information recorded in the irradiation spot, in the range to which the reproduction magnetic field is applied, in the irradiation spot, A magneto-optical reproducing method characterized in that the information of the recording layer is transferred to the reproducing layer in the region where Mathematical formula 1 holds, and the magnetization of the reproducing layer is in a fixed direction in a portion other than the irradiation spot.