JPH0554452A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve C/N by forming an exchange bond layer film consisting of a magnetic reproducing layer and a magnetic recording layer and providing an aluminum thin film layer having about 20 to 70Angstrom film thickness between the magnetic recording layer and an interference layer consisting of a dielectric substance. CONSTITUTION:The thin film layer 8 consisting of a material having the thermal conductivity higher than the thermal conductivity of any of the recording layer 4 and the 2nd dielectric layer is provided between the recording layer 4 and the 2nd dielectric layer. The temp. distribution of the magnetic recording layer 4 in a region irradiated with a laser beam is uniformized in this way and the temp. of this region exceeds the Curie temp. of the magnetic recording layer 4. The magnetization of the magnetic reproducing layer 3 eventually faces the direction of a modulating magnetic field. The parts by old data hardly remain this region in such a case and, therefore, the crosstalks from the old data are substantially not included in the signals when the reflected light of the laser for writing is monitored. An increase in sensitivity and an improvement in C/N are eventually resulted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium,
In particular, the present invention relates to a magneto-optical recording medium for recording / reproducing information with a laser beam by utilizing the magneto-optical effect.

[0002]

2. Description of the Related Art A magnetic material used in a magneto-optical recording medium, which has a low Curie temperature for easy recording, high coercive force and excellent storage stability, and has a Kerr rotation angle in the magneto-optical effect. It is difficult to find a single magnetic material that is large and has good read characteristics.
As disclosed in Japanese Patent No. 8652, there has been proposed a magneto-optical recording medium having a so-called exchange-coupling two-layer film in which two different magnetic materials are laminated by separating required functions. This magneto-optical recording medium has a recording layer that can be perpendicularly magnetized and has a relatively low Curie temperature and a relatively high coercive force, and a vertically magnetizable recording layer that has a relatively high Curie temperature and a relatively low coercive force. A reproducing layer having magnetic force is laminated,
The recording layer and the reproducing layer are exchange-coupled with each other. Information is recorded and stored in the recording layer having a low Curie temperature, the recorded information is transferred to the reproducing layer by exchange coupling, and the information is read out in the reproducing layer having a large Kerr rotation angle. .. Further, as a medium excellent in information stability, a magneto-optical recording medium using a rare earth-iron group amorphous alloy having a so-called compensation composition having a magnetic compensation temperature between room temperature and Curie temperature as a recording layer has been proposed. There is. This magneto-optical recording medium can be discussed similarly to the above discussion by adopting the magnetic compensation temperature instead of the Curie temperature.

The conventional recording method for the magneto-optical recording medium has been the CAV method, that is, the method of rotating the magneto-optical recording medium at a constant rotation speed and recording at a constant recording frequency. In this case, the recording mark length is different between the inner peripheral portion and the outer peripheral portion of the magneto-optical recording medium (the outer peripheral portion is longer). When the recording capacity of the magneto-optical recording medium is further increased, it is conceivable that the recording mark length of the outer peripheral portion is shortened to the same extent as that of the inner peripheral portion, and the M-CAV (Modified CAV) method is proposed as such a recording method. Has been done.
In this method, the recording frequency is changed between the inner peripheral portion and the outer peripheral portion having different linear velocities so that the recording mark length becomes constant. A pit edge recording method has also been proposed in which information of "0" and "1" is associated with the end of a recorded pit.

When the recording capacity is increased in this way, it is preferable to reduce the film thickness of the magnetic layer of the magneto-optical recording medium in order to increase the recording sensitivity. However, when the magnetic layer is made thin, the reflectance of light in the magnetic layer is lowered, and the magneto-optical signal is lowered. Therefore, as disclosed in Japanese Patent Laid-Open No. 60-25036, a magneto-optical recording medium having a structure in which a reflective film is provided on a magnetic layer composed of an exchange coupling two-layer film has been proposed.

Further, in order to improve the data transfer rate at the time of writing (recording) on the magneto-optical recording medium, there is a demand for an overwriting method which does not require an erasing pass. As such, a magnetic field modulation overwrite method, which modulates a magnetic field applied according to a recording signal, is considered promising. Generally, in a magneto-optical recording medium, a verify operation (an operation of reading the written data again to verify the written data) is performed to confirm whether or not the data is surely written at the time of recording. However, since such a verify operation is a process of re-reading the recording location of the magneto-optical recording medium, there is a problem that even if the recording time is shortened by overwriting, it takes extra time. Therefore, a one-beam direct verify method has been proposed, which can verify written data at the same time as writing. This is because even if the recording layer of the exchange-coupling two-layer film loses its magnetization above its Curie temperature during writing, the reproducing layer remains below its Curie temperature and remains magnetized. By utilizing the fact that data can be collated at the same time as writing by observing the magneto-optical effect due to this residual magnetization to the writing laser beam in the magnetic field modulation overwrite method.

FIG. 2 is a schematic sectional view showing the structure of a conventional magneto-optical recording medium having an exchange coupling two-layer film having a reflective film. This magneto-optical recording medium comprises an optically transparent substrate 1 made of glass or plastic and an undercoat layer 2 made of an inorganic dielectric material such as SiN _x for obtaining an interference effect and an anticorrosion effect, and a reproducing layer. Of the reproducing magnetic layer 3, the recording magnetic layer 4 having a coercive force larger than that of the reproducing magnetic layer 3 and a low Curie temperature, and the recording magnetic layer 4 serving as a recording layer, SiN _x for preventing the corrosion of the magnetic layers 3 and 4 and obtaining an interference effect. The interference layer 5 made of a dielectric material and the metal reflection layer 6 are sequentially laminated. The reproducing magnetic layer 3 and the recording magnetic layer 4 are arranged adjacent to each other and exchange-coupled with each other to form an exchange-coupling two-layer film 10. These layers 2 to 6 are continuously formed and formed by the vacuum film forming method without breaking the vacuum. And each of these layers 2 of the substrate 1
A protective coat film 7 made of an ultraviolet curable resin or the like is provided so as to cover the entire surface on which the to 5 are provided.

Next, writing of information on the magneto-optical recording medium by the one-beam direct verify method will be described with reference to FIG. Note that, in FIG. 3, only the exchange coupling two-layer film 10 including the reproducing magnetic layer 3 and the recording magnetic layer 4 is shown in the magneto-optical recording medium for facilitating the description, and the magnetization of each of the magnetic layers 3 and 4 is shown. The direction is indicated by an arrow.

First, while rotating the magneto-optical recording medium in the direction of the outlined arrow in the figure, a magnetic head 16 provided near the recording magnetic layer 4 side of the exchange-coupling two-layer film 10 applies a modulation magnetic field to the exchange-coupling two-layer film. Apply to membrane 10. This modulating magnetic field is generated by applying a rectangular wave voltage whose polarity changes positively and negatively at a constant cycle to the magnetic head 16. On the other hand, the laser beam 13 for writing is focused and irradiated as linearly polarized continuous light on the side of the reproducing magnetic layer 3 of the exchange coupling two-layer film 10. The central axis 11 of the laser light 13 is adapted to coincide with the central axis of the magnetic head 16, and the irradiation area of the laser light 13 is the recording area. In this recording area, the temperature of the exchange-coupling two-layer film 10 exceeds the Curie temperature T _c of the recording magnetic layer 4, the magnetization of the recording magnetic layer 4 disappears, and the magnetization direction of the reproducing magnetic layer 3 becomes the direction of the modulation magnetic field. At the time of cooling, the magnetization direction of the exchange coupling two-layer film 10 is aligned with the direction of the modulation magnetic field, and the new data 15 is written regardless of the old data 14. At this time, the reflected light of the laser beam 13 from the exchange-coupling two-layer film 10 has its polarization plane rotated by the magneto-optical effect due to the magnetization direction of the reproducing magnetic layer 3, so that the reflected light (reproducing light) is monitored. By measuring the rotation of the polarization plane of the lever, the direction of magnetization of the reproducing magnetic layer 3 in the writing process can be known. If the direction of the modulating magnetic field and the direction of magnetization of the reproducing magnetic layer 3 do not match, writing will be performed. Since it didn't work, you can check whether the writing was done correctly. The temperature distribution of the exchange coupling two-layer film 10 at this time is as shown in FIG. That is, since there is a heat capacity and it takes time to raise the temperature, the temperature is low at the portion where the laser beam 13 starts to hit, and the highest point 12 of the temperature shifts forward of the central axis 13 of the laser beam 13 in the rotational direction. And laser light 1
In the first part of hit 3, the old data 14 remains.

[0009]

In the above-described conventional magneto-optical recording medium, when writing is performed by the one-beam direct verify method, the maximum temperature of the recording area is rotated as compared with the central axis of the laser beam for writing. Direction forward,
There is a part where the old data remains in the part where the laser beam is applied. The signal due to the magneto-optical effect from the old data mixes with the signal based on the data after writing to cause crosstalk, which lowers the sensitivity and deteriorates the C / N ratio.

An object of the present invention is that writing is carried out by a one-beam direct verify method, and there is little crosstalk of old data to reproduction light monitored at the time of writing, high sensitivity, and C / N ratio. An object is to provide a high magneto-optical recording medium.

[0011]

The magneto-optical recording medium of the present invention comprises a first dielectric layer and a magnetic thin film having a large magnetic Kerr rotation angle and an easy axis of magnetization perpendicular to the film surface on a substrate. A reproducing layer, a recording layer formed of a magnetic thin film having an easy axis of magnetization perpendicular to the film surface, arranged adjacent to the reproducing layer and exchange-coupled with the reproducing layer, and a second dielectric layer are sequentially laminated. If the Curie temperature or the magnetic compensation temperature is lower than the magnetic compensation temperature, the reproducing layer has a higher zero magnetization temperature and a lower coercive force than the recording layer. In a small magneto-optical recording medium, a thin film formed between the recording layer and the second dielectric layer, the thin film being made of a material having a higher thermal conductivity than either the recording layer or the second dielectric layer. It is characterized in that a layer is provided.

[0012]

Since a thin film layer made of a material having a higher thermal conductivity than both the recording layer and the second dielectric layer is provided between the recording layer and the second dielectric layer, the thin film layer for writing is provided. When the laser light is continuously irradiated, heat is rapidly transferred to the recording layer and the reproducing layer along the rotation direction of the magneto-optical recording medium, and the temperature distribution in the recording layer is changed in the portion irradiated with the laser light. It becomes uniform and the old data disappears, and crosstalk of the old data to the reflected light (reproducing light) of the laser light for writing disappears to improve the sensitivity, and C / N
The ratio also improves.

The reproducing layer and the recording layer each have a thickness of 200.
It is selected so as to satisfy desired sensitivity and characteristics in the range of about 400 Å. The magnetic material forming the reproducing layer is preferably a material having a relatively high Curie temperature and a small coercive force, such as Gd-Fe or Gd-Fe-Co. Further, elements such as Cr, Ti and Ta may be added to improve durability. On the other hand, as the magnetic material forming the recording layer, Tb-Fe, Tb-Fe-Co, Dy-F are used.
A material having a relatively low Curie temperature and a large coercive force such as e-Co is preferable.

As the thin film layer, it is desirable to use a metal having a high thermal conductivity. This is to prevent the heat generated by absorbing the laser light from being transferred to the metal layer used as the reflective film, and to quickly transfer this heat into the recording layer. Examples of metals having good thermal conductivity include Cu, Au, Ag,
Although there is Al, etc., in order to prevent corrosion of the recording layer and the reproducing layer, it is desirable to use a metal that is electrochemically baser (has a greater ionization tendency) than those of the recording layer and the reproducing layer. Is preferred. However,
Since pure Al easily crystallizes, an Al alloy to which an element such as Ti, Cr or Ta is added may be used.

When Al is used for the thin film layer, if the film thickness is 70 Å or more, the polarization of the reproduction light becomes elliptically polarized, that is, the phase difference becomes large, and C / C depending on the drive device used for reproduction. The variation in N ratio becomes large. Further, the reflectance of this thin film layer becomes too large, and the recording sensitivity may be deteriorated. On the other hand, if the thickness is less than 20Å, the heat transfer will not be improved. Therefore, when Al is used as the thin film layer, the film thickness is 2
It is preferably 0 to 70Å, and may be determined within this range in consideration of the phase difference and sensitivity, the degree of improvement of the temperature distribution in the recording layer, and the like.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention.

This magneto-optical recording medium is based on an exchange-coupling two-layer film having a reflecting film, and is used to obtain an interference effect and an anticorrosion effect on an optically transparent substrate 1 made of glass or plastic. An undercoat layer 2 made of an inorganic dielectric such as SiN _x , a reproducing magnetic layer 3 serving as a reproducing layer, a recording magnetic layer 4 serving as a recording layer having a coercive force larger than that of the reproducing magnetic layer 3 and a low Curie temperature, and aluminum. An aluminum thin film layer 8, an interference layer 5 made of a dielectric material such as SiN _x for preventing corrosion of the magnetic layers 3 and 4 and obtaining an interference effect, and a metal reflection layer 6 serving as a reflection film are sequentially laminated. .. The reproducing magnetic layer 3 and the recording magnetic layer 4 are arranged adjacent to each other and exchange-coupled to each other, forming an exchange-coupling two-layer film 10. The thermal conductivity of the aluminum thin film layer 8 is higher than that of both the recording magnetic layer 4 and the interference layer 5. These layers 2 to 6 are continuously formed and formed by a vacuum film forming method without breaking the vacuum. A protective coat film 7 made of an ultraviolet curable resin or the like is provided so as to cover the entire surface of the substrate 1 on which these layers 2 to 5 are provided.

Next, the operation of this magneto-optical recording medium will be described. The operation of writing information on this magneto-optical recording medium by the one-beam direct verify method is the same as that described in the above-mentioned conventional technique. However, in the case of the magneto-optical recording medium of this embodiment, since the aluminum thin film layer 8 is provided between the recording magnetic layer 4 and the interference layer 5, when the writing laser beam is irradiated, the laser beam irradiation is performed. The temperature distribution of the recording magnetic layer 5 becomes uniform in the recorded region and the temperature of this region exceeds the Curie temperature of the recording magnetic layer 5, so that the magnetization of the reproducing magnetic layer 4 is oriented in the direction of the modulating magnetic field. Become. In this case, the portion of the old data hardly remains in this area. Therefore, the signal when the reflected light of the writing laser light is monitored contains almost no crosstalk from the old data, the sensitivity is increased, and the C / N ratio is improved.

Next, the magneto-optical recording medium of this embodiment will be described by giving specific numerical values. (Example 1) An undercoat layer 2 made of SiN having a thickness of 1200 Å and a Gd-having a thickness of 100 Å for preventing oxidation and an interference effect is provided on a substrate 1 made of polycarbonate having a diameter of 130 mm and having a pregroove. A reproducing magnetic layer 3 made of Fe-Co, a recording magnetic layer 4 made of Tb-Fe-Co having a thickness of 100Å, and an aluminum thin film having a thickness of 30Å which is a thin film layer for improving the temperature distribution of the magnetic layers 3 and 4. Each of the layer 8, the interference layer 5 made of SiN having a thickness of 450 Å for enhancing the oxidation prevention and the interference effect, and the metal reflection layer 6 made of Al are successively formed by using a magnetron sputtering device without breaking the vacuum. A film was formed and a sample of a magneto-optical recording medium was prepared.

The rotation speed of this sample was 1500 rp.
m, a signal with a frequency of 1 MHz is recorded at a radius of 30 mm from the center by the magnetic field modulation overwrite method, and then a signal with a frequency of 5 MHz is recorded by the 1-beam direct verify method. When the reflected light of the light was monitored and the signal was detected, the frequency 1M corresponding to the old data was detected.
The Hz signal component was reduced by -20 dB from the conventional one. (Example 2) An undercoat layer 2 made of SiN having a thickness of 1100 Å and a Gd- having a thickness of 100 Å for preventing oxidation and an interference effect is provided on a substrate 1 made of polycarbonate having a diameter of 130 mm and having a pre-groove. A reproducing magnetic layer 3 made of Fe-Co, a recording magnetic layer 4 made of Tb-Fe-Co having a thickness of 200Å, and an aluminum thin film having a thickness of 50Å which is a thin film layer for improving the temperature distribution of each magnetic layer 3, 4. The layer 8, the interference layer 5 made of SiN having a thickness of 300 Å for enhancing the oxidation prevention and the interference effect, and the metal reflection layer 6 made of Al are successively formed by using a magnetron sputtering device without breaking the vacuum. A film was formed and a sample of a magneto-optical recording medium was prepared.

The rotation speed of this sample was 1500 rp.
m, a signal with a frequency of 1 MHz is recorded at a radius of 30 mm from the center by the magnetic field modulation overwrite method, and then a signal with a frequency of 5 MHz is recorded by the 1-beam direct verify method. When the reflected light of the light was monitored and the signal was detected, the frequency 1M corresponding to the old data was detected.
The Hz signal component was reduced by -20 dB from the conventional one.

[0022]

As described above, the present invention provides a thin film between the recording layer and the second dielectric layer, which is made of a material having a higher thermal conductivity than both the recording layer and the second dielectric layer. By providing the layer, the temperature distribution in the recording layer at the time of writing is improved, and at the time of writing in the 1-beam direct verify method, the crosstalk from the old data to the reproduced light to be monitored is greatly reduced and the sensitivity is improved. , C / N
There is an effect that a magneto-optical recording medium having a good ratio can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a magneto-optical recording medium according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the configuration of a conventional magneto-optical recording medium.

FIG. 3 is a diagram illustrating writing of information by a modulation magnetic field overwrite method in a conventional magneto-optical recording medium.

[Explanation of symbols]

 1 Substrate 2 Undercoating Layer 3 Reproducing Magnetic Layer 4 Recording Magnetic Layer 5 Interference Layer 6 Metal Reflective Layer 7 Protective Coating Film 8 Aluminum Thin Film Layer 13 Laser Light 14 Old Data 15 New Data 16 Magnetic Head

Claims (3)

[Claims] 1. A first dielectric layer, a reproducing layer made of a magnetic thin film having a large Kerr rotation angle and having an easy axis of magnetization perpendicular to the film surface, and an easy axis of magnetization perpendicular to the film surface are provided on a substrate. A recording layer made of a magnetic thin film having the recording layer, which is disposed adjacent to the reproducing layer and exchange-coupled with the reproducing layer, and a second dielectric layer are sequentially laminated, and if there is a Curie temperature or a magnetic compensation temperature, a magnetic compensation temperature is obtained. In the magneto-optical recording medium, the reproduction layer has a higher zero magnetization temperature and a smaller coercive force than the recording layer when the lower one has a zero magnetization temperature. And a second dielectric layer, a thin-film layer made of a material having a higher thermal conductivity than either the recording layer or the second dielectric layer is provided. recoding media. 2. The magneto-optical recording medium according to claim 1, wherein the thin film layer is made of metal. 3. The magneto-optical recording medium according to claim 2, wherein the thin film layer contains Al as a main component.