JPH05205333A - Magnetooptical recording medium, recording method thereof and magnetooptical recorder - Google Patents

Abstract

PURPOSE:To provide the magnetooptical recording medium which is simple in structure, can be easily produced and enables stable recording in overwriting in spite of the presence of a change in temp., use environment or the intensity of irradiating light. CONSTITUTION:A recording layer 12 which exhibits perpendicular magnetic anisotropy and a recording auxiliary assist layer 14 which has intra-surface magnetic anisotropy at a temp. near room temp. and can be easily magnetized and oriented in the perpendicular direction at a prescribed recording temp. are laminated. The binary recording on this magneto-optical recording medium is executed by heating the medium up to about the Curie temp. Tc of the recording layer 12 to orient the recording layer 12 in the direction of Hb1 while impressing a bias magnetic field Hb1 to the medium from the recording layer 12 side and impressing a bias magnetic field Hb2 from the recording auxiliary assist layer 14 side (Hb1 and Hb2 are counterparallel and ¦Hb1¦<¦Hb2¦), [magnetization state (b)] or heating the medium up to the temp. Tm at which the recording auxiliary assist layer 14 is easily oriented in the perpendicular direction to orient the recording layer 12 in the direction of Hb2 [magnetization states (c) to (d)].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium, a recording method therefor, and a magneto-optical recording apparatus used for recording on a magneto-optical recording medium.

[0002]

2. Description of the Related Art In recent years, an optical information recording / reproducing apparatus capable of recording information at high density by converging and irradiating a light beam with an optical head (so-called pickup) has been put into practical use. Even in this optical information recording / reproducing apparatus,
An erasable and rewritable magneto-optical recording device
It can be used in place of a conventional magnetic recording device.

In a conventional magneto-optical recording apparatus, information is recorded by converging and irradiating a light beam with a bias magnetic field applied in the direction opposite to the magnetization direction of the magneto-optical recording medium. In this case, the recording information can be rewritten only after the operation of irradiating the light beam again with the direction of the bias magnetic field reversed to align the magnetization direction to the original state (erasing operation). That is, this apparatus cannot perform overwriting recording. Therefore, in order to allow rewriting without performing an erasing operation, a method such as a magnetic field modulation method in which a bias magnetic field is modulated according to recording information has been proposed. However, in this magnetic field modulation method, it is difficult to record at a high frequency due to the inductance of the coil, and it is difficult to record information at high speed and high density.

For this reason, a magneto-optical recording medium which can perform overwriting recording without applying a bias magnetic field from the outside has been studied, and a medium as disclosed in JP-A-62-154347 has been proposed. This magneto-optical recording medium is shown in FIG.
As shown in, the magneto-optical recording layer 52, the non-magnetic layer 53, and the bias magnetic layer 54 are sequentially laminated on the surface of the transparent substrate 51, and the protective layer 55 is further laminated on the bias magnetic layer 54. .. The temperature-saturation magnetization characteristics of the magneto-optical recording layer 52 and the bias magnetic layer 54 are shown in FIG. 9, and as can be seen from this figure, the bias magnetic layer 5
4 is room temperature and its Curie temperature (temperature at which magnetization disappears)
It is composed of a ferrimagnetic material having a temperature (compensation temperature) at which the direction of the spontaneous magnetization is reversed between and. On the other hand, the magneto-optical recording layer 52 is made of a magnetic material having a Curie temperature higher than the compensation temperature of the bias magnetic layer 54.

In this magneto-optical recording medium, the recording magnetic field applied to the magneto-optical recording layer 52 is controlled by converging and irradiating a light beam that is modulated into two intensities, large and small, according to the recording signal, and the overwriting is performed. The record is realized. Here, for the sake of explanation, in FIG. 3, it is assumed that the magnetization direction of the bias magnetic layer 54 is upward at room temperature. When the laser beam having the smaller intensity is irradiated, the bias magnetic layer 54 is heated to a temperature T _L which is somewhat lower than the compensation temperature, and the magneto-optical recording layer 52 is reduced in coercive force. Irrespective of the magnetization direction, the upward magnetization state is achieved by the bias magnetic field formed by the upward magnetization of the bias magnetic layer 54.
Meanwhile, when irradiated with laser light having an intensity larger, the bias magnetic layer 54 is heated to a higher temperature T _H than its compensation temperature, the downward reversed spontaneous magnetization orientation. As a result, the magneto-optical recording layer 52 becomes a downward magnetization state by the bias magnetic field formed by the downward magnetization of the bias magnetic layer 54. Since the coercive force of the magneto-optical recording layer 52 is large near room temperature, the magnetized state of the magneto-optical recording layer 52 is maintained independently of the magnetization direction of the bias magnetic layer 54. In this way, in this magneto-optical recording medium, binary overwriting recording becomes possible only by changing the intensity of the laser light without applying a bias magnetic field from the outside.

[0006]

However, the above-mentioned Japanese Unexamined Patent Publication No.
Magneto-optical recording medium as shown in JP-A-2-154347
In the body, at a temperature very close to the compensation temperature of the bias magnetic layer
It is necessary to record magnetization on the magneto-optical recording layer.
In addition, the Curie temperature of the magneto-optical recording layer also falls within these recording temperatures.
Because they're so close together, in reality
Difficult to do. That is, the
The engine becomes smaller. In addition, the bias magnetic layer generates
The magnitude of the bias field modulated by the laser beam
Is the magnetization of the bias magnetic layer at room temperature M_b(R)
The magnetization at the irradiation position depends on the irradiation intensity of the laser beam.
± M_bIf it changes to (C), it will be added to the magneto-optical recording layer.
The Yias magnetic field is (M
_b(R) -M_b(C))²And (M_b(R) + M _b(C))²Proportional to
Will be things. By the way, the value M near the compensation temperature_b(C)
Is close to zero, the bias magnetic field is actually
It will not change.

As described above, the above-described conventional magneto-optical recording medium is capable of overwriting in principle without applying a bias magnetic field from the outside, but it is difficult to actually perform overwriting. It is a thing.

In view of the above points, an object of the present invention is that the structure is simple and can be easily manufactured, and stable overwriting recording is possible even if there is a change in temperature, environment of use, irradiation light intensity, or the like. An object of the present invention is to provide a magneto-optical recording medium that can be performed, a recording method for the magneto-optical recording medium, and a magneto-optical recording device suitable for recording on the magneto-optical recording medium.

[0009]

A magneto-optical recording medium of the present invention comprises a recording layer having perpendicular magnetic anisotropy and a recording auxiliary layer having in-plane magnetic anisotropy at a temperature near room temperature on a substrate. Are laminated, and the recording auxiliary layer can be easily oriented in a direction perpendicular to the surface of the substrate at a predetermined recording temperature.

The magneto-optical recording method of the present invention is the magneto-optical recording method of the present invention.
A magnetic recording medium is used, and the recording layer and the recording layer of the magneto-optical recording medium are used.
And the recording auxiliary layer from the side of the recording layer.
Perpendicular to the magneto-optical recording medium at the irradiation position
Direction of the first bias magnetic field H _b1Apply the recording aid
From the side of the layer to the magneto-optical recording medium at the irradiation position
In the vertical direction, the first bias magnetic field H_b1Greater than
Second bias magnetic field H that is strong and reverse_b2Is applied
(A) The recording layer is close to the Curie temperature of the recording layer.
A laser beam that only heats up is applied to the magneto-optical recording medium.
The magnetization of the recording layer by irradiating
As magnetic field H_b1The first kind of recording oriented in the direction of
(B) The magnetization of the recording auxiliary layer is the second bias magnetic field.
H_b2Laser beam that can be heated up to the temperature to orient in
By irradiating the magneto-optical recording medium with
The magnetization direction of the recording auxiliary layer is set to the second bias magnetic field H._b2
Orientation, and then the direction of magnetization of the recording layer
A second type of recording in which the magnetization direction of the recording auxiliary layer is aligned,
The binary recording consisting of

A magneto-optical recording apparatus according to the present invention is provided with an objective lens which is provided so as to face one surface of a magneto-optical recording medium and focuses a laser beam. An actuator that moves the objective lens so as to form a focus at a predetermined recording position on a surface and a magneto-optical recording medium sandwiched between the actuator and the actuator, and are sufficient to converge the leakage magnetic field lines from the actuator. A high magnetic permeability member having a high magnetic permeability, and is fixed substantially at the center of the surface of the high magnetic permeability member on the side of the magneto-optical recording medium, and the leakage magnetic field line is opposite to the recording position from the other surface side. And a micro magnet that gives a parallel magnetic field.

[0012]

First, the operation of the magneto-optical recording medium and the magneto-optical recording method of the present invention will be described by explaining the magnetization process of the magneto-optical recording medium of the present invention with reference to FIG.

In the magneto-optical recording medium of the present invention, a recording layer 12 exhibiting perpendicular magnetic anisotropy and a recording auxiliary layer 14 exhibiting in-plane magnetic anisotropy at a temperature near room temperature are laminated on a substrate. It is a composition. The recording auxiliary layer 14 can be easily oriented in a direction perpendicular to the surface of the substrate at a predetermined recording temperature. Here, the recording position of the magneto-optical recording medium, a first bias magnetic field H _b1 is applied from the recording layer 12 side, applying a second bias magnetic field H _b2 from the recording auxiliary layer 14 side. The directions of the bias magnetic fields H _b1 and H _b2 are set to be opposite to each other, and the magnitude thereof is | H
_b1 | <| H _b2 | is established. Here, for the sake of explanation, the first bias magnetic field H _b1 is downward,
The second bias magnetic field _Hb2 is assumed to be upward. Of course, the bias magnetic fields H _b1 and H _b2 may be reversed.

At room temperature, since the recording auxiliary layer 14 is in-plane magnetically oriented, substantially only the first bias magnetic field H _b1 is applied to the recording layer 12. In addition, since the recording layer 12 has a sufficiently large coercive force at room temperature, it does not depend on the direction of the bias magnetic field H _b1 , and thus the recording layer 12 has one of two states of downward [magnetization state (a)] and upward [magnetization state (e)]. One of the states can be stably maintained.

The smaller intensity P of the two intensities_Lof
When the magneto-optical recording medium is irradiated with a laser beam, recording is performed.
Layer 12 has its Curie temperature T_cThe temperature is raised to the vicinity and the recording layer
The coercive force of 12 weakens. At this temperature, the recording auxiliary layer 14
Of the second bias magnetic field H_b2Vertically arranged by
The second bias magnetic field H_b2Is
It is shielded by the recording auxiliary layer 14 and is not added to the recording layer 12.
Yes. Therefore, it depends on the magnetization state before the laser beam irradiation.
Of the first bias magnetic field H _b1Porcelain
It is oriented in the magnetization direction and is in the downward magnetization state (b). Here?
If cooled from above, it will be in one stable magnetization state (a) at room temperature.
[Type 1 record].

On the other hand, the greater of the two intensities
P_HIrradiating this magneto-optical recording medium with a laser beam of
And the recording layer 12 has a Curie temperature T_cTemperature rises above
As a result, the recording auxiliary layer 14 also becomes higher than its Curie temperature.
The magnetization disappears, or the second bias magnetic field H_b2To
Therefore, the temperature T at which the vertical orientation is possible_mReach [Magnet
State (c)]. Here, the in-plane anisotropy of the recording auxiliary layer 14 is
It has been lost, and also | H_b1｜ ＜ ｜ H_b2｜ will be
Each bias magnetic field H_b1, H_b2Is set,
The recording layer 12 has a second bias magnetic field H_b2In the direction of | H
_b2|-| H_b1The recording magnetic field of the magnitude of |
It When the temperature is lowered from this state, the magnetic field of the recording auxiliary layer 14 is reduced.
The crystallization increases while being oriented vertically. This is the second
Bias magnetic field H _b2Is applied, the recording
The magnetization of the auxiliary layer 14 is oriented in the in-plane direction when the temperature rises.
Lower than the temperature oriented from the vertical direction to the recording layer 12
Curie temperature T_cBecause it will be much lower. this
Therefore, when the magnetization of the recording layer 12 is recovered by lowering the temperature,
The layer 12 has a second bias magnetic field H_b2The recording magnetic field in the direction of
In addition, the recording layer 12 has an upward magnetization state.
That is, the other magnetization state (e) is stable at room temperature [second
Seed record].

As described above, by modulating the intensity of the laser beam with the binary intensity P _H , P _L , the magnetization state after the irradiation is stable at room temperature regardless of the magnetization state before the irradiation of the laser beam. Can be any one of these, and overwrite recording will be achievable.

The magneto-optical recording medium of the present invention has a structure in which a recording layer and a recording auxiliary layer are provided on a substrate. However, in order to improve the recording stability and to make it less susceptible to the external environment, the usual recording medium is used. In this case, a transparent substrate is used as a substrate, a recording layer and a recording auxiliary layer are sequentially deposited and laminated on this transparent substrate, and a protective layer is further provided on the recording auxiliary layer. As the material of the transparent substrate, plastics such as acrylic resin, polycarbonate, and polyolefin, and glass are used.

As the material of the recording layer and the recording auxiliary layer, for example, rare earth elements such as Tb, Gd, Dy, Nd and Fe, Co,
An amorphous alloy with a transition metal element such as Ni can be used. In addition, alloys such as MnBi and PtCo, and intermetallic compounds may be used. Alternatively, an oxide-based magnetic material such as garnet or ferrite may be used.

The recording layer preferably has a coercive force of 1 kOe or more at room temperature, and its Curie temperature T _c is 10.
The temperature is preferably 0 to 400 ° C. It is necessary that the recording auxiliary layer does not have magnetization saturation in the direction perpendicular to the substrate surface due to the applied bias magnetic field at room temperature, and the magnetic field required for magnetization saturation in the perpendicular direction at room temperature is 1 kO.
It is desirable that it is e or more. Further, at the predetermined temperature (recording temperature) reached at the time of recording, this recording auxiliary layer needs to be magnetized in the perpendicular direction by the applied bias magnetic field or the magnetization should disappear. When the magnetization of the recording auxiliary layer disappears at the temperature reached during recording, it is easy for the magnetization direction to be perpendicular to the temperature immediately before the magnetization disappears (that is, the temperature near the Curie temperature of the recording auxiliary layer). Must be

A nonmagnetic layer may be provided between the recording layer and the recording auxiliary layer. Here, if a material having a lower thermal conductivity than the recording layer or the recording auxiliary layer is used for the non-magnetic layer, the recording sensitivity is improved. When the recording layer is such that recording / reproducing light is transmitted to some extent, a translucent non-magnetic layer is used to change the film thickness, thereby changing the reflectivity of the magneto-optical recording medium. You can also adjust the car rotation angle. Materials for the non-magnetic layer include SiO, Si ₃ N ₄ and MgF.
₂ , oxides, nitrides, fluorides of inorganic materials such as ZnS,
Sulfide or the like is used. In addition, organic polymer materials such as acrylic resin, polyethylene, and polystyrene may be used.

Further, a reflective layer may be provided between the recording layer and the recording auxiliary layer. This is because when the light transmitted through the recording layer is reflected by the recording auxiliary layer and the polar Kerr effect is applied at the boundary (domain wall) of each magnetic domain oriented in the in-plane direction of the recording auxiliary layer, the noise of the reproduced signal increases. Therefore, it is provided to prevent the increase of this noise. When the reflective layer is provided, light does not enter the recording auxiliary layer, so that an increase in noise due to the polar Kerr effect can be suppressed. The material of the reflective layer is A
It is desirable to use a material having a high reflectance such as l, AlCr, AlTi, AlTa. Further, as long as it is non-magnetic and serves as a reflective film, one layer can serve as the reflective layer and the non-magnetic layer.

When recording is performed on this magneto-optical recording medium using the above-mentioned magnetization process, the magnitudes of the first and second bias magnetic fields H _b1 and H _b2 are 100 to 1000 O, respectively.
It is desirable to set it to about e, and it is desirable to set the difference | H _b2 | − | H _b1 | of these bias magnetic field magnitudes to about 100 to 500 Oe.

Although the basic structure of the magneto-optical recording medium of the present invention has been described above, the present invention can be applied to a magneto-optical recording medium having a so-called exchange coupling two-layer film. From the exchange coupling two-layer film to the magneto-optical recording medium, a first magnetic layer (reading layer) having a relatively high Curie temperature and a small coercive force and a second magnetic layer having a relatively high Curie temperature and a large coercive force. A layer (recording layer) is laminated so as to be exchange-coupled with each other, and the recording made on the second magnetic layer is transferred to the first magnetic layer and reproduced mainly by using the first magnetic layer. Is to do. Here, the second magnetic layer (recording layer) of the magneto-optical recording medium of this exchange-coupling two-layer film is used as the recording layer of the above-mentioned magneto-optical recording medium of the present invention, and on this recording layer (that is, the first layer
The recording auxiliary layer may be provided on the side other than the magnetic layer (reading layer) side.

Next, the recording process of this magneto-optical recording medium having a further read layer will be described with reference to FIG. In this magneto-optical recording medium, a reading layer 17, a recording layer 12 showing perpendicular magnetic anisotropy exchange-coupled with the reading layer 17, and a recording showing in-plane magnetic anisotropy at a temperature near room temperature are formed on a substrate. The auxiliary layer 14 is laminated in this order. Of course, a nonmagnetic layer or a reflective layer may be provided between the recording layer 12 and the recording auxiliary layer 14. The recording auxiliary layer 14 can be easily oriented in a direction perpendicular to the surface of the substrate at a predetermined recording temperature.
Here, at the recording position of this magneto-optical recording medium, the reading layer 1
A first bias magnetic field H _b1 is applied from 7 side, applying a second bias magnetic field H _b2 from the recording auxiliary layer 14 side. The directions of these bias magnetic fields H _b1 and H _b2 are set to be opposite to each other, and | H _b1 | <| H _b2 | Here, for the sake of explanation, it is assumed that the first bias magnetic field H _b1 is downward and the second bias magnetic field H _b2 is upward. Further, it is assumed that the readout layer 17 and the recording layer 12 are in a stable state when their magnetization orientations are parallel to each other due to exchange interaction. Of course, the bias magnetic fields H _b1 and H _b2 may be reversed.

At room temperature, since the recording auxiliary layer 14 is magnetically oriented in the plane, substantially only the first bias magnetic field H _b1 is applied to the read layer 17 and the recording layer 12. In addition, since the recording layer 12 has a sufficiently large coercive force at room temperature, it does not depend on the direction of the bias magnetic field H _b1 , and thus the recording layer 12 has one of two states of downward [magnetization state (a)] and upward [magnetization state (e)]. One of the states can be stably maintained, and the read layer 17 is also magnetically oriented parallel to the magnetization direction of the recording layer 12.

When the magneto-optical recording medium is irradiated with a laser beam having a smaller intensity P _L of the two intensity values, the recording layer 12 is heated to a temperature near the Curie temperature T _c and the recording layer 12 is reached. The coercive force of is weakened. At this temperature, the magnetization of the recording auxiliary layer 14 is not oriented in the perpendicular direction by the second bias magnetic field H _b2 , and therefore the second bias magnetic field H _b2 is shielded by the recording auxiliary layer 14 to the recording layer 12. Does not join. Therefore, the recording layer 12 is oriented in the magnetization direction of the first bias magnetic field _Hb1 regardless of the magnetization state before the irradiation of the laser beam, and becomes the downward magnetization state (b). If cooled from here, one of the magnetization states (a) is stable at room temperature [first-type recording].

On the other hand, when the magneto-optical recording medium is irradiated with a laser beam having a higher intensity P _H of the binary intensity, the recording layer 12 is heated to the Curie temperature T _c or higher, and the recording auxiliary layer 14 is reached. Also, the magnetization disappears at the Curie temperature or higher, or the temperature reaches the temperature T _{m at} which the second bias magnetic field H _b2 enables the orientation in the vertical direction [magnetization state (c)]. Here, the in-plane anisotropy of the recording auxiliary layer 14 is lost, and the bias magnetic fields H _b1 and H _b2 are set in advance so that | H _b1 | <| H _b2 |
The recording layer 12 has | H in the direction of the second bias magnetic field H _b2.
A recording magnetic field having a magnitude of _b2 |-| H _b1 | is applied. At this time, since the read layer 17 has a small perpendicular magnetic anisotropy and a high Curie temperature, the magnetization is oriented in the in-plane direction,
The magnetic field lines of the first bias H _b1 are prevented from reaching the recording layer 12. As a result, the component of the recording magnetic field applied to the recording layer 12 parallel to the second bias magnetic field H _b2 is substantially increased, and the magnetization reversal of the recording layer 12 is assisted. When the temperature is lowered from this state, the magnetization of the recording auxiliary layer 14 increases while being oriented vertically. This is because the second auxiliary magnetic field H _b2 is applied to the recording auxiliary layer 1
The magnetization of No. 4 is oriented in the in-plane direction because it is lower than the temperature oriented in the vertical direction from the in-plane direction at the time of temperature rise and much lower than the Curie temperature T _c of the recording layer 12. For this reason,
When the magnetization of the recording layer 12 is recovered by lowering the temperature, the recording layer 12
A recording magnetic field in the direction of the second bias magnetic field H _b2 is applied to the recording layer 12, and the magnetization orientation of the recording layer 12 becomes upward.
Along with this, the magnetization orientation of the read layer 17 also becomes upward, and the other magnetization state (e) is stable at room temperature [second type recording].

As described above, by modulating the intensity of the laser beam with the binary intensity P _H , P _L , the magnetization state after irradiation is stable at room temperature regardless of the magnetization state before irradiation with the laser beam. Can be any one of these, and overwrite recording will be achievable.

In this magneto-optical recording medium, the material of the reading layer, the recording layer, and the recording auxiliary layer is, for example, Tb,
An amorphous alloy of a rare earth element such as Gd, Dy or Nd and a transition metal element such as Fe, Co or Ni can be used.
In addition, alloys such as MnBi and PtCo, and intermetallic compounds may be used. Alternatively, an oxide-based magnetic material such as garnet or ferrite may be used.

The read layer preferably has a coercive force of 0.5 kOe or less at room temperature and a Curie temperature of about 150 to 400 ° C. The recording layer preferably has a coercive force of 1 kOe or more at room temperature, and its Curie temperature T _c is preferably 100 to 400 ° C. It is necessary that the recording auxiliary layer does not undergo magnetization saturation in the direction perpendicular to the substrate surface by the bias magnetic field applied at room temperature, and it is desirable that the magnetic field required for magnetization saturation in the perpendicular direction at room temperature is 1 kOe or more. Further, at the predetermined temperature (recording temperature) reached at the time of recording, this recording auxiliary layer needs to be magnetized in the vertical direction by the applied bias magnetic field or the magnetization should disappear. When the magnetization of the recording auxiliary layer disappears at the temperature reached during recording, it is easy for the magnetization direction to be perpendicular to the temperature immediately before the magnetization disappears (that is, the temperature near the Curie temperature of the recording auxiliary layer). Must be

Next, the operation of the magneto-optical recording apparatus of the present invention will be described. This magneto-optical recording apparatus includes an actuator for focusing a laser beam by an objective lens, and a micro magnet provided on the opposite side of the magneto-optical recording medium from the actuator. The respective magnetic lines of force are parallel to each other at the recording position of the magneto-optical recording medium. Therefore, in order to generate two anti-parallel bias magnetic fields that are required in each of the above-mentioned magneto-optical recording media, no new magnetic field generating means is required except for one micro magnet. Further, since the high magnetic permeability member is arranged on the side opposite to the laser beam spot on the magneto-optical recording medium,
The leakage magnetic force lines from the actuator are separated from the micro magnets themselves because the directions of the magnetic force lines are antiparallel, but are easily collected in the high magnetic permeability member holding the micro magnets.
Therefore, the bias magnetic field (first bias magnetic field H from the actuator side of the surface of the magneto-optical recording medium is adjusted by adjusting the area ratio and the interval between the micro magnet and the high magnetic permeability member.
_b1 ) can be made stronger than when a large fixed magnet is used as a means for generating the other bias magnetic field (second bias magnetic field _Hb2 ). Therefore, even if the leakage magnetic field from the actuator is weak, a magnetic field sufficient for recording can be applied to the magneto-optical recording medium. In this magneto-optical recording device, only one minute magnet needs to be added, and the optical modulation overwrite can be achieved with a smaller device as compared with the conventional device having a large magnet.

[0033]

Embodiments of the present invention will now be described with reference to the drawings.

Example 1 FIG. 1 is a schematic sectional view showing the structure of a magneto-optical recording medium according to an example of the present invention. This magneto-optical recording medium includes an undercoat layer 18 made of a dielectric material, a recording layer 12 showing perpendicular magnetic anisotropy, a non-magnetic layer 13 on the surface of a transparent substrate 11 and an in-plane magnetic anisotropy at a temperature near room temperature. A recording auxiliary layer 14 having a property is sequentially deposited, and a protective layer 15 is further laminated on the recording auxiliary layer 14. The recording auxiliary layer 14 can be easily oriented in a direction perpendicular to the surface of the transparent substrate 11 at a predetermined recording temperature. Here, the result of actually producing this magneto-optical recording medium and evaluating its characteristics will be described.

Tb ₂₁ Fe ₇₄ Co ₅ was added to a sputtering system (Model 8ES manufactured by Tokuda Manufacturing Co., Ltd.) having three sputtering guns.
Alloy target of composition (atomic%, same below), Pt ₆₀
An alloy target having a Co ₄₀ composition and a powder sintering target of Si ₃ N ₄ were set. Next, a polycarbonate substrate (transparent substrate) having a thickness of 1.2 mm and a diameter of 130 mm, in which a pre-groove and a pre-format signal were formed, was set in this sputtering apparatus. Then, sputtering is sequentially performed under a pressure of 0.5 Pa while flowing an argon gas, and an undercoat layer made of a Si ₃ N ₄ film having a thickness of about 800 Å and a TbFeCo film having a thickness of about 400 Å are formed on the transparent substrate. Recording layer, non-magnetic layer made of Si ₃ N ₄ film having a thickness of about 500Å, auxiliary recording layer made of PtCo film having a thickness of about 800Å,
A protective layer made of a Si ₃ N ₄ film having a thickness of about 800 Å was sequentially laminated to complete a sample disk of a magneto-optical recording medium.

Separately, a thickness of 400 Å on a glass substrate
When only the TbFeCo film was formed, the film exhibited perpendicular magnetic anisotropy, and its coercive force at room temperature was about 10 kOe.
And the Curie temperature was 160 ° C. Further, when only a PtCo film having a thickness of 800 Å is formed on a glass substrate, this film exhibits in-plane magnetic anisotropy, and a magnetic field of about 5 kOe is required for magnetization saturation in the perpendicular direction at room temperature. It was The Curie temperature is about 250 ° C., and when heated to, for example, 200 ° C., it was possible to saturate the magnetization in the perpendicular direction with a magnetic field of about 200 Oe.

Next, a recording experiment was conducted on this sample disk by using an evaluation apparatus (model OMS-2000 manufactured by Nakamichi Co., Ltd.). The configuration of the main part of this evaluation device is shown in FIG. That is, the lens barrel 45 is provided so as to face a predetermined recording position of the magneto-optical recording medium 44, and the objective lens 43 for focusing the laser beam on the recording position is provided inside the lens barrel 45. Is provided. In this case, the magneto-optical recording medium 44 is the transparent substrate 1
The one side is arranged so as to face the objective lens 43. Further, a ring-shaped ferrite magnet 41 is attached to the end of the lens barrel 45 on the side of the magneto-optical recording medium 44, and the objective lens 4
The laser beam incident on the magneto-optical recording medium 44 from 3
The ferrite magnet 41 passes through the central opening. This ferrite magnet 41 has a first bias magnetic field H.
_b1 is applied downward to the magneto-optical recording medium 44. On the other hand, with respect to the magneto-optical recording medium 44, a magnet 42 for applying an upward second bias magnetic field H _b2 to the magneto-optical recording medium 44 is provided on the opposite side of the objective lens 43. The magnet 42 may be a permanent magnet or an electromagnet, but here, a bias electromagnet used for recording on a conventional magneto-optical recording medium is used. The magnitude of the first bias magnetic field H _b1 was set to be a magnetic field of 200 Oe on the substrate surface of the magneto-optical recording medium 44. On the other hand, the second bias magnetic field H _b2 is 0 to 0 at the substrate surface of the magneto-optical recording medium 44.
Recording experiments were conducted by changing the values to various values so that the magnetic field was in the range of -1000 Oe. Incidentally, Tagged the negative of the value of the second bias magnetic field H _b2, indicating that the first bias magnetic field H _b1 antiparallel.

In the recording experiment, the magneto-optical recording medium 44 was used.
Was moved at a linear velocity of 5 m / sec, and the binary laser power (P _L , P _H ) was changed within the range of 3 to 12 mW. The duty ratio of the laser pulse was 50%. Recording was performed under various conditions on the above-mentioned sample disk which was not erased (magnetization of the recording layer in one direction), the recorded information was read, and the ratio of carrier C and noise N, that is, C / The N ratio was evaluated. In addition,
The recording frequency at this time is 1 MHz, and the first bias magnetic field H _b1 is 200 Oe as described above. Some of the results are shown in Table 1 (Experiment Nos. 1 to 5) below.

[0039]

[Table 1] In Experiment Nos. 1 and 2, the Curie temperature T _{c of the} recording layer was determined by the one having the smaller intensity P _L of the binary laser power.
Since the temperature rises to the vicinity, the first type recording was performed,
Binary recording could not be performed because the second bias magnetic field H _b2 required for performing the second type recording was insufficient ("C, N change" is described in the comment column). On the other hand, in the experiment numbers 3 to 5, the second bias magnetic field H _b2
Is sufficiently large, it was possible to perform binary recording.

Overwriting recording was carried out under the same conditions except that the recording frequency was set to 1.5 MHz in the area recorded in Experiment No. 4, and it was found to be 1.5 MH during reproduction.
C / N ratio is 38 dB at z frequency and 1 MHz
It was confirmed that the carrier had disappeared. From this, it was confirmed that overwriting can be performed well.

Example 2 In the above example, only the non-magnetic layer was provided between the recording layer and the recording auxiliary layer of the magneto-optical recording medium, but here, in addition to the non-magnetic layer, the reflective layer was provided. It is provided. FIG. 3 is a schematic sectional view showing the structure of the magneto-optical recording medium of this embodiment. That is, in the magneto-optical recording medium of the above embodiment, the reflection layer 16 is provided between the non-magnetic layer 13 and the recording auxiliary layer 14.
Is provided. Here, the result of actually producing this magneto-optical recording medium and evaluating its characteristics will be described.

In a sputtering apparatus having four sputtering guns, an alloy target of Tb ₂₁ Fe ₇₄ Co ₅ composition and Pt were used.
An alloy target having a composition of ₆₀ Co _40, a powder sintering target of Si ₃ N ₄ , and an alloy target having a composition of Al ₉₅ Ti ₅ were set. Next, a polycarbonate substrate (transparent substrate) having a thickness of 1.2 mm and a diameter of 130 mm, in which a pre-groove and a pre-format signal were formed, was set in this sputtering apparatus. Then, while flowing argon gas, 0.5
Sputtering is sequentially performed under a pressure of Pa, and an undercoat layer made of a Si ₃ N ₄ film having a thickness of about 800 Å is formed on the transparent substrate.
A recording layer made of a TbFeCo film having a thickness of about 400Å, a non-magnetic layer made of a Si ₃ N ₄ film having a thickness of about 500Å, a thickness of about 35
Reflective layer consisting of 0Å AlTi film, P about 800Å thick
Recording auxiliary layer made of tCo film, Si _{3 of} about 800 Å
A protective layer made of N ₄ film was sequentially laminated to complete a sample disk of a magneto-optical recording medium.

Separately, a glass substrate having a thickness of 400 Å
When only the TbFeCo film was formed, the film exhibited perpendicular magnetic anisotropy, and its coercive force at room temperature was about 10 kOe.
And the Curie temperature was 160 ° C. Further, when only a PtCo film having a thickness of 800 Å is formed on a glass substrate, this film exhibits in-plane magnetic anisotropy, and a magnetic field of about 5 kOe is required for magnetization saturation in the perpendicular direction at room temperature. It was The Curie temperature is about 250 ° C., and when heated to, for example, 200 ° C., it was possible to saturate the magnetization in the perpendicular direction with a magnetic field of about 200 Oe.

Next, with respect to this sample disk, the evaluation device (Nakamichi
Recording experiments were conducted using a model OMS-2000 manufactured by Co., Ltd. Some of the results are shown in Table 1 (Experiment No. 6 to 10)
Shown in. The recording frequency at this time is 1 MHz, and the first bias magnetic field H _b1 is 200 Oe.

As a result, in Experiment Nos. 6 and 7, binary level
The smaller intensity P of the power_LDepending on
Curie temperature T of recording layer_cAs the temperature rises to near,
Seed recordings made, but second recordings made
Second bias magnetic field H required for _b22 because there is not enough
Value recording could not be done. In contrast, the experiment
In the numbers 8 to 10, the second bias magnetic field H_b2Is big enough
Therefore, binary recording was possible.

Overwriting recording was carried out under the same conditions except that the recording frequency was set to 1.5 MHz in the area recorded in Experiment No. 9, and it was 1.5 MH during reproduction.
C / N ratio is 43 dB at z frequency and 1 MHz
It was confirmed that the carrier had disappeared. From this, it was confirmed that overwriting can be performed well.

By comparing the results of Examples 1 and 2 shown in Table 1, it was found that the provision of the reflective layer reduces noise and improves the C / N ratio.

Example 3 In this example, the present invention is applied to a magneto-optical recording medium composed of an exchange coupling two-layer film. FIG. 4 is a schematic sectional view showing the structure of the magneto-optical recording medium of this example. As shown in the figure, this magneto-optical recording medium is the same as the magneto-optical recording medium of Example 1 except that the read layer 17 is provided between the undercoat layer 18 and the recording layer 12. The readout layer 17 is exchange-coupled with the recording layer 12,
The Curie temperature is relatively higher than the Curie temperature of the recording layer 12, and its coercive force at room temperature is relatively smaller than the coercive force at room temperature of the recording layer 12. Here, the result of actually producing this magneto-optical recording medium and evaluating its characteristics will be described.

In a sputtering apparatus having four sputtering guns, an alloy target of Tb ₂₁ Fe ₇₄ Co ₅ composition and Gd
An alloy target having a composition of ₂₄ Fe ₇₀ Co ₆ and Pt ₆₀ Co ₄₀
An alloy target composition was set and the powder sintered target of Si ₃ N _4. Next, thickness 1.2mm, diameter 130
A polycarbonate substrate (transparent substrate) on which a mm pregroove and a preformat signal were formed was set in this sputtering apparatus. And while flowing argon gas,
Sputtering is sequentially performed under a pressure of 0.5 Pa, and an undercoat layer made of a Si ₃ N ₄ film having a thickness of about 800 Å, a read layer made of a GdFeCo film having a thickness of about 400 Å, and a thickness of about 400 Å is formed on a transparent substrate. Recording layer made of TbFeCo film, non-magnetic layer made of Si ₃ N ₄ film having a thickness of about 500Å, auxiliary recording layer made of PtCo film having a thickness of about 800Å, protective layer made of Si ₃ N ₄ film having a thickness of about 800Å Were sequentially laminated to complete a sample disk of a magneto-optical recording medium.

For comparison, a GdFeCo film and a TbFeC film each having a thickness of 400 Å were formed on a glass substrate.
The o film exhibited perpendicular magnetic anisotropy, its coercive force at room temperature was about 10 kOe, and its Curie temperature was 160 ° C.
Further, when only a PtCo film having a thickness of 800 Å is formed on a glass substrate, this film exhibits in-plane magnetic anisotropy, and a magnetic field of about 5 kOe is required for magnetization saturation in the perpendicular direction at room temperature. It was The Curie temperature is about 250 ° C., and when heated to, for example, 200 ° C., it was possible to saturate the magnetization in the perpendicular direction with a magnetic field of about 200 Oe.

Then, a recording experiment was conducted on this sample disk in the same manner as in Example 1 by using an evaluation apparatus (model OMS-2000 manufactured by Nakamichi Co., Ltd.). The results are shown in Table 2 below. The recording frequency at this time is 1 MHz, and the first bias magnetic field H _b1 is 200 O
It is e.

[0052]

[Table 2]In experiment numbers 11 and 12, of the binary laser power
Smaller strength P_LCurie temperature of the recording layer depending on
Degree T_cSince the temperature rises to the vicinity, the first type recording is not performed.
However, the second bye required for the recording of the second kind
As magnetic field H_b2Binary recording due to lack of
Could not be made ("C, N change" is written in the comment field.
Posted). On the other hand, in Experiment Nos. 13 to 15, the second bar was used.
Iias magnetic field H _b2Is large enough to improve binary recording
I was able to do it.

Overwriting recording was carried out under the same conditions except that the recording frequency was set to 1.5 MHz in the area recorded in Experiment No. 14, and it was 1.5 M during reproduction.
C / N ratio becomes 44 dB at the frequency of Hz, and 1 MH
It was confirmed that the z carrier had disappeared. From this, it was confirmed that overwriting can be performed well.

Further, in comparison with the results of Example 1 described above, by applying the present invention to a magneto-optical recording medium composed of an exchange-coupling two-layer film, C was obtained without deteriorating the recording sensitivity.
It was found that the / N ratio can be improved. The main cause of the improvement of the C / N ratio is that the recording noise is reduced. This is because the read layer assists the magnetization reversal of the recording layer as described above and the high Curie temperature (Kerr rotation). It is considered that the read-out layer having a large angle and the recording layer having a low Curie temperature (small Kerr rotation angle) were exchange-coupled to each other at the same time.

Embodiment 4 Next, a magneto-optical recording apparatus according to an embodiment of the present invention will be described. This magneto-optical recording apparatus is applied to a magneto-optical recording medium such as the above-described magneto-optical recording medium of the present invention, which simultaneously applies antiparallel bias magnetic fields from both sides to perform recording. FIG. 5 is a schematic cross-sectional view of an essential part showing the configuration of this magneto-optical recording device.

The magneto-optical recording medium 30 to be recorded is detachably attached to a spindle (not shown) and is rotationally driven. An actuator 31 is provided so as to face one surface of the magneto-optical recording medium 30.
In the case of using the magneto-optical recording medium of each of the above-mentioned embodiments, the transparent substrate 11 side faces this actuator 31. The actuator 31 controls the distance between the objective lens 33 and the magneto-optical recording medium 30, and the objective lens 33 that focuses the laser beam from the laser generating means (not shown) on a predetermined recording position of the magneto-optical recording medium 30. It is composed of an electromagnet 32. The electromagnet 32 is designed so that the focus of the laser beam always coincides with the recording position.
The objective lens 33 is driven in a direction perpendicular to the surface of the magneto-optical recording medium 30. Further, the high magnetic permeability member 35 is placed so as to face the actuator 31 with the magneto-optical recording medium 30 interposed therebetween.
Is provided, and a micro magnet 34 is fixed to approximately the center of the surface of the high magnetic permeability member 35 on the magneto-optical recording medium 30 side.
The magnetic permeability of the high magnetic permeability member 35 is sufficient to converge the leakage magnetic force lines from the electromagnet 32. As the high magnetic permeability material forming the high magnetic permeability member 35, Fe—Ni
Various materials such as a system alloy, a Fe-Si system alloy, and a ferrite crystal can be used. In addition, the micro magnet 34
May be a minute permanent magnet or a minute electromagnet, and faces the objective lens 33 almost exactly across the recording position.
A magnetic field antiparallel to the leakage magnetic field lines from the electromagnet 21 is applied to this recording position. In the case of recording on the above-described magneto-optical recording medium, the leakage magnetic field from the actuator 31 becomes the first bias magnetic field H _b1 , and the magnetic field from the minute magnet 34 becomes the second bias magnetic field H _b2.
It turns out that.

Next, the operation of the present embodiment will be described by describing a case where the sample disk of the magneto-optical recording medium in the above-mentioned Embodiment 1 is actually recorded by using this magneto-optical recording apparatus. explain. In this case, as the magneto-optical recording device, an evaluation device (model OM manufactured by Nakamichi Co., Ltd.)
S-2000) with a high-permeability member 35 made of Ni-Zn-based ferrite and a minute magnet 34 attached thereto was used. As the minute magnet 34, a fixed permanent magnet for applying a normal fixed bias magnetic field or a moving electromagnet for magnetic field modulation is used, and the minute magnet 34 and the high magnetic permeability member 35 are opposed to the magneto-optical recording medium 30. The ratio of the areas of the surfaces to be processed was set to 1: 2. In addition, the first bias magnetic field H _b1 is 0 when the second bias magnetic field H _b2 is 0.
Is 200 Oe on the substrate surface of the magneto-optical recording medium 30.
To be. The magnitude of the second bias magnetic field H _b2 was set to be −800 Oe on the substrate surface of the magneto-optical recording medium 30.

First, the magneto-optical recording medium 30 was set in the magneto-optical recording device, and the magneto-optical recording medium 30 was rotated so that the linear velocity was 5 m / sec. Subsequently, a laser beam modulated to a binary intensity (P _H , P _L ) from a laser generator (not shown) is focused and irradiated onto a predetermined recording position of the magneto-optical recording medium 30 via the objective lens 33. In this magneto-optical recording device, since the magnetic field lines leaking from the actuator 31 are converged by the high magnetic permeability member 35, even if the magnetic field leaking from the actuator 31 is weak, the first magnetic field sufficient for recording can be obtained. Bias magnetic field H _b1 of Here, the binary laser power is set to 3
The duty ratio of the laser pulse is 50%, the recording frequency is 1 MHz, and the minute magnet 3
By changing the size and type of 4 variously, recording is performed on the above-mentioned sample disk which has not been erased (the recording layer is magnetized in one direction), the recorded information is read, and the carrier C and noise N are recorded. Was evaluated, that is, the C / N ratio. The results are shown in Table 3 below.

[0059]

[Table 3] As can be seen from the table, binary recording is performed in all cases, and the second bias magnetic field H in the first embodiment described above is used.
Compared with the case where _b2 is -800 Oe (Experiment No. 5), the C / N ratio is improved in all cases. Furthermore, the micro magnet 34
The C / N ratio was improved by decreasing. this is,
It is considered that the leakage magnetic field from the actuator 31 is efficiently applied to the recording position of the magneto-optical recording medium 30 by making the micro magnet 34 smaller.

Next, overwriting recording was performed in the recording area of Experiment No. 19 under the same conditions except that the recording frequency was 1.5 MHz.
It was confirmed that the C / N ratio was 42 dB at the frequency of 1.5 MHz and the carrier of 1 MHz was lost. From this, it was confirmed that the overwrite recording was satisfactorily performed.

From the above, it was confirmed that the recording characteristics are further improved by recording on the magneto-optical recording medium of the present invention using this magneto-optical recording apparatus.

[0062]

As described above, in the magneto-optical recording medium of the present invention, by providing the recording auxiliary layer for blocking the bias magnetic field at room temperature, the reverse bias magnetic field is applied from both sides of the magneto-optical recording medium. By irradiating the binary laser power, it is possible to stably perform binary overwriting recording.

Further, in the magneto-optical recording apparatus of the present invention, the leakage magnetic field of the actuator is converged by the high magnetic permeability member so that the leakage magnetic field of the actuator can be used as the bias magnetic field to the magneto-optical recording medium. Therefore, there is an effect that the light modulation overwrite can be realized with a small device.

[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 an apparatus used for recording.

FIG. 3 is a schematic cross-sectional view showing the structure of a magneto-optical recording medium having a reflective layer.

FIG. 4 is a schematic cross-sectional view showing the structure of a magneto-optical recording medium provided with a reading layer exchange-coupled with a recording layer.

FIG. 5 is a schematic cross-sectional view of a main part showing the configuration of a magneto-optical recording device according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating a magnetization process of the magneto-optical recording medium of the present invention.

FIG. 7 is a diagram illustrating a magnetization process of the magneto-optical recording medium of the present invention when a read layer exchange-coupled with the recording layer is provided.

FIG. 8 is a schematic cross-sectional view showing the structure of a conventional magneto-optical recording medium.

9 is a characteristic diagram showing temperature-saturation magnetization characteristics of each layer of the magneto-optical recording medium of FIG.

[Explanation of symbols]

 11 Transparent Substrate 12 Recording Layer 13 Non-Magnetic Layer 14 Recording Auxiliary Layer 15 Protective Layer 16 Reflective Layer 17 Read-out Layer 18 Undercoat Layer 30 Magneto-Optical Recording Medium 31 Actuator 32 Electromagnet 33 Objective Lens 34 Micro Magnet 35 High Permeability Member

Claims (8)

[Claims] 1. A magneto-optical recording medium capable of overwriting, comprising a recording layer having perpendicular magnetic anisotropy and a recording auxiliary layer having in-plane magnetic anisotropy at a temperature near room temperature on a substrate. A magneto-optical recording medium in which the recording auxiliary layer can be easily oriented in a direction perpendicular to the surface of the substrate at a predetermined recording temperature. 2. The magneto-optical recording medium according to claim 1, wherein the predetermined recording temperature is higher than the Curie temperature of the recording layer. 3. The magneto-optical recording medium according to claim 1, wherein a non-magnetic layer is provided between the recording layer and the recording auxiliary layer. 4. The magneto-optical recording medium according to claim 1, further comprising a reflective layer provided between the recording layer and the recording auxiliary layer. 5. A reading layer is provided in contact with the surface of the recording layer that is not the recording auxiliary layer side, the recording layer and the reading layer are exchange-coupled to each other, and the reading layer is higher than the Curie temperature of the recording layer. The magneto-optical recording medium according to claim 1, wherein the Curie temperature is relatively high, and the coercive force of the reading layer is relatively smaller than the coercive force of the recording layer. 6. The magneto-optical recording medium according to claim 1, wherein the irradiation position of the laser beam from the recording layer side with respect to the recording layer and the recording auxiliary layer of the magneto-optical recording medium. A first bias magnetic field H _b1 is applied to the magneto-optical recording medium in the direction perpendicular to the magneto-optical recording medium, and the direction perpendicular to the magneto-optical recording medium at the irradiation position from the recording auxiliary layer side
A second bias magnetic field _{Hb2, which} is larger than and opposite to the first bias magnetic field _Hb1, is applied, and (a) a laser beam is used to increase the temperature of the recording layer to near the Curie temperature of the recording layer. A first type of recording in which the magnetization of the recording layer is oriented in the direction of the first bias magnetic field H _b1 by irradiating the magnetic recording medium; and (b) the magnetization of the recording auxiliary layer is the second bias. By irradiating the magneto-optical recording medium with a laser beam sufficient to raise the temperature to the direction of the magnetic field H _b2 , the magnetization direction of the recording auxiliary layer is changed to the second bias magnetic field H _b2.
And a second type of recording in which the direction of magnetization of the recording layer is aligned with the direction of magnetization of the recording auxiliary layer, and binary recording is performed. 7. The magneto-optical recording medium according to claim 5, wherein the recording layer and the recording auxiliary layer of the magneto-optical recording medium are applied to the magneto-optical recording medium at a laser beam irradiation position from the recording layer side. On the other hand, a first bias magnetic field H _b1 is applied in the perpendicular direction, and in the perpendicular direction to the magneto-optical recording medium at the irradiation position from the recording auxiliary layer side,
A second bias magnetic field _{Hb2, which} is larger than and opposite to the first bias magnetic field _Hb1, is applied, and (a) a laser beam is used to increase the temperature of the recording layer to near the Curie temperature of the recording layer. By irradiating the magnetic recording medium, the magnetization of the recording layer is oriented in the direction of the first bias magnetic field H _b1 , and the direction of magnetization of the read layer is made stable with respect to the direction of magnetization of the recording layer. (B) irradiating the magneto-optical recording medium with a laser beam that heats up to a temperature at which the magnetization of the recording auxiliary layer is oriented in the direction of the second bias magnetic field H _b2. As a result, the magnetization direction of the recording auxiliary layer is changed to the second bias magnetic field H _b2.
And then aligning the direction of magnetization of the recording layer with the direction of magnetization of the recording auxiliary layer, and orienting the direction of magnetization of the read layer to a direction stable with respect to the direction of magnetization of the recording layer. A magneto-optical recording method for performing binary recording including the second type of recording. 8. A magneto-optical recording device used for recording on a magneto-optical recording medium, comprising an objective lens which is provided so as to face one surface of the magneto-optical recording medium and condenses a laser beam, An actuator that moves the objective lens so that the laser beam focuses at a predetermined recording position on the one surface by using a magnetic force, and an actuator that is provided to face the actuator with the magneto-optical recording medium sandwiched therebetween. A high magnetic permeability member having a magnetic permeability sufficient to converge the leakage magnetic force lines from the actuator; and a high magnetic permeability member fixed to substantially the center of the magneto-optical recording medium side surface of the high magnetic permeability member, from the other surface side. A magneto-optical recording apparatus comprising: a micro magnet that gives a magnetic field antiparallel to the leakage magnetic field line with respect to the recording position.