JPS63195844A - Magneto-optical recording medium and recording method - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium which has perpendicularly magnetized films of two-layered structure and is suitable for utilization in a recording method permitting overwriting by forming the above-mentioned recording medium in such a manner as to satisfy prescribed conditions. CONSTITUTION:Magnetic layers 2, 3 are laminated on a transparent substrate 1. The magnetic layer 2 has a low Curie point TL and high coercive force HH and the magnetic layer 3 has a high Curie point TH and low coercive force HL. The conditions expressed by the equation are required to be satisfied between the saturation magnetization MS2 and film thickness h2 of the magnetic layer 3 and the magnetic wall energy sigmaw between the two magnetic layers 2, 3. The magnetic layer 3 is required to satisfy TL<THCOMP when the compensation temp. of said layer is designated as THCOMP and said layer is required to satisfy (the value of the coercive force of the magnetic layer 3 at temp. TL)/(value HL of the coercive force of the magnetic layer 3 at room temp.)>0.5. The purpose is achieved by satisfying the above-mentioned conditions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a Curie point writing type magneto-optical recording medium that can be read using the magnetic Kerr effect, and an optically overwritable optical recording medium using the same. Related to magnetic recording methods.

[Conventional technology]

A magneto-optical disk is known as an erasable optical disk memory. Magneto-optical disks have advantages over magnetic recording media using conventional magnetic heads, such as high-density recording and non-contact recording and playback, but on the other hand, the recorded area must be erased before recording. It had the disadvantage that it cannot be magnetized in one direction (it must be magnetized in one direction). In order to compensate for this drawback, proposals have been made such as a method in which a recording/reproducing head and an erasing head are provided separately, or a method in which recording is performed while irradiating a continuous laser beam and simultaneously modulating the applied magnetic field.

[Problem that the invention seeks to solve]

However, these methods have drawbacks such as a large-scale apparatus, high cost, and the inability to perform high-speed modulation.

By eliminating the drawbacks of the above-mentioned known techniques and simply adding a magnetic field generating means with a simple structure to the conventional device configuration, it is possible to perform overwriting similar to that of a magnetic recording medium.
The applicant filed a patent application for the magneto-optical recording method on July 8, 1986. -158787 (filed on February 2, 1986)
(This will be a basic application with domestic priority in Japan).

However, since this method is a completely new recording method, there are still many research issues related to this method. In other words, we are searching for a magneto-optical recording medium that is more suitable for use in this recording.

As a result of further research, the present inventors obtained several results.

The present invention was thus completed, and its purpose is not only to provide an overwritable recording method, but also to provide a magneto-optical recording medium that is more suitable for use in the overwritable recording method. It is in.

[Means for solving problems]

The present invention, which can achieve the above objectives, has a low Curie point (TL) and a high coercive force (HH) at room temperature.
and a relatively high Curie point (TH) and low coercive force (HL) at room temperature compared to this magnetic layer.
A magneto-optical recording medium having a two-layer exchange-coupled perpendicular magnetization film on a substrate, the second magnetic layer having a saturation magnetization of Ms2 and a film thickness of h2. , If the domain wall energy between the two magnetic layers is σW, then the following is satisfied.Moreover, if the compensation temperature of the second magnetic layer is THCOMP, then T L < THCOMP and (the value of the coercive force of the second magnetic layer at the temperature TL) /(Value of coercive force of the second magnetic layer at room temperature: HL)>0.5 ... Using a magneto-optical recording medium that satisfies the condition (2), the following two This is a recording method characterized by recording values.

(a) With respect to the medium, at a location different from the recording head,
Applying a magnetic field B of a magnitude sufficient to magnetize the second magnetic layer with coercive force HL in one direction but not reversing the direction of magnetization of the first magnetic layer with coercive force HH, (b) Next, By applying a bias magnetic field using the recording head and at the same time irradiating the medium with enough laser power to raise the temperature of the medium to near the low Curie point (TL),
The first type of preliminary recording, in which the direction of magnetization of the first magnetic layer is aligned in a stable direction with respect to the second magnetic layer without changing the direction of magnetization of the second magnetic layer, or the Curie point is high while applying a bias magnetic field. By irradiating the medium with enough laser power to raise the temperature of the medium to around (T (C) Next, by moving the medium and passing the pre-recorded bits through the magnetic field B, For the bits formed by the preliminary recording of , the direction of magnetization of both the first magnetic layer and the second magnetic layer remains unchanged, and for the bits formed by the second type of preliminary recording,
Binary recording in which the direction of magnetization of the second magnetic layer is reversed in the same direction as the magnetic field B, and the direction of magnetization of the first magnetic layer is left unchanged.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 1(a) and 1(b) are schematic sectional views each showing an embodiment of a magneto-optical recording medium manufactured according to the present invention. The magneto-optical recording medium shown in FIG. 1(a) has a first magnetic layer 2 and a second magnetic layer 3 laminated on a transparent substrate 1 provided with a pre-group. The first magnetic layer 2 has a low Curie point (TL) and a high coercive force (HH), and the second magnetic layer 3 has a high Curie point (TH) and a low coercive force (HL).
). Here, "high" and "low" represent a relative relationship when comparing both magnetic layers (coercive force is compared at room temperature). However, normally the TL of the first magnetic layer 2 is 7.
0 to 180°C, H, 3 to 10 KOe, second magnetic layer 3
TH is preferably in the range of 150 to 400°C, and HL is preferably in the range of about 0.5 to 2 KOe.

As the material for each magnetic layer, materials that exhibit perpendicular magnetic anisotropy and magneto-optical effects can be used, but Gd(:o, G
dFe, TbFe, DyFe, GdTbFe,
TbDyFe, TbFeCo, GdTbC:o,
An amorphous magnetic alloy of a rare earth element and a transition metal element such as GdTbFeCo is preferred.

In the recording method using the magneto-optical recording medium according to the present invention, the first magnetic layer 2 is mainly involved in reproduction. That is, the magneto-optic effect exhibited by the first magnetic layer 2 is mainly used for reproduction, and the second magnetic layer 3 plays an important role in recording.

On the other hand, in the exchange-coupled double-layer film in the conventional magneto-optical recording method, conversely, the magnetic layer with a low Curie point and high coercive force is mainly involved in recording; The magnetic layer was mainly involved in reproduction.

In such a conventional exchange-coupled two-layer film, it is desirable that the following relationship exists between the saturation magnetization Ms of the magnetic layer mainly involved in reproduction, the film thickness, and the domain wall energy σW between the two layers. Ta.

HH>-> HL Msh However, in the exchange-coupled two-layer film of the recording medium used in the present invention, the following relationship exists between the saturation magnetization Ms2 and film thickness h2 of the second magnetic layer 3, and the domain wall energy σW between the two magnetic layers. relationship is necessary.

This is to ensure that the magnetization state of the bit finally completed by recording (shown in FIG. 2(f)) can stably exist (detailed reasons will be described later).

In order to satisfy this condition, the film thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of each magnetic layer may be appropriately set.

In addition to the above requirements, the magneto-optical recording medium of the present invention satisfies the above-mentioned special requirement (2), making it more suitable for overwritable recording methods. (described later).

Note that, in consideration of the magnitude of the effective bias magnetic field during recording or the stability of binary recorded bits, it is desirable that both magnetic layers 2 and 3 be exchange-coupled.

In FIG. 1(b) showing another aspect of the present invention, 4.5
is a protective film for improving the durability of both magnetic layers or for improving the magneto-optical effect.

6 is an adhesive layer for bonding the bonding substrate 7 together. If layers 2 to 5 are laminated on the bonding substrate 7 and bonded together, recording and reproduction can be performed on the front and back sides.

The recording process will be described below with reference to FIGS. 2 to 4. Before recording, the stable magnetization directions of both magnetic layers 2 and 3 may be parallel (same direction) or antiparallel (opposite directions). In FIG. 2, a case will be explained in which the stable directions of magnetization are parallel.

35 in FIG. 3 is a magneto-optical disk having the configuration described above. For example, suppose that the magnetization state of a certain part of this magnetic layer is initially as shown in FIG. 2(a). The magneto-optical disk 35 is rotated by a spindle motor and passes through the magnetic field generator 34 . At this time, if the magnitude of the magnetic field of the magnetic field generator 34 is set to a value between the coercive forces of both magnetic layers 2 and 3 (the direction of the magnetic field is upward in this embodiment), as shown in FIG.
As shown in b), the second magnetic layer 3 is magnetized in a uniform direction,
On the other hand, the magnetization of the first magnetic layer 2 remains unchanged.

Next, the magneto-optical disk 35 rotates to perform recording/reproduction.
1, laser beams having two types of laser power values (first type and second type) are irradiated onto the disk surface according to a signal from the recording signal generator 32. The first type of laser power is enough to raise the temperature of the disk to around the Curie point of the first magnetic layer 2, and the second type of laser power is enough to raise the temperature of the disk to around the Curie point of the second magnetic layer 3. It is a power that can be heated. That is, in FIG. 4, which shows an outline of the relationship between the coercive force and temperature of both magnetic layers 2.3, the first type of laser power increases the temperature of the disk to around TL, and the second type of laser power increases the temperature of the disk to around TH. Can rise.

The temperature of the first magnetic layer 2 is raised to near the Curie point by the first type of laser power, but the second magnetic layer 3 has a coercive force that allows bits to stably exist at this temperature, so the bias magnetic field during recording is By setting properly, Figure 2 (
A bit as shown in FIG. 2(C) is formed from any of the bits (b) (first type preliminary recording).

Here, setting the bias magnetic field appropriately means the following. That is, in the first type of preliminary recording, the magnetization of the first magnetic layer 2 receives a force (exchange force) that aligns it in a stable direction (here, in the same direction) as the direction of magnetization of the second magnetic layer 3. Therefore, a bias magnetic field is not originally required. but,
The bias magnetic field is set in a direction that assists magnetization reversal of the second magnetic layer 3 in preliminary recording using the second type of laser power (described later) (that is, in a direction that hinders the first type of preliminary recording). For convenience, it is preferable that the bias magnetic field is set to have the same magnitude and direction in preliminary recording with either the first type or the second type of laser power.

From this point of view, it is preferable to set the bias magnetic field to the minimum size necessary for preliminary recording of the second type of laser power based on the principle shown below, and settings that take this into account are the appropriate setting as mentioned above. It is a setting.

Regarding the first type of preliminary recording that forms this bit (C), the following is required to optimize the magnetic layer.

The magnitude of saturation magnetization of the first magnetic layer is M S, and the film thickness is hl.
(As mentioned above, the saturation magnetization of the second magnetic layer 3 is Ms2, the film thickness is h2, and the domain wall energy between the two magnetic layers is σ
W), HHef in descending order of the exchange force acting on the first and second magnetic layers.
f, HLeff) are respectively HHeff-σw/2
Ms, h.

It can be expressed as HLeff=σw/2M82h2.

In FIG. 2, in the state (b) before the first type of preliminary recording, when the magnetizations of the first and second magnetic layers are parallel, the state of each magnetic layer is stabilized by the exchange force, 1st
To reverse the magnetization of the magnetic layer) IH'+H□eff
(HH' and HHeff' represent the coercive force of the first magnetic layer and the exchange force acting on the first magnetic layer at a certain temperature t. Both are functions of the temperature t. In order to reverse the magnetization of the two magnetic layers, HL′ 1H
A magnetic field of L,,ff'(HL' and HLeff' indicate the coercive force of the second magnetic layer and the exchange force acting on the second magnetic layer at a certain temperature t. Both are functions of the temperature t) is required. It is. Therefore, even if a slight bias magnetic field is applied in either direction, the bit (
C) is formed. However, the state (b
), when the magnetizations of the first and second magnetic layers are antiparallel, each magnetic layer is oriented in a direction in which its magnetization is reversed by the exchange force. Due to this, the following (a) and (b)
It will be something like this.

(a) When the temperature of the magnetic layer rises to around T during the first type of preliminary recording, if) (H' Hll,, rt'< 0 ゛, the magnetization of the first magnetic layer is reversed, The first magnetic layer is aligned in a stable direction with respect to the magnetization of the second magnetic layer, and the first type of preliminary recording is completed.However, (b) if the HL'
If H+-eff'< 0, the magnetization of the second magnetic layer is aligned in a stable direction with respect to the magnetization of the first magnetic layer, and the first type of reserve is required to reverse the magnetization of the first magnetic layer. Recording becomes impossible.

Therefore, it is preferable to increase the value of HL' as much as possible. For this purpose, it is preferable to make HL a large value, but since the second magnetic layer needs to be magnetized in a uniform direction in the magnetic field generating section 34, It can only do up to 2 KOe at most. Therefore, in order to make the coercive force of the second magnetic layer as large as possible at a temperature near TL, the compensation temperature T1 of the second magnetic layer is
It is important to set 4COMP to a temperature near TL.

In this way, even if the saturation magnetization Ms of the second magnetic layer decreases,
At the compensation temperature THCOMP, the coercive force HL' of the second magnetic layer becomes infinite, so as the temperature increases to approach the compensation temperature THcoMP, the coercive force H of the second magnetic layer increases.
This will prevent a decrease in L'.

In addition, at temperatures where THCOMP and TH are close, T)ICOM
In the temperature range from P to T, there is a reversal of the magnetization Ms of the second magnetic layer and a sudden decrease in the coercive force HL', so in order to stably perform the first type preliminary recording, T L < THC
It is preferable to set it to OMP.

As will be demonstrated in the examples, in fact, if the compensation composition of the second magnetic layer is THCOMP, then T L < T HC
OMP , and (value of coercive force of the second magnetic layer at temperature TL)/(value of coercive force of the second magnetic layer at room temperature (=HH))
It was confirmed that stable first type preliminary recording can be performed by selecting the second magnetic layer such that the magnetic flux is greater than 0.5.

Among the materials mentioned above, a TbFeCo-based alloy rich in Tb element than the compensation composition is suitable as a material that satisfies requirement (2). A system in which an appropriate amount of an impurity element such as a metal element is added can be used.

Next, the second type of preliminary recording will be explained.

When the temperature of the second magnetic layer 3 is raised to near the Curie point using the second type of laser power (second type of preliminary recording), the direction of magnetization of the second magnetic layer 3 is changed by the bias magnetic field set as described above. is reversed. Subsequently, the magnetization of the first magnetic layer 2 is also aligned in a stable direction (here, in the same direction) with respect to the second magnetic layer 3.

That is, a bit as shown in FIG. 2(d) is formed from any of the bits shown in FIG. 2(b).

In this way, the bias magnetic field and the first
Depending on the laser power of the seed and the second type, each location on the magneto-optical disk is preliminarily recorded in the state shown in FIG. 2(C) or FIG. 2(d).

Next, when the magneto-optical disk 35 is rotated and the pre-recorded bits (C) and (d) pass through the magnetic field generating section 34 again, the size of the magnetic field generating section 34 changes between the magnetic layers 2 and 3 as described above.
The recording bit (
c) is the state of (e) without any change (final recording state). On the other hand, the recording bit (d) is recorded in the second magnetic layer 3.
causes magnetization reversal and becomes state (f) (another final recording state).

In order for the state of the recording bit (f) to exist stably, it is sufficient that the following relationship exists as described above.

Here, 0w72M5zh2 indicates the strength of the exchange force acting on the second magnetic layer. In other words, a magnetic field with a magnitude of 0w72M52h2 attempts to direct the magnetization direction of the second magnetic layer 3 in a direction that is stable with respect to the magnetization direction of the first magnetic layer 2 (in this case, the same direction). Therefore, in order to prevent the magnetization of the second magnetic layer 3 from being reversed against this magnetic field, it is sufficient that the coercive force of the second magnetic layer 3 is H, >σW/2M52h2, where Hl is the coercive force.

The states (e) and (f) of the recorded bits are controlled by the power of the laser during recording and do not depend on the state before recording, so overwriting is possible. Recording bits (e) and (f) are generated by irradiating a laser beam for reproduction and processing the reproduction light by a recording signal regenerator 33.
Can be played.

In the explanation of FIG. 2, an example was shown in which the first magnetic layer 2 and the second Wi layer 3 are stable when their magnetization directions are the same, but the same applies to magnetic layers that are stable when their magnetization directions are antiparallel. Conceivable. FIG. 5 shows the magnetization state during the recording process in this case, corresponding to FIG. 2.

〔Example〕

Example 1 A polycarbonate disk-shaped substrate with pregroup and preformat signals engraved thereon was placed in a sputtering apparatus equipped with three target sources at a distance of 11 mm from the target.
It was set at intervals of tlocm and rotated.

After evacuating the inside of the sputtering apparatus to below IX 1O-6 Torr, the sputtering was performed from the first target in argon at a sputtering speed of 100 people/min and a sputtering pressure of 5X 1O-3 Torr.
A protective layer of ZnS was formed to a thickness of 1000 mm. Next, in argon, a sputtering speed of 1 was applied from the second target.
TbFe alloy was sputtered at a sputtering rate of 00 people/min, a sputtering pressure of 5X 1O-3 Torr, and a film thickness of 300 people/min, TL=approx.
30°C, H, = about 10 KOe Tb1aFea2 first
A magnetic layer was formed.

Next, TbFeCo alloy was sputtered at a sputtering pressure of 5X 1O-3 Torr in argon, and the film thickness was 500 mm.
= Hl90℃, T HCOMP = 210℃, Ht=
A second magnetic layer of Tb27F e64cro9 with an Oe of about 1 Oe was formed.

Next, in argon, the first target is sputtered at a sputtering rate of 1
00 people/min, sputtering pressure 5 X I 0-3 Tor
ZnS was applied as a protective layer to a thickness of 3000 nm.

Next, the above substrate on which the film had been formed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to create a magneto-optical disk.

Here, when the coercive force of the second magnetic layer was measured by the method shown in Example 2 at a Curie temperature of 130° C. of the first magnetic layer, it was approximately 7000 e.

Set this magneto-optical disk in the recording/reproducing device, and
While passing through the magnetic field generation part of KOe at a linear velocity of 8 m/sec, a laser beam with a wavelength of 830 mm focused to approximately 1 μ is modulated at 2 MHz with a duty of 50%, and a binary signal of 4 mW and 8 mW is generated. Recording was done using laser power. The bias magnetic field was 1000e in the direction to reverse the magnetization of the second magnetic layer. Thereafter, when regeneration was performed by irradiating a laser beam of 1.5 mW, a binary signal could be regenerated.

Next, an experiment similar to the above was conducted on the magneto-optical disk after the entire surface had been recorded. As a result, previously recorded signal components were not detected, confirming that good overwriting was possible.

Example 2 and Comparative Example 1 100% ZnS was deposited on a glass substrate in the same manner as in Example 1.
0A%Tb, 8Fe82 first magnetic layer by 300 people, T
500 people, ZnS for the second magnetic layer of b27'es4Cog
Sample 2-1 (Example 2) of a magneto-optical disk laminated in this order has the same structure, but only the material of the second magnetic layer is Tb1gFea+ll:O+
A sample 2-2 (comparative example 1) was prepared in which sample 2-2 was replaced with sample 2-2 (comparative example 1).

Next, while gradually heating sample 2-1.2-2, each magnetic layer Tb+aFe2
((A)), Tb27Fes4CO9((B
) and Tb+5Fea+GO+ (referred to as (C)), the temperature change in the coercive force (Fig. 6) and the temperature change in the coercive Kerr exchange force (Fig. 7) were obtained.

In Figure 6, the coercive force HH of (A) at room temperature is approximately 10 KOe.
, Curie point TL was about 130°C.

Both (B) and (C) have a coercive force H of about IKOe at room temperature.
, the Curie point TH was about 190°C.

However, the compensation temperature is approximately 210°C in (B), and (C
), the temperature was approximately -130°C. Moreover, the coercive force values near the TL in (B) and (C) were about 70% and about 30%, respectively, of their values at room temperature.

In the graph of the coercive Kerr exchange force as a function of temperature change shown in FIG.
It represents the value of Heff' (the value shown by the first magnetic layer (A)).

A/B relates to sample 2-1 and A/C relates to sample 2-1.
Regarding 2.

The measurable value of coercive Kerr exchange force is HH' HH
It is only the smaller of the absolute values of eff' and HL'-HLerr'. (The larger value is smaller than the reversal magnetic field as the applied magnetic field is increased, and the magnetization of the magnetic layer with a small value is reversed, so it cannot be measured.) Regarding the contents shown in Figure 7: Explain.

When the temperature of the measurement sample is raised and the magnitude of the reversal magnetic field is investigated, the magnitude of HL'-HLeff' of the second magnetic layer is initially positive and shows a value of 200 to 3QOOe, but
HH'-)(He,...) of the first magnetic layer at ~50℃ lower temperature.
' takes a negative value, and the magnetic layer spontaneously becomes aligned in a direction stable with respect to the magnetization of the first magnetic layer. Roughly speaking, when the temperature is higher than TL, the magnetization of the first magnetic layer disappears and there is no exchange force, so only the coercive force value of the second magnetic layer is measured.

Focusing on the difference between samples 2-1 and 2-2, in sample 2-1, the first type of preliminary recording begins at a temperature approximately 50°C lower than the TL, and the magnetization of the first magnetic layer is reversed due to the strong exchange force. In contrast, in sample 2-2, the first type of preliminary recording is performed with a weak exchange force at a temperature about 20° C. lower than TL.

This difference is due to a temperature change in the coercive force of the second magnetic layer, that is, a difference in compensation temperature.As the temperature of the sample increases, the value of the coercive Kerr exchange force of the first magnetic layer changes from a large positive value to a negative value. At this time, if the value of the coercive Kerr exchange force of the second magnetic layer is positive and relatively large in the temperature range where the first type preliminary recording is performed, the first type During preliminary recording, a stronger exchange force (the value of the coercive Kerr exchange force is negative and the absolute value is large) acts on the first magnetic layer from a lower temperature, changing the magnetization of the first magnetic layer to the magnetization of the second magnetic layer. This shows that it is possible to arrange them in a stable direction relative to

In other words, the factors that determine the stability and sensitivity of the first type of preliminary recording are how the coercive force of the second magnetic layer changes with temperature, and the magnitude of the compensation temperature of the second magnetic layer and the Curie temperature of the first magnetic layer. It shows that a relationship is possible.

Example 3 and Comparative Examples Magneto-optical disk samples (Samples 1.2-4.2- 5゜2-6 is an example, 2-
1.2-2.2-3 was a comparative example). Recording and reproduction were performed under the same conditions as in Example 1. The results are shown in Table 1 below.

However, the coercive force HL of the second magnetic layer is approximately the same IKOe in all samples. In Table 1, the term "ratio of coercive force at rTL to the value at room temperature" refers to the temperature T of the first magnetic layer.
The value of coercive force at L (approximately 130°C in this example) is
It shows the value divided by the coercive force value at room temperature.

Further, the first type of recording threshold value indicates a laser power value at which recording is possible.

For the evaluation of the first and second types of recording, those in which a good reproduced signal with a C/N value of about 40 dB was obtained were indicated by △ if the O1 recorded signal could be confirmed, and those in which no recording was observed were indicated by ×.

From the results in Table 1, it is clear that type 1 recording was performed well because:
For samples with a ratio of coercive force at T, to the room temperature value of 0.5 or more (Example 1, Examples 2-4 to 2-6, Comparative Example 2)
-2 to 2-3) In these samples, the compensation temperature of the second magnetic layer is higher than the Curie temperature TL of the first magnetic layer, or the Curie temperature TI of the second magnetic layer is higher than that of other samples. (Comparative Example 2-2.2-3).

At the same time, the second type of recording was successfully performed when the Curie temperature TH of the second magnetic layer was lower than 200°C. (Example 1, Example 2-4.2-5.2-6) From the above, in order to perform type 1 and type 2 recording with good sensitivity, it is necessary to adjust the compensation temperature of the second magnetic layer. T. co,,,p
It can be seen that it is effective to set the Curie temperature TL higher than the Curie temperature TL of the first magnetic layer.

〔Effect of the invention〕

As explained in detail above, a magneto-optical medium having a two-layer perpendicular magnetization film that satisfies predetermined requirements is used, and during recording, a magnetic field generating section is provided at a separate position from the recording head, and recording is performed using a binary laser power. By doing so, good override characteristics were obtained.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) each show an example of the structure of the magneto-optical medium used in the present invention, and FIG. 2 shows the magnetization of the magnetic layers 2 and 3 during the recording method of the present invention. Diagram showing orientation, 3rd
The figure is a conceptual diagram of the recording/reproducing apparatus, and FIG. 4 is a schematic diagram showing the relationship between the coercive force of the inner magnetic layers 2 and 3 and temperature. FIG. 5 is a diagram showing the magnetization state of the magnetic layer in another embodiment of the present invention. FIG. 6.7 is a diagram showing the characteristics of the magneto-optical disks obtained in Example 2 and Comparative Example 1, respectively. 1 Transparent substrate with nibli groove, 2.3: Magnetic layer 4.5: Protective layer, 6: Adhesive layer, 7: Bonding substrate, 31: Recording/reproducing head, 32: Recording signal generator, 33 : Recorded signal regenerator 34 : Magnetic field generator 35 : Magneto-optical disk,

Claims (1)

[Claims] 1) Low Curie point (T_L) and high coercive force (H
The exchange-coupled two-layer structure consists of a first magnetic layer having a magnetic field (_H) and a second magnetic layer having a relatively high Curie point (T_H) and a low coercive force (H_L) at room temperature compared to this magnetic layer. A magneto-optical recording medium having a perpendicularly magnetized film on a substrate, where the saturation magnetization of the second magnetic layer is Ms_2, the film thickness is h_2, and the domain wall energy between the two magnetic layers is σw, H_H>H_L. >σw/(2Ms_2h_2)・・・
(1) is satisfied, and the compensation temperature of the second magnetic layer is T_H_C_O_M_
When P, T_L<T_H_C_O_M_P and (value of coercive force of the second magnetic layer at temperature T_L)/(value of coercive force of the second magnetic layer at room temperature: H_L)>0.5...(2 ) A magneto-optical recording medium characterized by satisfying the following conditions: 2) A low Curie point (T_L) and a high coercive force (H) at room temperature.
The exchange-coupled two-layer structure consists of a first magnetic layer having a magnetic field (_H) and a second magnetic layer having a relatively high Curie point (T_H) and a low coercive force (H_L) at room temperature compared to this magnetic layer. A magneto-optical recording medium having a perpendicularly magnetized film on a substrate, where the saturation magnetization of the second magnetic layer is Ms_2, the film thickness is h_2, and the domain wall energy between the two magnetic layers is σw, H_H>H_L. >σw/(2Ms_2h_2)・・・
(1) is satisfied, and the compensation temperature of the second magnetic layer is T_H_C_O_M_
When P, T_L<T_H_C_O_M_P and (value of coercive force of the second magnetic layer at temperature T_L)/(value of coercive force of the second magnetic layer at room temperature: H_L)>0.5 (2) A recording method characterized by recording the following binary values using a magneto-optical recording medium that satisfies the following conditions. (a) With respect to the medium, at a location different from the recording head,
Applying a magnetic field B having a magnitude sufficient to magnetize the second magnetic layer having a coercive force H_L in one direction and not reversing the direction of magnetization of the first magnetic layer having a coercive force H_H, (b) Next, By applying a bias magnetic field using the recording head and at the same time irradiating the medium with enough laser power to raise the temperature of the medium to near the low Curie point (T_L),
The first type of preliminary recording, in which the direction of magnetization of the first magnetic layer is aligned in a stable direction with respect to the second magnetic layer without changing the direction of magnetization of the second magnetic layer, or the Curie point is high while applying a bias magnetic field. By irradiating the medium with enough laser power to raise the temperature to around (T_H), the direction of magnetization of the second magnetic layer is reversed, and at the same time, the first magnetic layer is also oriented stably with respect to the second magnetic layer. Is it a second type of preliminary recording that magnetizes?
(c) then moving the medium to cause the pre-recorded bits to pass through said magnetic field B; For bits formed by the second type of preliminary recording without changing the direction of magnetization in both the magnetic layer and the second magnetic layer,
Binary recording in which the direction of magnetization of the second magnetic layer is reversed in the same direction as the magnetic field B, and the direction of magnetization of the first magnetic layer is left unchanged.