JPH03194744A - Overwritable magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a large Kerr rotation angle by setting the Curie temp. of a first magnetic layer higher than the Curie temp. of a second magnetic layer. CONSTITUTION:The Curie temp. of the first magnetic layer 3 is made higher than the Curie temp. of the second magnetic layer 4. Since the magneto-optical effect, namely the Kerr effect, becomes large as the higher Curie temp. of the first magnetic layer 3 is higher, the direction of the magnetic field for recording is set opposite to the direction for which the directions of magnetization in the first magnetic layer 3 are made uniform when the layer 3 is irradiated with laser beam of low intensity. Thereby, a large Kerr rotation angle can be obtained without decreasing the recording sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium that can be overwritten with a single beam.

[Conventional technology]

The cross-sectional structure of a conventional exchange-coupled magneto-optical two-layer film medium is as shown in FIG. 3, for example. On a transparent substrate 1 made of glass or the like provided with a guide groove for tracking, a dielectric layer 2 made of silicon nitride or the like is about 90 nm thick, a first magnetic layer 3 made of TbFaCo or the like is about 1100 nm long, and a second magnetic layer 4 made of TbDyFeCo or the like is formed. about 150 nm, and the protective layer 5 made of silicon nitride etc. about 200 nm.
The layers are stacked in nm order. The dielectric layer 2 multiple-reflects the laser beam incident from the substrate 1 side, and the first magnetic layer 3
It has the function of increasing the rotation of the plane of polarization (Kerr rotation) that occurs in The first magnetic layer 3 has a thickness of about 1100 to prevent light from passing through.
The film thickness is n.

Therefore, the light does not reach the second magnetic layer 4, and the light does not reach the first magnetic layer 3.
The plane of polarization is rotated by reflecting only the magnetization state of . The protective layer 5 has the function of protecting the first magnetic layer 3 and the second magnetic layer 4 from corrosion such as oxidation. The second magnetic layer 4 is the first magnetic N43
It is magnetically exchange-coupled with the beam and is used to perform single-beam overwriting as follows.

The Curie temperature (TCx) of the first magnetic layer 3 is the same as that of the second magnetic layer 4.
lower than the Curie temperature (Tcz) of, and at room temperature,
The coercive force of the second magnetic layer 4 is smaller than the coercive force of the first magnetic layer 3. Therefore, the magnetization of only the second magnetic film 4 can be aligned in one direction by simply applying an initializing magnetic field using a permanent magnet or the like (FIGS. 8(a) and 8(b)). When irradiated with a laser beam of relatively low intensity, the temperature of the first magnetic layer 3 exceeds the Curie point (Fig. 8 (c)), so that the magnetization of the first magnetic layer 3 is equal to that of the second magnetic layer 4 during subsequent cooling. The direction is aligned (Fig. 8 (e)).

Furthermore, when irradiated with a relatively strong laser beam, the temperature of the second magnetic layer 4 exceeds the Curie temperature (Fig. 8(d)).
), during subsequent cooling, the direction of magnetization of the second magnetic layer 4 aligns with the direction of the recording magnetic field applied externally by means such as a permanent magnet (FIG. 8(f)), and as the cooling progresses further, the direction of magnetization of the second magnetic layer 4 aligns with the direction of the recording magnetic field applied from the outside by means such as a permanent magnet. The magnetization of M3 is aligned with the direction of magnetization of the second magnetic M4 (Figure 8
(g) ), Therefore, if the intensity of the laser beam is modulated,
The direction of magnetization of the second magnetic layer 4 can be freely reversed, making single beam overwriting possible. This method is described in, for example, Japanese Unexamined Patent Publication No. 62-175948.

[Problem to be solved by the invention]

However, in the above conventional example, since it was necessary to make the Curie temperature of the first magnetic layer 3 lower than the Curie temperature of the second magnetic layer 4, the Kerr rotation angle that occurs when the first magnetic layer is irradiated with light is increased. However, there was a problem in that the sufficient C/N ratio became small.

This is because there is a relationship between the C/N ratio and the Curie temperature as shown in FIG. Regarding this, for example,
"The 12th Japanese Society of Applied Magnetics Academic Lecture Summary Collection, page 144"
It is stated in

On the other hand, in order to raise the Curie temperature of the first magnetic layer 3, it is necessary to simultaneously raise the Curie temperature of the second magnetic layer 4, but if the Curie temperature of the second magnetic layer 4 is made too high, the recording sensitivity will decrease. There was a problem.

An object of the present invention is to provide a high C/N magneto-optical recording medium that can obtain a large Kerr rotation angle without reducing recording sensitivity.

[Means to solve the problem]

In order to achieve the above object, the present invention uses the following means.

1. At least a first magnetic layer 3 having a relatively large coercive force at room temperature and a second magnetic layer 4 having a relatively smaller coercive force at room temperature than the first magnetic layer 3 are provided on the substrate 1. In the overwritable magneto-optical recording medium, the 1a property M
The Curie temperature (Tax) of No. 3 was set higher than the Curie temperature (Tcz) of the second magnetic layer 4. That is, it was made so that Tax>Tea.

As a result, the Kerr rotation angle of the first magnetic scrap 3 increases, so the signal output when reproducing recorded information is improved.
An overwritable magneto-optical recording medium with good recording and reproducing performance can be obtained.

2. Prior to overwriting information, the direction of magnetization of the second magnetic layer 4 is aligned in one direction, either upward or downward.

This makes it possible to provide new magnetization information to the second magnetic layer 4 regardless of the direction of previously recorded magnetization, thus making overwriting possible.

3. When the magneto-optical recording medium is irradiated with a laser beam of low intensity, the magnetization of the first magnetic layer 3 and the magnetization of the second magnetic layer W4 are strongly exchange coupled, so that the first
The direction of magnetization of the magnetic layer 3 is aligned in one direction, which is the same or opposite to the magnetization of the second magnetic layer 4, which has been magnetized in one direction in advance before overwriting information. That is, when the magneto-optical recording medium is irradiated with a laser beam of low intensity, the first magnetic property y! It becomes possible to align the direction of magnetization of 93 in one direction regardless of previously recorded information, and information is erased.

4. When the magneto-optical recording medium is irradiated with a high-intensity laser beam, the magnetization of the first magnetic layer 3 is in the same direction as or opposite to the direction of the externally applied recording magnetic field, and the low-intensity laser beam is The magnetization of the first magnetic layer 3 is aligned in the opposite direction to the direction in which the magnetization of the first magnetic layer 3 is aligned when laser light is irradiated.

For this purpose, the direction of the recording magnetic field may be set upward or downward as appropriate.

5. The first magnetic layer 3 is irradiated with a laser beam, and reproduction is performed by utilizing the fact that the polarization state of the reflected light of the laser beam changes due to the magneto-optic effect. This magneto-optical effect is the Kerr effect or the Faraday effect. Since the magnitude of this magneto-optic effect increases as the Curie temperature (Tc1) of the first magnetic layer 3 increases, the magneto-optic effect becomes larger by taking the above-mentioned means in item 1.
As a result, the signal power is increased.

That is, signal quality is improved.

6. The temperature that the first magnetic layer 3 and the second magnetic layer 4 reach when irradiated with the laser beam of low intensity is the Curie temperature (Tcz) of the first magnetic layer 3 and the second magnetic layer 3. The Curie temperature (Tcz) of layer 4 was lower than that of layer 4.

As a result, when the second magnetic layer 4 is irradiated with the laser beam of low intensity, the Curie temperature (Tax) of the second magnetic layer 4 is not exceeded, so that the direction of magnetization of the second magnetic layer 4 is changed. The directions of magnetization of the second magnetic layer 4 are maintained in the same direction before the information is overwritten.

Therefore, the direction of the magnetization of the first magnetic layer 3, which is aligned by strong exchange coupling between the magnetization of the first magnetic layer 3 and the magnetization of the second magnetic layer 4, may be upward or downward prior to overwriting information. The magnetization is aligned in one direction, either the same or opposite to the magnetization direction of the 2111-th magnetic layer 4, which is aligned in one direction. Therefore, by irradiating the laser beam with a low intensity, the direction of magnetization of the first magnetic layer 3 is changed to either upward or downward, regardless of the information previously recorded in the first magnetic layer 3. It can be arranged.

7. When irradiated with the above-mentioned high-intensity laser light,
The temperatures reached by the first magnetic layer 3 and the second magnetic layer 4 were set higher than the Curie temperature (T(!4)) of the second magnetic layer 4.

As a result, when a high intensity laser beam is irradiated, the temperature reached by the second magnetic layer 4 becomes higher than the Curie temperature (Tax) of the second magnetic layer 4, so the second magnetic layer 4 loses its magnetization. Therefore, only the first magnetic layer 3 is affected by the recording magnetic field. Therefore, by irradiating the laser beam with high intensity, the magnetization of the first magnetic layer 3 can be set either upward or downward, regardless of the previous magnetization direction.

Therefore, the direction of magnetization in which the first magnetic layer 3 is aligned when irradiated with a laser beam of high intensity is opposite to the direction of magnetization in which the first magnetic layer 3 is aligned when irradiated with a laser beam of low intensity. By setting the direction of the recording magnetic field in advance so that
Overwriting is possible.

8. After irradiating the laser beam with high intensity, the magnetization of the second magnetic layer 4 changes from that of the first magnetic layer 3 when the temperature of the first magnetic Jw 3 and the second magnetic layer 4 decreases. The direction in which the direction of magnetization of the second magnetic layer 4 is aligned in the same direction or opposite to the direction of magnetization of the first magnetic layer 3 and prior to overwriting the information by exchange coupling is I decided to align it in the opposite direction.

As a result, the direction of magnetization of the first magnetic layer 3, which is aligned under the influence of the recording magnetic field when irradiated with a laser beam of high intensity, is determined by the temperature of the first magnetic layer 3 and the second magnetic layer 4. Even if the temperature reaches the temperature that the first magnetic layer 3 and the second magnetic layer 4 reach when irradiated with a laser beam of low intensity as The direction of magnetization of the first magnetic layer 3, which is aligned when irradiated with laser light, is maintained in the opposite direction.

Therefore, by irradiating the laser beam with high intensity, the magnetization of the first magnetic layer 3 can be set either upward or downward, regardless of the previous magnetization direction, and overwriting becomes possible.

[Effect]

a first magnetic scrap 3 having a high coercive force (Hat) at room temperature;
A magneto-optical recording medium in which a second magnetic layer 4 which is magnetically exchange-coupled with the first magnetic layer 3 and has a relatively low coercive force (Hcz) at room temperature is laminated on a substrate is used to record information. First, the magnetization direction of the second magnetic layer 4 is aligned in one direction upward or downward, and a high intensity laser beam (Hw) is applied to the magneto-optical recording medium while applying an upward or downward recording magnetic field (Hw). By forming marks with upward or downward magnetization on the first magnetic layer 3 when irradiated with laser light (PH), and forming marks with magnetization in the other direction when irradiated with low-intensity laser light (PL), overlapping can be achieved. When performing write recording and reproducing overwritten information, a laser beam is irradiated from the first magnetic layer 3 side, and the laser beam produces a magneto-optic effect due to the magnetization of the first magnetic layer 3. Uke is a method that utilizes the change in the polarization state of reflected light of the laser beam, in which the Curie temperature (Tel) of the first magnetic layer 3 is made higher than the Curie temperature (TC1) of the second magnetic layer 4. This makes it possible to increase the Curie temperature of the first magnetic layer 3. On the other hand, since the higher the Curie temperature, the larger the Kerr rotation angle tends to be, as a result, the signal output (polarization plane of reflected light rotation angle) increases, and it is possible to obtain an overwritable magneto-optical recording system and magneto-optical recording medium with a high CZN ratio as shown by the solid line in FIG.

Further, at room temperature (TR), the magnetic exchange coupling is relatively weak to the extent that the 1a magnetic layer 3 and the second magnetic layer 4 are independently magnetized, and At the temperature (T t,) at which the first magnetic layer 3 and the second magnetic layer 4 are heated when irradiated with a low laser beam (PL), the magnetic exchange coupling occurs between the first magnetic layer 3 and the second magnetic layer 4. The direction of magnetization of the layer 3 is large enough to be aligned with the direction of magnetization of the second magnetic layer 4, and when irradiated with the low-intensity laser light (P), the first magnetic layer 3 and the Second
By setting the humidity (To) at which the magnetic layer 4 is heated to be higher than the Curie temperature of the second magnetic layer 4, an initialization magnetic field (HINI) of an appropriate magnitude is applied to the magneto-optical recording medium at room temperature. ) can be applied to align only the direction of magnetization of the second magnetic layer 4 in one direction, and when irradiated with the low-intensity laser light (PL), the first
The direction of magnetization of the magnetic debris 3 can be aligned to be the same as or opposite to the direction of magnetization of the second magnetic layer 4. Further, when the high-intensity laser beam (Po) is irradiated, the temperature (TH) of the second magnetic layer 4 is higher than the Curie temperature (Tax), so the magnetization disappears. The direction of magnetization of the first magnetic layer 3 is determined by the recording magnetic field (Hw
) direction. Therefore, the direction of the recording magnetic field is
By setting the direction opposite to the direction in which the magnetization of the first magnetic layer 3 is aligned when irradiated with the low-intensity laser light (PL), when irradiated with the high-intensity laser light (PH), Marks having upward or downward magnetization are formed on the first magnetic layer 3, and low intensity laser light (PL) is applied to the first magnetic layer 3.
When irradiated with , it is possible to form a mark having magnetization in the other direction. That is, overwriting is realized.

〔Example〕

Examples of the present invention will be shown below and explained in more detail.

(Example 1) FIG. 1 shows a laminated structure of a recording medium according to an example of the present invention. First, a 5.25-inch transparent glass substrate 1 provided with a guide groove for tracking was loaded into a high-frequency magnetron sputtering device, and after evacuation to below 0.1 mPa, a mixed gas of Ar and Nz was introduced. 1
．． Reactive sputtering was performed using Si as a target at a gas pressure of 3 P a to form a dielectric layer 2 of 7
0 nm layered. Thereafter, sputtering was performed using a T b Fe Co alloy target at an Ar gas pressure of 0.7 Pa, and transition metal-rich TbzzF was formed as the first magnetic layer 3.
Zero-order TbDyFeC with 50nm stacked esxcoss amorphous alloy thin films.

The alloy target was sputtered at the same Ar gas pressure (Q, 7 Pa), and rare earth-rich T was sputtered as the second magnetic layer 4.
bzaDyzaFesoCoa amorphous alloy thin film 110
Laminate 0n. The first magnetic layer 3 laminated in this way
and the second magnetic layer 4 are magnetically exchange coupled to each other.
Next, after evacuation to below 0.1 mPa, a mixed gas of Ar gas and N2 gas was introduced, and the pressure was reduced to 1.3 Pa.
Reactive sputtering was performed using Si as a target at a gas pressure of 1,100 nm to form a protective layer 5 of SiNx.

In this embodiment, the Curie temperature (T
cx) is 300°C, and the Curie temperature (Tcz) of the second magnetic layer 4 is 250°C. Furthermore, at room temperature, the coercive force (3 kOe) of the second magnetic layer 4 is equal to the coercive force (3 kOe) of the first magnetic layer 3.
10kOe) (Figure 4 (, ))
Moreover, the difference in exchange coupling force is not very large, and the first magnetic layer 3 and the second magnetic layer 4 used in the embodiment of the present invention
Since is a rare earth transition metal amorphous alloy film, the direction of magnetization of each layer changes depending on whether there is more moment of rare earth or transition metal coupled in opposite directions. Therefore, materials with a large amount of rare earth moments are called rare earth-rich, and materials with a large amount of transition metal are called transition metal-rich.

In general, rare earth-rich materials often change to transition metal-rich materials at high temperatures.The overwriting mechanism will be explained in detail below using FIG. 6.

As shown in FIGS. 6(a) and 6(b), the magnetization of only the second magnetic layer 4 can be aligned in one direction by simply applying an initializing magnetic field (HILf) using a permanent magnet or the like at room temperature.

Here, since the second magnetic layer 4 has a rare earth-rich composition, the direction of magnetization and the direction of the transition metal moment are opposite at room temperature. The temperature (T t,) when such a recording medium is irradiated with a laser beam (PL) of relatively low intensity
Then, due to exchange coupling, the moment of the transition metal in the first magnetic layer 3 is aligned in the same direction as the moment of the transition metal in the second magnetic layer 4 (Fig. 6(d)). PH), the temperature of the second magnetic layer 4 (T
Since H) exceeds the Curie temperature (Tcz), the direction of magnetization (direction of transition metal moment) of the first magnetic layer 4 is aligned with the direction of the magnetic field applied from the outside by a permanent magnet or the like (Fig. 6(f)). ). Thereafter, during the cooling process, the direction of the magnetization (transition metal moment) of the second magnetic layer M4 changes from the direction of the magnetization (transition metal moment) of the first magnetic layer (
(transition metal moment) and alignment (Fig. 6(e)),
As the temperature further decreases, the laser beam (P
The direction of magnetization remains the same even if the temperature reaches the same temperature as when the laser beam was irradiated (Fig. 6 (C)). Therefore, by modulating the intensity of the laser beam, overwriting can be performed with a single beam. It is possible to do so.

When the recording and reproducing characteristics of the magneto-optical recording medium of this example were investigated, a C/N ratio of 62 dB was obtained at a recording mark length of 5 pm, as shown in FIG.

Further, the laser power required for recording at the outermost circumference of a 5 inch 3600 rpm was about 14 mW.

(Example 2) As shown in Fig. 1, first, a 5.25-inch transparent glass substrate 1 provided with a guide groove for tracking was loaded into a high-frequency magnetron sputtering device, and the temperature was increased to a high vacuum of 0.1 mPa or less. After evacuation, a mixed gas of Ar gas and N2 gas was introduced, and reactive sputtering was performed using a Si target at a gas pressure of 1.3 Pa to form the dielectric layer 2.
Layer SiNx to a thickness of 80 nm. Then T b Fe
Sputtering was performed using a Co alloy target at an Ar gas pressure of 0.7 Pa to form the first magnetic layer 3 with T bxa
Fe8x, Got.

0-order stacking of 22 nm amorphous alloy thin film, T b D
y F e Co alloy target with the same <o, 7P
Tb is sputtered at an Ar gas pressure of a to form the second magnetic layer 4.
z7DyzsFeeocoa amorphous alloy thin film 55nm
Laminate. The first magnetic layer 3 and the second a-magnetic layer 4 laminated in this way are magnetically exchange-coupled with each other, and after being evacuated to 0.1 mPa or less, Ar gas and Nx gas are removed. A mixed gas was introduced and reactive sputtering was performed using Si as a target at a gas pressure of 1.3 Pa, and 1100 nm of SiNx was deposited as a protective layer 5.

In this embodiment as well, the recording medium 7 is used as a single beam overwrite medium, as in the first embodiment.

In this example, the Curie temperature (T
c1) is 300°C, and the Curie temperature (Tax) of the second magnetic layer 4 is 250'C. Further, at room temperature, the coercive force (3 kOe) of the second magnetic layer 4 is smaller than the coercive force (8 kOe) of the first magnetic M43. As for their magnetic properties, as shown in FIG. 4(b), both had rare earth-rich compositions. The difference in exchange coupling force between the two layers is not very large.

This film could also be overwritten in the same manner as in Example 1.

Although the C/N ratio is about 60 dB, which is inferior to that of Example 1,
Conventional overwritable magneto-optical recording medium CC/N57
dB), it is larger due to the higher Curie temperature of the first magnetic layer.

Furthermore, since the overall recording film thickness was made thinner, the recording sensitivity was greatly improved to 8 mW at the outermost circumference at 5 inches and 3600 rpm.

(Example 3) FIG. 9 shows a laminated structure of an example of the present invention. First, 5, 25 with a guide groove for tracking
After loading the inch transparent glass substrate 1 into a high-frequency magnetron sputtering device and evacuation to 0.1 mPa or less, a mixed gas of Ar gas and Nx gas was introduced, and the pressure was 1.3 Pa.
Reactive sputtering was performed using Si as a target at a gas pressure of
m layers.

After that, using a T b Fe Co alloy target, 0
．． Sputtering is performed at an Ar gas pressure of 7 Pa to form the first magnetic layer 3.
As the second magnetic layer 4, a 20 nm thick TbzzFeIIsCozz amorphous alloy thin film is deposited. Next, a TbDyFeCo alloy target is sputtered at the same Ar gas pressure of <0.7 Pa to form a TbxoDyxxF esac 010 amorphous film as the second magnetic layer 4. A 35 nm thick alloy thin film is laminated. The first magnetic layer 3 and the second magnetic layer 4 thus laminated are magnetically exchange-coupled with each other. After the primary layer is again evacuated to 0.1 mPa or less, a mixture of Ar gas and Nz gas is applied. Introduce gas, 1.3
At a gas pressure of P a , reactive sputtering is performed using Si as a target, and SiNx is deposited to a thickness of 40 nm as a protection layer M5. Furthermore, using an AfiTi alloy target, 0
．． Sputtering is performed at an Ar gas pressure of 7 Pa to form a metal layer 6.
AQTix was 60nmMM.

This metal layer 7 serves both as a reflective layer to increase the Kerr rotation angle through optical interference effects, and as a heat diffusion layer to prevent the recording film from being exposed to extremely high temperatures and increase the number of rewrites. .

In this embodiment, the Curie temperature (T
CI) is 320° C., and the Curie temperature (TO) of the second magnetic layer 4 is 270° C. At room temperature, the coercive force (4 kOe) of the second magnetic layer 4 is.

This is smaller than the coercive force (12 koe) of the first magnetic layer 3. As shown in FIG. 4(a), the first magnetic layer 3 has a transition metal-rich composition, and the second magnetic layer M4 has a rare earth-rich composition.

In this embodiment, overwriting is possible as well as in the above two embodiments. In this embodiment, the C/N ratio is 64 dB at a recording mark length of 5 μm, which is even better than in the first embodiment. The N ratio has been obtained.

The structure of the medium of the present invention is not limited to the above example.

(1) For example, 1 as the dielectric layer 2 or the protective layer 5.

SiOx, AJNx, 5iAQON, Zn5x.

ZrOx or the like is used.

(2) Gd as the first magnetic layer 3 and the second magnetic layer 4.

Rare earths such as Tb, Nd, Dy, Pr, Sm and Fe, G
An alloy with a transition metal such as O, Ni, or Cr is used. Nb to improve corrosion resistance.

Ti, Pt, Cr, Ta, Ni, etc. may be added.

〔Effect of the invention〕

By using the present invention, it is possible to obtain an overwritable high C/N magneto-optical recording medium that can obtain a large Kerr rotation angle without reducing recording sensitivity.

This is because the Curie temperature of the first magnetic layer 3, which is a recording layer and a reproduction layer, can be increased.

Generally speaking, the higher the Curie temperature, the larger the Kerr rotation angle.

[Brief explanation of drawings]

1v4, FIG. 2, and FIG. 9 are cross-sectional structural diagrams of the magneto-optical recording medium of the present invention, FIG. 3 is a cross-sectional structural diagram of the conventional magneto-optical recording medium, and FIG. A diagram showing the magnetic properties of the first magnetic layer and the second magnetic layer, FIG. 5 is a diagram showing the magnetic properties of the first magnetic layer and the second magnetic layer of a conventional magneto-optical recording medium, FIGS. 6 and 7 8 is a diagram explaining the principle of the present invention, and FIG. 8 is a diagram explaining the principle of the conventional overwrite method. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Dielectric layer, 3... First magnetic layer, 4... Second magnetic layer, 5... Protective layer, 6... Direction of transition metal moment, 7 ... Metal layer, 8a, 8b.
...Direction of magnetization. 9... Direction of initializing magnetic field, 10... Direction of recording magnetic field. Fig. 3 Fig. 3. Fig. 3. Fig. 3. Fig. 3. Fig. 3. Fig. 3. Fig. 3.

Claims (1)

[Claims] 1. At least a first magnetic layer having a relatively large coercive force at room temperature and a second magnetic layer having a relatively smaller coercive force at room temperature than the first magnetic layer are formed on a substrate. An overwritable magneto-optical recording medium comprising: a Curie temperature of the first magnetic layer is higher than a Curie temperature of the second magnetic layer. 2. The overwritable magneto-optical recording medium according to claim 1, characterized in that, prior to overwriting information, the direction of magnetization of the second magnetic layer is aligned in one direction, either upward or downward. 3. When the magneto-optical recording medium is irradiated with a laser beam of low intensity, the magnetization of the first magnetic layer and the magnetization of the second magnetic layer are strongly exchange coupled, so that the direction of the magnetization of the first magnetic layer is changed. 3. The overwritable magneto-optical recording medium according to claim 2, wherein the magnetization of the second magnetic layer is aligned in the same direction as or in the opposite direction. 4. When the magneto-optical recording medium is irradiated with a laser beam of high intensity, the magnetization of the first magnetic layer is in the same direction as or opposite to the direction of the externally applied recording magnetic field, and the laser beam of low intensity is irradiated. When irradiating the first
4. The overwritable magneto-optical recording medium according to claim 3, wherein the magnetization of the magnetic layer is aligned in a direction opposite to the direction in which the magnetization is aligned. 5. Reproduction is performed by irradiating the first magnetic layer with a laser beam and utilizing the fact that the polarization state of the reflected light of the laser beam changes due to a magneto-optical effect. The overwritable magneto-optical recording medium according to items 4 to 4. 6. The temperature that the first magnetic layer and the second magnetic layer reach when irradiated with the low-intensity laser light is
6. The overwritable magneto-optical recording medium according to claim 1, wherein the Curie temperature of the magnetic layer is lower than the Curie temperature of the second magnetic layer. 7. The first magnetic layer and the second magnetic layer reach a temperature higher than the Curie temperature of the second magnetic layer when irradiated with the high-intensity laser light. 6. The overwritable magneto-optical recording medium according to any one of 6. 8. After irradiating the high intensity laser beam, the first
When the temperature of the magnetic layer and the second magnetic layer decreases, the magnetization of the second magnetic layer changes in the same direction as or in the opposite direction to that of the first magnetic layer due to exchange coupling with the first magnetic layer. 9. The overwrite according to claim 2, wherein the magnetization direction of the second magnetic layer is aligned in a direction opposite to the direction in which the magnetization direction of the second magnetic layer is aligned prior to overwriting the information. A writable magneto-optical recording medium.