JPH06187678A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve cross talk due to heat in a magneto-optical disk for optical modulated overwriting using an exchange bonded film and to increase recording density by further laminating a nonmagnetic layer and a 3rd magnetic layer besides the 1st and 2nd magnetic layers of the disk. CONSTITUTION:A dielectric layer 2, a 1st magnetic layer 3 and a 2nd magnetic layer 4 are laminated on a substrate 1 to obtain a magneto-optical disk and information is reproduced by utilizing the fact that reflected light generated by irradiating the disk with laser light from the layer 3 side receives a magneto- optical effect. In this case, a nonmagnetic layer 5 and a 3rd magnetic layer 6 are further laminated on the layer 4 side and the magnetic layer 6 is protected with an oxidation preventing layer 7. Each of the three magnetic layers is made of an amorphous film of a rare earth metal transition metal such as Tb-Fe-Co, Gd-Dy-Fe-Co or Gd-Tb-Fe-Co. The rare earth metal content has been regulated to 15-40 atomic% so that the amorphous film acts as a perpendicularly hardened film. The thickness of the 3rd magnetic layer 6 is regulated to <=200nm because semiconductor laser has an output limit and the thickness of the nonmagnetic layer 5 is regulated to <=50nm so as to reduce a leakage magnetic field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium,
In particular, it relates to an overwritable magneto-optical recording medium.

[0002]

2. Description of the Related Art Magneto-optical recording is optical recording capable of recording, reproducing and erasing information. In addition to these functions, a new magneto-optical recording system that enables overwriting has been proposed in recent years. Overwritable magneto-optical recording methods are roughly divided into two types. That is, there are two methods, a magnetic field modulation method and a light intensity modulation method. When comparing the two methods, the point that high speed modulation and high speed recording is possible,
The latter method is more advantageous because it can have a structure in which two magneto-optical recording media are bonded together.

In order to realize the light intensity modulation, Japanese Patent Laid-Open No.
A magneto-optical recording medium as described in JP 62-175948 A is used. That is, as the magnetic layer, an exchange coupling composed of a first magnetic layer having a low Curie temperature and a high coercive force and a second magnetic layer having a relatively high Curie temperature and a low coercive force as compared with this magnetic layer. It is a two-layered film and is a magneto-optical recording medium that can be overwritten by modulating the intensity of laser light.

A light intensity modulation method using this exchange coupling will be described with reference to FIGS. As shown in FIG. 4, at room temperature Tr, the coercive force 12 of the first magnetic layer 3 is larger than the coercive force 13 of the second magnetic layer 4, and the Curie temperature Tc ₂ of the second magnetic layer is the first magnetic layer. It is higher than the Curie temperature Tc _{1 of the} layer.

First, the initialization operation will be described with reference to FIG. In FIG. 5, (a) is an explanatory diagram before initialization and (b) is an explanatory diagram after initialization. The magnetization 10 of the second magnetic layer 4 is generated by the magnetic field (initialization magnetic field) 12 generated by the initialization magnet 19.
Are aligned in the direction of the initialization magnetic field 12. The rare earth-transition metal alloy used here has a property that the moments of the rare earth metal and the transition metal are oriented in opposite directions, and the difference between them is the magnetization. Therefore, this magnetization is indicated by an outline arrow. Also, the arrow in the white arrow indicates the direction of the moment of the transition metal. That is, when the magnetic moment of the transition metal is larger than that of the rare earth metal, the white arrow and the arrow of the transition metal point in the same direction, and when the magnetic moment of the rare earth metal is larger than the compensating composition, The magnetization and the magnetic moment of the transition metal point in opposite directions. In addition,
The compensating composition is a composition when the magnetic moments of the rare earth and the transition metal become equal at room temperature. Here, the magnitude of the initialization magnetic field 12 is set to be larger than the coercive force 13 of the second magnetic layer 4 at room temperature and smaller than the coercive force 14 of the first magnetic layer 3 as shown in FIG. Even if the initializing magnetic field 12 is applied, the direction of the magnetization 9 of the first magnetic layer 3 does not change.

FIG. 6 shows a recording operation and FIG. 7 shows an erasing operation. When recording information, the intensity of the laser beam is adjusted to a high laser power level (hereinafter referred to as Ph) and a low laser power level (hereinafter referred to as P) under a constant bias magnetic field.
It is modulated between ( ₁ ). As shown in FIG. 6A, the laser light 13 is narrowed down by the narrowing lens 8 and irradiated onto the magnetic film.

When the laser light intensity is Ph, the temperature of the region irradiated with the laser light is close to the Curie temperature Tc ₂ of the second magnetic layer 4 as shown in FIG. The magnetization 9 of the layer 3 disappears and the magnetization 10 of the second magnetic layer 4 points in the direction of the bias field 15 applied by the permanent magnet 14. When the irradiation of the laser beam is finished and the magnetic film is cooled, the magnetization 9 of the first magnetic layer is also generated in the direction of the bias magnetic field 15 as shown in FIG. 6B.

On the other hand, when the laser light intensity is P ₁ , as shown in FIG.
As shown in (a), the temperature of the region irradiated with the laser light is close to the Curie temperature Tc ₁ of the first magnetic layer 3.
Therefore, since the coercive force 10 of the second magnetic layer 4 is larger than the bias magnetic field 15, the reversal of magnetization does not occur. When the irradiation of the laser beam is finished and the magnetic film is cooled, the magnetization 9 of the first magnetic layer 3 is changed to the magnetization 10 of the second magnetic layer 4 and the bias magnetic field 1.
Since it has an exchange coupling force larger than 5, the magnetization 9 of the first magnetic layer 3 also faces in the direction opposite to the bias magnetic field 15.

[0009]

DISCLOSURE OF THE INVENTION In magneto-optical recording,
To increase the recording density, it is necessary to narrow the track and reduce the mark interval. In the above-mentioned optical modulation overwrite method in the prior art, recording is performed with high level laser power and erasing is performed with low level laser power. Therefore, when the recording marks are recorded at a narrow pitch, there is a risk that the temperature outside the recorded marks rises and the adjacent mark portion reaches the erasing temperature and is erased. This is called thermal crosstalk, which greatly limits the recording density.

An object of the present invention is to provide a magneto-optical recording medium in which the problem of thermal crosstalk which is inevitably caused by using an exchange-coupled bilayer film is improved.

[0011]

In order to achieve the above object, the present invention has the following features.

(1) A substrate has a two-layer magnetic layer in which at least a first magnetic layer and a second magnetic layer are laminated, laser light is irradiated from the side of the first magnetic layer, and the reflected light is magnetic. A magneto-optical recording medium for reproducing information by utilizing the optical effect is characterized in that a non-magnetic layer is provided on the second magnetic layer side, and a third magnetic layer is further provided thereon.

(2) In (1), both the first magnetic layer and the second magnetic layer are alloys composed of a rare earth metal and a transition metal, and the rare earth element of the first magnetic layer is less than the compensating composition. It is characterized in that the magnetic layer contains more rare earth elements than the compensation composition.

(3) In (1) or (2), the thickness of the third magnetic layer is 200 nm or less.

(4) In (1), (2) or (3), the thickness of the nonmagnetic layer is 50 nm or less.

(5) In (1) to (4), a dielectric layer is arranged on the surface of the first magnetic layer opposite to the surface in contact with the second magnetic layer, and the nonmagnetic layer of the third magnetic layer is arranged. An antioxidant layer is provided on the opposite side in contact with the layer.

(6) In any one of (1) to (5), the third magnetic layer is an alloy composed of a rare earth metal and a transition metal.

(7) In the magneto-optical recording medium of (6),
The rare earth element composition of the third magnetic layer is in the range of 15 to 40 atomic%.

(8) In the magneto-optical recording medium described in any one of (1) to (7), the compensation temperature of the rare earth-transition metal alloy of the third magnetic layer is in the range of 100 to 160 degrees and Curie. The magnetization direction of the third magnetic layer at a temperature of 200 ° C. or higher is the same as the magnetization direction of the second magnetic layer initialized at room temperature.

(9) In any one of (1) to (6), when the rare earth element in the third magnetic layer is more than the compensation composition, the compensation temperature is in the range of 50 to 100 degrees and the Curie temperature is Is lower than 200 degrees, and at room temperature, the magnetization direction of the third magnetic layer is opposite to the magnetization direction of the initialized second magnetic layer.

(10) In (1) to (6), when the rare earth element in the third magnetic layer is less than the compensating composition,
The Curie temperature of the third magnetic layer is lower than 200 degrees, and at room temperature, the magnetization direction of the third magnetic layer is the same as that of the initialized second magnetic layer.

(11) In the method for producing a non-magnetic layer described in (4), the dielectric layer described in (5) is used, or the first, second and third magnetic layers are non-nitrided. Use a magnetized one.

In the present invention, as the first magnetic layer, the second magnetic layer or the third magnetic layer, it is preferable to use an amorphous film made of a rare earth and a transition metal. For example, Tb-F
e-Co, Gd-Dy-Fe-Co, Gd-Tb-Fe
-Co alloy or the like is used. In order for these alloys to form a perpendicularly magnetized film, the proportion of rare earth metal is preferably 15 to 40 at%.

Since the semiconductor laser used for magneto-optical recording has a limit in output, there is also a limit in the thickness of the recording film. Therefore, the thickness of the third magnetic layer is preferably 200 nm or less. Further, when the thickness of the non-magnetic layer is large, the leakage magnetic field of the third magnetic layer is greatly attenuated in the first and second magnetic layers, so it is necessary to set the thickness of the non-magnetic layer to 50 nm or less. .

Since the third magnetic layer is composed of a metal that is easily oxidized, it is necessary to provide an antioxidation layer.

[0026]

FIG. 2 shows the leakage magnetic field distribution of the third magnetic layer and the temperature distribution of the entire film when the recording high laser power is irradiated when the recording marks are close to each other. In this case, the third magnetic layer contains a rare earth metal in excess of the compensating composition. Here, consider a case where the erasing temperature of the recording mark 16 is 140 degrees and the compensation temperature of the third magnetic layer is 150 degrees. Thus, the edge portion 1 of the recording mark 16 adjacent to the laser irradiation portion 17
The temperature of 8 has reached the erasing temperature of 140 degrees, and this portion is erased when there is no third magnetic layer. However, when the third magnetic layer is present, the leakage magnetic field concentrates on the edge portion of the recording mark because the compensation temperature of the third magnetic layer is 150 degrees. The direction of this leakage magnetic field acts in a direction that hinders the erasure of the recording mark, so erasure does not occur. That is, the erasing temperature is effectively increased and the thermal crosstalk is improved. There is a limit to the output of the semiconductor laser that is considered to be used, and since the erasing temperature in this method is considered to be approximately 100 to 160 degrees due to the durability of the recording film, the compensation temperature of the third magnetic layer also It is preferably within this temperature range. Therefore, the Curie temperature of the third magnetic layer at this time is equal to or higher than the compensation temperature and is equal to or higher than 200 degrees.

In addition to the above conditions, the magnetic characteristics of the third magnetic layer for preventing thermal crosstalk can be considered. For example, it is a method of setting the Curie temperature of the third magnetic layer near the erasing temperature of the recording mark. The erase temperature of the recording mark is set to 140
FIG. 3 shows the leakage magnetic field distribution formed by the third magnetic layer and the temperature distribution of the entire film when the high laser power for recording is irradiated when the Curie temperature of the third magnetic layer is 150 degrees. At this time, the rare earth composition of the third magnetic layer may be either larger or smaller than the compensation composition. The temperature of the edge portion 18 of the recording mark 16 adjacent to the laser irradiation portion 17 has reached the erasing temperature, and this portion is erased when there is no third magnetic layer. However, when there is the third magnetic layer, the leakage magnetic field of the third magnetic layer is concentrated on the edge portion 18 of the recording mark 16. The direction of this leakage magnetic field is a direction that hinders the erasure of the recording mark, and the erasure does not occur.

[0028]

【Example】

<Embodiment 1> FIG. 1 shows a cross section of a disk according to an embodiment of the present invention. This disk was formed by depositing each layer on the substrate 1 by the sputtering method. The creation conditions are as follows. The ultimate vacuum was 5 × 10 ⁻⁷ Torr or less, Ar was used as the sputtering gas, the gas pressure was 5 mTorr, the input power was 200 W, and the sputtering rate was 0.1 to 0.2 nm / sec.
As the rare earth transition metal alloy, a TbFeCo alloy was used for the first magnetic layer 3 and a TbDyFeCo alloy was used for the second magnetic layer 4. A GdTbFeCo alloy was used for the third magnetic layer 6.
The respective film thicknesses are 30, 90 and 200 nm. Further, the dielectric layer 2, the non-magnetic layer 5 and the antioxidant layer 7 are made of SiN.
And the respective film thicknesses were set to 65, 15, and 20 nm. Since the erasing temperature of the recording mark was 140 degrees, the compensation temperature of the third magnetic layer 6 was set to 150 degrees.

As a result, the thermal crosstalk due to the provision of the third magnetic layer 6 was improved by about 20%. This corresponds to an increase in recording density of 20%.

Example 2 In this example as well, a disk was produced under the same conditions as in Example 1. However, the Curie temperature of the third magnetic layer 6 was set to 150 degrees this time. As a result, the thermal crosstalk due to the provision of the third magnetic layer 6 is 12%.
The degree was improved. This corresponds to an increase in recording density of 12%.

[0031]

According to the present invention, thermal crosstalk is improved in a light modulation overwrite magneto-optical disk using an exchange coupling film. This can significantly improve the recording density.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical disk according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a disc and a leakage magnetic field distribution diagram of a third magnetic layer when marks recorded on the magneto-optical disc according to the present invention are close to each other.

FIG. 3 is a sectional view of a disk and a leakage magnetic field distribution map of a third magnetic layer when a recording mark is close to the magneto-optical disk according to the present invention.

FIG. 4 is a characteristic diagram of temperature dependence of coercive force (Hc) of the first magnetic layer and the second magnetic layer.

FIG. 5 is a cross-sectional view showing the magnetization states of the first magnetic layer and the second magnetic layer before and after the initial stage.

FIG. 6 is a cross-sectional view showing magnetization states of a first magnetic layer and a second magnetic layer during recording.

FIG. 7 is a cross-sectional view showing the magnetization states of the first magnetic layer and the second magnetic layer during erasing.

[Explanation of symbols]

1 ... Substrate, 2 ... Dielectric layer, 3 ... First magnetic layer, 4 ... Second magnetic layer, 5 ... Non-magnetic layer, 6 ... Third magnetic layer, 7 ... Antioxidant layer.

Claims (11)

[Claims] 1. A method in which at least a first magnetic layer and a second magnetic layer are laminated on a substrate, laser light is irradiated from the side of the first magnetic layer, and the reflected light receives a magneto-optical effect is utilized. A magneto-optical recording medium for reproducing information, wherein a non-magnetic layer is provided on the second magnetic layer side, and a third magnetic layer is further provided thereon. 2. The first magnetic layer and the second magnetic layer according to claim 1, wherein both the first magnetic layer and the second magnetic layer are alloys composed of a rare earth metal and a transition metal, and the rare earth element of the first magnetic layer is less than the compensation composition. A magneto-optical recording medium in which the rare earth element in the second magnetic layer is larger than the compensation composition. 3. The magneto-optical recording medium according to claim 1, wherein the third magnetic layer has a thickness of 200 nm or less. 4. The magneto-optical recording medium according to claim 1, wherein the thickness of the nonmagnetic layer is 50 nm or less. 5. The dielectric layer according to claim 1, 2, 3 or 4, wherein a dielectric layer is disposed on a surface of the first magnetic layer opposite to a surface in contact with the second magnetic layer. A magneto-optical recording medium having an anti-oxidation layer on the side opposite to the non-magnetic layer. 6. The method according to claim 1, 2, 3, 4 or 5.
The magneto-optical recording medium, wherein the third magnetic layer is an alloy composed of a rare earth metal and a transition metal. 7. The magneto-optical recording medium according to claim 6, wherein the composition of the rare earth element in the third magnetic layer is in the range of 15 to 40 atomic%. 8. The compensation temperature of the rare earth-transition metal alloy of the third magnetic layer according to claim 1, 2, 3, 4, 5, 6 or 7, and the Curie temperature is 200. A magneto-optical recording medium in which the magnetization direction of the third magnetic layer at this time is the same as that of the second magnetic layer initialized at room temperature. 9. The compensation temperature according to claim 1, 2, 3, 4, 5 or 6, when the rare earth element of the third magnetic layer is more than the compensation composition, the compensation temperature is in the range of 50 to 100 degrees, and The Curie temperature is lower than 200 degrees, and at room temperature, the magnetization direction of the third magnetic layer is opposite to the initialized magnetization direction of the second magnetic layer. 10. The method according to claim 1, 2, 3, 4, 5, or 6, wherein the rare earth element in the third magnetic layer is less than the compensation composition, and the Curie temperature of the third magnetic layer is lower than 200 degrees. A magneto-optical recording medium in which the magnetization direction of the third magnetic layer is the same as that of the initialized second magnetic layer at room temperature. 11. A magneto-optical recording device according to claim 4, wherein the dielectric layer according to claim 5 is used or the first, second and third magnetic films are demagnetized by nitriding treatment or the like. Medium.