JPH06267125A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To make possible optically modulated overwriting in a magneto-optical recording medium in a perfectly no magnetic field. CONSTITUTION:This magneto-optical recording medium has a memory layer 15, a bias layer 19 generating a levitating magnetic field and an initialized layer 23. The bias layer 19 is a TbFeCo film 20 having a compsn. ratio determined so as to regulate the compensation temp. to room temp. or below. The memory layer 15 is a DyFeCo film 16 having a compsn. ratio determined so as to regulate the compensation temp. to room temp. or below.

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 a magneto-optical recording medium applicable to optical modulation overwrite.

During optical modulation overwrite, the magnetic layer of the magneto-optical recording medium is irradiated with laser light to be temporarily heated to the Curie temperature and then cooled to room temperature.

Therefore, in the magneto-optical recording medium, the material of each magnetic layer is important in order to improve the recording characteristics, and the compensation temperature is important because it is cooled to room temperature.

Here, the compensation temperature means that the magnitude of magnetization of the transition metal component (Fe, Co, etc.) and the magnitude of magnetization of the rare earth metal component (Dy, etc.) in the composition of the magnetic layer are equal, and apparently, The temperature at which the magnetization of the magnetic layer disappears.

[0005]

2. Description of the Related Art Conventionally, a memory layer for recording / reproducing, a bias layer for generating a stray magnetic field for recording, and an initialization layer for initializing the bias layer are provided, and an optical field without an external magnetic field is required. A magneto-optical recording medium capable of modulation overwrite has been proposed by, for example, Japanese Patent Laid-Open No. 3-156751.

[0006]

However, in the conventional device, the compensation temperature is not taken into consideration, and in some cases, the light modulation overwrite may not be normally performed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to make the magnetic layer a structure in consideration of the compensation temperature so that the complete magnetic field-free optical modulation overwrite can be normally performed.

[0008]

According to the invention of claim 1, there is provided a recording / reproducing device comprising a rare earth-transition metal thin film having a composition having perpendicular magnetic anisotropy and having a compensation temperature below room temperature. It is composed of a memory layer and a rare earth-transition metal thin film having a composition having perpendicular magnetic anisotropy and having a compensation temperature at room temperature or lower, and exchange-coupled with the memory layer to prevent a stray magnetic field for recording. A bias layer to be generated, and having a perpendicular magnetic anisotropy, and when recording / reproducing, when irradiated with a laser beam in the case of erasing, is composed of a rare earth-transition metal thin film whose composition does not reverse the direction of magnetization. The bias layer is exchange-coupled with the bias layer and has a structure including an initialization layer for initializing the bias layer.

According to a second aspect of the present invention, there is provided a memory layer for recording / reproducing comprising a rare earth-transition metal thin film having a composition having perpendicular magnetic anisotropy and having a compensation temperature above room temperature, and a perpendicular magnetic layer. Rare earth having a composition having anisotropy and having a compensation temperature below room temperature-consisting of a transition metal thin film, exchange-coupled with the memory layer, and a bias layer for generating a stray magnetic field for recording, It has perpendicular magnetic anisotropy, and when irradiated with laser light for recording / reproducing and erasing,
It is composed of a rare earth-transition metal thin film having a composition that does not reverse in the direction of magnetization, is exchange-coupled with the bias layer, and has an initialization layer for initializing the bias layer.

According to the invention of claim 3, the bias layer is made of TbF.
The structure is an eCo film or a GdTbFeCo film.

According to a fourth aspect of the invention, the memory layer is DyFe.
The structure is a Co film or a GdDyFeCo film.

[0012]

According to a first aspect of the present invention, the bias layer has a composition having a compensation temperature below room temperature and the memory layer has a composition having a compensation temperature below room temperature. The direction of the stray magnetic field acting on the part heated by the magnetic field acts in the direction opposite to the direction of the magnetization of the memory layer, and during the cooling process to room temperature, the part of the memory layer heated by the laser beam is heated. It acts so that the direction of magnetization is not reversed.

That is, the direction of magnetization of the portion of the memory layer that is not irradiated with the laser light is the direction of magnetization of the portion of the memory layer that is irradiated with the laser light when it is heated to the room temperature and then cooled to room temperature. It works in the opposite direction.

According to a second aspect of the present invention, the bias layer has a composition having a compensation temperature below room temperature and the memory layer has a composition having a compensation temperature above room temperature. The stray magnetic field acting on the part heated by the magnetic field acts in the same direction as the magnetization direction of the memory layer, and in the cooling process to room temperature, the part of the memory layer heated by the laser beam is heated. It acts so that the direction of magnetization is reversed.

That is, the direction of magnetization of the portion of the memory layer which is not irradiated with the laser light is the direction of magnetization of the portion of the memory layer which is irradiated with the laser light in the state where the memory layer is heated to the room temperature and then cooled to room temperature. It works in the opposite direction.

In the structure in which the bias layer of claim 3 is formed of the TbFeCo film or the GdTbFeCo film, the bias layer acts so as to form a large stray magnetic field of about 250 Oe.

In the structure in which the memory layer of claim 4 is formed of the DyFeCo film or the GdDyFeCo film, the memory layer surely has the perpendicular magnetic anisotropy.

[0018]

1 shows a magneto-optical recording medium 10 according to a first embodiment of the present invention.

The magneto-optical recording medium 10 has a substrate 12 on the side on which the laser light 11 is incident, and on the lower surface of the substrate 12, in order,
Tb—SiO ₂ film 14 as protective layer 13, memory layer 1
5, the film thickness t ₁ = 50 nm, and the film thickness t as the DyFeCo film 16 and the control layer 17 having perpendicular magnetic anisotropy.
The film thickness t ₃ = 150 nm as the GdFeCo film 18 and the bias layer 19 of ₂ = 10 nm, and the film thickness t ₄ = as the TbFeCo film 20 having the perpendicular magnetic anisotropy and the control layer 21.
A TbFeCo film 22 having a thickness of 10 nm, a film thickness t ₅ = 80 nm as the initialization layer 23, and TbC having a perpendicular magnetic anisotropy.
o film 24 and Tb—SiO ₂ film 2 as protective layer 25
6 has a laminated structure.

The memory layer 15 is a layer for recording / reproducing.

The bias layer 19 generates a stray magnetic field for recording.

The initialization layer 23 initializes the bias layer 19.

The control layer 17 controls the exchange coupling force between the memory layer 15 and the bias layer 19.

The control layer 21 controls the exchange coupling force between the bias layer 15 and the initialization layer 23.

For convenience of explanation, the magnetization of a material having a composition containing a rare earth metal and a transition metal will be described.

The magnetization of the transition metal component is called "T magnetization", and the magnetization of the rare earth metal component is called "R magnetization". The directions of T magnetization and R magnetization are opposite to each other, and here, T magnetization is upward (+) and R magnetization is downward (-).

The total magnetization of T magnetization and R magnetization is called "N magnetization". Regarding the compensation temperature, the temperature at which the T magnetization and the R magnetization have the same magnitude is the compensation temperature.

When the transition metal component is rich, the material has a compensation temperature.

When the rare earth metal component is rich, the material has no compensation temperature.

When the degree of richness of the transition metal component is small, the compensation temperature is higher than room temperature (25 ° C.).

As the degree of richness of the transition metal component increases, the compensation temperature decreases.

Therefore, the compensation temperature can be appropriately determined by appropriately determining the ratio of the rare earth metal component and the transition metal component. Regarding the temperature dependence of N magnetization, as the material temperature approaches the Curie temperature, both T magnetization and R magnetization become smaller.

When the temperature of the material is below the compensation temperature,
The R magnetization is large and the T magnetization is small, so the N magnetization is downward.

When the temperature of the material is higher than the compensation temperature,
The T magnetization is large and the R magnetization is small, so the N magnetization is upward.

Therefore, the N magnetization of the material having the compensation temperature T _comp lower than the _room temperature T _room changes as shown by the line I in FIG. 2 due to the temperature change.

The N magnetization of the material having the compensation temperature T _comp higher than the _room temperature T _room changes as the temperature changes, as shown by the line II in FIG.

Next, the magnetic characteristics of the layers and films constituting the magneto-optical recording medium 10 of FIG. 1 will be described. The Curie temperature T _C of the DyFeCo film 16 as the memory layer 15 is 180 ° C.

The DyFeCo film 16 is made of F which is a transition metal.
e, Co is located as considerably composition is rich (TM-rich composition) in comparison to Dy is a rare earth metal, the compensation temperature T _{co mp} is lower than the room temperature T _room (25 ℃).

Therefore, the magnetization of the DyFeCo film 16 changes depending on the temperature as shown by the line III in FIG. The Curie temperature T _C of the TbFeCo film 20 as the bias layer 19 is 220 ° C.

The TbFeCo film 20 is formed of F which is a transition metal.
e, Co is located as considerably composition is rich (TM-rich composition) in comparison with Tb is a rare earth metal, the compensation temperature T _{co mp} is lower than the room temperature T _{room room.}

Therefore, even in the magnetization of the TbFeCo film 20,
Depending on the temperature, it changes as shown by the line IV in FIG.

The Curie temperature T _C is 220 ° C., which is higher than the Curie temperature T _C = 180 ° C. of the film 16 described above. Therefore, the film 20 has the magnetization A even at the temperature of 180 ° C.

Therefore, even at a high temperature of 180 ° C., the film 20
Can form a sufficiently large stray magnetic field of 250 Oe. The TbCo film 24 as the initializing layer 23 has a Curie temperature T _C of 300 ° C. or higher.
It is considerably higher than the Curie temperature T _{C of} 6,20.

The transition metal Co is richer than the rare earth metal Tb (TM rich composition), the compensation temperature T _comp is higher than the _room temperature T _room , and the films 16 and 22 have the same composition. It is 200 ° C., which is a temperature close to T _C.

Therefore, the magnetization of the TbCo film 24 changes as shown by the line V in FIG. 4 depending on the temperature.

The direction of magnetization of the TbCo film 24 does not reverse even when irradiated with laser light.

Next, the operation when information is recorded on the magneto-optical recording medium 10 of FIG. 1 will be described with reference to FIG.

In FIG. 5, the horizontal axis shows the temperature. Room temperature T on the left
_room , the temperature on the right is slightly above the Curie temperature T _C (20
0 ° C). The upper part shows the heating process and the lower part shows the cooling process.

The white arrows indicate the direction and magnitude of N magnetization.

The hatched arrows indicate the magnitude and direction of the magnetic field of the stray magnetic field.

FIG. 5A shows the initial state at room temperature. Memory layer 15, bias layer 19 and initialization layer 2
3 is taken out and shown, and the control layers 17 and 21 are omitted.

The N magnetization 30 of the memory layer 15 is upward, the N magnetization 31 of the bias layer 19 is upward, and the N magnetization 32 of the initialization layer 23 is upward.

The initialization layer 23 has such a composition that the direction of the N magnetization 32 is not reversed even when it is heated by being irradiated with laser light. Therefore, the N magnetization 32 of the initialization layer 23 is always shown in the same size in the upward direction regardless of the temperature.

There is no means for generating a magnetic field outside.

The laser beam 11 is radiated after being modulated as shown in FIG. 6 or 7.

The recording method of FIG. 6 is a general one,
The recording method of FIG. 7 is disclosed in JP-A-1-19941, JP-A-1-
119942.

When the laser light 11 is temporarily irradiated, the portion 34 of the layer 15 and the portion 35 of the layer 19 are exposed to the light beam.
It is heated to about 00 ° C., and the state shown in FIG.

That is, in the portion 34, the N magnetization 30 is lost.

In the portion 35, the N magnetization 31 disappears, and the downward stray magnetic field 36 is generated by the N magnetization 31 in the unheated portion of the layer 19 around the portion 35.
Occurs.

In the downward direction, which is the direction of the stray magnetic field 36,
This is opposite to the orientation of the N magnetization 31 of the unheated part of 9.

The strength of the stray magnetic field 36 is as large as 250 Oe.

When the irradiation of the laser beam is cut off, the parts 34,
The temperature of 35 decreases and N magnetization gradually occurs.

As shown in FIG. 5C, first, regarding the portion 35, the portion is aligned in the same direction as the stray magnetic field 36,
A small downward N magnetization 37 is obtained.

As for the portion 34, the layers 19 and 15
Due to the exchange coupling force between and, the downward small magnetization 38 is aligned with the small N magnetization 37.

As can be seen from the lines IV and III in FIG. 4, as the temperature decreases, the above small N magnetizations 37 and 38 are reduced.
Grows.

At room temperature, the state shown in FIG.

As for the memory layer 15, the N magnetization 39 of the portion 34 is directed downward as opposed to the N magnetization 30 of the other portions, whereby information is recorded in the memory layer 15. .

As for the bias layer 19, the small N magnetization 37 is increased and the layers 19 and 23 are increased.
The exchange coupling force between and aligns the orientation of the N magnetization 32 of the layer 23, and the portion 35 becomes the upward N magnetization 40.

This means that the magneto-optical recording medium 10 was completely overwritten with no magnetic field.

Next, the conditions and C / N when actually overwriting will be described.

The magneto-optical recording medium 10 was rotated at a linear velocity of 10 m / s, and the mark length of 0.8 μm was applied on the signal of the mark length of 1.5 μm.
The μm signal was overwritten.

In the case of the recording method shown in FIG. 6, the high power of the laser light was set to 8.5 mW and the low power was set to 3.5 mW.

The C / N ratio was 49.2 dB.

In the case of the recording method of FIG. 7, the erased portion is 9
MHz.

The C / N ratio was 49.5 dB.

Both have sufficient signal quality.

As the memory layer 15 in FIG. 1, Dy
Instead of the FeCo film 16, a GdDyFeCo film having a composition ratio having a temperature characteristic of magnetization indicated by a line III in FIG. 4 may be provided.

Further, as the bias layer 19 in FIG.
Instead of the bFeCo film 20, a GdTbFeCo film having a composition ratio having a temperature characteristic of magnetization shown by a line IV in FIG. 4 may be provided. The GdTbFeCo film forms a stray magnetic field of 240 Oe.

FIG. 8 shows a magneto-optical recording medium 10A according to the second embodiment of the present invention.

The magneto-optical recording medium 10A is the same as the medium 10 of FIG. 1 except for the memory layer and the bias layer.
In the figure, the portions corresponding to those in FIG.

The DyFeCo film 16A as the memory layer 15A is in the TM rich state in which the composition ratio of Dy, Fe and Co is TM rich as in the case of FIG. 1 and the degree of richness is smaller than that in the case of FIG. .

As a result, the DyFeCo film 16A has a compensation temperature of 30 ° C., which is slightly higher than room temperature.
It has a magnetization temperature characteristic indicated by A.

FIG. 10A shows the initial state at room temperature.

The N magnetization 50 of the memory layer 15A is downward.

The laser beam 11 is temporarily irradiated without providing any means for generating a magnetic field outside. As a result, the portions 34A and 35 are heated.

First, as shown in FIG. 10B, the portion 3
As for No. 5, the N magnetization 31 becomes small and the N magnetization 51 becomes small.

Regarding the portion 34A, the N magnetization 50 becomes smaller as the direction is reversed, and the N magnetization 5 becomes smaller.
It becomes 2.

When further heated, as shown in FIG. 10C, the N magnetization disappears in the portions 34A and 35, and a downward stray magnetic field 36 is generated in the portion 35.

When the irradiation of the laser beam is cut off, the parts 34A, 3
When the temperature of 5 starts to decrease, it becomes as shown in FIG.

That is, first, the stray magnetic field 36 causes the portion 35 to have a small downward N magnetization 37, and the layers 19 and 1
Due to the exchange coupling force with 5A, the portion 34A becomes the downward small magnetization 38 aligned with the small N magnetization 37.

As can be seen from the line IV in FIG. 9, the N magnetization 37 increases as the temperature decreases.

Also, as can be seen from the line IIIA in FIG.
As the temperature decreases, the downward N magnetization 38 is temporarily increased, then decreases, becomes zero at the compensation temperature T _comp, below the compensation temperature T _comp, are inverted orientation,
The upward N magnetization 52 results.

At room temperature, the state shown in FIG.

As for the memory layer 15A, the portion 34
The N magnetization 52 of A is directed upward, which is opposite to the N magnetization 50 of the other portions, which means that information is recorded in the memory layer 15A.

Regarding the bias layer 19, the N magnetization 3
7 is aligned with the direction of the N magnetization 32 of the layer 23 by the exchange coupling force between the layers 19 and 23, and the portion 35 has the upward N magnetization 40.

As a result, the complete magnetic field-free optical modulation overwrite has been performed on the magneto-optical recording medium 10A.

Next, the condition and C / N when actually overwriting will be described.

The magneto-optical recording medium 10A was rotated at a linear velocity of 10 m / s, and a mark length of 0.
The 8 μm signal was overwritten.

In the case of the recording system shown in FIG. 6, the high power of the laser light is set to 8.5 mW and the low power is set to 3.5 mW.

The C / N ratio was 49.2 dB.

In the case of the recording method of FIG. 7, the erased portion is 9
MHz.

The C / N ratio was 49.5 dB.

Both have sufficient signal quality.

As the memory layer 15A in FIG. 10,
Instead of the DyFeCo film 16, a GdDyFeCo film having a temperature characteristic of magnetization shown by line IIIA in FIG. 9 may be provided.

Further, as the bias layer 19 in FIG.
Instead of the TbFeCo film 20, a GdTbFeCo film having a composition ratio having a temperature characteristic of magnetization shown by a line IV in FIG. 9 may be provided. The GdTbFeCo film forms a stray magnetic field of 240 Oe.

In each of the above embodiments, the films 16, 1
By appropriately setting the film forming conditions of 6A, 20, 24,
The membranes 18, 22 (control layers 17, 21) can be omitted.

In each of the above embodiments, the memory layer 1
The materials of 5, 15 A and the bias layer 19 are obtained by the following procedure.

The material of the bias layer is determined from the viewpoint of whether the stray magnetic field is sufficiently large (the stray magnetic field needs to be 200 Oe or more in order to realize the complete field-free optical modulation overwrite).

From the viewpoint of whether the C / N ratio can be made sufficiently large, the material of the memory layer that matches the material of the bias layer defined above is determined.

At this time, a material having no Curie temperature is not suitable for the memory layer. This is because the film easily becomes an in-plane film.

[0111]

As described above, according to the first aspect of the present invention, the direction of the magnetization of the portion irradiated with the laser beam is changed in the state where it is cooled to room temperature after being irradiated with the laser beam. The direction of magnetization of a portion not irradiated with laser light can be opposite to that.

Therefore, according to the magneto-optical recording medium of the first aspect of the present invention, the optical modulation overwrite can be performed without the need for an external magnetic field, that is, without a magnetic field.

According to the second aspect of the present invention, the direction of magnetization of the portion irradiated with the laser beam is changed to the magnetization direction of the portion irradiated with the laser beam in a state where the temperature is cooled to room temperature after being irradiated with the laser beam. The direction can be reversed.

Therefore, according to the magneto-optical recording medium of the second aspect of the present invention, the optical modulation overwrite can be performed without the need for an external magnetic field, that is, without a magnetic field.

According to the third aspect of the present invention, the direction of magnetization of the portion of the bias layer heated by the laser beam can be reliably determined, and the C / N ratio can be made sufficiently good.

According to the invention of claim 4, an information signal can be recorded in the memory layer, and the C / N ratio can be made sufficiently good.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a magneto-optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating temperature dependence of N magnetization of a material having T _comp <T _room .

FIG. 3 is a diagram illustrating the temperature dependence of N magnetization of a material having T _comp > T _room .

FIG. 4 is a diagram illustrating temperature dependence of magnetization of films 16, 20, and 24 in FIG.

FIG. 5 is a diagram for explaining a complete magnetic field-free optical modulation overwrite on the magneto-optical recording medium of FIG.

FIG. 6 is a diagram showing an example of a recording method.

FIG. 7 is a diagram showing another example of a recording method.

FIG. 8 is a diagram showing the structure of a magneto-optical recording medium according to a second embodiment of the present invention.

9 is a diagram showing the temperature dependence of the magnetization of the layer (film) in FIG.

FIG. 10 is a diagram for explaining a complete magnetic field-free optical modulation overwrite on the magneto-optical recording medium of FIG.

[Explanation of symbols]

10,10A magneto-optical recording medium 11 the laser beam 12 substrate 13, 25 protective layer 14, 26 Tb-SiO ₂ layer 15,15A memory layer 16, 16A DyFeCo film 17 and 21 control layer 18 GdFeCo film 19 bias layers 20, 22 TbFeCo Film 23 Initialization layer 24 TbCo film 30 N magnetization of memory layer 15 N magnetization of bias layer 19 32 N magnetization of initialization layer 23 34, 34A, 35 Part 36 Stray magnetic field 37, 38, 51 Small N magnetization 39, 40 N magnetization 50 N magnetization of the memory layer 15A 52 Upward N magnetization

Claims (4)

[Claims] 1. A recording / reproducing memory layer (15) comprising a rare earth-transition metal thin film having a composition having perpendicular magnetic anisotropy and a compensation temperature below room temperature, and a perpendicular magnetic anisotropy. And a bias layer (19) which is composed of a rare earth-transition metal thin film having a composition having a compensating temperature below room temperature and which is exchange-coupled with the memory layer and generates a stray magnetic field for recording. , A rare earth-transition metal thin film having perpendicular magnetic anisotropy and having a composition that does not reverse to the direction of magnetization when irradiated with a laser beam for recording / reproducing and erasing, and exchanges with the above bias layer. A magneto-optical recording medium, characterized in that the magneto-optical recording medium is composed of an initialization layer (23) which is coupled to the bias layer and initializes the bias layer. 2. A memory layer (15A) for recording / reproducing, which comprises a rare earth-transition metal thin film having a composition having perpendicular magnetic anisotropy and a compensation temperature above room temperature, and a perpendicular magnetic anisotropy. And a bias layer (19) which is composed of a rare earth-transition metal thin film having a composition having a compensating temperature below room temperature and which is exchange-coupled with the memory layer and generates a stray magnetic field for recording. , A rare earth-transition metal thin film having perpendicular magnetic anisotropy and having a composition that does not reverse to the direction of magnetization when irradiated with a laser beam for recording / reproducing and erasing, and exchanges with the above bias layer. A magneto-optical recording medium, characterized in that the magneto-optical recording medium is composed of an initialization layer (23) which is coupled to the bias layer and initializes the bias layer. 3. The magneto-optical recording medium according to claim 1, wherein the bias layer is a TbFeCo film (20) or a GdTbFeCo film. 4. The magneto-optical recording medium according to claim 1, wherein the memory layer is a DyFeCo film (16) or a GdDyFeCo film.