JPH06295478A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the large-capacity magneto-optical recording medium. CONSTITUTION:This magneto-optical recording medium consists of >=2 layers of recording films and has a process of transferring the magnetization state of the recording film 2 nearer the light irradiation side next to the recording film 1 to the recording film nearest the light irradiation side at the time of forming recording marks. The boundary magnetic wall energy, effective perpendicularly anisotropic magnetic fields, film thickness, etc., of both layers are controlled at this time, by which the magnetization from the recording film 2 to the recording film 1 is effectively transferred. As a result, the recording film 1 having a large Curie temp., large coercive force, etc., are made usable. The magneto-optical recording medium of high reproduced output is obtd. The recording film having recording characteristics of the recording film 2 is produced. The recording characteristics are changed by changing the recording film 2 even if the recording film 1 is not changed.

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, and more particularly to a magneto-optical recording medium suitable for high density recording.

[0002]

2. Description of the Related Art In a conventional magneto-optical recording medium, a reproducing perpendicularly magnetized film (reading layer) having a high Curie temperature and a large Kerr rotation angle and a perpendicular magnetic film having a low Curie temperature and a relatively small Kerr rotation angle. There is a medium referred to as a high-sensitivity two-layer film in which the magnetization film (recording layer) is exchange-coupled to increase the reproduction signal intensity and increase the recording power.
Such media are disclosed in JP-A-62-184644, JP-A-63-16444 and JP-A-63-18544.
Japanese Patent Laid-Open No. 63-18545 and Japanese Patent Laid-Open No. 63-18545 disclose many recording marks in these media.
In the vicinity of the Curie temperature of the recording layer, the magnetization of the reading layer starts to reverse, and the magnetization of the reading layer is transferred to the recording layer in the process of lowering the temperature. At room temperature, since the coercive force of the recording layer is high, the recording mark is fixed and can exist stably. A characteristic of this high-sensitivity two-layer film different from the conventional single-layer film medium is high recording magnetic field sensitivity due to the small coercive force of the reading layer.

[0003]

In the conventional high-sensitivity two-layer film, since the formation of the recording mark depends on the reversal of the reading layer, the coercive force of the reading layer is sufficient near the Curie temperature of the recording layer. It must be made small, and it was not possible to use a recording film having a large coercive force or a recording film having a too high Curie temperature for the reading layer. Also, the recording characteristics (such as recording magnetic field dependence) are dominated by the read layer,
It was not easy to change the recording characteristics. An attempt to reflect the recording characteristics of a recording film farther from the light irradiation side than the recording film on the recording film closest to the light irradiation side is disclosed in Japanese Patent Laid-Open Publication No. Hei 4 (1999) -43.
As disclosed in Japanese Patent Publication No. 184734, etc., at least three recording films are required, and the Curie temperature is lowered for even-numbered recording films from the light irradiation side so that the exchange interaction between the recording films on both sides is caused. I had to have the role of a switch that cuts and connects.

An object of the present invention is to solve such problems and provide a large capacity magneto-optical recording medium.

[0005]

A magneto-optical recording medium according to the present invention has a recording film having two or more layers, and when a recording mark is formed, the first recording film closest to the light irradiation side is It is characterized in that it has a process of transferring the magnetization state of the second recording film next to the light irradiation side next to the first recording film.

The magneto-optical recording medium of the present invention has at least the first recording film and the second recording film,
There is a temperature region in which the interface domain wall energy density of the second recording film is higher than the interface domain wall energy density of the first recording film in a temperature region from the Curie temperature of the second recording film to room temperature. Characterize.

Further, the magneto-optical recording medium of the present invention has at least the first recording film and the second recording film,
In the temperature region from the Curie temperature to the room temperature of the second recording film, the thickness of the interface domain wall formed at the interface between the first recording film and the second recording film is larger than that of the first recording film. Characterized by being large.

Further, in the magneto-optical recording medium of the present invention, an effective perpendicular anisotropy magnetic field (Hk−) is generated near the Curie temperatures of the first recording film, the second recording film and the second recording film. 4π
Ms) or a third recording film having a small coercive force, and the interface domain wall energy density of the second recording film is in the temperature range from the Curie temperature of the second recording film to room temperature. There is a temperature region that is higher than the interface domain wall energy density of the recording film, and near the Curie temperature of the second recording film, the effective anisotropic magnetic field (H
k-4πMs) or coercive force is less than or equal to the recording bias magnetic field.

Further, the magneto-optical recording medium of the present invention has at least the first recording film, the second recording film and the third recording film, and the Curie of the second recording film. In the temperature range from temperature to room temperature, the thickness of the interface domain wall formed at the interface between the first recording film and the second recording film is larger than the film thickness of the first recording film, and the second recording film Near the Curie temperature of the third recording film, the effective anisotropic magnetic field (Hk-
4πMs) or the coercive force is less than or equal to the recording bias magnetic field.

In the magneto-optical recording medium of the present invention, near the Curie temperature of the second recording film, the effective perpendicular anisotropic magnetic field (Hk-4πMs) or coercive force of the first recording film causes the recording bias. It may be higher than the magnetic field.

[0011]

By transferring the magnetization state of the second recording film to the first recording film, a recording film having the recording characteristics (recording magnetic field dependency, etc.) of the second recording film can be manufactured. Thus, the recording characteristics can be easily changed by changing the second recording film without changing the first recording film.

In the magneto-optical recording medium utilizing the exchange coupling force, the interface magnetic wall at the interface of the recording film generated at the time of forming the recording mark moves toward the recording film having the small interface magnetic field energy density, and recording having the small interface magnetic wall energy density. Punch through the membrane. If the recording film is made thinner than the thickness of the interface domain wall that should occur in the recording film, the interface domain wall punches through the recording film regardless of the energy density of the interface domain wall. This is equivalent to transferring the state of a certain recording film to another recording film (a film in which the interface domain wall is punched through).

In a conventional magneto-optical recording medium utilizing exchange coupling force, when a reading layer having a large coercive force or a high Curie temperature is used, recording marks are formed on the recording layer. In many cases, recording marks are not formed well on the read layer. In this case, since the reproduction signal is obtained from the reading layer, the expected reproduction output cannot be obtained.

Therefore, by utilizing the above-mentioned two principles, the interface domain wall punches through the first recording film, and the recording mark of the second recording film which is well formed is formed on the first recording film. When transferred, good recording marks can be formed on the first recording film even when a material having a large coercive force or a material having a high Curie temperature is used for the first recording film, and an expected reproduction output can be obtained.

On the other hand, when the first recording film having a large coercive force or a high Curie temperature is used,
The characteristics (such as high recording magnetic field sensitivity) due to the small coercive force of the first recording film, which is exhibited by the conventional high-sensitivity two-layer film, are weakened. Therefore, if a third recording film having a weak coercive force is provided on the second recording film to assist the formation of the recording mark of the second recording film, it has the characteristics of the conventional high-sensitivity two-layer film and has a higher reproduction output. Can be produced. In this case, the recording mark is formed in the following process. First, in the vicinity of the Curie temperature of the second recording film, the third recording film causes the magnetization reversal, and at the same time, the magnetization of the second recording film is reversed. Then, in the temperature decreasing process, the recording mark formed on the second recording film is transferred to the first recording film, thereby completing the writing of the recording mark.

In the vicinity of the Curie temperature of the second recording film, the effective perpendicular anisotropic magnetic field or coercive force of the first recording film is larger than the bias magnetic field, and even if no recording mark is formed on the first recording film, an interface is formed. If the domain wall is punched through from the second recording film to the first recording film, the recording mark of the second recording film is transferred to the first recording film during the temperature decrease process, and the expected reproduction output can be obtained.

[0017]

EXAMPLE FIG. 1 shows the structure of a disk using the two-layer film of the present invention. This disc is obtained by sequentially forming an interference film 4, a recording film 1, a recording film 2, and a protective film 5 on a substrate 3.

As an example, the substrate 3 has a diameter of 130 m.
m, a polycarbonate substrate having a track pitch of 1.6 μm is used. On the substrate 3, a silicon nitride film having a thickness of 80 nm is used as the interference film 4, and a GdTbFeCo film having a thickness of 30 is used as the recording film 1.
nm, a TbFeCo film as a recording film 2 of 100 nm, and a silicon nitride film of 80 nm as a protective film 5.

The Curie temperature of the GdTbFeCo film is 25.
Interfacial domain wall energy density at 0 ℃ and room temperature is 1.5 erg
/ Cm ² . The Curie temperature of the TbFeCo film is 150 ° C., and the interface domain wall energy density at room temperature is 2.3.
erg / cm ² . Thereby, punch-through of the interface domain wall from the TbFeCo film to the GdTbFeCo film can be caused.

When recording was performed on this medium at 5.6 m / s at 1 MHz and a duty of 50%, C / 55 dB was obtained.
N was obtained. The recording magnetic field at this time is 400 Oe, and the laser wavelength is 830 nm. The recording power dependence of this medium was similar to the recording power dependence of the TbFeCo film of the recording film 2.

As another example, TbFeC is used as the recording film 1.
A 20 nm thick O film and a 100 nm thick TbFeCo film having a composition slightly different from that of the recording film 1 were formed as the recording film 2. The other membranes are the same as in the above example. TbF of recording film 1
The Curie temperature of the eCo film is 300 ° C., and the interface domain wall energy density at room temperature is 2.7 erg / cm ² . Also,
The Curie temperature of the TbFeCo film of the recording film 2 is 150 ° C.,
Interface domain wall energy density at room temperature is 2.3 erg / cm
^{Is 2} . In this case, since the recording film 1 is thinner than the thickness of the interface domain wall that should be formed, punch-through of the interface domain wall from the recording film 2 to the recording film 1 occurs. 5.6m on this medium
When recording was performed at 1 MHz and a duty of 50%, a C / N of 54 dB was obtained. The recording magnetic field at this time is 400 Oe, and the laser wavelength is 830 nm. The recording power dependence of this medium depends on the TbFeCo of the recording film 2.
It was similar to the recording power dependence of the film.

As another example, GdDyF is used as the recording film 1.
An eCo film having a thickness of 30 nm and a recording film 2 having a TbFeCo film having a thickness of 100 nm were formed. The other membranes are the same as in the above example. The Curie temperature of the GdDyFeCo film is 4
Interface domain wall energy density at room temperature of 00 ° C and 1.8er
It is g / cm ² . Curie temperature of TbFeCo film is 1
The interface domain wall energy at 50 ° C and room temperature is 2.3 erg /
cm ² . In the vicinity of the Curie temperature of the TbFeCo film, the effective anisotropic magnetic field of the GdDyFeCo film is 1 kOe, and the magnetization of this film does not reverse under the bias magnetic field of 400 Oe. When recording was performed on this medium at 5.6 m / s at 1 MHz and a duty of 50%, a C / N of 54 dB was obtained. The recording magnetic field at this time is 400 Oe, and the laser wavelength is 830 nm. The recording power dependence of this medium was similar to the recording power dependence of the TbFeCo film of the recording film 2.

The structure of a disk using the three-layer film of the present invention is shown in FIG. This disc is obtained by sequentially forming an interference film 4, a recording film 1, a recording film 2, a recording film 6 and a protective film 5 on a substrate 3. As an example, a polycarbonate substrate having a diameter of 130 mm and a track pitch of 1.6 μm is used as the substrate 3, a silicon nitride film having a thickness of 80 nm is used as the interference film 4, and a GdTbFeC film is used as the recording film 1 on the substrate 3.
The O film is 30 nm, and the TbFeCo film is 10 as the recording film 2.
0 nm, a GdFeCo film as a recording film 6 having a thickness of 30 nm and a silicon nitride film as a protective film 5 having a thickness of 80 nm were sequentially formed.

The Curie temperature of the GdTbFeCo film is 25.
Interfacial domain wall energy density at 0 ℃ and room temperature is 1.5 erg
/ Cm ² . The Curie temperature of the TbFeCo film is 150 ° C., and the interface domain wall energy density at room temperature is 2.3.
erg / cm ² . The Curie temperature of the GdFeCo film is 310 ° C., and the coercive force at room temperature is as small as several tens Oe. As a result, punch-through of the interface domain wall from the GdFeCo film to the GdTbFeCo film through the TbFeCo film can be caused.

When recording was performed on this medium at 5.6 m / s at 1 MHz and a duty of 50%, C / N of 53 dB was obtained.
was gotten. The recording magnetic field at this time is 400 Oe, and the laser wavelength is 830 nm. In addition, the magnetic field at which carriers start to emerge is -50 Oe, and the magnetic field at which carriers saturate is 50 Oe.
And has high recording magnetic field sensitivity.

As another example, TbFe is used as the recording film 1.
The Co film is 20 nm, the recording film 2 is a TbFeCo film having a composition slightly different from that of the recording film 1, and the recording film 6 is G.
A dFeCo film having a thickness of 30 nm was prepared. The other membranes are the same as in the above example.

The Curie temperature of the TbFeCo film of the recording film 1 is 300 ° C., and the interface domain wall energy density at room temperature is 2.7.
erg / cm ² . In addition, the TbFeCo of the recording film 2
The Curie temperature of the film is 150 ° C., and the interfacial domain wall energy density at room temperature is 2.3 erg / cm ² . Also, GdF
The Curie temperature of the eCo film is 310 ° C., and the coercive force at room temperature is as small as several tens of Oe. In this case, since the recording film 1 is thinner than the thickness of the interface domain wall that should be formed, punch-through of the interface domain wall from the recording film 2 to the recording film 1 occurs. In this medium,
When recording was performed at 1 MHz and a duty of 50% at 5.6 m / s, a C / N of 52 dB was obtained. The recording magnetic field at this time is 400 Oe, and the laser wavelength is 830 nm. Further, the magnetic field at which carriers start to emerge is -100 Oe, and the magnetic field at which carriers are saturated is 50 Oe, which has high recording magnetic field sensitivity.

As another example, GdDyF is used as the recording film 1.
The eCo film is 30 nm, the TbFeCo film is 100 nm as the recording film 2, and the GdFeCo film is 30 nm as the recording film 6.
A film was produced. The other membranes are the same as in the above example. The Curie temperature of the GdDyFeCo film is 400 ° C., and the interface domain wall energy density at room temperature is 1.8 erg / cm ^2.
Is. The Curie temperature of the TbFeCo film is 150 ° C., and the interfacial domain wall energy at room temperature is 2.3 erg / cm ² . The Curie temperature of the GdFeCo film is 310 ° C.,
The coercive force at room temperature is as small as tens of Oe. In the vicinity of the Curie temperature of the TbFeCo film, the effective anisotropic magnetic field of the GdDyFeCo film is 1 kOe, and the magnetization of this film does not reverse under the bias magnetic field of 400 Oe.

When recording was performed on this medium at 5.6 m / s at 1 MHz and a duty of 50%, C / N of 53 dB was obtained.
was gotten. The recording magnetic field at this time is 400 Oe, and the laser wavelength is 830 nm. In addition, the magnetic field at which carriers start to emerge is -50 Oe, and the magnetic field at which carriers saturate is 50 Oe.
And has a high recording magnetic field sensitivity.

[0030]

As described above, according to the present invention, not only the recording characteristics of the recording film closest to the light irradiation side but also the recording characteristics of other recording films can be obtained. Further, the Kerr rotation angle is large, but the coercive force is too large or the Curie temperature is too high, so that a recording film which cannot be used by the conventional method can be used. Further, it is possible to manufacture a medium having a characteristic of high recording magnetic field sensitivity. Therefore, the density of the magneto-optical recording medium can be increased and a large-capacity optical disc can be realized.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a disk according to an embodiment of the present invention.

[Explanation of symbols]

 1 First Recording Film 2 Second Recording Film 3 Substrate 4 Interference Film 5 Protective Film 6 Third Recording Film

Claims (6)

[Claims] 1. A recording film having two or more layers, wherein when a recording mark is formed, the first recording film is closest to the light irradiation side.
2. A magneto-optical recording medium having a step of transferring the magnetization state of the second recording film next to the light irradiation side of the second recording film. 2. The magneto-optical recording medium according to claim 1, which has at least the first recording film and the second recording film, and has a temperature range from a Curie temperature of the second recording film to a room temperature. In the magneto-optical recording medium, there is a temperature region in which the interface domain wall energy density of the second recording film is higher than the interface domain wall energy density of the first recording film. 3. The magneto-optical recording medium according to claim 1, which has at least the first recording film and the second recording film, and has a temperature range from a Curie temperature of the second recording film to a room temperature. The magneto-optical recording medium is characterized in that the thickness of the interface domain wall formed at the interface between the first recording film and the second recording film is larger than the film thickness of the first recording film. 4. The magneto-optical recording medium according to claim 1, wherein the effective perpendicular anisotropic magnetic field is near the Curie temperatures of the first recording film, the second recording film and the second recording film. (Hk-4πMs) or a third recording film having a small coercive force, and the interface domain wall energy density of the second recording film is in the temperature range from the Curie temperature of the second recording film to room temperature. There is a temperature region that is higher than the interface domain wall energy density of the first recording film, and near the Curie temperature of the second recording film, the effective anisotropic magnetic field (Hk-4πMs) of the third recording film or A magneto-optical recording medium having a coercive force equal to or less than a recording bias magnetic field. 5. The medium for magneto-optical recording according to claim 4, comprising at least the first recording film, the second recording film, and the third recording film, and the second recording. In the temperature range from the Curie temperature of the film to room temperature, the thickness of the interface domain wall formed at the interface between the first recording film and the second recording film is larger than the film thickness of the first recording film, The magneto-optical recording medium, wherein the effective anisotropic magnetic field (Hk-4πMs) or coercive force of the third recording film becomes equal to or lower than the recording bias magnetic field near the Curie temperature of the recording film. 6. The magneto-optical recording medium according to claim 1, wherein the effective perpendicular anisotropic magnetic field (Hk) of the first recording film is near the Curie temperature of the second recording film. −
4πMs) or coercive force is equal to or higher than the recording bias magnetic field, a magneto-optical recording medium.