JP3333389B2 - Magneto-optical information storage medium and reproducing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention records information by forming magnetic domains by laser light and an external magnetic field,
The present invention relates to a magneto-optical information storage medium for reading the magnetic domain by the magneto-optical effect, and a reproducing method therefor, and in particular, to increase a modulation degree of a recording mark smaller than a resolution determined by a reproducing laser beam wavelength and an objective lens numerical aperture, and The present invention relates to a magneto-optical information storage medium capable of suppressing a decrease in the degree of modulation of a recording mark larger than the above resolution and a method of reproducing the same.

[0002]

2. Description of the Related Art A typical magneto-optical disk as a magneto-optical information storage medium has a magnetic film having perpendicular magnetic anisotropy.
In recording on this magneto-optical disk, the magnetic film is locally heated by condensing a laser beam on the disk, and at the same time, a magnetic field is applied from the outside to form a magnetic domain in which the direction of magnetization is modulated according to information. It is done by doing.

On the other hand, at the time of reproduction, a linearly polarized laser beam having a smaller power than at the time of recording is irradiated on the magneto-optical disk. Since the magnetization having the direction corresponding to the information remains in the magnetic film of the magneto-optical disk, the polarization plane of the laser beam reflected by the magneto-optical disk rotates. This is called the Kerr rotation effect, and the rotation angle of the polarization plane is called the Kerr rotation angle. Since the Kerr rotation angle changes depending on the direction and magnitude of the magnetization, information is reproduced by detecting the Kerr rotation angle.

In order to improve the recording density by the above-described method, it is necessary to reduce the size of the recording mark and the track pitch. However, not only magneto-optical discs but also optical discs that reproduce signals using laser beams, the spot diameter of laser light condensed on the optical disc, that is, the resolution during reproduction depends on the wavelength of the reproduction laser beam and the aperture of the objective lens. Determined by the number,
This has been a limiting factor in reducing the size of the recording mark.

[0005] In recent years, as a method for solving the above-mentioned problem in the magneto-optical disk, many techniques called magnetic super-resolution for reproducing a recording mark much smaller than the reproducing laser beam spot diameter have been proposed. This technology provides a magneto-optical disk with at least a recording magnetic film and a reproducing magnetic film,
By utilizing the fact that the temperature on the disc by the laser beam varies depending on the position in the spot, the magnetization of the recording magnetic film is transferred to the reproducing layer only in a limited temperature region, and the recording magnetic property is recorded in the temperature region not corresponding to the temperature region. The resolution is improved by forming a magnetic mask in which the magnetization of the reproducing layer is directed in one direction regardless of the magnetization of the film.

As a typical example of magnetic super-resolution, a technique described in Japanese Patent Application Laid-Open No. 3-93056 will be briefly described with reference to FIG. In FIG. 5, 22 is a reproducing magnetic film, 24 is an intermediate layer magnetic film, and 25 is a recording magnetic film.
It is assumed that a recording mark smaller than the reproducing laser beam spot diameter is formed on the recording magnetic film 25. The reproducing magnetic film 22, the intermediate magnetic film 24, and the recording magnetic film 25 are magnetically coupled at room temperature, for example, by an exchange coupling force.

Here, when the recording mark is read out by the reproducing laser beam spot, a temperature distribution occurs in the spot, and the temperature in the front portion becomes high when viewed in the medium running direction. At this time, when the temperature of the front portion is higher than the Curie point of the intermediate magnetic film 24, the coupling between the reproducing magnetic film 22 and the recording magnetic film 25 is broken at the front portion. In this state, when an external magnetic field larger than the coercive force in the temperature rising region in front of the reproducing magnetic film 22 is applied, the magnetization in the temperature rising region in the front follows the direction of the external magnetic field as shown in FIG. The low temperature region follows the direction of magnetization of the recording magnetic film 25. Therefore, the temperature rising area in front becomes as if masked, and the magnetization recorded in this area apparently disappears, and the resolution increases.

The method disclosed in JP-A-3-93056 is an example of a magnetic super-resolution technique, and various other magnetic super-resolution techniques have been proposed. In either case, the reproduction is performed by increasing the resolution by transferring the magnetization of the recording layer to the reproduction layer only in a predetermined temperature region using the temperature distribution in the beam spot.

[0009]

As described above, magnetic super-resolution is an excellent technique for increasing the resolution at the time of reproduction without changing the main parameters of an optical pickup or the like. There are two problems.

One of the reasons is that, since the reproduced portion of the recording mark is a part of the laser beam spot, when reproducing a recording mark longer than the laser beam spot diameter, a normal super-resolution technique is not used. Another problem is that the modulation factor is lower than that of a magneto-optical disk. Another problem is that when a short recording mark is reproduced, the reproduction is still performed with a large laser beam spot diameter. Is an inevitable problem.

It is an object of the present invention to minimize the decrease in the degree of modulation at the time of reproducing a long recording mark, which is a problem of the magnetic super-resolution technique, and to reduce the degree of modulation at the time of reproducing a short recording mark by the conventional magnetic super resolution technique. The purpose is to make the degree of modulation larger than that by the super-resolution technique.

[0012]

According to the present invention, a first magnetic film having perpendicular magnetic anisotropy is provided on a substrate as a magneto-optical information storage medium, and an in-plane anisotropy at room temperature is provided. And a third magnetic film having perpendicular magnetic anisotropy, and a non-magnetic layer is provided between the second magnetic film and the third magnetic film. Alternatively, the first magnetic film having perpendicular magnetic anisotropy and the second and third magnetic films having in-plane anisotropy at room temperature are formed on a substrate,
A non-magnetic layer is provided between the magnetic film and the third magnetic film. In the magneto-optical information storage medium, magneto-optical information is recorded on the first magnetic film.

Hereinafter, a signal reproducing method will be described. As described above, the second magnetic film has in-plane magnetic anisotropy at room temperature. For example, the second magnetic film has a property that the magnetic anisotropy changes from in-plane to perpendicular with an increase in temperature. The temperature at which the magnetic anisotropy changes vertically from within the plane is defined as Tcr.

Thus, when the reproducing laser beam is applied to the magneto-optical information storage medium, the magnetic anisotropy of the second magnetic film is changed from in-plane in a region where the temperature in the spot is equal to or higher than Tcr. At the same time, the magnetization of the first magnetic film is transferred to the second magnetic film by, for example, exchange coupling force. At this time, Tcr is adjusted so that the diameter in the medium running direction of the region where Tcr or more is equal to or less than the diameter of the magnetic domain recorded in the first magnetic film in the medium running direction. Thereby, the magnetic domains generated in the second magnetic film have a single magnetic domain structure having one-way magnetization. A magnetic field is generated from the magnetization transferred to the second magnetic film. Since a non-magnetic layer is provided between the second magnetic film and the third magnetic film, the third magnetic film receives only a leakage magnetic field from the second magnetic film. As a result, the second magnetic film and the third magnetic film are magnetostatically coupled. As described above, a non-magnetic layer is provided between the second magnetic film and the third magnetic film. Since the magnetic domain existing in the second magnetic film has a single magnetic domain structure, the leakage magnetic field from the second magnetic film extends over a wider range than the diameter of the magnetic domain transferred from the first magnetic film to the second magnetic film. . That is, the minute magnetic domains recorded on the first magnetic film are enlarged in size and transferred to the third magnetic film. As a result, a reproduction characteristic having a flat recording mark length dependency of the degree of modulation can be obtained.

Note that the laser beam spot causes the second
In the region where the magnetization is expanded from the magnetic film to the third magnetic film and transferred, the direction of the magnetization must always be constant. Therefore, when a perpendicular magnetization film is used as the third magnetic film, or when the temperature at which the magnetic anisotropy of the third magnetic film changes from the in-plane to the vertical direction is low, the laser beam for reproduction is irradiated at the same time. And a very weak external magnetic field smaller than the leakage magnetic field from the second magnetic film.

Instead of the non-magnetic film between the second magnetic film and the third magnetic film, a magnetic film having a Curie temperature lower than Tcr may be used.

In the above, a non-magnetic layer is also provided between the first magnetic film and the second magnetic film, and the first magnetic film and the second magnetic film are magnetostatically coupled instead of exchange-coupled. Is also good.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view showing the magneto-optical disk according to the first embodiment of the present invention. In FIG. 2, reference numeral 1 denotes a protective film made of an ultraviolet curable resin, and 2 denotes a first magnetic film made of TbFeCo.
Is a recording film that has perpendicular magnetic anisotropy, has a sufficiently large coercive force at room temperature, and records magneto-optical information. 3 is G
a second magnetic film made of dFeCo at a predetermined temperature T
A magnetic film whose magnetic anisotropy changes from in-plane to perpendicular at cr or more. 4 is a non-magnetic film made of silicon nitride, 5 is Tb
This is a third magnetic film made of FeCo, and the magnetic film 5 has a perpendicular magnetic anisotropy and a small coercive force. 6
Is a substrate made of polycarbonate, acrylic, glass, or the like.

FIG. 1 illustrates a method of reproducing information from the magneto-optical disk shown in FIG. When the reproducing laser beam 6 is applied to the magneto-optical disk, the temperature distribution of the magneto-optical disk exhibits a distribution substantially similar to the light intensity distribution. That is, the temperature is high near the center of the laser beam spot, and low near the periphery. The magnetic anisotropy of the second magnetic film 3 changes vertically from the in-plane direction as described above in a portion where the temperature becomes equal to or higher than Tcr due to the laser light spot, and the first magnetic film 2 and the second magnetic film 2 Since the magnetic film 3 is exchange-coupled, a cylindrical single magnetic domain is formed in the second magnetic film 3.
FIG. 3 shows a vertical magnetic field intensity distribution generated from the single magnetic domain.
Shown in

Since the nonmagnetic film 4 exists between the second magnetic film 3 and the third magnetic film 5, the third magnetic film 5 receives only the leakage magnetic field from the second magnetic film 3, As can be seen from FIG. 3, the vertical magnetic field intensity distribution extends over a wider area than the area of the single magnetic domain.
The magnetization of the first magnetic film 2 is transferred in a range larger than the single magnetic domain generated in the magnetic film 3. In the present embodiment, a magnetic film having perpendicular magnetic anisotropy is used for the third magnetic film 5, so that the magnetization direction must always be constant except for the portion where the magnetization is transferred. Therefore, at the same time as irradiating the reproduction laser beam, a very weak external magnetic field 12 smaller than the leakage magnetic field from the second magnetic film 3 is used.
Is provided by a magnetic head (not shown).

As described above, the minute magnetic domains recorded on the first magnetic film 2 are enlarged in size and transferred to the third magnetic film 5. As a result, a reproduction characteristic having a flat recording mark length dependency of the degree of modulation can be obtained.

Next, a second embodiment of the present invention will be described.
FIG. 4 is a view for explaining a method for reproducing a magneto-optical disk according to the second embodiment of the present invention.

The magneto-optical disk of the present embodiment is the same as the first
The third magnetic film of the embodiment has an in-plane magnetic anisotropy at room temperature and a temperature Tcr2 at which the magnetic anisotropy changes in the vertical direction.
However, the second magnetic film 3 is replaced with a film having a temperature lower than the temperature Tcr at which the magnetic anisotropy of the second magnetic film 3 changes from in-plane to perpendicular. As the third magnetic film 5 of the present embodiment, for example, Gd
An alloy film such as FeCo is used.

In this embodiment, as in the first embodiment, since the non-magnetic film 4 exists between the second magnetic film 3 and the third magnetic film 5, the third magnetic film 5 is Although only the leakage magnetic field from the magnetic film 3 is received, as can be seen from FIG. 3, the vertical magnetic field intensity distribution extends over a larger area than the area of the single magnetic domain. The magnetization of the first magnetic film 2 is transferred in a range larger than the single magnetic domain generated in the magnetic film 3.

In this embodiment, the third magnetic film 5 has in-plane magnetic anisotropy at room temperature, and the temperature Tcr2 at which the magnetic anisotropy changes in the vertical direction is determined by the magnetic difference of the second magnetic film 3. A magnetic film is used which is smaller than the temperature Tcr at which the anisotropy changes from in-plane to vertical, and this Tcr2 is set as follows.

The range in which the vertical magnetic field intensity generated from the single magnetic domain generated in the second magnetic film 3 is the same as the magnetization direction of the single magnetic domain is the magnetic anisotropy of the second magnetic film 3 in the temperature distribution. Is greater than a range where the temperature is equal to or higher than the temperature Tcr at which the temperature changes from in-plane to vertical. Therefore, the temperature Tcr2 at which the magnetic anisotropy of the third magnetic film 5 changes from in-plane to perpendicular is lower than Tcr and generated from a single magnetic domain generated in the second magnetic film 3 as shown in FIG. In this case, the temperature is set to a temperature or higher that satisfies a range in which the vertical magnetic field strength is the same as the magnetization direction of the single magnetic domain.
Accordingly, the direction of magnetization is an in-plane direction except for the portion where the magnetization is transferred, and is always a constant direction. That is, unlike the first embodiment, there is no need to apply an external magnetic field at the same time as irradiating the reproduction laser beam.

As described above, the minute magnetic domains recorded on the first magnetic film 2 are enlarged in size and transferred to the third magnetic film 5. As a result, a reproduction characteristic having a flat recording mark length dependency of the degree of modulation can be obtained.

When Tcr2 is set to a lower temperature, an external magnetic field may be applied at the same time as irradiation with the reproducing laser beam, as in the first embodiment. Also, T
The setting of cr and Tcr2 can be achieved by adjusting the composition of the alloy film.

In the first and second embodiments, the second
Instead of the nonmagnetic layer 4 provided between the magnetic film 3 and the third magnetic film 5, a magnetic film having a Curie point smaller than the Tcr may be provided. As a result, the second magnetic film 2
When a single magnetic domain is formed in the magnetic film 3, the second magnetic film 3
Since the third magnetic film 5 and the third magnetic film 5 are magnetostatically coupled like the first and second embodiments, the same effects as those of the first and second embodiments can be obtained.

A non-magnetic layer is also provided between the first magnetic film 2 and the second magnetic film 3 so that the first magnetic film 2 and the second magnetic film 3 are magnetostatically coupled. Good. At this time, for example, the first
Is formed so as to have a compensation composition at room temperature. Thereby, a more stable single magnetic domain is generated in the second magnetic film 3, and the same effect as in the first and second embodiments can be obtained.

[0031]

As described above, according to the present invention, the first magnetic film serving as the recording layer has an in-plane magnetic anisotropy at room temperature and a magnetic anisotropy at a certain temperature. A second magnetic film changing from the inner direction to the vertical direction and a third magnetic film serving as a reproducing layer are formed, and a non-magnetic layer or a Curie point between the second magnetic film and the third magnetic film is formed. By providing a low magnetic layer, the minute magnetic domains recorded in the first magnetic film are:
The size is enlarged and transferred to the third magnetic film. That is, it is possible to reduce a decrease in the modulation factor when reproducing a minute recording mark and a decrease in the modulation factor when reproducing a long mark in the conventional magnetic super-resolution technique. That is, a reproduction characteristic having a flat recording mark length dependence of the modulation degree can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method of reproducing a minute mark using a magneto-optical disk according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the magneto-optical disk according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a magnetic field intensity distribution generated from a magnetic domain formed in a second magnetic film in the magneto-optical disk according to the present invention.

FIG. 4 is an explanatory diagram showing a method of reproducing a minute mark using a magneto-optical disk according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a method of reproducing a minute mark using a magneto-optical recording medium according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Protective film 2 1st magnetic film 3 2nd magnetic film 4 Non-magnetic film 5 3rd magnetic film 6, 26 Laser light beam 22 Magnetic film for reproduction 24 Intermediate layer magnetic film 25 Magnetic film for recording

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Yonezawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Multimedia System Development Division, Hitachi, Ltd. 1-88 Hitachi Maxell Co., Ltd. (72) Inventor Junmi Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Inspection Director, Multimedia Systems Development Division, Hitachi, Ltd. Masaaki Kurano (56) References 9-198731 (JP, A) JP-A-6-295479 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/105

Claims (6)

(57) [Claims] A first magnetic film having perpendicular magnetic anisotropy, and having in-plane magnetic anisotropy at room temperature, wherein the magnetic anisotropy is changed from in-plane direction to perpendicular direction at a predetermined temperature higher than room temperature. And a third magnetic film having perpendicular magnetic anisotropy.
A magneto-optical information storage medium comprising: a third magnetic film, a second magnetic film, and a first magnetic film formed in this order on a substrate; A magneto-optical information storage medium, comprising a non-magnetic layer between the second magnetic film and the third magnetic film. 2. A first magnetic film having perpendicular magnetic anisotropy, and having in-plane magnetic anisotropy at room temperature, wherein the magnetic anisotropy is changed from in-plane direction to perpendicular direction at a predetermined temperature higher than room temperature. When the predetermined temperature is Tcr, the second magnetic film has in-plane magnetic anisotropy at room temperature, and has the in-plane magnetic anisotropy at a predetermined temperature higher than room temperature and lower than Tcr. A third magnetic film that changes from the direction to the vertical direction, and each magnetic film is formed on the substrate in the order of the third magnetic film, the second magnetic film, and the first magnetic film. A magneto-optical information storage medium, comprising a non-magnetic layer between the second magnetic film and the third magnetic film. 3. A first magnetic film having perpendicular magnetic anisotropy, and having in-plane magnetic anisotropy at room temperature, wherein the magnetic anisotropy is perpendicular to in-plane direction at a predetermined temperature higher than room temperature. And a third magnetic film having perpendicular magnetic anisotropy.
A magneto-optical information storage medium comprising: a third magnetic film, a second magnetic film, and a first magnetic film formed in this order on a substrate; Wherein the predetermined temperature is Tcr, a magnetic film having a Curie point smaller than Tcr is provided between the second magnetic film and the third magnetic film. . 4. A first magnetic film having perpendicular magnetic anisotropy, and having in-plane magnetic anisotropy at room temperature, wherein the magnetic anisotropy is changed from in-plane direction to perpendicular direction at a predetermined temperature higher than room temperature. When the temperature is Tcr, the second magnetic film has in-plane magnetic anisotropy at room temperature, and has a Tcr higher than room temperature.
A third magnetic film in which the magnetic anisotropy changes from an in-plane direction to a vertical direction at a lower predetermined temperature Tcr2, and the third magnetic film, the second magnetic film, The first
A magneto-optical information storage medium in which each magnetic film is formed in the order of the above magnetic films, wherein Tcr is provided between the second magnetic film and the third magnetic film.
A magneto-optical information storage medium having a magnetic film having a Curie point smaller than 2. 5. A one of of claims 1 to 4, wherein the first magneto-optical information storage medium and providing a non-magnetic layer between the magnetic layer and the second magnetic layer . 6. A method for reproducing a magneto-optical information storage medium which irradiates a laser beam onto a magneto-optical information storage medium on which magneto-optical information is recorded and reproduces a difference in the polarization state of the reflected laser light as a signal. Item 6. A weak external magnetic field which is smaller than a leakage magnetic field received by the third magnetic film from the second magnetic film when the laser light is applied, using any one of the magneto-optical information storage media according to items 1 to 5. A method for reproducing a magneto-optical information storage medium, comprising: