JP2000242983A - Magneto-optical recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a domain wall mobile magneto-optical recording medium suitable to record micromagnetism and to stably keep its state. SOLUTION: This magneto-optical recording medium has at least first, second third and fourth magnetic layers 131, 132, 133, 134 successively laminated. The first magnetic layer 131 consists of a magnetic layer having relatively small coercive force of magnetic domains and higher mobility of magnetic domains compared to the third magnetic layer 133 at a temp. near the ambient temp. The second magnetic layer 132 consists of a magnetic layer having lower Curie temp. than those of the first magnetic layer 131 and the third magnetic layer 133. The third magnetic layer 133 consists of a perpendicular magnetization film, and the fourth magnetic layer 134 consists of an in-plane magnetization film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high-density magneto-optical recording medium utilizing movement of a domain wall during reproduction and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, a magneto-optical disk has been attracting attention as a rewritable high-density recording medium, but there is an increasing demand for a higher-capacity recording medium by further increasing the recording density of the magneto-optical disk. The linear recording density of an optical disk largely depends on the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens, and the spatial frequency at the time of signal reproduction is at the limit of about NA / λ. Therefore, in order to realize a higher density in a conventional optical disk, it is necessary to shorten the laser wavelength λ of the reproducing optical system and increase the numerical aperture NA of the objective lens. However, there is a limit in improving the laser wavelength and the numerical aperture of the objective lens. For this reason, several techniques have been proposed to improve the recording density by devising the configuration of the recording medium and the reading method.

For example, the present inventors have disclosed in Japanese Patent Laid-Open No. 6-290.
No. 496 proposes a magneto-optical recording medium capable of reproducing a signal having a period equal to or less than the diffraction limit of light at a high speed without lowering the reproduction signal amplitude, a reproducing method therefor, and a reproducing apparatus therefor. That is, when a temperature distribution is formed in the reproducing layer of the magneto-optical recording medium by a heating means such as a light beam, a distribution is generated in the domain wall energy density, so that the domain wall can be instantaneously moved to a lower domain wall energy. As a result, the reproduced signal amplitude is always constant and the maximum amplitude irrespective of the interval between recorded domain walls (that is, the recording bit length). That is, the inevitable decrease in the reproduction output accompanying the improvement in the linear recording density is greatly improved, and the density can be further increased.

[0004]

[0006] Here, conventionally,
Whereas the limit of the recording density of an optical recording medium is determined by the limit of “reproduction (method)”, the above-mentioned Japanese Patent Application Laid-Open No. 6-290496 has been proposed.
According to the domain wall displacement type magneto-optical recording medium and the reproducing method disclosed in the above publication, the limit of the recording density depends on the limit of “recording”. That is, in the domain wall displacement type magneto-optical recording medium,
A new problem arises: "How to record and maintain stable magnetic domains." The present invention has been made in view of the above problems, and has as its object to provide a domain wall displacement type magneto-optical recording medium suitable for recording a micro magnetic domain and stably holding the magnetic domain.

[0005]

The above object is achieved by the following means.

That is, the present invention provides at least a first
A magneto-optical recording medium in which second, third, and fourth magnetic layers are sequentially stacked, wherein the first magnetic layer is relatively close to the third magnetic layer at a temperature near ambient temperature. A magnetic layer having a small domain wall coercive force and a large domain wall mobility (moving layer and reproducing layer), wherein the second magnetic layer has a lower Curie temperature than the first magnetic layer and the third magnetic layer. (Switching layer), the third magnetic layer is a perpendicular magnetization film,
This invention proposes a magneto-optical recording medium characterized in that the fourth magnetic layer is an in-plane magnetized film, wherein the fourth magnetic layer is in-plane magnetized in the circumferential direction of the disk, And that the in-plane magnetization direction of the fourth magnetic layer in the land / groove substrate is opposite between the land and the groove.

Further, the present invention relates to a magneto-optical recording medium in which at least first, second, third and fourth magnetic layers are sequentially laminated, wherein the first magnetic layer is located near an ambient temperature. At the temperature of the second magnetic layer, the magnetic layer has a relatively small domain wall coercive force and a large domain wall mobility as compared with the third magnetic layer, and the second magnetic layer includes the first magnetic layer and the third magnetic layer. In a method for manufacturing a magneto-optical recording medium comprising a magnetic layer having a lower Curie temperature than a layer, a fourth magnetic layer comprising an in-plane magnetic film is laminated on a third magnetic layer comprising a perpendicular magnetic film. A method for manufacturing a magneto-optical recording medium is proposed, wherein the fourth magnetic layer is in-plane magnetized in the circumferential direction of the disk, a land / groove substrate is used as the substrate, In the substrate, the in-plane magnetization direction of the fourth magnetic layer is Including that in the soil and the groove are opposite.

According to the present invention, the (perpendicular) recording magnetization of minute marks recorded in the memory layer is formed by laminating an in-plane magnetic layer as the fourth magnetic layer on the memory layer which is the third magnetic layer. Forms a closed loop (U-shape) by the opposite (perpendicular) recording magnetization of the adjacent recording mark and the in-plane magnetization of the fourth in-plane magnetic layer, and stably forms a minute recording magnetic domain recorded in the memory layer. It can be recorded and retained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a schematic sectional view showing the film configuration of the magneto-optical recording medium of the present invention.

On a transparent substrate 11, a first dielectric layer 12,
The magnetic layer 13 and the second dielectric layer 14 are sequentially laminated.

As the transparent substrate 11, for example, glass,
Polycarbonate, polymethyl methacrylate, thermoplastic norbornene-based resin, and the like can be used.

The magnetic layer 13 may be a single layer or a multilayer, and is not particularly limited.
Following the first, second, and third magnetic layers disclosed in Japanese Patent No. 290496, an in-plane magnetic film is formed as a fourth magnetic layer. That is, the first magnetic layer 131 has a smaller domain wall coercive force and a larger domain wall mobility in the vicinity of the ambient temperature than the third magnetic layer (moving layer and reproducing layer).
The second magnetic layer 132 includes the first magnetic layer and the third magnetic layer 132.
The third magnetic layer 133 is a magnetic recording layer (memory layer) having excellent storage stability of magnetic domains, and the fourth magnetic layer 134 is a magnetic layer having a lower Curie temperature than the magnetic layer (switching layer). Is an in-plane magnetized film that assists in maintaining a recording magnetic domain recorded in the third magnetic layer 133 (memory layer).

The in-plane magnetized film is magnetized in the in-plane direction before recording / reproducing data on the magneto-optical disk, and the direction and magnitude of the magnetization are also increased in the process of recording / reproducing data on the magneto-optical disk. This is an in-plane magnetized film that does not change.

Each magnetic layer is continuously formed by physical vapor deposition such as sputtering or vacuum vapor deposition, and the first, second, and third magnetic layers are exchange-coupled or magnetostatically coupled to each other. In addition, between the third and fourth magnetic layers, the fourth magnetic layer is a magnetic layer having a large magnetic anisotropy, a high saturation magnetization, a high coercive force, etc. (used in a heart disk or the like) made of microcrystals. Therefore, coupling such as exchange coupling or magnetostatic coupling is not performed.

As the magnetic layer 131, for example, GdCo
Materials such as rare earth-iron group amorphous alloys having a relatively small magnetic anisotropy, such as garnet, GdFe-based, GdFeCo-based, and TbCo-based alloys, and garnet are preferable.

The magnetic layer 132 is, for example, a Co-based or Fe-based alloy magnetic layer having a Curie temperature of
1 and a layer having a saturation magnetization smaller than that of the magnetic layer 133 is preferable. Here, the Curie temperature can be adjusted by the addition amount of Co, Cr, Ti, and the like.
Specifically, the Curie temperatures of the first to fourth magnetic layers are 150 to 320 ° C. for the first magnetic layer, 60 to 220 ° C. for the second magnetic layer,
The temperature of the third magnetic layer is preferably adjusted in the range of 180 to 320 ° C.

As the magnetic layer 133, for example, TbFe
Rare earths such as Co, DyFeCo, TbDyFeCo
A material that has a large perpendicular magnetic anisotropy and can stably maintain a magnetized state, such as an iron-based amorphous alloy or a platinum group-iron-based periodic structure film such as Pt / Co and Pd / Co, is preferable.

The magnetic layer 134 is made of, for example, CoCr.
An alloy such as Ta, CoCrPt, and CoNi, which has been put into practical use or studied for practical use in the field of hard disks, has a microcrystalline structure, and has large in-plane magnetic anisotropy, saturation magnetization, and coercive force. Further, once the magnetic layer 134 is magnetized in-plane, the magnetized state hardly changes during the magneto-optical recording / reproducing process. This utilizes the fact that the temperature dependence of the magnetic properties of the magnetic layer 134 is small.

The dielectric layers 12, 14 are not particularly limited, but are preferably SiN, SiAlON, SiO ₂ , ZnS and the like. Further, a protective layer 15 made of an ultraviolet resin or the like may be formed on the dielectric layer 14 as needed.

As shown in FIG. 2, the magnetic layer 134 is magnetized in the in-plane direction by rotating the magneto-optical disk 21 and using a magnetic head or a permanent magnet 22 to rotate the magnetic disk. Magnetization is performed so that the easy axis of magnetization is oriented in the direction (direction along the track).

For a magneto-optical disk using a land / groove substrate, when the axis of easy magnetization is oriented in the same direction over the entire disk (FIG. 3), the axis of easy magnetization is opposite to the land and groove. Are oriented (FIG. 4). In the latter case, an in-plane magnetized film is first magnetized in one rotation direction on the entire disk, and then the second step is performed with a magnetic field intensity such that the magnetic field reaches only the land (the magnetic field reaches the groove). The magnetic field is formed by applying an opposite magnetic field only to the land portion to invert the atomic spin of the in-plane magnetization film.

In this way, as shown in FIG. 5, the presence of the magnetic layer 134 which has been magnetized in the in-plane direction in advance allows the pair of recording magnetic domains (atomic spins a and b) recorded in the memory layer 133 to be changed. And the direction of magnetization (atomic spin c) of the in-plane magnetic layer 134 is matched to form a closed loop d.
Since the (U-shaped closed magnetic path) is formed, the effect of more stably maintaining the magnetization state of minute magnetic domains recorded in the memory layer can be obtained.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following specific examples.
The present invention is not limited to the following embodiments. <Embodiment 1> FIG. 1 is a schematic sectional view showing a layer structure of a magneto-optical recording medium of the present invention.

In FIG. 1, the polycarbonate substrate 11
Has a land width of 0.7 μm, a groove width of 0.7 μm,
A land with a groove depth of 190 nm and a groove taper angle of 70 degrees
It is a groove substrate. On the polycarbonate substrate 11, an SiN layer 12 is formed as a first dielectric layer (interference layer) by 90 n.
m and then Gd as the first magnetic layer (domain wall moving layer).
The FeCr layer 131 is 30 nm, the TbFeCr layer 132 is 10 nm as a second magnetic layer (switching layer), and the third
TbFeCoCr layer 133 as magnetic layer (memory layer)
Is 80 nm, and CoC is used as the fourth magnetic layer (in-plane magnetized film).
An rTa layer 134 was sequentially formed by sputtering to a thickness of 25 nm. At this time, the magnetostatic properties of the CoCrTa in-plane magnetic layer 134 were such that the coercive force (in-plane) was 2,300 Oe (Oersted) and the saturation magnetization was 450 emu / cc. Finally, the SiN layer 14 is formed as a second dielectric layer (protective layer) by 8
0 nm was formed. Further, as a protective layer, an ultraviolet curable resin was applied and formed to a thickness of 10 μm.

The magneto-optical disk thus obtained is rotated at 3600 rpm, and a magnetic head (a general-purpose ring head used for a hard disk) having a track width of 3.5 μm and a gap length of 0.4 μm is used. The entire surface of the disk was magnetized. The ring head is installed on the opposite side of the optical disk from the substrate (FIG. 2), maintains a spacing between the head and the disk of about 0.1 μm, and generates a magnetic field large enough to magnetize the fourth magnetic layer. . As shown in FIG. 3, the magnetization was performed on the entire surface of the land 31 and the groove 32 without switching the polarity. That is, the magneto-optical disk of the present invention has a fourth magnetic layer (in-plane magnetized film).
Are spin-magnetized in one direction.

A mark length of 0.07 was formed on the groove surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
After continuously recording 5 μm at intervals of 0.15 μm, reproduction is performed using the “domain wall displacement type expansion reproduction method utilizing the temperature gradient of the magnetic layer (see JP-A-6-290496)” which has already been proposed by the inventors. As a result, the wavelength 680 nm, NA
In an optical system of 0.6 (1.5 m / s relative velocity), C
/N39.0 dB was obtained with good reproducibility. Further, the error rate was at a level having no problem in practical use.

As described above, the in-plane magnetic layer 13 is used as the fourth magnetic layer.
As shown in FIG. 5, the magnetic path of the atomic spin 51 is changed in the order of the memory layer (a) / the in-plane magnetic layer (c) / the memory layer (b) to form a closed loop (U-shaped closed magnetic field) as shown in FIG. Road d)
Is formed, it is possible to more stably exist the recording mark of the memory layer, and even in the recording / reproducing of a minute mark such as 0.075 μm, the reproduced signal and the error rate can be obtained at a practical level and stably. Became. Comparative Example 1 Example 1 was the same as Example 1 except that the CoCrTa layer 134 was not formed as the fourth magnetic layer (in-plane magnetic film).

The pit length of 0.07 was formed on the groove surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
After recording continuously at 5 μm and pit interval 0.15 μm,
The inventor has already proposed a "domain wall displacement type enlargement reproduction method using a temperature gradient of a magnetic layer (Japanese Patent Laid-Open No. 6-290496).
), The wavelength was 680 nm,
In the optical system of A0.6 (1.5 m / s relative velocity),
Although the C / N was 39.0 dB equivalent to that of Example 1, the reproducibility was poor, and the error rate was about 100 times or more lower than that of Example 1, which was a practical problem. <Embodiment 2> In the magneto-optical disk of Embodiment 1, the fourth
By changing the magnetization method of the magnetic layer (in-plane magnetized film) of FIG. 4, the fourth magnetic layer is formed so that the directions of the atomic spins 43 are reversed in the land portion 41 and the groove portion 42 as shown in FIG. The layer (in-plane magnetized film) was magnetized. That is, using the same magnetic head as in the first embodiment, first, the magnetization direction of the fourth magnetic layer (in-plane magnetic film) as shown in FIG. 3 over the entire surface of the disk (both land portions and groove portions). Is magnetized so that the direction of the circle is along the groove (circumferential direction). Next, using only the magnetic field intensity at which the magnetic field reaches only the land portion, only the magnetization direction of the land portion was reversed, and magnetization was performed so that the direction of the atomic spin of the land portion was opposite to that of the groove portion.

A mark length of 0.07 was formed on the groove surface of the magneto-optical disk thus obtained by a normal magnetic field modulation method.
After continuously recording 5 μm at intervals of 0.15 μm, reproduction is performed using the “domain wall displacement type expansion reproduction method using the temperature gradient of the magnetic layer (see JP-A-6-290496)” which has already been proposed by the inventors. As a result, the wavelength 680 nm, NA
In an optical system of 0.6 (1.5 m / s relative velocity), C
/N40.5 dB was obtained with good reproducibility. Further, the error rate was at a level having no problem in practical use.

The following two points can be considered as reasons why the C / N is improved as compared with the first embodiment. That is, since the magnetization directions of the in-plane magnetic layers of the land portion and the groove portion are opposite to each other, 1) the magnetization state of the inclined portion between the land and the groove is apparently demagnetized.
The effect of dividing the magnetic layer between the grooves was obtained. 2) Since the direction of rotation of the closed magnetic path due to the atomic spin is opposite between adjacent tracks, interference from the adjacent tracks may be reduced.

As described above, the in-plane magnetic layer 1 is used as the fourth magnetic layer.
34, and the magnetization directions thereof were reversed in the land portion and the groove portion, so that a reproduction signal and an error rate of a practical level could be stably obtained even in a minute pit of 0.075 μm.

[0033]

As described above, according to the magneto-optical recording medium of the present invention, the magneto-optical recording medium disclosed in Japanese Patent Application Laid-Open No. 6-290496 (by a domain wall displacement type enlarging reproduction method utilizing a temperature gradient of a magnetic layer). , The recording density and transfer speed are greatly improved), an in-plane magnetic layer as a fourth magnetic layer is formed on a recording layer (memory layer) as a third magnetic layer,
Before recording / reproducing on the magneto-optical disk, the fourth magnetic layer is magnetized in the in-plane direction (track direction) in advance to record and reproduce minute magnetic domains of 0.1 μm or less (0.075 μm). Can be realized stably with good reproducibility.

In the case where a land / groove substrate is used, the magnetization direction of the in-plane magnetic layer, which is the fourth magnetic layer, is reversed between the land portion and the groove portion.
The recording of minute magnetic domains of 1 μm or less (0.075 μm) and the storage stability thereof were further improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a layer configuration in Examples 1 and 2 of a magneto-optical recording medium according to the present invention.

FIG. 2 is a simplified diagram in which a fourth magnetic layer (in-plane magnetic film) in Examples 1 and 2 of the magneto-optical recording medium of the present invention is magnetized.

FIG. 3 is an image diagram showing a state where a fourth magnetic layer (in-plane magnetized film) is magnetized in Example 1 of the magneto-optical recording medium of the present invention. FIG. 3 is a diagram showing the directions of atomic spins of a layer (in-plane magnetic film).

FIG. 4 is an image diagram showing a state where a fourth magnetic layer (in-plane magnetized film) is magnetized in Example 2 of the magneto-optical recording medium of the present invention. FIG. 3 is a diagram showing the directions of atomic spins of a layer (in-plane magnetic film).

FIG. 5 is a diagram showing a closed loop (U-shape) of the magnetic path due to the atomic spin of the third magnetic layer (memory layer) and the fourth magnetic layer (in-plane magnetized film) in Examples 1 and 2 of the magneto-optical recording medium of the present invention. FIG. 4 is an image diagram showing a state where a mold closed magnetic circuit) is formed.

[Explanation of symbols]

Reference Signs List 11 transparent substrate (polycarbonate substrate) 13 magnetic layer 131 first magnetic layer (moving layer and reproducing layer) 132 second magnetic layer (switching layer) 133 third magnetic layer (memory layer) 134 fourth magnetic layer ( In-plane magnetic layer) 12, 14 Dielectric layer 15 Protective layer (ultraviolet curable resin) 21 Magneto-optical disk 22 Magnetic head or permanent magnet 31, 41 Land 32, 42 Groove 33, 43 Magnetization direction of in-plane magnetized film ( Atomic spin direction) 51 Atomic spin a, b, c Atomic spin d Closed magnetic path

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/10 541 G11B 11/10 541D

Claims (8)

[Claims] 1. A magneto-optical recording medium in which at least first, second, third, and fourth magnetic layers are sequentially stacked,
The first magnetic layer is disposed at a temperature near ambient temperature.
The second magnetic layer is composed of a magnetic layer having a smaller domain wall coercive force and a larger domain wall mobility than the magnetic layer of the first magnetic layer.
Wherein the third magnetic layer is a perpendicular magnetic film and the fourth magnetic layer is an in-plane magnetic film in a magneto-optical recording medium comprising a magnetic layer having a lower Curie temperature than the third magnetic layer. A magneto-optical recording medium characterized by the following. 2. The magneto-optical recording medium according to claim 1, wherein the fourth magnetic layer is in-plane magnetized in a circumferential direction of the disk. 3. The magneto-optical recording medium according to claim 1, wherein a land / groove substrate is used as the substrate. 4. The magneto-optical recording medium according to claim 3, wherein in the land / groove substrate, the in-plane magnetization direction of the fourth magnetic layer is opposite between the land and the groove. 5. A magneto-optical recording medium in which at least first, second, third, and fourth magnetic layers are sequentially laminated,
The first magnetic layer is disposed at a temperature near ambient temperature.
The second magnetic layer is composed of a magnetic layer having a smaller domain wall coercive force and a larger domain wall mobility than the magnetic layer of the first magnetic layer.
In the method for manufacturing a magneto-optical recording medium comprising a magnetic layer having a lower Curie temperature than the third magnetic layer, the fourth magnetic layer comprising an in-plane magnetic film on the third magnetic layer comprising a perpendicular magnetic film A method for manufacturing a magneto-optical recording medium, comprising laminating layers. 6. The method according to claim 5, wherein the fourth magnetic layer is in-plane magnetized in a circumferential direction of the disk. 7. The method according to claim 5, wherein a land / groove substrate is used as the substrate. 8. The method of manufacturing a magneto-optical recording medium according to claim 7, wherein in the land / groove substrate, the in-plane magnetization direction of the fourth magnetic layer is opposite between the land and the groove.