JPH11162029A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve C/N, etc., in the reproduction by preventing the interference of signal by reproduction of plural recording marks. SOLUTION: The magneto-optical recording medium mI having a magnetic domain expanding layer 1 which is in an intra-surface magnetization state at room temp. and may be changed to a perpendicular magnetization state at above a prescribed temp. and a recording layer 4 having the coercive force larger than the coercive force of this magnetic domain expanding layer 1 is provided with a gate layer 3 which is in the intra-surface magnetization state at room temp. and is lower in Curie temp. than the magnetic domain expanding layer 1 and the recording layer 4.

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 for recording binary information by irradiating a laser beam or the like and reproducing the information by a magneto-optical effect such as the Kerr effect. About things.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional magneto-optical recording medium (hereinafter, referred to as a medium) capable of reproducing magnetic domains. This drawing is a partial cross-sectional view of a conventional medium m2, and explains the state of the magnetization direction during reproduction.

In FIG. 1, reference numeral 11 denotes a magnetic domain expansion layer made of GdFeCo or the like, 12 denotes a reflection layer made of an Al alloy or the like,
3 is a recording layer made of TbFeCo or the like, 14 is an objective lens, and 15 is a laser beam. In this configuration, when the laser 15 is irradiated to the magnetic domain expansion layer 11 during reproduction and the temperature near the beam spot is raised to about 120 ° C., the in-plane magnetization of the magnetic domain expansion layer 11 changes to perpendicular magnetization, Is easily magnetized by the external magnetic field. Also, the recording layer 13
As a result, the magnetization direction is transferred to the magnetic domain expansion layer 11.

When an external magnetic field of about 260 Oe is applied in the same direction as the magnetization direction transferred to the magnetic domain enlarging layer 11, the transferred magnetic domain of the magnetic domain enlarging layer 11 expands to almost the same size as the beam spot. At this time, since the magnetic material of the recording layer 13 has a high coercive force, the magnetization direction is not affected by the influence of heat or an external magnetic field (Nikkei Electronics 19).
97.16.16 (No. 691), JP-A-1-1430
No. 41).

[0005]

However, as shown in FIG. 2, when the recording marks on the recording layer 13 are made smaller to increase the linear recording density, a plurality of recording marks near the center of the beam spot are formed on the magnetic domain enlarging layer. No. 11, there was a problem that the signal interfered and the C / N ratio was lowered.

In order to solve the above problem, a magnetic layer called a gate layer is provided between the magnetic domain expansion layer 11 and the recording layer 13, and only one recording mark having the highest temperature is extracted by the gate layer. A configuration in which the image is transferred to the magnetic domain expansion layer 11 has also been proposed (Nikkei Electronics 1997.6.1).
6 (No. 691)). However, there has been no example in which the magnetic characteristics and the like of the gate layer have been described in detail.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to specify a gate layer provided between a magnetic domain expansion layer and a recording layer in a medium capable of magnetic domain expansion reproduction. It is to improve the resolution at the time of reproduction, that is, the C / N ratio, etc. as a result of obtaining magnetic characteristics.

[0008]

The magneto-optical recording medium of the present invention has a magnetic domain expansion layer which can change its in-plane magnetization state at room temperature to a perpendicular magnetization state at a predetermined temperature or higher at room temperature, and has a coercive force higher than that of the magnetic domain expansion layer. A magneto-optical recording medium having a large recording layer,
A gate layer, which is in an in-plane magnetization state at room temperature and has a lower Curie temperature than the magnetic domain expansion layer and the recording layer, is provided between the magnetic domain expansion layer and the recording layer. Only one of the recording marks of the layer is extracted to enable enlarged reproduction, and as a result, the resolution at the time of reproduction, C / N
The ratio can be improved.

In the present invention, preferably, an intermediate layer is provided between the magnetic domain enlarging layer and the gate layer to block exchange coupling between them.

[0010]

FIG. 1 shows a medium m1 of the present invention.
FIG. 3 is a partial cross-sectional view of the medium m1 for explaining a change in the magnetization state due to temperature.

In FIG. 1, 1 is a magnetic domain expansion layer made of GdFeCo or the like, 2 is an intermediate layer also serving as a reflection layer made of an Al alloy or the like, 3 is a gate layer, 4 is a recording layer made of TbFeCo or the like, and 5 is an objective lens. , 6 are laser beams for reproduction.
These layers are sequentially laminated from a magnetic domain enlarging layer 1 on a disk-shaped transparent substrate (not shown) made of a transparent material such as plastic such as polycarbonate or glass or the like. Also, a transparent material made of sialon (amorphous film of Si, Al, O, N), yttrium sialon (amorphous film of Y, Si, Al, O, N), Si ₃ N ₄ , SiO ₂ , AlN, etc. The dielectric layer may be provided between the transparent substrate and the magnetic domain expansion layer 1, between layers, on the outermost magnetic layer, or the like to prevent oxidation and damage of the magnetic layer.

As shown in FIG. 1, the temperature of the portion of the medium m1 irradiated with the beam spot of the laser beam 6 rises,
At about 20 ° C., the magnetization of the gate layer 3 weakens or disappears, and due to magnetostatic coupling due to a stray magnetic field (white arrow), magnetization in the same direction as the magnetization direction of the recording layer 4 is generated in the magnetic domain expansion layer 1.

Each of the above magnetic layers is basically made of Cr, Fe, C
Transition metal elements such as o, Ni, and Cu
lement, hereinafter referred to as TM), Nd, Sm, Gd,
Rare Earth element such as Tb, Dy, Ho, etc.
, Hereinafter referred to as RE). For example, each magnetic layer is made of TbFe, TbFeCo, GdFeC.
o, GdTbFeCo and the like.

The gate layer 3 of the present invention is in an in-plane magnetization state at room temperature and has a lower Curie temperature than the magnetic domain expansion layer 1 and the recording layer 4. That is, the magnetic domain expansion layer 1 has a Curie temperature of about 320 ° C., and at 120 ° C. or higher, the in-plane magnetization changes to perpendicular magnetization. At this time, the magnetization direction is transferred by the leakage magnetic field of the recording layer 4. The Curie temperature is as high as about 270 ° C. because its perpendicular magnetization must be maintained within the range from room temperature to the maximum temperature for reproduction (from room temperature to about 150 ° C.). Therefore, the Curie temperature of the gate layer 3 is 100
About 140 ° C. (about 120 ° C.), preferably 100 ° C.
When the temperature is less than the above, the leakage magnetic field in FIG. 1 becomes too wide at the reproducing temperature (about 120 ° C.), that is, the gate becomes too wide, and the magnetization direction of the surrounding recording layer 4 is transferred, so that the resolution is deteriorated. On the other hand, if the Curie temperature of the gate layer 3 exceeds 140 ° C., on the other hand, the gate becomes narrower, and the transfer speed in the magnetization direction decreases. More preferably, it is 110 to 130 ° C.

In order to obtain the above magnetic characteristics, the composition of the gate layer 3 is preferably GdFe, GdFeCo, or the like. G
In the case of dFe, the composition ratio is 28 at (atomic)% ≦ G
d ≦ 34 at%, 66 at% ≦ Fe ≦ 72 at% is good, and if Gd exceeds 34 at%, the Curie temperature becomes 100.
° C, and no perpendicular magnetization over the entire operating temperature range. On the other hand, when Gd is less than 28 at%, the Curie temperature becomes 150 ° C. or higher, and a perpendicular magnetization state occurs at room temperature.

The thickness of the gate layer 3 is preferably 50 to 200 °. If the thickness is less than 50 °, the magnetization determined by the product of the saturation magnetization and the film thickness is too small to function as a mask layer for in-plane magnetization. On the other hand, if it exceeds 200 °, the leakage magnetic field from the recording layer 4 becomes weak, and the transfer of the magnetization direction from the recording layer 4 to the magnetic domain expansion layer 1 becomes insufficient.

In the present invention, it is preferable to provide an intermediate layer between the magnetic domain expansion layer 1 and the gate layer 3 for interrupting exchange coupling between them.
When the magnetization direction is transferred to the magnetic domain enlarging layer 1 and the magnetic domain is expanded, the exchange coupling force of the gate layer 3 is not affected. That is,
The effect of the magnetization direction of each of the TM and RE included in the gate layer 3 and the recording layer 4 is compared with the TM and RE included in the magnetic domain expansion layer 1.
And these magnetic layers need only be magnetostatically coupled. Therefore, the selectivity (degree of freedom) of the composition of these magnetic layers is dramatically increased. Further, the strength of the magnetostatic coupling acting on the magnetic domain expansion layer 1 from the recording layer 4 can be adjusted by the intermediate layer.

The composition of the intermediate layer having such characteristics is as follows:
Amorphous AlN (denoted as a-AlN), a-Si
N, a-SiO, a-TiN, a-TiO, a-Ta
O, Sialon, Yttrium Sialon, and the like are preferable. These are nonmagnetic materials and can be easily formed by a sputtering method or the like. Further, the thickness of the intermediate layer is preferably from 10 to 200 °, and if it is less than 10 °, the distribution of the transfer characteristics in the circumferential direction of the disk becomes large in a disk-shaped medium such as a magneto-optical disk. If it exceeds 200 °, the magnetostatic coupling between the magnetic domain expansion layer 1 and the recording layer 4 becomes weak, and the transfer of the magnetization direction becomes insufficient.

In order to obtain the characteristic that the magnetic domain expansion layer 1 changes to a perpendicular magnetization state at a predetermined temperature (about 120 ° C.) or more in an in-plane magnetization state at room temperature, its composition is GdFeCo,
GdTbFe, GdTbFeCo, GdDyFeCo,
It is preferably made of GdDyFe or the like. In addition, the magnetic domain expansion layer 1
The thickness is preferably 100 to 300 °, and if it is less than 100 °, the laser light is easily transmitted and is not reflected, so that the C / N ratio is lowered. On the other hand, if it exceeds 300 °, the speed of expansion and contraction of the magnetic domain decreases, and the resolution deteriorates.

The recording layer 4 must have a compensation temperature near room temperature and a Curie temperature of about 180 ° C. to 280 in order to have a characteristic that the coercive force is larger than that of the magnetic domain expansion layer 1.
C is preferred. Below 180 ° C., the C / N ratio decreases,
When the temperature exceeds 280 ° C., the temperature becomes equal to or higher than the Curie temperature of the recording auxiliary layer, if any, so that the transferable temperature range when transferring from the recording auxiliary layer to the recording layer 4 becomes narrow, and it becomes difficult to set the recording power. .

The composition of the recording layer 4 for obtaining the above characteristics is TbFeCo, TbDyFeCo, TbGdFe
Co, TbGdDyFeCo and the like are preferable.

The composition ratio of the recording layer 4 is TbFeC
In the case of o, 20 at (atomic)% <Tb <28 at%, 6
6 at% <Fe <72 at%, 8 at% <Co <14a
t%, in the case of TbDyFeCo, 18 at% <Tb <2
6 at%, 1 at% <Dy <4 at%, 66 at% <F
e <72 at%, 9 at% <Co <15 at% are preferred. In the case of TbGdFeCo, 18 at% <Tb
<26 at%, 1 at% <Gd <4 at%, 66 at%
<Fe <74 at%, 7 at% <Co <13 at%, T
In the case of bGdDyFeCo, 16 at% <Tb <24 a
t%, 1 at% <Gd <4 at%, 1 at% <Dy <4
at%, 66 at% <Fe <74 at%, 8 at% <C
Preferably, o <14 at%.

The thickness of the recording layer 4 is preferably 200 to 600 °. If the thickness is less than 200 °, the magnetostatic coupling from the recording layer 4 to the magnetic domain expansion layer 1 is weakened, so that the transfer of magnetization becomes difficult.
If the recording auxiliary layer is present, if the recording auxiliary layer is present, it is difficult to transfer the magnetization from the recording auxiliary layer to the recording layer 4 by the exchange coupling force.

Further, on the recording layer 4, a recording auxiliary layer, a control layer,
An initialization layer or the like may be provided to enable overwriting. Further, an exchange coupling force adjusting layer for adjusting the exchange coupling force may be provided between the recording layer 4 and the recording auxiliary layer.

Thus, according to the present invention, only one of the recording marks on the recording layer can be extracted and enlarged and reproduced, and interference of a plurality of signals due to reproduction of the plurality of recording marks can be prevented. And the C / N ratio can be improved.

In the present invention, the recording density may be doubled by laminating each magnetic layer on both sides of the substrate or by sticking two substrates having each magnetic layer laminated on one surface.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0028]

Embodiments of the present invention will be described below. The medium m1 in FIG. 1 was constructed as follows. A transparent dielectric layer (not shown) made of amorphous SiN (800 °) was formed on a disk-shaped transparent substrate (not shown) made of polycarbonate by a sputtering method.

Next, a magnetic domain enlarging layer 1 made of Gd ₃₀ Fe ₄₅ Co _{25 having} an RE-rich thickness of about 200 ° and a Curie temperature of about 320 ° C., a reflective layer (intermediate layer) 2 made of a-AlN having a thickness of about 100 °, A gate layer 3 made of Gd ₃₀ Fe _{70 having} RE richness, a film thickness of about 100 ° and a Curie temperature of about 120 ° C.
Compensation composition at room temperature, film thickness about 400mm, Curie temperature about 27
Recording layer 4 made of Tb ₂₅ Fe ₆₅ Co _{10 at} 0 ° C., a-Si
A transparent dielectric layer (not shown) made of N (800 °) was sequentially formed by a sputtering method, and a resin protective layer (not shown) for preventing ultraviolet rays was further coated thereon to produce a magneto-optical disk. .

FIG. 3 is a graph of the C / N ratio characteristics during reproduction when the recording mark length (μm) of the recording layer 4 is changed. Marked data b is a conventional example of FIG. 2 and square data c is a comparative example, which is the same as that of the embodiment of FIG. 1 except that the gate layer 3 is changed. In the case of data b, the medium is the same as that of the present embodiment except that the medium m2 has no gate layer and the reflective layer 12 is made of a-AlN having a thickness of about 200 °. In the case of data c, the gate layer 3 is made of RE-rich, Gd ₃₀ Fe ₅₀ Co ₃₀ having a thickness of about 100 ° and a Curie temperature of about 300 ° C.

As shown in the graph of FIG. 2, the C / N ratio is required to be about 45 dB or more in practical use, whereas in the present embodiment (data a), even when the recording mark length is 0.050 μm, the C / N ratio is 45 d.
B is exceeded. In the conventional example (data c), the C / N ratio was 45 dB or more when the recording mark length was 0.150 μm or more, and the C / N ratio was deteriorated as compared with this embodiment. In the comparative example (data b), the recording mark length was 0.12.
At 5 μm or more, the C / N ratio became 45 dB or more.

In the case of the comparative example (data b), the region where the magnetization is perpendicular near the center of the beam spot of the gate layer 3 is wider than that of the present embodiment (the dashed line portion of the gate layer 3 in FIG. 1). This is considered to be due to the influence of the surrounding recording marks. Therefore, it is presumed that the gate layer 3 did not function completely, and as a result, the C / N ratio deteriorated.

[0033]

According to the present invention, a gate layer which is in an in-plane magnetization state at room temperature and has a lower Curie temperature than the magnetic domain expansion layer and the recording layer is provided between the magnetic domain expansion layer and the recording layer. As a result, only one of the recording marks on the recording layer can be extracted and enlarged and reproduced, signal interference due to reproduction of a plurality of recording marks can be prevented, and as a result, C /
This has the effect of improving the N ratio and the like.

The magneto-optical recording medium of the present invention is not limited as long as it can perform magnetic domain expansion reproduction, and can be applied to a magneto-optical disk, a magneto-optical card, a magneto-optical tape, and the like.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a medium m1 for explaining a magnetization state during reproduction of a magneto-optical recording medium of the present invention.

FIG. 2 is a partial cross-sectional view of a medium m2 for explaining a magnetization state during reproduction of a conventional magneto-optical recording medium.

FIG. 3 shows the recording mark length and C / C of the magneto-optical recording medium of the present invention.
It is a graph which shows the correlation of N ratio.

[Explanation of symbols]

 1: magnetic domain expansion layer 2: reflection layer (intermediate layer) 3: gate layer 4: recording layer 5: objective lens 6: laser beam

Claims (2)

[Claims] 1. A magneto-optical recording medium comprising: a magnetic domain expansion layer capable of changing to a perpendicular magnetization state at a predetermined temperature or more in an in-plane magnetization state at room temperature; and a recording layer having a larger coercive force than the magnetic domain expansion layer. A magneto-optical recording medium, wherein a gate layer which is in an in-plane magnetization state at room temperature and has a lower Curie temperature than the magnetic domain expansion layer and the recording layer is provided between the magnetic domain expansion layer and the recording layer. . 2. The method according to claim 1, wherein the magnetic domain expansion layer and the gate layer are
2. The magneto-optical recording medium according to claim 1, further comprising an intermediate layer for interrupting the exchange coupling.