Magneto-optical recording device with three distinct layers

Details Magneto-optical recording device with three distinct layers Magneto-optical recording device with three distinct layers

1999-08-31

2002-08-06

Neyzari, Ali (Department: 2653)

Dynamic information storage or retrieval

Storage or retrieval by simultaneous application of diverse...

Magnetic field and light beam

C369S013460, C369S013440, C369S275200

Reexamination Certificate

active

06430115

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to magneto-optical recording media including a magneto-optical disk, a magneto-optical tape, and a magneto-optical card adopted for a magneto-optical recording/reproducing device, and further concerns a reproducing device thereof.
BACKGROUND OF THE INVENTION
Conventionally, as a rewritable optical recording medium, a magneto-optical recording medium has been put into practical use. Such a magneto-optical recording medium has the drawback of degrading reproducing property when a diameter and spacing of a recording bit, that serve as a domain, become smaller relative to a beam diameter of a light beam, that is emitted from a semiconductor laser and is converged on the magneto-optical recording medium.
Such a drawback is caused by an adjacent recording bit which enters the beam diameter of the light beam converged on a desired recording bit so that individual recording bits are not separately reproduced.
In order to overcome the above-mentioned disadvantage, Japanese Published Unexamined Patent Application No. 320134/1997 (Tokukaihei 9-320134, published on Dec. 12, 1997) discloses a magneto-optical recording medium shown in
FIGS. 30 and 31
. The magneto-optical recording medium has a construction in which a reproducing layer a
1
and a recording layer a
4
are stacked via a non-magnetic intermediate layer a
3
. The reproducing layer a
1
is in a state of in-plane magnetization at room temperature and enters a state of perpendicular magnetization at higher temperatures. The recording layer a
4
is made of a perpendicularly magnetized film. In the magneto-optical recording medium which has a magnetostatic combination of the reproducing layer a
1
and the recording layer a
4
, an in-plane magnetization layer a
2
is formed so as to be adjacent to the reproducing layer a
1
. With this construction, in a region whose temperature is lower than the Curie temperature in the in-plane magnetization layer a
2
, it is possible to firmly fix the magnetization direction of the reproducing layer a
1
at an in-plane direction, that is horizontal to the film surface. In a region whose temperature is not raised by irradiation of a light beam a
5
, namely, in a region whose temperature is lower than the Curie temperature in the in-plane magnetization layer a
2
, the reproducing layer a
1
enters a state of complete in-plane magnetization so as to mask a recording domain a
9
.
Meanwhile, the reproducing layer a
1
is in a perpendicular magnetization in a region which is irradiated with light beam up to more than the Curie temperature in the in-plane magnetization layer a
2
. The perpendicular magnetization direction of the reproducing layer a
1
is allowed to correspond to a direction of leakage flux appearing in the recording layer a
4
so as to transfer a recording domain a
8
of the recording layer a
4
onto the reproducing layer a
1
; thus, it is possible to reproduce merely the recording domain a
8
which exists inside a light beam spot a
6
.
Here, the reproducing layer a
1
needs to have in-plane magnetization at room temperature and enter a state of perpendicular magnetization at higher temperatures; therefore, unlike a compensation composition in which magnetic moment of a rare-earth metal(RE) and magnetic moment of a transition metal(TM) balance each other, RErich composition containing a large amount of rare-earth metal is necessary. Hence, in the reproducing layer, the transition metal(TM) moment and total magnetization oppose each other, and as shown in
FIG. 31
, TM moment and leakage flux are arranged in opposite directions in a region a
7
which is raised in temperature.
As described above, the recording domain a
8
, which has merely an area raised in temperature, is transferred onto the reproducing layer a
1
prior to reproduction, so that it is possible to reproduce a signal recorded in a period, which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce.
However, upon reproduction using the conventional reproducing medium, when the recording domain a
8
becomes smaller, a domain all transferred to the reproducing layer a
1
also becomes smaller, resulting in reduction in intensity of a reproduction signal.
SUMMARY OF THE INVENTION
The objective of the present invention is to provide a magneto-optical recording medium and a reproducing device that reproduce a signal recorded in a period, which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, without reducing an amplitude of the reproduction signal.
In order to achieve this objective, the magneto-optical recording medium of the present invention includes a reproducing layer which has perpendicular magnetization from room temperature to the Curie temperature in a single layer, an in-plane magnetic layer which has in-plane magnetization from room temperature to the Curie temperature, and a recording layer which has perpendicular magnetization from room temperature to the Curie temperature, wherein Tc
2
<Tc
1
and Tc
2
<Tc
3
are satisfied, where Tc
1
represents the Curie temperature of the reproducing layer, Tc
2
represents the Curie temperature of the in-plane magnetic layer, and Tc
3
represents the Curie temperature of the recording layer; and the reproducing layer includes an area which has a temperature of less than Tc
2
and has in-plane magnetization due to an exchange coupling with the in-plane magnetic layer, and an area which has a temperature of more than Tc
2
and has single-domain perpendicular magnetization due to expansion and transfer of magnetization information from the recording layer to the reproducing layer.
With this arrangement, magnetization information recorded in the recording layer is expanded and transferred to an area whose temperature is more than Tc
2
in the reproducing layer, so that a large single domain is formed in the reproducing layer. Hence, even in the case when small bit information is recorded in the recording layer, a domain reflecting the bit information is expanded to the reproducing layer. Further, as described above, in the reproducing layer, a domain reflecting a specific bit information is expanded, so that a reproduction signal becomes less prone to the influence of a bit located around the specific bit. Therefore, even when a signal is recorded in the recording layer in a period which does not allow a reproduction light beam having a light beam spot diameter determined by an optical diffraction limit to reproduce, it is possible to reproduce the signal without reducing an amplitude of the reproduction signal.
Moreover, the magneto-optical recording medium of the present invention includes the reproducing layer which has perpendicular magnetization from room temperature to the Curie temperature, in a single layer, the in-plane magnetic layer which has in-plane magnetization from room temperature to the Curie temperature, and the recording layer which has perpendicular magnetization from room temperature to the Curie temperature, wherein Tc
2
<Tc
1
and Tc
2
<Tc
3
are satisfied, where Tc
1
represents the Curie temperature of the reproducing layer, Tc
2
represents the Curie temperature of the in-plane magnetic layer, and Tc
3
represents the Curie temperature of the recording layer; and the reproducing layer and the recording layer have maximum total magnetization values at a temperature higher than Tc
2
.
With this arrangement, at a temperature higher than Tc
2
, in an area whose temperature is nearly a temperature where total magnetization of the reproducing layer and total magnetization of the recording layer reach maximum values, a heating operation is performed so as to include merely a single bit recorded in the recording layer; thus, leakage flux appearing merely from the bit can be magnetostatically coupled to magnetization of the reproducing layer whose temperature is more than Tc
2
. Therefore, it is possible to form a large domain in the reproducing layer

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