Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2002-12-03
2004-09-14
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013080
Reexamination Certificate
active
06791908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magneto-optical recording medium and reproducing method thereof to carry out recording and reproducing information by using a laser light by applying a magneto-optical effect, more specifically relates to the magneto-optical recording medium and reproducing method thereof to make a high density recording signal possible.
2. Related Art of the Invention
In magneto-optical recording being a high density, writable, recording and reproducing method, a part of layered magnetic films (a recording film structure) of a magneto-optical recording medium is locally heated to a Curie temperature or a temperature above a compensation temperature by radiating laser light, and an information signal is recorded in a predetermined part of the magnetic film contained in the recording film structure by forming a recordable magnetic domain in an external magnetic field, and this information is read by using a magneto-optical effect.
One of such magneto-optical recording system for the magneto-optical recording medium is the magnetic field modulation recording system. In this system, thermal magnetic recording is performed in a predetermined part by using an external magnetic field of which direction has been modulated according to a recording signal after raising entirely the temperature of a recording magnetic film by radiating a laser light of a certain strength using a semiconductor laser or the like. The other of the recording system is the light intensity modulation recording system. In this system, thermal magnetic recording is performed in the direction of the external magnetic field by raising the temperature of the recording magnetic film of a predetermined part by radiating the laser light which has been modulated according to the strength of the recording signal, applying the external magnetic field of a certain strength.
At the time of reproducing the recorded signal, when the laser light (reproducing light) of which polarization direction is arranged to be identical, is condensed on the magneto-optical recording medium, the direction of magnetization of recording magnetic domain is detected as the rotation of the polarization direction of the reflected light or transmitted light by a magneto-optical effect caused by the magneto-optical recording medium. By this effect, the information signal recorded is reproduced.
However, in the conventional magneto-optical recording medium, when the size of the recording magnetic domain becomes smaller than that of the light spot (reproducing-light spot) of a reproducing light on the magneto-optical recording medium, not only the recording magnetic domain to be reproduced, but also the recording magnetic domain located in front and back of the position becomes contained in the reproducing-light spot, i.e., a detection range. Therefore, some problems occur exemplified as follows: the reproducing signal becomes small to lower an S/N ratio or the reproducing signal is not outputted, because of an interference by those recording magnetic domains.
To solve these problems, a magnetic field modulation recording system using magnetically induced super resolution has been proposed to read the reproducing signal from a part of domain of the reproducing-light spot.
(I) The following is a description of a magneto-optical record reproducing system by using the magnetically induced super resolution named a double mask system which is a system of the magnetically induced super resolution.
FIG. 12
shows a configuration in reproducing by the double mask system. FIG.
12
(A) is a plane view of showing a part of track of the magneto-optical recording medium
60
in the conventional double mask system.
12
(B) is a sectional view showing the configuration (particularly the direction of magnetization) of a recording film structure of the magneto-optical recording medium
60
.
As shown in the sectional view of FIG.
12
(B), the recording film structure of the magneto-optical recording medium
60
is configured by including a reproduction layer
63
, a reproduction supporting layer
64
, a middle layer
65
, and a recording layer
66
, which are layered on a substrate (not illustrated) in order. An arrow
160
shown in the FIG.
12
(B) is a movement direction along with the track of the magneto-optical recording medium
60
. Arrows illustrated in respective layers
63
to
66
are show directions of magnetization in respective positions.
This conventional magneto-optical recording medium
60
requires reproducing magnetic field generating means
61
applied to the domain of the reproducing-light spot
67
, initialized magnetic field generation means
62
located in the frontal position of the reproduction magnetic field generating means
61
in the movement direction
160
. Hereafter, reference numerals
61
and
62
are used for a description of a reproducing operation of generated magnetic field generated by the reproducing magnetic field generating means
61
and an initialized magnetic field generated by the initialized magnetic field generation means
62
, respectively. The following is the magneto-optical recording medium
60
of the double mask system configured by such manner.
First, a signal (information) is previously recorded by thermal magnetization as the recording magnetic domain
69
in the recording layer
66
. Before the laser light is radiated in reproducing, the direction of magnetization of the reproduction layer
63
is arranged in the direction of the initialized magnetic field
62
. At the time of reproducing, as shown in the FIG.
12
(A), the reproducing laser light is radiated to the rotating magneto-optical recording medium
60
to make the reproducing-light spot
67
and raise a temperature of the recording film structure. According to this step, the distribution of temperatures as shown in the FIG.
12
(A) occurs on the magneto-optical recording medium
60
to form a low temperature region
71
, a high temperature region
72
, and a intermediate temperature region
70
.
The direction of magnetization of the reproduction layer
63
in the low temperature region
71
near a room temperature is arranged in the direction of the initialized magnetic field
62
by blocking of a exchange coupling between the reproduction layer
63
and the recording layer
66
by the middle layer
65
. In the intermediate temperature region
70
, the exchange coupling between the reproduction layer
63
and the recording layer
66
becomes dominant by decrease in coercive force of the reproduction layer
63
according to temperature rise caused by radiation of the reproducing laser light and also by transition of the middle layer
65
from a in-plane magnetized film having in-plane magnetic anisotropy to a perpendicular magnetized film having perpendicular magnetic anisotropy. Therefore, The direction of magnetization of the reproduction layer
63
is arranged in the direction of magnetization of the recording layer
66
.
In the high temperature region
72
of the reproduction supporting layer
64
becoming a Curie temperature Tc, the exchange coupling between the reproduction layer
63
, the middle layer
65
, and the recording layer
66
is blocked by extinction of magnetization of the reproduction supporting layer
64
to arrange the direction of magnetization of the reproduction layer
63
, of which coercive force is small, to the direction of the reproducing magnetic field
61
. Therefore, a recording magnetic domain
69
is masked by both the low temperature region
71
and the high temperature region
72
inside the reproducing-light spot
67
and information can be read as a reproducing signal through the reflected light from only the recording magnetic domain
69
presented in the intermediate temperature region
70
.
The direction of the reproducing magnetic field
61
is an opposite direction to the initialized magnetic field
62
. After the reproducing-light spot
67
passed, the temperature of the recording layer
66
dropped again and the recording layer
66
and
Hino Yasumori
Murakami Motoyoshi
Sakaguchi Takeshi
Dinh Tan
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
LandOfFree
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