Magneto-optical reproducing method using a magnified...

Details Magneto-optical reproducing method using a magnified... Magneto-optical reproducing method using a magnified...

1999-06-02

2001-10-02

Dinh, Tan (Department: 2651)

Dynamic information storage or retrieval

Storage or retrieval by simultaneous application of diverse...

Reexamination Certificate

active

06298015

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information reproducing method and an information recorder/reproducer.
2. Related Background Art
There have conventionally been proposed a variety of reproducing methods which reproduce information signals by detecting magnetized areas from magneto-optical media on which information signals are recorded at high densities by forming the magnetized areas. A reproducing method which was proposed by Koyata Takahashi et al. in Joint MORIS/ISOM '97, Tu-E-05 in particular is characterized in that it transfers a magnetized area formed on a memory layer to a transfer region formed on a displacement layer and detects the transferred magnetized area in a magnified condition. A reproducing method of this kind has thereafter been referred to as magnetic domain magnifying reproduction. It has been reported that the magnetic domain magnifying reproduction was capable of detecting a magnetized area formed on the memory layer even when it was smaller than a light spot of a reproducing light beam.
Description will be made below of the conventionally proposed magnetic domain magnifying reproduction.
FIGS. 1A and 1B
are partially enlarged diagrams of a magneto-optical medium
10
which is used for the magnetic domain magnifying reproduction.
FIG. 1A
is a top view, whereas
FIG. 1B
is a sectional view. The magneto-optical medium
10
consists of a substrate (not shown) and a magnetic layer
11
disposed on a surface of the substrate. The magnetic layer
11
is composed of three layers made of magnetic materials, that is, a memory layer
14
made of TbFeCo, a switching layer
13
made of GdFe and a displacement layer
12
made of GdFeCo. The memory layer
14
is a perpendicular magnetization film, whereas the switching layer
13
is an internal magnetization film at a temperature lower than T
3
but a perpendicular magnetization film at a temperature higher than T
3
and has a Curie temperature of T
4
. Furthermore, displacement layer
12
is an internal magnetization film at a temperature not exceeding T
3
but a perpendicular magnetization film at a temperature higher than T
3
and assumed to have a Curie temperature higher than T
4
. In the memory layer
14
, circular magnetized areas R
1
, R
2
, R
3
, . . . having a diameter of 0.5 &mgr;m which are magnetized downward as shown in FIG.
1
B and enclosed by domain walls Q
1
, Q
2
, Q
3
, . . . , are formed in a row as well as surroundings thereof which are magnetized upward. These circular magnetized areas R
1
, R
2
, R
3
, . . . are formed by a recording method which displaces the magneto-optical medium
10
relative to a recording light beam while irradiating the magnetic layer
11
with a recording light beam which has an intensity modulated by information signals to be recorded and is condensed into a fine spot, and simultaneously applying a magnetic field to a location irradiated with the recording light beam in a definite direction (light modulation recording method).
Then, a principle of the magnetic domain magnifying reproduction will be described with reference to
FIGS. 2A through 2D
. Description will be made taking as an example a case where a magnetized area is detected from the magneto-optical medium
10
shown in
FIGS. 1A and 1B
by the magnetic domain magnifying reproduction. To detect the magnetized area, the magneto-optical medium
10
is first displaced relative to a reproducing light beam while irradiating the magnetic layer
11
of the magneto-optical medium
10
with the reproducing light beam.
FIGS. 2A through 2D
sequentially shows status changes which occur in the magnetic layer
11
as time elapses. An arrow A in the drawing indicates a displacement direction of the magneto-optical medium
10
.
When the magnetic layer
11
is irradiated with the reproducing light beam as described above, it is partially heated, thereby forming an isothermal line indicating the temperature T
3
and another isothermal line indicating the temperature T
4
which are represented by numerals
15
and
16
respectively in
FIGS. 2A through 2D
. In a region outside the isothermal line
15
of the displacement layer
12
wherein temperature is lower than T
3
, the switching layer
13
and the displacement layer
12
are the internal magnetization films. In a transfer region
17
which is line
15
of the displacement layer
12
wherein temperature is higher than T
3
, the displacement layer
12
is the perpendicular magnetization film. Furthermore, switching layer
13
is the perpendicular magnetization film in a region between the isothermal line
15
and the isothermal line
16
where temperature is higher than T
3
and lower than T
4
, but demagnetized in a region enclosed by the isothermal line
16
where the temperature is higher than T
4
. Both the displacement layer
12
and the switching layer
13
are subjected to exchange coupling with the memory layer
14
in the region between the isothermal line
15
and the isothermal line
16
where both the layers
12
and
13
are the perpendicular magnetization films, whereas the displacement layer
12
is not subjected to exchange coupling with the memory layer
14
in the region enclosed by the isothermal line
16
where the switching layer
13
is demagnetized.
In the status shown in
FIG. 2A
first, the magnetized areas R
1
, R
2
, R
3
, . . . which are formed on the memory layer
14
are not located right under a transfer region formed on the displacement layer
12
and the memory layer
14
located right under a transfer region
17
is magnetized upward. As a result of exchange coupling with the memory layer
14
, the magnetization of the memory layer
14
is transferred to the transfer region
17
, thereby magnetizing it upward. In addition, an area of the transfer region
17
which is enclosed by the isothermal line
16
is not subjected to exchange coupling with the memory layer
14
, but follows the upward magnetization which is transferred and formed to and in the transfer region
17
due to exchange coupling of surroundings thereof since no cause for downward magnetization is constituted. When the magneto-optical medium
10
displaces with a time lapse, a portion of the magnetized area R
2
formed on the memory layer
14
is partially located right under the transfer region
17
, as shown in FIG.
2
B. At this time, the portion of the magnetized area R
2
which is located right under the transfer region
17
is transferred to the transfer region
17
due to exchange coupling, thereby forming a magnetized area Re
2
which is magnetized downward and enclosed by a domain wall Qe
2
.
When the magneto-optical medium
10
displaces with a further time lapse, a portion of the magnetized area Re
2
which is transferred and formed to and on the transfer region
17
enters the region enclosed by the isothermal line
16
from the front (left side in the drawing) of the isothermal line
16
as shown in FIG.
2
C. At this stage, driving forces directed toward a higher temperature, i.e., toward a center of the transfer region
17
, are exerted to portions of the domain wall Qe
2
as indicated by arrows D. The domain wall Qe
2
is restrained in the region between the isothermal line
15
and the isothermal line
16
where the displacement layer
12
is in exchange coupling with the memory layer
14
, whereas the domain wall Qe
2
is liable to be displaced by actions of the driving forces in the region enclosed by the isothermal line
16
where the displacement layer
12
is not in exchange coupling with the memory layer
14
. When energy is imparted by applying a magnetic field having an adequate magnitude (for example, −110 [Oe]) in a direction corresponding to a magnetization direction of the magnetized area Re
2
which is transferred and formed, the domain wall Qe
2
can be prolonged and the magnetized area Re
2
is magnified within the region enclosed by the isothermal line
16
as shown in FIG.
2
D.
When the magneto-optical medium
10
displaces with a further time lapse and

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