Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-11-16
2002-11-19
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013280
Reexamination Certificate
active
06483783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magneto-optical disk apparatuses employing a magnetic field and a laser beam to reproduce a signal from a magneto-optical recording medium having a magnetic domain formed therein to record a signal, and methods of reproducing the same.
2. Description of the Background Art
A magneto-optical recording medium has been noted as a recording medium which is rewritable, has a large storage capacity and is highly reliable, and it has been put to practical use as computer memory or the like. Furthermore, in recent years a magneto-optical recording medium having a storage capacity of 6.0 Gbytes is standardized as the Advanced Storaged Magneto Optical (AS-MO) disk standard and it is about to be put to practical use.
Furthermore, there has also been proposed a magneto-optical recording medium having a recording capacity of 14 Gbytes allowing a magnetic domain to be transferred from a recording layer to a reproducing layer and enlarged in the reproducing layer to reproduce a signal. In this magnetic domain enlargement and reproduction system, a signal is reproduced by applying to a magneto-optical recording medium an alternating magnetic field having a predetermined angle to an in-plane direction of the recording medium. More specifically, as shown in
FIG. 26A
, the magneto-optical recording medium includes a recording layer
5
having a magnetic domain of a different length and in the magnetic domain enlargement and reproduction system an alternating magnetic field is applied and a laser beam is directed to transfer each magnetic domain from recording layer
5
via a non-magnetic layer
4
to a reproducing layer
3
and enlarge it therein. The enlarged magnetic domain is detected by a laser beam. Herein, the alternating magnetic field is applied to recording layer
5
at substantially the center of each magnetic domain. If a magnetic domain in recording layer
5
varies in length a magnetic field leaking from the magnetic domain of recording layer
5
via non-magnetic layer
4
to reproducing layer
3
also has a different intensity profile. A leaking magnetic field for a magnetic domain having a unit domain length has an intensity increasing in the direction from an end of the magnetic domain to the center thereof. A leaking magnetic field for a magnetic domain having a length more than twice the unit domain length, has a high intensity at an end of the magnetic field and a low intensity at the center thereof. As such, if an alternating magnetic field is applied to each magnetic domain at the center thereof, magnetic domains having different lengths cannot be accurately transferred to and enlarged in reproducing layer
3
.
To overcome this disadvantage, there has been proposed applying to a magnetic domain at an end thereof (i.e., a boundary between magnetic domains) an alternating magnetic field Hex
1
having a predetermined angle to an in-plane direction of a magneto-optical recording medium, to enlarge and reproduce the magnetic domain. Recording layer
5
has magnetic domains each having a boundary with a leaking magnetic field
190
-
194
and when the boundaries with leaking magnetic fields
190
,
192
,
194
receive alternating magnetic field Hex
1
magnetic domains
195
-
197
have their respective ends readily, initially transferred to reproducing layer
3
. This principle will now be described with reference to
FIGS. 27A-27D
. As shown in
FIG. 27A
, if a signal is reproduced, reproducing layer
3
is initialized, magnetized in a predetermined direction. Furthermore, recording layer
5
has magnetic domains
220
-
222
having a signal recorded therein. Herein, a leaking magnetic field of magnetic domain
221
in a vertical direction, i.e., a direction to reproducing layer
3
has an intensity profile as shown in FIG.
27
B.
In contrast, a leaking magnetic field of magnetic domain
221
in an in-plane direction has an intensity profile as shown in FIG.
27
C. More specifically, it is a leaking magnetic fields having opposite directions and a uniform intensity at opposite ends of magnetic domain
221
and if the leaking magnetic field at the boundary of magnetic domains
220
and
221
is directed in the direction from magnetic domains
221
to
220
then the leaking magnetic field at the boundary of magnetic domains
221
and
222
is directed in the direction from magnetic domains
221
to
222
. As such, a leaking magnetic field in the in-plane direction that comes from magnetic domain
221
to affect reproducing layer
3
has opposite directions and a uniform intensity, and a magnetic force acting to invert the reproducing layer
3
magnetization in the direction of the magnetic domain
221
magnetization is balanced at the opposite ends of magnetic domain
221
. As a result, magnetic domain
221
does not have one end thereof preferentially transferred to reproducing layer
3
.
However, when magnetic domain
221
receives a magnetic field containing magnetic field component having the in-plane direction, a leaking magnetic field in the in-plane direction that comes from magnetic domain
221
has an intensity profile as shown in
FIG. 27D
, and when a magnetic field is applied in a direction from magnetic domains
221
to
220
a leaking magnetic field
225
at the boundary of magnetic domains
221
and
220
is intensified as compared to a leaking magnetic field
226
at the other boundary thereof. As such, a leaking magnetic field
224
acts on the reproducing layer's magnetic domain
223
corresponding to an end of magnetic domain
221
closer to magnetic domain
220
to readily invert the magnetic domain
223
magnetization in the same direction as the magnetic domain
221
magnetization. As a result, if magnetic domain
221
is transferred to reproducing layer
3
it is transferred initially at an end thereof closer to magnetic domain
220
and in reproducing layer
3
at magnetic domain
223
there is created a species domain magnetized in the same direction as magnetic domain
221
is magnetized, and a magnetic field having a direction perpendicular to reproducing layer
3
that is the same direction as magnetic domain
221
is magnetized is applied to enlarge the species domain.
Thus, applying a magnetic field containing a magnetic field component having an in-plane direction facilitates transferring a magnetic domain to a reproducing layer.
Again with reference to
FIGS. 26A and 26B
, when alternating magnetic field Hex
1
is applied to a magneto-optical recording medium at a predetermined angle to an in-plane direction of the recording medium and it is thus applied to each magnetic domain at a boundary thereof, and a laser beam LB is directed to enlarge and reproduce the magnetic domain, the following problem arise.
More specifically, when alternating magnetic field Hex
1
is applied at a timing as shown in
FIG. 26B
at (a) and in the direction as indicated in
FIG. 26A
, only at a timing at which a positive (+) magnetic field
198
is applied to the boundaries of the magnetic domains having leaking magnetic fields
190
,
192
and
194
recording layer
5
has magnetic domains
195
-
197
each transferred to and enlarged in reproducing layer
3
and a reproduced signal (b) is detected as shown in FIG.
26
B. As such, if alternating magnetic field Hex
1
is applied to the domains' boundaries having leaking magnetic fields
191
and
193
, the magnetic domains are not transferred from recording layer
5
to reproducing layer
3
. As a result, the magnetic domain
195
length having a domain length larger than a unit domain length cannot be detected accurately nor can magnetic domain
201
, a domain adjacent to domain
195
, be detected. More specifically, in reproduced signal (b) a component
199
indicates a start point of magnetic domain
195
and the component detected subsequent to component
199
is a component
200
. As such the end point of magnetic domain
195
is thus not clearly indicated nor is the start point of magnetic domain
201
, a domain adjacen
Ishida Hiroki
Mitani Kenichiro
Nakatani Morio
Noguchi Hitoshi
Takagi Naoyuki
Armstrong Westerman & Hattori, LLP
Dinh Tan
Sanyo Electric Co,. Ltd.
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