Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1999-01-21
2002-12-31
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S047280
Reexamination Certificate
active
06501707
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for recording with a magneto-optical recording medium. More particularly, the invention relates to a method and apparatus for recording with a magneto-optical recording medium, wherein the recording medium includes a recording layer and a reproducing layer for recording magnetic domains within the recording layer upon recordation and transfer of the record domains to the reproducing layer upon reproduction.
2. Description of the Prior Arts
The magneto-optical recording mediums and recording/reproducing apparatuses of this kind are disclosed, for example, in Japanese Patent Laying-open No. H6-295479 (Oct. 21, 1994) G11B 11/10, Japanese Patent Laying-open No. H8-7350 (Jan. 12, 1996) G11B 11/10, and so on.
The magneto-optical recording medium
10
includes, as shown in
FIG. 1
, a recording layer
14
and a reproducing layer
16
that are formed by a magnetic layer on a substrate
12
. An intermediate layer
18
is formed between the recording layer
14
and the reproducing layer
16
, while a protection layer
20
is provided on the recording layer
14
. The intermediate layer
18
, although formed herein by a non-magnetic layer, may be formed by a magnetic layer. Meanwhile, the recording layer
14
and the reproducing layer
16
may be formed by an arbitrary known magnetic material. Referring to
FIG. 2
, microscopic domains
22
can be recorded within the recording layer
14
of the magneto-optical recording medium
10
by using a magnetic head (not shown). During reproduction, the record domain
22
is transferred from the recording layer
14
to the reproducing layer
16
by irradiation of a laser beam
24
as shown in FIG.
3
.
More specifically, a temperature profile is given in the magneto-optical recording medium
10
by irradiating the laser beam
24
as shown in FIG.
3
. The temperature is highest at around a spot center and gradually decreases as an outer side is approached. Note that, in the case where the magneto-optical recording medium is for example a disc, the temperature profile is different in slant at between the front side and the rear side with respect to a moving direction of the magneto-optical recording medium. The temperature gradient is more abrupt at a region of the disc coming into a laser spot than that of a region going out of the laser spot. The magneto-optical recording medium
10
is increased in temperature at a desired point by utilizing such a temperature profile.
Returning to FIG.
2
(A), if a laser beam
24
is irradiated to the magneto-optical recording medium
10
, the magneto-optical recording medium
10
is increased in temperature to provide such a temperature profile as shown in FIG.
3
. Here, the reproducing layer
16
is formed by a magnetic layer which is rich in transition metal and assumes a form of a magnetic thin film with perpendicular magnetization within a range from the room temperature to the Curie temperature Tc. As a consequence, the reproducing layer
16
, if irradiated by a laser beam
24
, is raised in temperature and decreased in coercive force. Due to this, the irradiation of the laser beam
24
causes the reproducing layer
16
to rise in temperature and hence decrease in coercive force, so that the record magnetic domain
22
of the recording layer
14
is transferred through the intermediate layer
18
to the reproducing layer
16
by the action of static magnetic coupling, thus forming a transferred magnetic domain
26
within the reproducing layer
16
. The transferred magnetic domain
26
is formed at a position corresponding to the record magnetic domain
22
.
After forming the transferred magnetic domain
26
within the reproducing layer
16
, an external magnetic field Hep is applied by a not-shown magnetic head as shown in FIG.
2
(B). This external magnetic field Hep is an alternating magnetic field. At least one period, preferably 2 to 4 periods, of an alternating magnetic field is applied during each time period that one magnetic domain passes through a hot spot
24
a
(see
FIG. 3
) caused by the laser beam
24
. If an alternating magnetic field or external magnetic field Hep is applied in the same direction (same polarity) as that of the transferred magnetic domain
26
, then the transferred magnetic domain
26
is increased in diameter to have enlarged magnetic domains
26
a
and
26
b
. As a result, transfer of the record magnetic domain
22
is effected with magnification. If a laser beam for reproduction is irradiated to the transferred magnetic domain
26
as well as to the enlarged magnetic domains
26
a
,
26
b
by using the optical head (not shown), reproduction is made of a magnetization state or record signals from the reproducing layer
16
.
There is known one approach to realize high density recording, in the magneto-optical recording medium and recording/reproducing apparatus of this kind, wherein record magnetic domains are provided different in domain length 1T, 2T, 3T, . . . , as shown in FIG.
4
.
In this conventional recording method, however, there encounters variation in a state of a leakage magnetic field passing through the reproducing layer of the magneto-optical recording medium due to difference in domain length. Thus there has been a problem that the optimal reproducing condition is different for each domain length thus resulting in worsened reproducibility.
More specifically, if considering a long domain as shown in FIG.
5
(B), the reproducing layer has a leakage magnetic field that is strong at a domain end P
1
but weak at a domain central region P
2
. Meanwhile, through an outside point P
3
of the domain is caused a leakage magnetic field in a direction opposite to that of the domain end P
1
. In such a state, if an external alternating magnetic field be applied, the leakage magnetic field at the domain outer point P
3
acts to prevent the magnetic domain from being transferred into and enlarged within the reproducing layer to a satisfactory extent.
On the other hand, where the domain is excessively short as shown in FIG.
5
(A), the leakage magnetic field is less distributed throughout the domain. There is also reduction in the opposite directional leakage magnetic field at the domain outer side area. Accordingly, the application of an external alternating magnetic field causes the magnetic domain to be transferred to and enlarged in the reproducing layer with sufficiency.
It is therefore difficult, for the conventional high-density recording method to record by varying the domain length, to obtain a reproduction characteristic with uniformity, because of uneven transfer and enlargement of the magnetic domains into and within the reproducing layer due to the difference in domain length.
SUMMARY OF THE INVENTION
It is therefore a primary object of the present invention to provide a method and apparatus for recording with the magneto-optical recording medium.
It is another object of the present invention to provide a method and apparatus for recording with a magneto-optical recording medium which can stably reproduce under a same condition signals having been recorded by changing the domain length.
The present invention is a method for recording with a magneto-optical recording medium having a recording layer and a reproducing layer formed as a layer on a substrate, comprising the step of: recording a signal onto one part of a unit domain length (1T).
An apparatus for recording a signal on a magneto-optical recording medium according to the present invention, comprising: a modulating means for modulating a record signal; a timing signal creating means for creating a first timing signal based on the record signal modulated by the modulating means; and a magnetic field applying means for applying one period of an alternating magnetic field to a unit domain length in response to the first timing signal.
The physical length for recording a unit bit is taken as a unit domain length. In the case that the unit domain length is 1T, a signal “1” is recorded, for example, in 1T/2. Mo
Takagi Naoyuki
Yamaguchi Atsushi
Armstrong Westerman & Hattori, LLP
Neyzari Ali
Sanyo Electric Co,. Ltd.
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