Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1998-07-01
2001-10-09
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C369S053200
Reexamination Certificate
active
06301199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magneto-optical recording medium and recording/reproducing apparatus used therefor, and more particularly to a magneto-optical recording medium having a recording layer and a reproducing layer so that microscopic magnetic domains can be recorded within the recording layer during recording and the magnetic domains thus recorded are magnified and transferred to the reproducing layer during reproduction, and recording/reproducing apparatus used therefor.
2. Description of the Related Art
There are magneto-optical recording mediums and recording/reproducing apparatuses of this kind disclosed as examples, e.g. in Japanese Laying-open Patent Publication No. H6-295479 (Oct. 21, 1994), G11B 11/10, Japanese Laying-open Patent Publication No. H8-7350 (Jan. 12, 1996), G11B 11/10, and so on.
The magneto-optical recording medium
10
includes a recording layer
14
and a reproducing layer
16
each formed by a magnetic layer on a substrate
12
, as shown in FIG.
1
. The recording layer
14
and the reproducing layer
16
have an intermediate layer
18
therebetween. A protecting layer
20
is formed on the recording layer
14
. Incidentally, the intermediate layer
18
herein is formed by a non-magnetic layer, but can be by a magnetic layer. Meanwhile, the recording layer
14
and the reproducing layer
16
can be desirably formed of a known magnetic material.
Referring to
FIG. 2
, microscopic magnetic domains (hereinafter referred to also as “record magnetic domains”)
22
are recorded within the recording layer
14
of this magneto-optical recording medium
10
by using a magnetic head (not shown.). During reproduction, the record magnetic domain
22
in the recording layer
14
is transferred to the reproducing layer
16
by irradiating a laser beam
24
as shown in FIG.
3
. More specifically, the laser beam
24
has a temperature profile as shown in
FIG. 3
, wherein the temperature assumes a maximum at and close to a spot center and gradually decreases toward the outside. However, where the magneto-optical recording medium is for example an optical disc, the temperature profile on the magneto-optical recording medium is different in slant at between the frontward and the rearward with respect to a moving direction. That is, the slant is more abrupt at the rearward than the frontward. By utilizing such a temperature profile by the laser beam
24
, the magneto-optical recording medium
10
is raised in temperature at only a desired point thereof.
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 according to a temperature profile as shown in FIG.
3
. Here, the reproducing layer
16
is formed of a magnetic layer assuming rich in sub-lattice magnetization of transition metals and as a magnetic thin film with perpendicular magnetization over a range from a room temperature to a Curie temperature Tc. Accordingly, when the laser beam
24
is irradiated, the reproducing layer
16
is increased in temperature and decreases in coercive force. This causes the record magnetic domain
22
of the recording layer
14
to be transferred, due to static magnetic coupling, through the intermediate layer
18
to the reproducing layer
16
, thus forming a transferred magnetic domain (hereinafter referred also to as “seed magnetic domain”)
26
within the reproducing layer
16
. The transferred or seed magnetic domain
26
is formed at a location corresponding to the record magnetic domain
22
. After forming the seed magnetic domain
26
within the reproducing layer
16
, an external magnetic field Hep is applied thereto by a not-shown magnetic head, as shown in FIG.
2
(B). This external magnetic field Hep is an alternating magnetic field, and applied for at least one period, preferably 2-4 period, while one minimum sized magnetic domain is passing through a hot spot
24
a
(see
FIG. 3
) formed by the laser beam
24
. If the alternating or external magnetic field Hep applied is in a same direction (same polarity) as the transferred magnetic domain
26
, the seed magnetic domain
26
is enlarged in magnetic-domain diameter to provide enlarged magnetic domains
26
a
and
26
b,
resulting in transfer of the record magnetic domain
22
through enlargement. If a reproducing laser beam is irradiated to the transferred magnetic domain
26
and the enlarged magnetic domains
26
a
and
26
b
by using an optical head (not shown), a state of magnetization in the reproducing layer
16
, i.e. a record signal, is reproduced.
In such a magneto-optical recording medium, there is tendency of transfer error to occur as the size of the record magnetic domain
22
within the recording layer decreases in size. This is due to decrease of resolution as the transferred magnetic domain area
26
within the reproducing layer
16
becomes greater than the diameter of the record magnetic domain. On the other hand, the size of the transferred magnetic domain
26
of the reproducing layer
16
is determined by the size of a hot spot of the laser beam
24
. In order to increase the record density by decreasing the size of the record magnetic domain
22
, there is a necessity of decreasing the size of the hot spot
24
a
of the laser beam
24
, that is, the size of the transferred magnetic domain
26
within the reproducing layer
16
.
The laser beam has a temperature profile variable depending upon an output of the laser beam. Accordingly, the decrease in size of the hot spot
24
a
only require the reduction in output of the laser beam
24
. However, the laser beam output has an effect upon reproducibility, which has to be taken into consideration for optimal setting.
In any of the prior arts, however, nothing has been considered as to optimize the laser beam output from such a point of view.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of this invention to provide a magneto-optical recording medium and recording/reproducing apparatus used therefor, which can optimize the output of a laser beam.
It is another object of this invention to provide a magneto-optical recording medium and recording/reproducing apparatus that can further enhance the recording density.
A magneto-optical recording medium according to this invention, which allows a magnetic domain in a recording layer to be transferred, through enlargement, to a reproducing layer raised in temperature by irradiation of a laser beam, comprises: a calibration area including a calibration magnetic domain recorded in a predetermined pattern in the recording layer.
The calibration magnetic domain may include an isolated magnetic domain recorded at an interval not to detect at a same time the magnetic domain in plurality of number.
A reproducing apparatus according to this invention, comprises: an optical head for irradiating the laser beam to the magneto-optical recording medium and reproducing the calibration magnetic domain to output a reproduced signal; and an output adjusting means for causing the optical head to adjust an output of the laser beam depending upon the reproduced signal.
This invention is, further, a recording/reproducing apparatus for a magneto-optical recording medium including a recording layer and a reproducing layer, comprising: a recording means for recording a calibration magnetic domain in a predetermined pattern in the recording layer by means of a magnetic head; a transfer means for transferring the calibration magnetic domain to the reproducing layer by irradiating a laser beam; a reproducing means for reproducing a transferred calibration magnetic domain transferred to the reproducing layer to output a reproduced signal; and a laser output adjusting means for adjusting an output of the laser beam depending upon the reproduced signal.
A calibration area is formed on the magneto-optical recording medium. This calibration area may be previously formed. Where using a recording/reproducing apparatus, calibration areas can be prov
Awano Hiroyuki
Ohta Norio
Shirai Hiroshi
Sumi Satoshi
Takagi Naoyuki
Armstrong Westerman Hattori McLeland & Naughton LLP
Neyzari Ali
Sanyo Electric Co,. Ltd.
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