Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-09-27
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
C428S064200
Reexamination Certificate
active
06483784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magneto-optical recording media and particularly to those providing a heat sink effect.
2. Description of the Background Art
Magneto-optical recording media have been noted as a recording medium which is rewritable, has a large recording capacity and is highly reliable, and they are put to use for example as computer memory. Furthermore recently a magneto-optical recording medium provided in the form of a 120 mm&phgr; disc having a storage capacity of 6 Gbytes is about to be put to use as an Advanced Storage Magneto-Optical (AS-MO) disk standard. To reproduce a signal from such a high-density magneto-optical recording medium a laser beam is directed thereto to form at a reproducing layer thereof a detection window smaller than the laser beam's spot diameter and a magnetic domain of the recording layer is transferred to the detection window and the transferred magnetic domain is thus detected. This technique is referred to as magnetically induced super resolution (MSR).
Furthermore, there has also been developed a technique applying an alternate magnetic field to a magneto-optical recording medium and transferring a magnetic domain from a recording layer to a reproducing layer and enlarging the transferred magnetic domain to reproduce a signal. Using this magnetic-domain enlargement and reproduction technique, there has also been suggested a magneto-optical recording medium having a recording capacity of 14 Gbytes.
A magneto-optical recording medium is irradiated with a laser beam to record or reproduce a signal. As such, to diffuse heat generated through the laser beam radiation, to prevent the laser beam's focus from blurring, and to prevent a magnetic layer of the recording medium from being oxidized, the recording medium has sputtered on a substrate a magnetic layer including a recording layer and a reproducing layer, and a protection layer, e.g., of SiN and/or a heat diffusing layer for example of Al then added thereon.
More specifically, with reference to
FIG. 14
, a conventional magneto-optical recording medium
70
has a transparent substrate
71
and has formed thereon an underlying layer
72
formed of SiN, a reproducing layer
73
formed of GdFeCo, a non-magnetic layer
74
formed of SiN, a recording layer
75
formed of TbFeCo, a protection layer
76
formed of SiN and a heat diffusing layer
77
formed of Al, successively stacked in layers, as seen in cross section. In general, after heat diffusing layer
77
is formed UV ray cured resin or the like is used to coat the recording medium to prevent the recording medium from being oxidized and damaged.
Heat diffusing layer
77
, provided after reproducing layer
73
and recording layer
75
are sputtered, also prevents reproducing layer
73
and recording layer
75
from being oxidized. As such, heat diffusing layer
77
is provided opposite to transparent substrate
71
.
However, as its recording density increases, recording layer
75
has formed therein a magnetic domain reduced in size. As such, when in reproducing a signal a laser beam is directed to the recording medium and a detection window is formed in reproducing layer
73
, a plurality of magnetic domains are transferred from recording layer
75
to the detection window formed in reproducing layer
73
. Thus, accurate signal reproduction cannot be achieved.
More specifically, conventional magneto-optical recording medium
70
has reproducing layer
73
posed between SiN forming underlying layer
72
and SiN forming non-magnetic layer
74
. As such, the heat generated in reproducing layer
73
through laser beam radiation is not so much emitted therefrom. This increases a region heated to a temperature allowing a magnetic domain of recording layer
75
to be transferred. Consequently, a plurality of magnetic domains are transferred from recording layer
75
to reproducing layer
73
and accurate signal reproduction can thus not be achieved.
SUMMARY OF THE INVENTION
The present invention therefore contemplates a magneto-optical recording medium capable of forming in a reproducing layer a detection window having a size approximately corresponding to a shortest length of a magnetic domain formed in a recording layer.
The present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a reproducing layer receiving the magnetic domain transferred from the recording layer, and a heat sink layer formed in contact with the reproducing layer and the recording layer and blocking exchanging-coupling between the reproducing layer and the recording layer.
When the present magneto-optical recording medium is irradiated with a laser beam, the reproducing layer generates heat, which diffuses from the reproducing layer to the heat sink layer and the reproducing layer has in an in-plane direction thereof a steep temperature profile. The reproducing layer has formed therein a detection window each receiving an individual magnetic domain transferred from the recording layer. Furthermore, the heat sink layer is provided also in contact with the recording layer. As such, the heat generated in the recording layer through laser beam radiation also diffuses from the recording layer to the heat sink. layer to allow the recording layer to have a steep temperature profile. Thus in the present invention if the recording layer has a magnetic domain reduced in length each magnetic domain of the recording layer can be detected with high resolution. Furthermore in the present invention the recording layer can have formed therein a magnetic domain reduced in length to record a signal densely.
Furthermore the present invention provides a magneto-optical recording medium including a recording layer having formed therein a magnetic domain magnetized according to a signal to be recorded, a first reproducing layer receiving the magnetic domain transferred from the recording layer, a second reproducing layer receiving the magnetic domain transferred to the first reproducing layer and further transferred from the first reproducing layer through magnetostatic-coupling, and a heat sink layer formed in contact with the first reproducing layer and the recording layer and blocking exchanging-coupling between the first reproducing layer and the recording layer, wherein the second reproducing layer is formed of a magnetic material allowing the transferred magnetic domain to be enlarged by an external magnetic field.
When the present magneto-optical recording medium is irradiated with a laser beam, the first reproducing layer generates heat, which diffuses from the first reproducing layer to the heat sink layer to allow the first reproducing layer to have in an in-plane direction thereof a steep temperature profile. The recording layer has formed therein a detection window each receiving an individual magnetic domain transferred from the recording layer through magnetostatic-coupling. The magnetic domain transferred to the first reproducing layer is further transferred to the second reproducing layer through magnetostatic-coupling. The magnetic domain transferred to the second reproducing layer is enlarged by an external magnetic field and detected by a laser beam directed thereto. Furthermore, the heat sink layer is provided also in contact with the recording layer. As such, the heat generated in the recording layer through laser beam radiation also diffuses from the recording layer to the heat sink layer to allow the recording layer to have a steep temperature profile. Thus in the present invention if the recording layer has a magnetic domain reduced in length each magnetic domain of the recording layer can be detected in the first reproducing layer with high resolution and also enlarged and thus reproduced in the second reproducing layer. Furthermore in the present invention the recording layer can have formed therein a magnetic domain reduced in length to allow a signal to be recorde
Nakatani Morio
Tanase Kenji
Armstrong Westerman & Hattori, LLP
Dinh Tan
Sanyo Electric Co,. Ltd.
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