Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1999-11-18
2001-08-21
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C428S064200, C428S690000
Reexamination Certificate
active
06278668
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magneto-optical storage media, such as magneto-optical disks, magneto-optical tapes, and magneto-optical cards, that are used with magneto-optical storage and reproduction devices.
BACKGROUND OF THE INVENTION
Conventionally, magneto-optical storage media have been commercially manufactured as rewritable optical storage media. A drawback of the magneto-optical storage medium is that its reproduction properties deteriorate with a decrease in the size of the recording bit (magnetic recording domain) and in the interval between adjacent recording bits, relative to the size of a light beam that is emitted from a semiconductor laser device and then converged on the magneto-optical storage medium.
This is because the light beam converged on the targeted recording bit encompasses adjacent recording bits within its coverage and fails to separately reproduce the individual recording bits.
To overcome the drawback, various magnetic super high resolution reproduction technologies have been developed using a magnetic multi-layer film. These magnetic super high resolution reproduction technologies reduces interference between plus and minus signals during reproduction by forming a magnetic masking area and thus forming a magnetic aperture that is smaller than the beam spot, and enables reproduction of signals whose cycles do not exceed diffraction limits of light.
Nevertheless, the magnetic super high resolution reproduction technologies have a problem that the strength of reproduced signals decreases with a decrease in the recording cycle for the magnetic recording domain, because the aperture also needs to be reduced in size.
To solve the problem, a method is suggested to enable magnetic domain expansion reproduction without applying a.c. external magnetic fields (Magnetic Domain Expansion Readout with DC laser and DC magnetic field [Magnetic Amplifying Magneto-Optical System, or MAMMOS]), an article from resumes for lectures in 44th Conference organized in spring 1997 by the Society of Applied Physics Researchers, 30a-NF-3, page 1068).
Now, referring to FIG.
28
through
FIG. 30
, a magneto-optical storage medium based on the method will be explained.
FIGS. 28 and 29
are plan and cross-sectional views schematically illustrating magnetization of the magneto-optical storage medium during reproduction.
FIG. 30
is a cross-sectional view showing the medium arrangement of a magneto-optical disk that is an application of the magneto-optical storage medium.
As shown in
FIG. 29
, the magneto-optical storage medium is arranged from stacked layers including a reproduction layer
201
, a supplementary reproduction layer
202
, and a storage layer
204
. The reproduction layer
201
and the supplementary reproduction layer
202
exhibit an in-plane magnetization state at room temperature, and changes to a perpendicular magnetization state as temperature is elevated by projection of a converged light beam
205
(light beam spot
205
′ in FIG.
28
). The storage layer
204
is made of a perpendicular magnetization film, where magnetic information is stored as magnetization directions in magnetic domains
206
and
207
.
The reproduction layer
201
is specified to change to a perpendicular magnetization state at a temperature lower than the temperature at which the supplementary reproduction layer
202
changes to a perpendicular magnetization state. Consequently, on heating using the light beam
205
, the magnetic domain
209
where the reproduction layer
201
has changed to a perpendicular magnetization state grows larger than the magnetic domain
208
where the supplementary reproduction layer
202
changes to a perpendicular magnetization state.
The magnetization direction in the magnetic domain
208
, where the supplementary reproduction layer
202
changes to a perpendicular magnetization state due to the heating with the light beam
205
, is determined by coupling with the storage layer
204
through exchange forces. Hence, the magnetic information in the magnetic domain
206
in the storage layer
204
is duplicated to the supplementary reproduction layer
202
so that the direction of the auxiliary grating moment of the supplementary reproduction layer
202
conforms to that of the storage layer
204
.
Next, the magnetic information in the magnetic domain
208
, where the supplementary reproduction layer
202
has changed to a perpendicular magnetization state, is duplicated to the reproduction layer
201
so that the direction of the transition metal (TM) moment of the reproduction layer
201
conforms to that of the supplementary reproduction layer
202
. Here, since the magnetic domain
209
, where the reproduction layer
201
changes to a perpendicular magnetization state, grows larger than the magnetic domain
208
, where the supplementary reproduction layer
202
changes to a perpendicular magnetization state, the magnetization state of the supplementary reproduction layer
202
, i.e., the magnetization state of the storage layer
204
, is amplified and duplicated to the reproduction layer
201
.
As described above, in the magneto-optical storage medium in accordance to the aforementioned method, the magnetic information in the storage layer
204
is amplified and duplicated to the reproduction layer
201
; therefore magnetic recording domains with a reduced recording cycle still allows reproduction of strong signals.
It should be noted that as shown in
FIG. 30
the magneto-optical storage medium, having the arrangement shown in
FIG. 29
, constitutes a magneto-optical disk when stacked together with a substrate
210
, a transparent dielectric protective layer
211
, and a protective layer
212
.
However, since the storage layer
204
, the supplementary reproduction layer
202
, and the reproduction layer
201
are coupled together through exchange forces, the transition from an in-plane magnetization state to a perpendicular magnetization state of the supplementary reproduction layer
202
and the reproduction layer
201
proceeds gradually with rising temperature; therefore the magneto-optical storage medium used for magnetic domain expansion reproduction in accordance with the method still has a problem that reproduction resolution is difficult to improve.
Further, the supplementary reproduction layer
202
and the reproduction layer
201
need to be thick so that the transition from an in-plane magnetization state to a perpendicular magnetization state of the supplementary reproduction layer
202
and the reproduction layer
201
takes place with rising temperature in a stable manner; however, greater thicknesses of the layers degrade playback sensitivity, which is yet another problem.
SUMMARY OF THE INVENTION
The present invention has an object to offer a magneto-optical storage medium, having satisfactory playback sensitivity, that can reproduce signals whose cycles do not exceed diffraction limits of light without reducing the amplitude of the reproduced signals.
In order to achieve the above object, the magneto-optical storage medium in accordance with the present invention includes:
a reproduction layer exhibiting an in-plane magnetization state at room temperature and changing to a perpendicular magnetization state at a transition temperature Tp
1
;
a supplementary reproduction layer exhibiting an in-plane magnetization state at room temperature and changing to a perpendicular magnetization state at a transition temperature Tp
2
;
a non-magnetic intermediate layer for breaking exchange coupling between a storage layer and the supplementary reproduction layer; and
the storage layer made of a perpendicular magnetization film generating a leakage magnetic flux at temperatures around the transition temperature Tp
2
,
the layers being deposited in this order,
wherein Tp
1
<Tp
2
According to the arrangement, the reproduction layer and the supplementary reproduction layer are specified so as to have such magnetic properties that the layers exhibit an in-plane magnetization state at room temperature and
Hirokane Junji
Iwata Noboru
Takahashi Akira
Conlin David G.
Dike Bronstein Roberts & Cushman
Dinh Tan
Sharp Kabushiki Kaisha
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