Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse...
Reexamination Certificate
1999-06-02
2001-04-03
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
C428S690000
Reexamination Certificate
active
06212137
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magneto-optical storage medium, such as a magneto-optical disc, used as an information storage medium, and also to a magneto-optical storage device therefor.
BACKGROUND OF THE INVENTION
In recent years, magneto-optical discs boast increasingly high storage density features as computer storage devices and package media for music and image information. Information is written on a magneto-optical disc by either of the following two methods: an optical modulation method of storing information by modulating light intensity of a laser beam according to the information, and a magnetic field modulation method of storing information by modulating an external magnetic field according to the information. The magnetic field modulation method yields a higher storage density than the optical modulation method, and is adopted in many of the commercialised magneto-optical storage and reproduction devices.
According to the magnetic field modulation method, a high frequency magnetic field needs be applied to a storage film of the medium, and a magnetic head therefore needs be disposed in a proximity of the storage film. For these reasons, as shown in
FIG. 25
, a conventional storage medium includes a translucent dielectric layer
62
, a storage layer
63
, a non-magnetic layer
64
, a reflection layer
65
, and a protection layer
66
provided in this order on a translucent substrate
61
. A magneto-optical storage and reproduction device includes an optical head (not shown) and a magnetic head
70
. The optical head has an objective lens
71
, and structured to emit a light beam
72
onto the magneto-optical disc from the side on which the translucent substrate
61
is provided. The magnetic head
70
is constituted by a magnetic core
701
and a coil
702
. Since the translucent substrate
61
is as thick as about 1 mm, the magnetic head
70
is provided on the opposite side to the optical head with respect to the translucent substrate
61
so as to be positioned near the storage layer
63
.
If the magnetic head is provided on the opposite side to the optical head with respect to the storage medium as noted above, problems occur that the device increases in size and that a pasted disc cannot be used.
Also, if the magnetic head is provided on the same side as the optical head with respect to the storage medium, problems occur that the magnetic field produced by the magnetic head at the position of the storage layer becomes smaller and that information cannot be stored.
By contrast, Japanese Laid-Open Patent Application No. 63-204533/1988 (Tokukaisho 63-204533) discloses an arrangement in which a optical head and a magnetic head coil are provided on the same side with respect to the storage medium, and a ferromagnetic material is provided either on the opposite side to the optical head and the magnetic head coil with respect to the storage medium or in the storage medium.
That conventional arrangement has an object to prevent an external magnetic field flux from diverging when information is being stored on the storage medium. However, a large electric power is essential to store information on the storage medium, and no commercialised usages has been established so far.
Another conventional approach is to use no external magnetic field in a storing operation. For example, Japanese Laid-Open Patent Application No. 5-182278/1993 (Tokukaihei 5-182278) discloses a direct overwrite method by use of a storage layer and a supplementary layer, and a medium to work the method.
However, in the case of the storing on a magneto-optical storage medium, storage density can be more readily improved with magnetic field modulation than with optical modulation, and there is a popular demand for memory with a larger capacity. Accordingly, a storage medium, device, and method for magnetic field modulation which can use both sides of the disc need be developed.
SUMMARY OF THE INVENTION
The present invention has objects to provide a magneto-optical storage medium that is capable of storing information with a smaller external magnetic field, and to offer a low power-consuming magneto-optical storage device for storing information on such a magneto-optical storage medium with optical and magnetic heads disposed on the same side with respect to the magneto-optical storage medium.
To achieve the above objects, a magneto-optical storage medium in accordance with the present invention is characterised in that it includes:
a storage layer having a coercive force that decreases with a rise in temperature;
a storage supplementary layer made of a ferrimagnetic material having a compensation temperature near room temperature and exhibiting an increased saturation magnetisation near a Curie point of the storage layer, and having a magnetisation that changes an orientation thereof at a portion of the storage supplementary layer according to a modulated external magnetic field, the portion having been heated in a storing operation; and
a first non-magnetic layer disposed between the storage layer and the storage supplementary layer.
With the above arrangement, the magnetic moment of the storage supplementary layer heated in a storing operation follows a small external magnetic field, and produces a relatively large magnetic field at the position of the storage layer. Therefore, even if the applied external magnetic field is small, owing to the relatively large magnetic field produced by the magnetic moment of the storage supplementary layer at the position of the storage layer, the magnetic moment of the storage layer follows the external magnetic field.
Typically, according to a magnetic field modulation method, information is stored by reducing the coercive force of the storage layer with heat and then applying an external magnetic field modulated according to the information that is to be stored to reverse the magnetisation of the storage layer in accordance with the orientation of the external magnetic field. Therefore, with the magneto-optical storage medium in accordance with the present invention can store information with a small external magnetic field.
This enables the magneto-optical storage medium to store information with a smaller magnetic field than a conventional magneto-optical storage medium, and the device for storing information onto the magneto-optical storage medium with a magnetic field modulation method to be driven with a reduced amount of electric power.
Moreover, the magneto-optical storage medium preferably further includes a ferromagnetic material layer disposed, via a second non-magnetic layer, on a side of the storage supplementary layer on which the first non-magnetic layer is not provided.
With the above arrangement, the additional provision of the ferromagnetic material layer via the second non-magnetic layer on a side of the storage supplementary layer on which the first non-magnetic layer is not provided, i.e., the existence of the ferromagnetic material layer in the storage medium, causes concentration of a magnetic flux, and therefore enables information to be stored with an even smaller external magnetic field.
This enables the magneto-optical storage medium to store information with a smaller magnetic field than a conventional magneto-optical storage medium, and the device for storing information onto the magneto-optical storage medium with a magnetic field modulation method to be driven with a reduced amount of electric power. Moreover, this enables information to be stored by using a device (generally, regarded as being capable of producing only a small magnetic field at the position of the storage layer) in which optical and magnetic heads are disposed on the same side with respect to the magneto-optical storage medium.
Furthermore, a magneto-optical storage device in accordance with the present invention is a magneto-optical storage device for storing information on a magneto-optical storage medium including: a storage layer having a coercive force that decreases with a rise in temperature; a storage supplementary layer made o
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Dinh Tan
Hartnell, III George W.
Sharp Kabushiki Kaisha
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