Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-02-17
2004-01-06
Neyzari, Ali (Department: 2655)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013240
Reexamination Certificate
active
06674693
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording/reproducing method, a recording/reproducing apparatus and a magneto-optical head for magneto-optical recording media. More specifically, the invention relates to a recording/reproducing method, a magneto-optical recorder and a magneto-optical head which are suitable for extra-high-density recording.
2. Description of Related Art
Recording media such as magneto-optical recording media are known as external memories for computers etc. The magneto-optical recording media can take or cover a great quantity of data such as dynamic images and voice, and are therefore used frequently as recording media in this multimedia era. It is desired that the storage capacity of magneto-optical recording media is increased.
A known method for increasing the storage capacity of a magneto-optical recording medium involves forming recording magnetic domains densely in the recording layer of the medium with a light spot having a minimized or minute diameter. For optical recording, the diameter of the light spot formed by a laser beam is represented by &lgr;/NA where &lgr; is the wavelength of the beam, and NA is the numerical aperture of the objective lens condensing the beam. It is therefore possible to minimize the light spot by either shortening the wavelength of the laser beam or increasing the numerical aperture of the objective lens. This makes it possible to form minute recording magnetic domains in the recording layer. However, if a plurality of minute recording magnetic domains exist in a reproducing light spot, there is need for a method for discriminating them and reproducing information from them.
As a method for reproducing information individually from the minute recording magnetic domains existing in a reproducing light spot, a technique for enlarging a magnetic domain and reproducing information from it as disclosed in WO98/02878 is proposed. A magneto-optical recording medium according to this technique includes a recording layer and a magnetically soft reproducing layer. It is possible to reproduce information from the recording medium by magnetically transferring the recording magnetic domains in the recording layer to the reproducing layer, and enlarging the transferred domains in the reproducing layer. This makes it possible to detect the minute recording magnetic domains inside a reproducing light spot individually as amplified signals from the reproducing layer.
It is possible to record information on a magneto-optical recording medium by irradiating the medium with a laser beam to form a heat spot based on the light intensity distribution in the light spot, then decreasing the coercive force in a high temperature region of the heat spot, and subsequently applying a recording magnetic field uniformly to the heat spot region including the high temperature region to reverse the magnetization of the high temperature region, where the coercive force has decreased, to form recording magnetic domains. In general, a magnetic coil is used to apply a magnetic field to a magneto-optical recording medium. In general, a magnetic coil is positioned on that side of a magneto-optical recording medium which is opposite to the substrate of the medium, that is to say, on the side of the medium where a recording film is formed. In general, a lens for condensing a laser beam is positioned on the side of the recording medium where the substrate lies.
If a high NA objective lens is used to minimize the light spot formed on a magneto-optical recording medium, it is necessary to shorten the distance between the lens and the adjacent surface of the recording medium because the focal distance of the lens is short. Therefore, as is the case with the magnetic coil, the high NA objective lens is positioned on the side of the recording medium where a recording film lies. The magnetic coil is constructed in such a manner that it does not intercept the light beam outgoing from the objective lens. For example, a solid immersion lens (SIL) may be used as a high NA lens. In this case, as shown in
FIG. 16
, a coil is wound around a SIL
10
to form a magnetic coil
104
. The magnetic coil
104
can apply a magnetic field to the whole area of a light spot on a magneto-optical recording medium. The size of the recording magnetic domains formed in the recording layer of the recording medium depends on the size of the high temperature region of the heat spot. Therefore, in order to form minute recording magnetic domains, it has been necessary to minimize the heat spot. However, it has been difficult to control the size of the high temperature region of the heat spot because the size varies with the light intensity, the materials of the recording medium, etc. Consequently, it has not been easy to form smaller recording magnetic domains than the heat spot. The shape of the heat spot is reflected as the shape of recording magnetic domains. Accordingly, if the magnetic domains are overwritten, they take the form of feathers of an arrow, which is not necessarily desirable as the shape of magnetic domains for high density recording.
SUMMARY OF THE INVENTION
In view of the foregoing points, it is a first object of the present invention to provide a recording method for extra-high-density recording, and a recording/reproducing apparatus and a magneto-optical head which are suitable therefor.
It is a second object of the invention to provide a reproducing method for reproduction at high reproducing resolution of extra-high-density information recorded on a magneto-optical recording medium.
In accordance with a first aspect of the invention, a recording method is provided for recording information on a magneto-optical recording medium by applying a magnetic field to a heat spot heated by a light spot, the method comprising the steps of:
moving the light spot relative to the recording medium in such a manner that a high temperature region of the heat spot is formed outside the light spot; and
applying a magnetic field to the high temperature region of the heat spot.
The recording method according to the first aspect of the invention includes forming on the track of a magneto-optical recording medium a light spot moving relative to the medium, and forming outside the light spot a high temperature region of the heat spot produced by the light spot. This method also includes applying a recording magnetic field to the formed high temperature region to form a recording magnetic domain in the recording layer of the recording medium. In order to apply a magnetic field only to a narrow region such as the high temperature region of the heat spot, a magnetic head may be used which includes a magnetic field generating section a width of which is narrower in the direction along the track than the light spot. In this specification, the “high temperature region” conceptionally means a temperature region including the heat center, that is, the highest temperature point of the heat spot produced by a light spot which is formed on and moving relative to a magneto-optical recording medium. During information recordation, the coercive force of the recording layer of the recording medium decreases in the high temperature region so that a recording magnetic domain can be formed in this region of the recording layer. During information reproduction, the coercive force of the reproducing layer of the medium decreases in the high temperature region so that a recording magnetic domain of the recording layer can be transferred to this region of the reproducing layer. Herein, the terms “outside the (a) light spot” mean the outside of the region defined by the radial position where the light intensity is 1/e
2
of its maximum value in the light intensity distribution is a radial direction of the light spot formed on a magneto-optical recording medium.
In the recording method according to the invention, a high temperature region of a heat spot may be formed outside the associated light spot on a rotating magneto-optical recording medium by increasing the
Awano Hiroyuki
Sekine Masaki
Yamazaki Yuji
Hitachi Maxell Ltd.
Neyzari Ali
Oliff & Berridg,e PLC
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