Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1998-11-16
2002-07-23
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C428S690000
Reexamination Certificate
active
06424601
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magneto-optical recording medium, method for reproducing it and a reproducing apparatus therefor; in more detail it relates to a magneto-optical recording medium, method for reproducing it and a reproducing apparatus therefor suitable for high density recording whereby minute recording magnetic domains smaller than the reproducing light spot can be magnified and reproduced.
BACKGROUND ART
Since in magneto-optical recording media the recorded information can be re-recorded, storage capacity is large and reliability is high, they have started to be implemented as external memories etc. for computers. However, with increases in the amount of information and increased compactness required of the apparatus, further demands are being made on high-density recording and reproducing techniques. To record information on a magneto-optical recording medium, the magnetic field modulation method is employed, wherein a magnetic field of polarity corresponding to the recording signal is applied to a region of the magneto-optical recording medium which has been raised in temperature by directing a laser beam onto it. With this method, over-write recording is possible and furthermore high-density recording with for example a shortest mark length of 0.15 &mgr;m can be achieved. Furthermore overwrite recording is possible and has been implemented with an optical modulation recording system in which recording is performed under a constant applied magnetic field, using a light-beam whose power is modulated in accordance with the recording signal.
However, the optical reproduction resolution, which is determined by the spot radius of the reproducing light-beam, presents a problem when recording marks which are recorded at high density are to be reproduced. For example, it is not possible to identify and reproduce minute marks of magnetic domain length 0.2 &mgr;m using a reproducing light beam of spot diameter 1 &mgr;m. As one approach to eliminating restrictions on reproduction resolution resulting from the optical spot radius of the reproducing light beam, a Magnetically Induced Super Resolution (MSR) technique has been proposed as described in for example Journal of Magnetic Society of Japan, Vol. 17 Supplement No. S1, pp. 201 (1993). In this technique, the effective spot radius that contributes to the reproduction signal is reduced by generating a magnetic mask within the spot by using a temperature distribution generated in the magnetic film within the reproducing light beam spot when the reproducing light beam is directed onto the magneto-optical recording medium. By using this technique, the reproduction resolution can be raised without actually decreasing the spot radius of the reproducing light beam. However, with this technique, the spot radius is effectively reduced by means of the magnetic mask, so the amount of light contributing to the reproduction output is lowered, and so the reproduction C/N is correspondingly lowered. As a result, it is difficult to obtain a satisfactory C/N.
Japanese Patent Laid-Open Publication No. 1-143041 discloses a method of reproducing a magneto-optical recording medium in which reproduction is performed by magnifying the recording magnetic domain of a first magnetic film using a magneto-optical recording medium comprising a first magnetic film, a second magnetic film and a third magnetic film that are mutually magnetically coupled at room temperature and in which, if the Curie temperatures of the first magnetic film, second magnetic film and third magnetic film are assumed to be T
C1
, T
C2
and T
C3
, then T
C2
>room temperature while T
C2
<T
C1
and T
C3
, the coercivity H
C1
of the first magnetic film being sufficiently small in the vicinity of the Curie temperature T
C2
of the second magnetic film and the coercivity H
C3
of the third magnetic film being sufficiently greater than the required magnetic field in the temperature range from room temperature up to a required temperature T
PB
higher than T
C2
. In this method, utilising the rise in temperature of the medium on illumination by the reproducing light beam, magnetic coupling of the first and third magnetic films is cut off and in this condition the magnetic domain of the first magnetic film is magnified by a demagnetising field acting on the recording magnetic domain and an externally applied magnetic field. It should be noted that, in this method, a second magnetic film is employed whose Curie temperature is set lower than the temperature of the reproduction portion during reproduction, but in the present invention a magnetic film having such a magnetic characteristic is not employed.
Japanese Patent Laid-Open Publication No. 6-295479 discloses a magneto-optical recording medium having a first magnetic layer in which magnetization direction changes from an in-plane direction to a perpendicular direction at a certain transition temperature above room temperature and a second magnetic layer (recording layer) consisting of perpendicularly magnetizable film. The transition temperature of the first magnetic layer becomes higher in the film thickness direction from the side where the light enters, either continuously or stepwise. The first magnetic layer of this magneto-optical recording medium is constituted by a reproducing layer, a first intermediate layer and a second intermediate layer; the temperatures at which the transition takes place from in-plane magnetization to perpendicular magnetization are set to be higher in the order: reproducing layer, first intermediate layer and second intermediate layer, so on information reproduction, due to the relationship of the transition temperatures of the respective layers and the temperature distribution within the reproducing light beam spot, the magnetic domain of the recording layer is magnified and is transferred to the reproducing layer. However, in this publication, there is no detailed description regarding the thickness of the intermediate layers; the total film thickness of the intermediate layers of the magneto-optical recording medium used in an embodiment is 10 nm.
An object of the present invention is to provide a magneto-optical recording medium and a signal reproducing method and reproducing apparatus therefor whereby a reproduction signal with satisfactory C/N can be obtained even when minute magnetic domains are recorded.
DISCLOSURE OF THE INVENTION
According to a first aspect of the present invention, there is provided a magneto-optical recording medium comprising, at least a magneto-optical recording layer on which information is recorded, a first auxiliary magnetic layer and a second auxiliary magnetic layer in which, when irradiated with a reproducing light beam, a recording magnetic domain recorded in the magneto-optical recording layer is magnified and transferred (transmitted) to the second auxiliary magnetic layer through the first auxiliary magnetic layer and information is reproduced from this magnetic domain of the second auxiliary magnetic layer which has thus been magnified and transferred, characterized in that,
the thickness of the first auxiliary magnetic layer is not less than the thickness of the magnetic wall of this first auxiliary magnetic layer.
According to a second aspect of the present invention, there is provided a magneto-optical recording medium comprising at least a magneto-optical recording layer on which information is recorded, a first auxiliary magnetic layer and a second auxiliary magnetic layer wherein, when irradiated with a reproducing light beam, a recording magnetic domain recorded in the magneto-optical recording layer is magnified and transferred to the second auxiliary magnetic layer through the first auxiliary magnetic layer and information is reproduced from this magnetic domain of the second auxiliary magnetic layer which has thus been magnified and transferred, characterized in that,
the thickness of the first auxiliary magnetic layer exceeds 10 nm.
An example of major parts of a magneto-optical recording medium according to the pres
Awano Hiroyuki
Nagai Nobuyuki
Ohta Norio
Oonuki Satoru
Shimazaki Katsusuke
Birch & Stewart Kolasch & Birch, LLP
Hitachi Maxell Ltd.
Neyzari Ali
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