Dynamic information storage or retrieval – Specific detail of information handling portion of system
Patent
1993-08-18
1995-06-27
Epps, Georgia Y.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
369 13, 369107, 369116, G11B 1110
Patent
active
054285941
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a magneto-optic recording and more particularly to a magneto-optic recording method in which information is recorded in a magneto-optic overwritable recording medium.
BACKGROUND ART
FIGS. 1(A) and 1(B) show the principle of a magneto-optic recording method in which a magneto-optic overwritable recording medium is used. Referring to FIG. 1(A), a magneto-optic overwritable medium 10 is configured such that a magnetic layer embodying a memory layer 12 is formed on the main surface of a disc-shaped substrate 11 made of a glass or a polycarbonate, and such that a magnetic layer embodying a recording layer 13 is formed on the memory layer 12, the memory layer 12 and the recording layer 13 being coupled by exchange interaction. While the overwritable medium 10 is made to rotate at several thousand rpm, a laser light beam is applied to the medium through the substrate 11 thereof. A bias magnet 15 is provided opposite a part of the recording layer 13 to which part the laser light beam is applied. An initializing magnet 16 is provided in front of the bias magnet 15 so that the two magnets are separated at a distance along the circumferential direction of the medium. The bias magnet 15 and the initializing magnet 16 face the recording layer 13 in opposite directions in terms of polarity.
Temperature--coercive force characteristics of the memory layer 12 and of the recording layer 13 are as indicated by L.sub.12 and L.sub.13 of FIG. 1(B), respectively. A Curie point. TC.sub.R of the recording layer 13 is prescribed to be higher than a Curie point TC.sub.M of the memory layer 12. A broken line indicates the intensity of the bias magnetic field of the bias magnet 15, and an alternate long and short dash line indicates the intensity of the initial magnetic field of the initializing magnet 16.
In such a magnetic medium 10, the recording layer 13 is magnetized, at a room temperature, in a direction specified by the initializing magnet 16. Accordingly, information recorded in the recording layer 13 as variations in magnetization is erased by means of the magnet 16. When a laser light beam 14 having a large power (P.sub.H) is applied to the memory layer 12 so as to heat it beyond a temperature TH, a subsequent cooling process ensures that the directions of magnetization of the recording layer 13 and the memory layer 12 are aligned with the magnetization direction of the bias magnet 15, so that record marks are formed. When the power of the applied laser light beam 14 is low (P.sub.L), and the memory layer 12 is heated to a temperature within a range between TL and TH, the recording layer 13 is not magnetized by the bias magnet 15, and the magnetization direction of the memory layer 12 is aligned with the magnetization direction of the recording layer 13 (the magnetization direction of the initial magnetizing magnet), due to exchange interaction. In such an information recording process, an overwrite process not involving an erasing process can be carried out on the magneto-optic overwritable medium 10.
In a magneto-optic recording process, information modulated through (2, 7) RLL coding (run length limited coding) is generally recorded, an example of how this modulation is effected being shown in FIG. 2(A). In (2, 7) RLL coding, it is stipulated that two channel bits "1" be separated by a sequence of between two and seven channel bits "0". That is, the conventional recording is performed such that the light beam power P.sub.H is used, as shown in FIG. 2(B), to correspond to a state "1" of recorded data shown in FIG. 2(A) and such that light beam power P.sub.L is used to correspond to "0". This way, a pit position recording can be effected in which record marks as shown in FIG. 2(C) are formed. A restored waveform as shown in FIG. 2(D) is obtained when the information is read. Referring to FIG. 2(C), hatched areas indicate record marks where there are reversions in magnetization direction. With such a (2, 7) RLL coding, there is no fear of synchronization being lost
REFERENCES:
patent: 5087532 (1992-02-01), Challener, IV
patent: 5163031 (1992-11-01), Osato
patent: 5233578 (1993-08-01), Yamamoto et al.
patent: 5263015 (1993-11-01), Niihara et al.
patent: 5282095 (1994-01-01), Spruit et al.
Izumi Haruhiko
Moritsugu Masaharu
Taguchi Masakazu
Chu Kim-Kwok
Epps Georgia Y.
Fujitsu Limited
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