Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1990-04-20
1993-06-01
LaRoche, Eugene R.
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
G11B 370
Patent
active
052166635
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a magneto-optic recording medium that is directly overwritable by optical modulation, enabling new information to be written directly over old information, and to a manufacturing method for this magneto-optic recording medium.
BACKGROUND ART
In FIG. 99, (a) is an oblique view of the main parts of a prior-art magneto-optic read-write device as shown, for example, in Preprints of the 34th Joint Congress of Applied Physics, Spring 1987, 28 P-Z L-3; (b) is a sectional view illustrating optical reading and writing of the recording medium; and (c) is a plot of the laser power variations for writing information in areas on the recording medium. In these drawings, 1 is a magneto-optic recording medium comprising a glass or plastic substrate 2, a first magnetic layer 3, and a second magnetic layer 4. An exchange coupling force acts between the first and second magnetic layers 3 and 4, tending to align their magnetization in the same direction. A laser beam is focused by an objective lens 5 onto a spot 6 on the information medium 1. The numeral 7 indicates areas in which the direction of magnetization in the first magnetic layer 3 is upward in FIG. 99 (b), this indicating the recording of binary "1" data. An initializing magnet 9 generates a magnetic field of substantially 5000 oersteds to initialize the second magnetic layer 4. A bias magnet 8 disposed facing the objective lens 5 with the information medium 1 in between generates a magnetic field of substantially 200 to 600 oersteds. In FIG. 99 (c) laser power is shown on the vertical axis and areas are indicated on the horizontal axis. The laser power is modulated to record the information "1" in the region R1 and the information "0" in the region R0. The dash-dot line in FIG. 99 (a) separates new data (DN) on the left from old data (DO) on the right.
The operation will be explained next. The recording medium 1 is rotated in the direction of the arrows in FIG. 99 (a) and (b) by a support and driving mechanism not shown in the drawing. The first magnetic layer 3 has the same properties as the recording layer in the media used in general magneto-optic disks comprising, for example, Tb.sub.21 Fe.sub.79, and here too it functions as a reading and writing layer. The second magnetic layer 4, called the auxiliary layer, comprises Gd.sub.24 Tb.sub.3 Fe.sub.73, for example, and provides the overwrite function, enabling new information to be written over old information in real time. The Curie temperatures Tc1 and Tc2 of the first and second magnetic layers 3 and 4, their room-temperature coercivities Hc1 and Hc2, and their room-temperature exchange coupling strengths Hw1 and Hw2 satisfy the following relations:
First the reading of information recorded in the first magnetic layer 3 (the recording layer) will be explained. As shown in FIG. 99 (b), the first magnetic layer 3 is magnetized in the up direction to represent a "1" and in the down direction to represent a "0." When this information is read, the first magnetic layer 3 is illuminated by the beam spot 6, and the magnetic orientation of the first magnetic layer 3 in the beam spot 6 is transformed by the well-known optical Kerr effect to optical information, in which form it is detected. FIG. 100 indicates the temperature changes in the magnetic layers in the spot caused by the laser beam power, with A corresponding to the intensity of the laser beam that illuminates the recording medium 1 during reading. At this intensity the maximum temperature increase in the first and second magnetic layers 3 and 4 in the beam spot 6 does not attain the Curie temperatures Tc1 and Tc2 of these layers, so the illumination in the beam spot does not erase the direction of magnetization; that is, it does not erase the recorded information.
Next the overwriting operation will be explained. The initializing magnet 9 in FIG. 99 generates a magnetic field of intensity Hini in the direction of the arrow b (up) in the drawing. This field Hini is related to the coercivity and exchange coupling str
REFERENCES:
patent: 4649519 (1987-03-01), Sun et al.
patent: 4878132 (1989-10-01), Aratani et al.
patent: 4908809 (1990-03-01), Tadokoro et al.
patent: 5025430 (1991-06-01), Tadokoro et al.
Fukami Tatsuya
Nakaki Yoshiyuki
Taguchi Motohisa
Tokunaga Takashi
Tsutsumi Kazuhiko
LaRoche Eugene R.
Mitsubishi Denki & Kabushiki Kaisha
Nguyen Tan
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