| 摘要 |
A read-only optomagnetic disk which comprises at least a supporting base and a magnetic layer formed on it, and is provided with a first group of regions ( alpha 1) (corresponding to pits or marks) which are magnetizable in given directions by the irradiation with a laser beam for reproduction, and a second group of regions ( alpha 0) which are not magnetizable in given directions. One region of the first or second groups is handled as an information unit. The presence of this information unit, the length, or the edge position, represents information. Only when a region ( alpha 1) is positioned in the heat accumulated area (a) in the irradiated spot, the coercive force in it is reduced. Therefore, the magnetization is orientated in a given direction ANd by the influence of an auxiliary magnetic field ANd (heated out). In any other area than the ( alpha 1) in the spot, the magnetism is not orientated in the direction ( ANd ). Even if a region ( alpha 0) is in the heat accumulated area (a), magnetism in the whole spot is not in the given directions. Therefore, it is possible to detect the region ( alpha 1) which is smaller than the diameter of the spot. |
