JPS6419503A - Bias magnetic field impression device - Google Patents

Abstract

PURPOSE:To shorten the reversal time of polarity, by providing plural excitation coils which are arranged adjacently to a rotatable permanent magnet having four magnetic poles and generate torque in the permanent magnet. CONSTITUTION:A laser beam from a laser beam source 11 is diaphragmed to a micro spot with a diameter of 1-2mum on the magnetic layer 8 of a disk medium 7 by an objective lens 10, and the temperature of the medium is increased, and simultaneously, a bias magnetic field is impressed, and a reversal magnetic domain is formed on the layer 8, then, recording is performed, and erasure is performed by arranging the magnetizing direction of the layer 8 in the same direction. The bias magnetic field is generated from the magnetic pole on the medium side of the permanent magnet 2. To perform the recording and the erasure, it is required to change the polarity of the bias magnetic field, and a cylindrical magnet 2 having four magnetic poles magnetized in the normal direction of an outer periphery is reversed. Currents are permitted to flow on the excitation coils 4a, 4b, and 4c so that the magnetic poles 501a and 501b at a side neighboring to the magnet 2 of an excitation core can be set as an S-pole and the magnetic pole 501c as an N-pole, and the N-pole of the magnet 2 is attracted to the magnetic poles 501a and 501b, and the S-pole to the magnetic pole 501c, then, the torque is generated in the magnet 2, and the polarity is reversed by right-turning at 90 deg..