Magnetic domain formation in Tb/sub 23/Fe/sub 77/ thin film on a moving magneto-optical disk with magnetic field modulation recording

In this paper, the magnetic domain formation process on a moving disk for Tb/sub 23/Fe/sub 77/ magneto-optical recording thin film under the magnetic field modulation recording was investigated by a new simulation method. The simulation results showed that the convex prior edge of the domain was instantly formed and pinned when the magnetic field changed from low state to high state. Then, the domain boundary was lengthened opposite to the disk moving direction without changing the width during the high state of the applied magnetic field. As the magnetic field changed from high state to low state, the concave posterior edge of the domain was simultaneously formed and pinned, and the domain became a closed chevron shape. Both edges closely resemble the Curie temperature contour. There existed a threshold applied magnetic field strength, and the domain could not be formed when the applied field strength was below the threshold value, The value of the threshold field was approximately the same as the demagnetizing field around Tc, but reversed in polarity, and it increased with the laser power. The domain width increased as the applied field increased above the threshold value, and it rapidly became saturated when the applied field was about 30 Oe greater than the threshold value, There also existed a threshold laser power, below which the domain could not be formed. The threshold power was 3.3 mW for Tb/sub 23/Fe/sub 77/. The domain width increased monotonically with the laser power for high applied magnetic field, and it increased (then decreased) with the laser power when the applied magnetic field was closed to the threshold value.