Domain expansion phenomena in exchange-coupled multilayer magneto-optical films

We investigated the readout signal waveforms from domains recorded with light intensity modulation in exchange-coupled? multilayer magneto-optical (MO) films. It was found that particular waveforms observed with a steep lending edge were caused by a magnetic domain expansion. When the recorded domain reached the unstable area where the wall coercivity of the readout layer was smaller than the readout magnetic field (H-r), it was expanded by an H-r parallel to the magnetization direction of the readout layer. When the recorded domain entered the unstable area completely, it shrunk and collapsed. It was considered that the domain expansion and the collapse occurred rapidly, and produced the rectangular waveforms with steep leading and trailing edges.