Magnetisation distributions in thin film recording heads by Type II contrast

The magnetic domain structure of the polepieces of thin-film magnetic recording heads and its variation with drive current and frequency are of interest in understanding the read/write properties of the head. The authors describe the setting up of the synchronous detection mode of type II backscattered electron contrast in a 200-kV electron microscope and its application to the study of domain wall movement in the P2 polepieces of heads with and without the 15-20-μm-thick alumina overlayer in place. Extension of the method to allow evaluation of the changes in magnetization directions under AC drive conditions is described. The authors also demonstrate a novel technique which gives information on the remanent state of the domain structure in the P2 polepiece and its changes under DC drive conditions. It is concluded that these improvements in technique, taken together with the capability of the synchronous detection method to provide information on changes of magnetic structure with depth, mean that this experimental tool will be invaluable in its own right as well as complementary to the Kerr imaging methods