Temperature Dependence and Critical Temperature of Magnetic Domain Structures in Thin Films

Magnetic domain structures of Ni-Fe and Ni-Co films, which were vacuum-condensed on NaCl single crystals at various temperatures (20-600°C) or prepared by polishing bulk crystals, have been observed at elevated temperatures up to 800°C by transmission electron microscopy. In general, no change was observed in domain configuration except in the ripple structure at temperatures below a certain critical temperature T d c ; however, there were exceptions: with polished films showing large magnetostriction or with condensed films, especially those consisting of fine grains, which showed large magnetostriction, it was often observed that the domain structure did change in this temperature range. The domain structures seemed to disappear at T d c , which was 0-200°C lower than the Curie point T c and was different from film to film depending on the film composition, grain size and effective anisotropy. When the temperature was decreased from T d c , an isotropic mesh-like domain configuration appeared just below T d c , which at lower temperatures, was rearranged into a configuration of domains with larger sizes. Such a mesh pattern was not observed with polished films.