Domains and domain-wall motion in grain-oriented 50-percent Ni-Fe tapes

Domains and domain-wall motion in grain-oriented 50-percent Ni-Fe tapes were studied using a Kerr magnetooptical apparatus. The domain walls were quite straight under a slowly increasing field, and the nucleation of a reversed domain always occurred at either or both sides of the tapes. The 90° walls, such as those observed in a single crystal, often appeared even in the samples which were not strained to conserve the magnetization continuity. Under pulse fields the nucleation sites of reversed domains were distributed on the tape surface, and many isolated small domains appeared. It was found, however, that the domain configurations under the successive pulse field drive of much shorter length were similar to those under a slowly increasing field. Domain-wall velocities were measured for the samples of the thickness range from 25 μm to 81 μm, keeping the distance of wall displacement nearly constant by setting properly the pulse field amplitude and length. The measured dependence of the velocity on pulse field amplitude was not linear, and the mobilities increased with increasing field amplitude. This is discussed from the dynamic behavior of domain walls in tapes.