The thermal behavior of the critical magnetic field in amorphous ribbons

Abstract

Initial magnetization curves of soft magnetic amorphous ribbons are essentially similar to their polycrystalline counterpart. They exhibit a nearly linear reversible magnetization behavior at low magnetic applied field, as well as an irreversible, hysteretic range for high applied fields, above a well-defined ‘‘critical field.’’ In the domain-wall size model approach for polycrystalline materials, the critical magnetic field is related to the depinning of the magnetic domain wall. For lower applied fields, the magnetic domain wall is pinned to the grain boundaries and the net magnetization is produced by a bulging mechanism; for higher applied fields, a depinning and displacement mechanism is responsible for the important magnetization increase. In this paper we present a study of the temperature dependence of the critical magnetic field in Vitrovac-type magnetic amorphous ribbons, from 80 up to 500 K. Taking into account the geometry of the toroidally wound amorphous ribbon we assume that the magnetic domain-wall pinning occurs at the external surface of the sample. We compare these results with experimental results obtained on polycrystalline nickel ferrite. The general behavior of the critical fields as a function of temperature are very similar in spite of the large differences in materials, except for the high-temperature region where relaxation phenomena seem to take place in the amorphous ribbons.