Bulk and surface magnetic study of Fe80B20 crystallization

We report a study relating the evolution of coercivity H-c, both in the bulk and in the surface region, to the microstructural changes occurring during the first stage of the crystallization process of Fe80B20 amorphous samples. The coercive field H-c has been studied with a magneto-optical Kerr ellipsometer in the surface and with a vibrating sample magnetometer in the bulk. The observed behavior of H-c can be accounted for by considering its dependence on the number density of grains and gives information on the domain wall dynamic indicating the occurrence of a two dimensional bending of the domain walls. In addition, the evolution of H-c is substantially insensitive to the details of the internal structure of the grains. This study reveals that the surface crystallization occurs via the same processes as in the bulk but it takes place at lower temperature with respect to the bulk. We also measured the Curie temperature of the surface region of the amorphous ribbon and we obtained a lower value with respect to the bulk. (C) 1997 American Institute of Physics