DOMAIN OBSERVATION ON NANOCRYSTALLINE MATERIAL

Bulk polycrystalline material with a grain size in the nanometer range can be prepared by controlled crystallization of certain metallic glass alloys. The material shows excellent soft magnetic properties which are attributed to an effective averaging of the local crystal anisotropy over the scale of a Bloch wall width. The general appearance of observed domain patterns resembles those of metallic glasses. Wide in-plane domains as well as the characteristic stress patterns are observed. On annealing beyond the optimum temperature the coercivity rises which manifests itself by an irregular domain appearance. An interesting behavior is found if the samples are observed at temperatures beyond approximately 320-degrees-C. At this temperature the amorphous ferromagnetic grain boundary phase which couples the iron-rich crystallites becomes paramagnetic. The domains reversibly show a similar character as the overannealed samples. This observation indicates that overannealing leads in this material not only to grain growth beyond the optimum, but also to an interruption of the ferromagnetic coupling between the grains.