Mössbauer spectroscopic studies of the moment distribution in Fe73.5Cu1Nb3Si13.5B9

Abstract

Fe 57 Mössbauer spectroscopy can be used to determine the distribution of moment directions in magnetic materials. Here, we have applied this technique to a study of Fe73.5Cu1Nb3Si13.5B9 (isocompositional with FINEMET). We are particularly interested in establishing the distribution of moment directions in the nanophase material, obtained by devitrification from an amorphous precursor. The nanophase material consists of Fe–Si grains embedded in an amorphous matrix. Current understanding of the resulting magnetic properties, which involves application of the random anisotropy model to these materials, assumes that the magnetization in the grains is exchange coupled to neighbors, giving a long exchange length compared with the nanometer grain size. We present data for the amorphous precursor, the standard nanophase material, and nanophase material devitrified in an external magnetic field. If σu and σv represent the Gaussian widths of the out-of-plane and in-plane moment direction distributions respectively, we have found that σu=14° and σv=68° for the amorphous precursor, σu=14° and σv=92° for the standard nanophase material, and σu=22° and σv=79° for a magnetic field aligned specimen. We interpret these data as demonstrating that standard devitrification does result in grains with a wide spread of moment direct ions over the volume sampled by this technique, even allowing for exchange coupling. These results and the implications for macroscopic magnetic properties such as anisotropy will be discussed.