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

Fe-57 Mossbauer spectroscopy can be used to determine the distribution of m oment directions in magnetic materials. Here, we have applied this techniqu e to a study of Fe73.5Cu1Nb3Si13.5B9 (isocompositional with FINEMET). We ar e particularly interested in establishing the distribution of moment direct ions in the nanophase material, obtained by devitrification from an amorpho us precursor. The nanophase material consists of Fe-Si grains embedded in a n amorphous matrix. Current understanding of the resulting magnetic propert ies, which involves application of the random anisotropy model to these mat erials, 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 sigma(u) and sigma(v) represent the Gaussian widths of the out-of-plane and in-plane moment direction distributions respectively, we have found th at sigma(u)=14 degrees and sigma(v)=68 degrees for the amorphous precursor, sigma(u)=14 degrees and sigma(v)=92 degrees for the standard nanophase mat erial, and sigma(u)=22 degrees and sigma(v)=79 degrees for a magnetic field aligned specimen. We interpret these data as demonstrating that standard d evitrification does result in grains with a wide spread of moment direct io ns over the volume sampled by this technique, even allowing for exchange co upling. These results and the implications for macroscopic magnetic propert ies such as anisotropy will be discussed. (C) 2000 American Institute of Ph ysics. [S0021-8979(00)25308-5].