Annealed FINEMET ribbons: Structure and magnetic anisotropy as revealed by the high velocity resolution Mössbauer spectroscopy

The high velocity resolution 57Fe Mössbauer spectroscopy was used in order to elucidate structural and compositional details of FINEMET (Fe73.5Si15.5Nb3B7Cu1) alloys obtained via the annealing (with and without external magnetic field) of rapidly quenched ribbons. The analysis of the measured Mössbauer spectra was carried out, on one hand, by considering the possibility of a random distribution of iron atoms substituting Si at the D sites in the well crystallized DO3 Fe-Si phase, on the other hand, by allowing for an arbitrary-shape hyperfine magnetic field distribution for the case of the amorphous matrix. The results refer to the influence of the next-nearest-neighbor configurations on the magnitude of iron magnetic moments at the D sites in the precipitated nanocrystalline Fe-Si phase. The applied analysis method enables us to draw conclusions regarding the relative occurrence of the various iron microenvironments in the nanocrystalline phase and amorphous matrix, and the associated Si concentration of the precipitated nanocrystalline DO3 Fe-Si phase. The studied samples provide further evidence concerning the correlation between the induced magnetic anisotropy and the magnetic permeability in annealed FINEMET ribbons.