A correlation between the magnetic and structural properties of isochronally annealed Cu-free FINEMET alloy with composition Fe72B19.2Si4.8Nb4

In this paper, structural changes in Cu-free FINEMET alloy (Fe72B19.2Si4.8Nb4) invoked by isochronal thermal annealing were investigated by synchrotron X-ray diffraction (SXRD) and X-ray absorption near-edge spectroscopy techniques. Detailed radial distribution function analysis of SXRD data showed that the first coordination shell in the amorphous matrix is preserved for annealing up to 400 A degrees C (1 h), whereas changes were observed in the second coordination shell. Annealing at 600 A degrees C (1 h) showed crystalline phase emanating over the amorphous background in SXRD data and a corresponding large decrease in the width of the first coordination shell. The width of the second coordination shell decreased with increasing annealing temperature. The magnetic properties such as remanence field, saturation magnetization and loss were found to have a positive correlation with the changes in the structural parameters of the second coordination shell, for all the samples (as quenched as well as annealed at various temperatures). We propose that the rearrangement of magnetic amorphous matrix on annealing also contributes to modifying the exchange interaction between ferromagnetic nanocrystalline domains and hence changes magnetic parameters, in addition to the growth of these domains, on annealing.