Local Order in Amorphous and Nanocrystalline Iron-Based Ribbons

This work presents the results of studies of Fe-based alloy ribbons in the as-quenched state and after isothermal annealing. The ribbons were produced by melt spinning and subsequently annealed in a vacuum for 30 min at 800 K — a temperature corresponding to the onset of crystallization. The aim of the study was to determine changes in local order and their effect on the magnetic properties of the alloy. The sample structure was examined using X-ray diffraction. For the as-quenched sample, a broad maximum characteristic of an amorphous structure was observed. Mössbauer measurements confirmed a change in the local environment of Fe atoms. After annealing, the mean hyperfine field increased, while the hyperfine-field distributions remained bimodal. The structural changes were reflected in the magnetic properties. After annealing, an increase in saturation magnetization and a decrease in the coercive field were observed. Analysis of the initial magnetization curves showed that, above the effective anisotropy field, the magnetization process is related to fluctuations in local anisotropy caused by structural inhomogeneities.