Heat Treatment and Its Effect on the Hyperfine Structure and Magnetization Process of Classical Amorphous Iron-Based Alloys

The investigated materials were Fe-based amorphous alloy ribbons in the as-quenched state and after isothermal annealing below the Curie temperature. The aim of this study was to determine the relaxation-induced changes occurring in the amorphous matrix and their effect on local magnetic order and the magnetization process. The structure was examined by X-ray diffraction. Mössbauer spectra were recorded at room temperature using a 57Co source in a rhodium matrix. The spectra consisted of broad, asymmetric, overlapping lines characteristic of amorphous materials. The derived hyperfine-field distributions were bimodal. After annealing, a slight change in their shape and an increase in the mean hyperfine field were observed, indicating a change in the local magnetic order of the amorphous matrix. Measurements performed with a vibrating sample magnetometer also revealed changes in the coercive field and saturation magnetization. Analysis of the initial magnetization curves made it possible to assess the influence of structural defects on the magnetization process up to the Holstein–Primakoff paraprocess region. Changes in the magnetic properties were also analysed using the spin-wave stiffness parameter.