The Influence of Chemical Composition on the Hyperfine Field Induction Distribution at 57Fe Nuclei and the Process of Approaching Ferromagnetic Saturation

This paper presents the results of investigations of two Fe-based bulk amorphous alloys, Fe70Nb1Mo4Y5B20 and Fe70Nb2Mo3Y5B20. The objective was to determine the effect of a small change in chemical composition on the local environment of Fe atoms and the process of approaching ferromagnetic saturation. The structure of the samples was examined using X-ray diffraction. Both alloys exhibited diffraction patterns characteristic of amorphous materials. The room-temperature Mössbauer spectra consisted of broad, overlapping lines characteristic of a heterogeneous local environment of Fe atoms. The resulting hyperfine magnetic field distributions were bimodal. Magnetic properties were measured using a vibrating sample magnetometer. The initial magnetization curves were analysed according to the theory of the approach to ferromagnetic saturation. At the highest fields, the suppression of thermally excited spin waves was also analysed, and the spin-wave stiffness parameter was determined. The combined results allow the effect of the Nb/Mo ratio on the local magnetic state and magnetization mechanisms to be assessed while the amorphous character of both alloys is retained.