The rf–Mössbauer study of the magnetic properties of nanocrystalline alloys

Abstract

The conventional Mössbauer investigations of the soft magnetic nanocrystalline alloys, produced utilizing the first step of crystallisation of amorphous alloys, allow the identification of phases formed due to annealing of amorphous precursor and the evaluation of their relative content but do not provide information on the magnetic properties (anisotropy field, magnetostriction). Unconventional rf–Mössbauer technique, which employs the radio-frequency (rf) fields, allows us to study soft magnetic nature of the alloys by observing the degree of rf-induced collapse of the hyperfine fields. The Mössbauer experiment, in which the rf collapse and rf sideband effects are used, allows the soft nanocrystalline bcc phase to be distinguished from magnetically harder microcrystalline ones. Qualitative information concerning the distribution of anisotropy fields in the nanocrystalline grains can be inferred from the dependence of the rf-collapsed spectra on the rf-field intensity. The rf-sideband effect reveals the changes of magnetostriction due to the formation of the nanocrystalline phase. The rf–Mössbauer technique provides a unique opportunity to study the microstructure and magnetic properties of each phase formed in the amorphous precursor.The principles of the rf–Mössbauer technique and examples of its application will be discussed for Fe–M–B–Cu (M: Ti, Ta, Nb, Mo) and FeNiZrB nanocrystalline alloys.Application of the rf–Mössbauer technique in the study of the short-range order (SRO) in amorphous alloys is discussed. The rf-collapse of the magnetic hyperfine structure in the Mössbauer spectra is employed to direct study of the short-range order in amorphous FeZrBCu and Fe–M–B–Cu alloys using the electric quadrupole hyperfine interaction.