Temperature variation of the magnetic properties of mechanochemically synthesized (Fe₂O₃)_1−x(Al₂O₃)_x solid solutions through the Mössbauer spectroscopy

Abstract

Mössbauer spectroscopy experiments were carried out on corundum-type structured (Fe₂O₃)_1−x(Al₂O₃)_x solid solutions (x = 0–0.67) synthesized by the mechanical alloying method to clarify the contribution of temperature and aluminum concentration to the magnetic properties. The Mössbauer spectra at room temperature gradually change from a sextet (weak ferromagnetism) to a doublet (paramagnetism) with increasing aluminum contents. As the temperature decreases down to 10 K, the sextet component develops for lower aluminum substitution, while the doublet profile changes to sextet for higher aluminum region. The absolute values of quadrupole splitting for the weak ferromagnetic component slightly increase with the aluminum substitution, primarily due to the reduction of the symmetry of the crystal field. The isomer shift δ decreases with the aluminum concentration due to the shrinkage of the lattice, and it also decreases with increasing temperature for the enhanced lattice vibration. Additionally, the hyperfine magnetic field B_hf weakens with the aluminum substitution presumably due to a diminished interaction between the nuclear magnetic moments, which can be observed in the lower temperatures.