Probing magnetoelastic coupling and structural changes in magnetoelectric gallium ferrite

Temperature dependent x-ray diffraction and Raman spectroscopic studies were carried out on flux-grown single crystals of gallium ferrite with a Ga:Fe ratio of 0.9:1.1. Site occupancy calculations from the Rietveld refinement of the x-ray data led to an estimated magnetic moment of ∼0.60 μB/f.u. which was in good agreement with the experimental data. A combination of these two measurements indicates that there is no structural phase transition in the material between 18 and 700 K. A detailed line shape analysis of the Raman mode at ∼374 cm-1 revealed a discontinuity in the peak position data indicating the presence of spin-phonon coupling in gallium ferrite. A correlation of the peak frequency with the magnetization data led to two distinct regions across a temperature ∼180 K with appreciable change in the spin-phonon coupling strength from ∼0.9 (T < 180 K) to 0.12 cm-1 (180 K < T < Tc). This abrupt change in the coupling strength at ∼180 K strongly suggests an altered spin dynamics across this temperature. (paper)