Brillouin scattering studies in Fe3O4 across the Verwey transition

Abstract

Brillouin scattering studies have been carried out on high quality single crystals of Fe3O4 with f100g and f110g faces in the temperature range of 300–30 K. The room temperature spectrum shows a surface Rayleigh wave sSRWd mode at 8 GHz and a longitudinal acoustic sLAd mode at 60 GHz. The SRW mode frequency shows a minimum at the Verwey transition temperature TV of 123 K. The softening of the SRW mode frequency from about 250 K to TV can be quantitatively understood as a result of a decrease in the shear elastic constant C44, arising from the coupling of shear strain to charge fluctuations. On the other hand, the LA mode frequency does not show any significant change around TV, but shows a large change in its intensity. The latter shows a maximum at around 120 K in the cooling run and at 165 K in the heating run, exhibiting a large hysteresis of 45 K. This significant change in intensity may be related to the presence of stress-induced ordering of Fe3+ and Fe2+ at the octahedral sites, as well as to stress-induced domain wall motion.