The magneto-elastic and optical properties of multiferroic GaFeO3-δ

Abstract

Temperature-dependent Raman spectroscopy, X-ray absorption near-edge spectroscopy (XANES), optical absorption spectroscopy (OAS) and ac-susceptibility measurements have been carried out on GaFeO3 samples to understand the effect of sintering temperature (TS) on optical and magneto-elastic properties. The temperature-dependent ac-susceptibility measurements suggest the systematic scaling in the values of ferri-magnetic transition temperature (TC) with TS. The observed variation has been understood in terms of enhancement in the Goodenough-Kanamori-Anderson coupling. Instead of expected anharmonic behavior in Raman spectra around TC, several vibrational modes of rigid FeO6 units were found to show anomalous behavior, which suggests the significant magneto-elastic coupling contributions to phonon frequencies. The strength of magneto-elastic coupling has been quantified by using the phonon renormalization function (Δw) and is found to scale systematically with TS. Further, optical absorption study demonstrates the increase in intensity and red shift in charge-neutral d-d transitions, which infers the increase in oxygen non-stoichiometry with TS. The oxygen non-stoichiometry has been further quantified by the XANES measurements. The present investigations on GaFeO3 samples reveal that TC can be tuned by varying the oxygen stoichiometry and can be very beneficial for spintronic devices applications.