Analysis of optical magnetoelectric effect in GaFeO3

We study the optical-absorption spectra in a polar ferrimagnet GaFeO3. We consider the E1, E2, and M1 processes on Fe atoms. It is shown that the magnetoelectric effect on the absorption spectra arises from the E1-M1 interference process through the hybridization between the 4p and 3d states in the noncentrosymmetric environment of Fe atoms. We perform a microscopic calculation of the spectra on a cluster model of FeO6 consisting of an octahedron of O atoms and an Fe atom displaced from the center with reasonable values for Coulomb interaction and hybridization. We obtain the magnetoelectric spectra, which depend on the direction of magnetization, as a function of photon energy in the optical region 1.0-2.5 eV, in agreement with the experiment.