We study the optical absorption spectra in a polar ferrimagnet GaFeO_3. Weconsider the E1, E2 and M1 processes on Fe atoms. It is shown that themagnetoelectric effect on the absorption spectra arises from the E1-M1interference process through the hybridization between the 4p and 3d states inthe noncentrosymmetry environment of Fe atoms. We perform a microscopiccalculation of the spectra on a cluster model of FeO_6 consisting of anoctahedron of O atoms and an Fe atom displaced from the center with reasonablevalues for Coulomb interaction and hybridization. We obtain the magnetoelectricspectra, which depend on the direction of magnetization, as a function ofphoton energy in the optical region 1.0-2.5 eV, in agreement with theexperiment.
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