Directional Dichroism of X-Ray Absorption in a Polar Ferrimagnet GaFeO3

We study the directional dichroic absorption spectra in the x-ray region in a polar ferrimagnet GaFeO3. The directional dichroism on the absorption spectra at the Fe pre-K-edge arises from the E1-E2 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 model of FeO6 with reasonable parameter values for Coulomb interaction and hybridizations. We obtain the difference in the absorption coefficients when the magnetic field is applied parallel and antiparallel to the c axis. The spectra thus obtained have similar shapes to the experimental curves as a function of photon energy in the Fe pre-K-edge region, although they have opposite signs.