Second harmonic generation in a polar ferrimagnet GaFeO3
arXiv:1007.1856 · doi:10.1103/PhysRevB.82.024424
Abstract
We have studied second harmonic generation (SHG) in a polar ferrimagnet GaFeO_3, employing a FeO_6 cluster model in which the Fe atom is slightly shifted from the center of the octahedron. The electric-dipole transition could take place between the 3d states through the effective hybridization of the 4p states with the 3d states, due to the breaking of the space-inversion symmetry. In the third-order perturbation with H_{int} = -(j.A)/c, we calculate the probability per unit time, I_{ηaa}, for the process that two photons are absorbed with polarization parallel to the axis and one photon is emitted with polarization parallel to the η(=a,b,c) axis. The calculated SHG intensities consist of several peaks as a function of two-photon energy in agreement with the experiments. It is found that the corresponding amplitude S_{aaa} at each Fe site changes its sign while S_{baa} remains the same with the reversal of the direction of the local magnetic moment. This implies that I_{aaa} would disappear while I_{baa} would survive in the paramagnetic phase in accordance with the experiment.
17 pages, 4 figures, to be published in Phys. Rev. B