Second harmonic generation in a polar ferrimagnet GaFeO3

TL;DR

This paper investigates second harmonic generation in polar ferrimagnet GaFeO3 using a cluster model, revealing how magnetic reversal affects SHG intensities and aligning with experimental observations.

Contribution

It introduces a FeO6 cluster model to explain SHG in GaFeO3, highlighting the role of symmetry breaking and magnetic reversal effects on SHG amplitudes.

Findings

SHG intensities show multiple peaks matching experiments.

Amplitude S_{aaa} changes sign with magnetic reversal.

I_{aaa} disappears in the paramagnetic phase.

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_{\eta aa}, for the process that two photons are absorbed with polarization parallel to the $a$ axis and one photon is emitted with polarization parallel to the \eta (=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.