Magnetoelectric and second-harmonic spectra in antiferromagnetic Cr2O3

We present a microscopic model to understand the magnetoelectric and second-harmonic spectra of Cr2O3 and the interference effect between the magnetic (chi(m)) and electric (chi(e)) second-order optical polarizations. The spin-orbit interaction and the crystalline fields of correct symmetry around the Cr3+ ion, i.e., the axial and twisted crystalline field of C-3 symmetry, are treated as perturbation on the trigonal states of the d(3) system of Cr3+. By these treatments we attempt to describe the observed phenomena associated with the transitions between (4)A(2g) and T-4(2g) states in Cr2O3. It is possible to reproduce the observed spectra of the polarization rotation and ellipticity, and the second-harmonic generation spectra described by the nonlinear susceptibilities chi(m) and chi(e) The estimated theoretical magnitudes of these quantities are in reasonable agreement with the observed magnitudes. [S0163-1829(98)07415-3].