INTERFERENCE OF 2ND-HARMONICS DUE TO ELECTRIC AND MAGNETIC DIPOLES INANTIFERROMAGNETIC CR2O3

The second-harmonic (SH) spectra arising from magnetic- and electric-d ipole contributions and the interference of these two channels are ana lyzed for antiferromagnetic Cr2O3. A microscopic model which corn; pri ses boundary conditions and local-field corrections for electromagneti c waves is introduced far the nonlinear nonreciprocal optical response s. Effects of cross relaxation between the different Cr3+ 3d levels ar e also taken into account. Among these dissipative processes, the loca l-field correction for the magnetic field seems to be the most importa nt. The origin of this correction is found to come from the presence o f a coupling of orbital angular momenta of two magnetic Cr3+ ions whic h makes possible the excitation transfer between them. Only through th e inclusion of this effect are the phases of the magnetic and electric susceptibilities appreciably different from each other, leading thus to the interference effect of the two channels in agreement with exper imental observations.