BWO quasi-optical spectroscopy of Cr2O3 : Gyrotropic birefringence at antiferromagnetic resonance

We have studied a propagation of the electromagnetic waves through the magnetoelectric (ME) crystal Cr 2 O 3 by means of the quasi-optical backward-wave-oscillator (BWO) technique in the frequencies v = 3.2 - 13 cm −1 at temperature T = 3.4 - 300 K. A noticeable rotation of an optical indicatrix α(v) and increase of an ellipticity ρH(ν) have been revealed near antiferromagnetic resonance (AFMR) which present a manifestation of a gyrotropic birefringence. Theoretical calculations and computer simulations made possible to describe the observed spectra, taking into account the resonance behavior magnetic, magnetoelectric and electric susceptibilities, and to determine corresponding parameters, in particular, AFMR mode contribution to the static magnetoelectric susceptibility.