MAGNETOOPTIC EFFECTS IN WEAKLY FERROMAGNETIC RHOMBOHEDRAL ANTIFERROMAGNETS.

Abstract

A study is made of the change in the polarization of light traveling in a direction close to the principal symmetry axis of weakly ferromagnetic rhombohedral antiferromagnets. The contributions of all the complex components of the permittivity tensor are included and the effects of rotation of the major axis of the polarization ellipse and of the ellipticity are also considered. New methods of measurement of magnetooptic constants governing the Faraday and Cotton-Mouton effects are proposed. A method which can be used to determine the fourth-order magnetic anisotropy constant from magnetooptic measurements is described. The calculated results are compared with measurements on FeBO//3 single crystals at T equals 78 K. The contributions of the quadratic and bilinear terms to the Cotton-Mouton effect are determined. Measurements of the magnetic anisotropy constant which governs the deviation of the ferromagnetic component of the sublattice spins out of basal plane are reported.