On the possibility of direct measurement of the magnetic field-induced phase transition in hematite by means of magnetooptical method

Abstract

It is shown that a rotation ϱ and a deformation κ of the optical indicatrix appear during the transverse magnetic field-induced phase transition in hematite. Analytic expressions for ϱ and κ are deduced from the magnetization-dependent electromagnetic energy in the crystal. It is shown that during the phase transition, induced by increasing the temperature, the electromagnetic energy in the crystal. It is shown that during the phase transition, induced by increasing the temperature, the antiferromagnetic vector L = M 1 - M 2 is rotating from the three-fold C 3 axis toward the basal plane, which implies that the main axis of the optical indicatrix is not aligned in a general case with the magnetic field or the crystallographic axis although the magnetic moment ( M 1 + M 2) is always parallel to the field. The linear magnetic birefringence is very sensitive to the magnetic phase in hematite, as described in previous experimental work, but the present analysis shows that a direct determination of the transverse field-induced phase transition can be obtained in hematite, by means of a magnetooptical method, only when large and non-uniform rotation (up to ninety degrees) and variation of the shape of the indicatrix are taken into account.