Light scattering by the mixed antiferromagnetic-paramagnetic state of FeCl2

Abstract

When crystals of Fe${\mathrm{Cl}}_2$ in magnetic fields along [111] are in a mixed antiferromagnetic-paramagnetic state they are found to scatter light strongly. Furthermore, the scattering is markedly different for the two senses of circular polarization producing an apparent dichroism. The scattering appears to be a general property of such transparent metamagnets, and constitutes a useful means of determining the mixed-phase region of the phase diagram. On the other hand, the apparent dichroism is clearly not a general property. Under some circumstances its use to explore the Fe${\mathrm{Cl}}_2$ phase diagram could be deceptive. An explanation is offered in terms of the refractive indices of the two states.