Nonreciprocal phase behavior in reflection of electromagnetic waves from magnetic materials

Abstract

Most experimental and theoretical treatments of reflection of electromagnetic radiation from magnetic materials have concentrated on the intensity of the reflected and transmitted waves. We point out that the behavior of the phase of these waves can be quite different from the intensity, and that it can have direct experimental consequences. In particular, the reflected intensity from a magnetic material with low damping in the Voigt geometry is reciprocal, i.e., the intensity is the same when the reflected and incident waves are interchanged. In contrast, the phase of the reflected wave is strongly nonreciprocal. This nonreciprocity in phase produces a nonreciprocal intensity in a structure where a dielectric film is placed on an antiferromagnet. We explore the general properties of the phase and amplitude of reflected and transmitted waves in a variety of geometries using the antiferromagnet ${\mathrm{FeF}}_{2}$ as an example. General thermodynamic arguments are used to support some of the specific results.