Nonreciprocal reflection from semi-infinite antiferromagnets

We discuss the possibility of asymmetry in the reflection coefficient of magnetic materials as the angle of incidence is reversed. A detailed balance argument is presented which shows the possibility for nonreciprocal reflectance without nonreciprocal absorption mechanisms. Numerical calculations of the reflectance of polarized light from a nonabsorbing antiferromagnet illustrate this nonreciprocity. For ${\mathrm{MnF}}_2$, at frequencies in the 200–300-GHz range, the reflectance is nonreciprocal when the illuminating wave is circularly polarized. For applied magnetic fields of less than approximately 200 G, linearly polarized incident light also exhibits nonreciprocal reflection. We find the degree of nonreciprocity depends strongly on the frequency of the illuminating wave.