Nonreciprocal Optical Rotation in Antiferromagnets

We consider nonreciprocal optical effects in classical Néel antiferromagnets, where the purely macroscopic electrodynamics does not provide any rotation. The nonzero result appears as a correction linear in the scattering theory parameter $a/\lambda$, atomic distance over wavelength. The recent experiment on C${\mathrm{r}}_2$ ${\mathrm{O}}_3$, where optical nonreciprocity already exists with the macroscopic approach, is also discussed.