NONRECIPROCAL OPTICAL-ROTATION IN CUBIC ANTIFERROMAGNETS

A recent multipole theory of light propagation in non-magnetic crystals is extended to non-absorbing magnetic crystals to the order of electric octopoles and magnetic quadrupoles. The theory distinguishes contributions of property tensors of different multipole order, each of which has both a time-symmetric and time-antisymmetric part. Within the electric octopole-magnetic quadrupole approximation there are six such contributions; five of which are associated with known optical effects. The sixth contains time-antisymmetric tensors of electric octopole-magnetic quadrupole order and is shown to describe a novel non-reciprocal (or Faraday-type) rotation which may occur even in the absence of net magnetization. For propagation along a body diagonal in certain cubic antiferromagnets this rotation is not masked by other effects. The related circular birefringence is comparable in magnitude to the linear birefringence that has been observed in some cubic systems, which is due to time-symmetric tensors of the same multipole order.