Electric dipole effects in magnetic crystals

A consistent multipole theory which is able to describe optical phenomena to any selected multipole order is applied to nonabsorbing magnetic crystals in the electric dipole approximation. Magnetic effects are shown to depend on an antisymmetric polar tensor of rank 2, and the magnetic point groups for which such a tensor may exist are listed. In addition to yielding certain known results the theory also predicts a new effect, namely that when a monochromatic plane light wave propagates along a crystallographic axis perpendicular to the magnetization in a ferromagnet, the Poynting vector of the so-called extraordinary ray does not coincide with the wave normal. An estimate of the angular deviation in EuSe suggests that the effect should be observable.