The role of the spin-orbit coupling strength in the MO effects of magnetic insulators

It is currently admitted that the spin-orbit (SO) couplings play a determinant role in the origin of the magneto-optical (MO) properties of magnetic materials. It is unambiguously confirmed that the role of SO coupling of the excited configuration is very weak and that the SO coupling of the ground configuration has a great influence on the MO properties. Furthermore, the symmetry of the magnetic ion environment is a crucial factor. However, contrary to the theoretical results for the Kerr rotation of the transition metals Fe, Ni, Co and of MnBi, the Faraday rotation is not a linear function of the SO coupling strength of the ground configuration.