Magnetic Ions in Solids

Abstract

This series of four lectures present in a comprehensive way the energy levels of ions in solids. The first lecture deals with basic concepts of group theory and with the interrelations between group theory and quantum mechanics. The second lecture starts with the consideration of the groups of interest for free atoms and atoms in a homogeneous magnetic field; the concept of a complete set of commuting operators is stressed. The energy levels of atoms are then considered with a perturbational approach making use of both symmetry and quantum mechanical concepts. The third lecture deals with magnetic ions in solids; the concept of crystalline field is introduced. By proper use of symmetry concepts and of the complete set of commuting operators, the various schemes (weak field, intermediate field, strong field) corresponding to the strength of the crystalline interaction are treated. The last lecture deals with the effect of covalent bonding on the energy levels of magnetic ions in crystalline solids; this more comprehensive treatment of ions in crystals illustrates the occurrence of states generally high in energy which produce very strong absorption transitions and that are associated with the phenomenon of charge transfer.