Crystal field effects and the co-operative state I. A primitive theory

Abstract

A primitive theory is developed for treating magnetic substances where exchange interaction is com parable with crystal field effects. The properties primarily considered are the Curie temperature and the saturation magnetization at 0°K ; the possibility of anisotropic exchange effects is considered briefly. Approximate formulae are found for the case where matrix elements of the exchange interaction between two low-lying states only are important. A fuller analysis is given for the special case of two singlet states, and the conditions for a co-operative state are com pared with those for an unsplit doublet.