THEORY OF MAGNETISM AND METAL- NONMETAL TRANSITION

Abstract

The unique feature of the transition metals is the presence of somewhat tightly bound electrons in d-bands and more mobile electrons in the s band. The magnetism of the transition metals is presunably associated with the d banns. However the electrons in the s band are magnetically polarised due to the magnetism associated with the d electrons.. Therefore for the discussion of the magnetic properties of the transition metals the s and d bands should be considered simultaneously. At this early stage of the theory, it is excusable if we ignore the fivefold degeneracy of the d-bands. ' Accordingly (re limit our study to a single nondegenerate d band described by the tight binding form. and a nearly free electron like s band. Anderson' s -theory of dilute allays. of the transition metals is able to explain the occurrence of the localized magnetic moment on transition metal impurities dissolved in a nonmagnetic metal. In .Anderson's model' the band states of the host metal are treated as independent quasi-particles. The impurity is introduced as. an extra-localized orbital which interacts with the band states by a hybrid matrix element. All two-body Coulomb interactions are neglected except the -Coulomb interaction between the opposite spin electrons on , the localized orbital. As an extension of this model, a transition metal can be imagined as a system having a localized d orbital at each lattice site.