Magnetic moment and valence fluctuations in a model for rare earth compounds

Abstract

The ionic model proposed by Jefferson and Stevens (see ibid., vol.9, p.2151 (1976)) for the magnetic properties of rare earth compounds that display intermediate valence-behaviour is studied. The f-electrons of the rare earth ions are described by localised atomic-like configurations which are hybridised with a conduction band. The free energy and susceptibility are calculated perturbationally in powers of the hybridisation matrix element mod V mod to order mod V mod ⁴. When only virtual valence transitions are possible the leading correction to the Curie law susceptibility is due to the Kondo moment flip scattering. An effective interaction between the f- and conduction electrons is derived in this regime which is a generalisation of that given by Coqblin and Schrieffer (1969). The one-electron Green function is also calculated perturbationally and the results indicate that the spectral density has a virtual bound state resonance due to the incoherent scattering of the f-moments similar to that caused by impurity scattering.