Magnetic instability with increasing hybridization in cerium compounds.

Abstract

A synthesis of a phenomenological theory of orbitally driven magnetic ordering of moderately delocalized light rare-earth systems and ab initio electronic structure calculations has been applied to investigate the change in magnetic behavior on going from CeSb to CeTe, both of which have rocksalt structure with a small decrease in lattice parameter. The hybridization-potential matrix elements and the band energies entering the Anderson-lattice Hamiltonian are obtained from linear-muffin-tin-orbital (LMTO) electronic-structure calculations with the Ce 4f states treated as core states. The position of the Ce 4f energy level relative to the Fermi energy and the intra-atomic Coulomb energy U are obtained by use of a sequence of three total-energy supercell calculations with one out of four Ce sites constrained to ${\mathit{f}}^{\mathit{n}}$ occupation with n=0,1,2, successively. The calculations elucidate the origins, in the electronic structure, of the variation of the f-state resonance width and hybridization potential on going from CeSb to CeTe, and the resultant sensitivity of the hybridization dressing of the crystal-field splitting and the hybridization-induced exchange interactions to chemical environment. The effect of opening up successive angular momentum scattering channels of the ab initio calculated two-ion exchange-interaction matrix on the nature of the magnetic ordering is examined. The calculated magnitude and range dependence of the two-ion exchange interactions changes sharply from CeSb to CeTe, yielding a change in magnetic behavior in qualitative agreement with experiment. The nonlinear hybridization effects on the hybridization dressing of the crystal-field splitting have been examined. These effects, which are associated with the self-consistent determination of both the band states and f states in the presence of band-f hybridization, are found to be small in both systems.