Anisotropic excitation behavior from hybridization-mediated exchange in CeBi

Abstract

The excitation spectrum of CeBi in the type-I antiferromagnetic phase, as measured by Rossat-Mignod et al. using neutron scattering, is quite unusual. The excitations with wave vector $\overrightarrow{\mathrm{q}}$ perpendicular to the ferromagnetic (001) planes are dispersionless (with an energy of about 1 THz=48 K); whereas for a wave vector within the (001) plane, a dispersion has been found with a minimum in energy at the zone boundary. The equilibrium behavior of CeBi has been explained previously by Siemann and Cooper using an interionic interaction arising from band-$f$ electron hybridization (Coqblin-Schrieffer interaction) as mediated by band electrons. Using the same theory, calculations of the excitation spectrum are reported in the present paper. These calculations give results that compare well with the experimental excitation behavior on using a set of parameters giving equilibrium behavior similar to experiment.