Hybridization-mediated anisotropic coupling and excitation behavior in cerium monopnictides

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Abstract
The neutron scattering measurements of Rossat‐Mignod et al. on CeBi in the type I antiferromagnetic phase give unusual excitation behavior. The dispersion is anisotropic, being very flat for q∥k (the propagation vector of the structure), and showing a minimum at the zone boundary for q⊥k. Previously, the equilibrium behavior of CeBi has been explained using an interionic interaction arising from band‐f electron hybridization (Coqblin–Schrieffer interaction) as mediated by the band electrons. The resulting interaction is very anisotropic, giving strong coupling within planes, with a much weaker coupling between planes transverse to a saturated moment. Using the same theory, we find that calculations of the excitation spectrum in the RPA at T=0 for a set of parameters giving equilibrium behavior similar to experiment, give results that compare well with the experimental excitation behavior of CeBi. The dispersionless behavior for q∥k and the minimum in energy at the zone boundary for q⊥k are both reproduced by our theory.