Neutron-Scattering Study of TmSb: A Model Crystal-Field-Only Metallic Paramagnet

Inelastic-neutron-scattering studies have been carried out on the paramagnetic metallic compound TmSb. The Tm³⁺ ground-state multiplet ³H₆ is split by the octahedral crystal field into six levels Γ₁, Γ₄, Γ₅⁽²⁾, Γ₂, Γ₅⁽¹⁾, Γ₃. Transitions between these levels have been observed and the parameters A₄〈r⁴〉=(6.86±0.10) meV, A₆〈r⁶〉=(0.44±0.04) meV have been deduced. The fourth-order term is consistent with that expected on the basis of a simple nearest-neighbor point-charge model, whereas the sixth-order term is an order of magnitude too large; this is in marked contrast with previous results in PrSb and other praseodymium pnictides and chalcogenides where the effective-point-charge model is quantitatively correct for both terms. It is found that the actual spectra can be reproduced in detail using ordinary crystal-field theory together with a simple approximation to the instrumental-resolution function. Furthermore, no appreciable exchange broadening of the transitions is observed at low temperatures, thus confirming TmSb as a model crystal-field-only metallic paramagnet.