Inelastic neutron scattering study of Ni-substituted Ce_0.5Fe₄Sb₁₂ skutterudite compounds

An inelastic neutron scattering study of the filled and partially-filled skutterudite compounds RFe₄Sb₁₂ and R_0.5Fe_2.75Ni_1.25Sb₁₂ (where R = Ce and La) was carried out to understand the nature of the spin dynamics. Strong magnetic scattering was observed in Ce_0.5Fe_2.75Ni_1.25Sb₁₂ at ~ 5 meV. The integrated intensity of this peak does not follow the Ce³⁺ form factor, but exhibits a maximum at a momentum transfer (|Q|) of 2 Å⁻¹. We attribute this feature to a Ce³⁺ crystal field excitation in the presence of magnetic exchange interactions. This picture is supported by thermodynamic and magnetic properties. Finally, we confirm the presence of a spin gap in CeFe₄Sb₁₂ suggested by our previous work.