Magnetic Form Factor of α -Ce: Towards Understanding the Magnetism of Cerium

A favored interpretation of the γ↔α phase transition in cerium postulates the transformation of the localized $4f$ state in γ-Ce to a weakly correlated itinerant $4f$ band in α-Ce. However, results of high-energy neutron inelastic scattering measurements, presented here, show clearly that the magnetic susceptibility response from α-Ce follows the Ce³⁺ form factor despite the large, 30-fold, increase in its spectral width relative to that in γ-Ce. This observation provides, for the first time, indisputable evidence for the localized character of the $4f$ state in the α phase. The present findings appear consistent with recent calculations combining dynamical mean-field theory with the local density approximation that indicate a strongly correlated $4f$ state in α-Ce. The localized $4f$ state is also fundamental to the Kondo volume collapse theories for the γ↔α phase transition in cerium.