α-γ transition in cerium: Magnetic form factor and dynamic magnetic susceptibility in dynamical mean-field theory

The nature of the elemental cerium phases, undergoing an isostructural volume collapse transition, cannot be understood using conventional solid-state concepts. Using the combination of density functional theory and dynamical mean-field theory, we study the magnetic properties of both the alpha and the gamma phases. We compute the magnetic form factor and show that it is very close to the free ion behavior in both the local moment gamma phase as well as the more itinerant alpha phase, in agreement with neutron scattering experiments. In sharp contrast, the dynamic local magnetic susceptibility of the two phases is strikingly different. In the gamma phase, the sharp low energy peak due to local moment formation and consequently low Kondo temperature dominates the spectra. In alpha phase two broad peaks can be identified, the first is due to Kondo screening and the second is due to Hund's coupling. This shows that hybridization plays a central role in the alpha-gamma transition in cerium, and that from the point of view of magnetic properties, the 4 f electrons are strongly correlated in both phases.