Magnetic formfactor and dynamic magnetic susceptibility within DMFT for $\alpha - \gamma$ transition in Cerium and $\delta$- Plutonium

Using LDA+DMFT we study the magnetic properties of the isostructural volume collapse transition between $\alpha$ and $\gamma$ Cerium. We compute the magnetic formfactor F(q), and show that it is very close to free ion behavior in both the local moment $\gamma$ phase as well as the more itinerant $\alpha$ phase, in excellent agreement with neutron scattering experiments. In sharp contrast, the dynamic local magnetic susceptibility $\chi_{loc}(\omega)$ of the two phases is strikingly different. In the $\gamma$ phase, the spectra is dominated by the sharp low energy peak due to local moment formation,whereas in the $\alpha$ phase we see two broad peaks, the first due to Kondo screening and the second due to Hund's coupling. We also calculate the magnetic spectral function $S(q,\omega)$ where we achieve excellent agreement with experiment. This shows that hybridization plays a central role in the $\alpha$ - $\gamma$ transition in cerium, and that the 4f electrons are strongly correlated in both phases. We also study the magnetic properties of $\delta$-Plutonium where our results give us important clues about the magnetic excitations of the system.