Itinerant Ferromagnetism for Mixed Valence Systems

We investigate the Periodic Anderson model in the regime of itinerant ferromagnetism. We compare Quantum Monte Carlo (QMC) results with results obtained using the Gutzwiller approximation (GA). As expected, the energy of the paramagnetic state is overestimated by the GA in comparison with QMC results; however, the partially saturated ferromagnetic (FM) state energies obtained by both methods are surprisingly similar. While the GA gives the ferromagnetic instability too easily, its results for the FM ground state, once its existence is confirmed by more dependable methods, can be used for further examination. This thesis is confirmed by a direct comparison of the mean values of the occupation numbers n k obtained using both methods.