Ferromagnetism in a Realistic Two Band Model: A Slave Boson Study

Using a slave boson representation of multi band Hubbard models, we investigate a two band model relevant to layered perovskites in the vicinity of half filling. Beside the strong influence of the Hundʹs rule coupling, we obtain that the phase diagram separates into two regions: a weak to moderate coupling region where the effective mass is weakly renormalized, and a strong coupling regime where it is strongly renormalized. The transition between these two regimes is very sharp. It takes place in a (vanishingly) small domain. A ferromagnetic instability in only found in the strongly correlated regime, and is triggered by the Hundʹs rule coupling. The results are compared to La doped layered ruthenates.