Mott transition near the ferromagnetic state

We consider the Hubbard model, either in a magnetic field (model I) or with a general nearest-neighbor interaction (model II). For these models we determine criteria for the instability of the fully polarized ferromagnet. We show that the ground state below the instability contains an exactly soluble Mott transition. The transition occurs at a critical interaction ${\mathit{U}}_{\mathit{c}}$, at which perturbation theory breaks down. Extended metallic states are found for U<${\mathit{U}}_{\mathit{c}}$, insulating bound states for U>${\mathit{U}}_{\mathit{c}}$. Details of the transition strongly depend on dimension.