Ferromagnetism in Hubbard models with nearest-neighbor Coulomb repulsion

We propose a mechanism which leads to ferromagnetism in an extended Hubbard model on the one-dimensional trestle lattice. For this model, we show that the ferromagnetic ground state is stabilized in the quarter filling case through a third-order electron exchange process around a triangle when both on-site repulsive interaction and nearest-neighbor one are much larger than the hopping terms. Numerical calculations give the evidence that the ground state is ferromagnetic not only in the quarter filling case but also away from quarter-filling