  We propose a new mechanism which can lead to ferromagnetism in Hubbard models
containing triangles with different on-site energies. It is based on an
effective Hamiltonian that we derive in the strong coupling limit. Considering
a one-dimensional realization of the model, we show that in the quarter-filled,
insulating case the ground-state is actually ferromagnetic in a very large
parameter range going from Tasaki's flat-band limit to the strong coupling
limit of the effective Hamiltonian. This result has been obtained using a
variety of analytical and numerical techniques. Finally, the same results are
shown to apply away from quarter-filling, in the metallic case.
