FERRIMAGNETIC LONG-RANGE ORDER OF THE HUBBARD-MODEL

In this paper, we show rigorously that there exists the ferrimagnetic long-range order in the ground state of the positive-U Hubbard model a t half filling on some bipartite lattices. When N-A > N-B (N-A and N-B are the total site numbers of two sublattices A and B), except for th e ferromagnetism which was found by Lieb [Phys. Rev, Lett. 62, 1201 (1 989)], there also exists the antiferromagnetic long-range order in the ground state. This result only requires U > O and is independent of t he dimension of the lattices.