We present an exact diagonalization study of the half-filled Hubbard model on bipartite quasi-one-dimensional lattices. In particular, we emphasize the dependence of the ferrimagnetic ground state properties, and its associated magnetic excitations, on the Coulomb repulsion U.

The various types of magnetizations of a four-sublattice mixed-spin Heisenberg ferrimagnetic system are investigated with the help of the double-time temperature-dependent Green’s function technique. One obtains the first-order phase transitions from ferrimagnetic states to ferrimagnetic or...