Tetrahedral magnetic cluster embedded in metallic matrix: electron correlation effects

The magnetic properties of itinerant electrons and the effects of the electron-correlations are studied on a tetrahedral cluster surrounded by nonmagnetic metallic atoms in the framework of the Hubbard model. This model takes into account the kinetic energy which describes the electronic hopping between nearest neighbor atoms and the on-site Coulomb repulsion only on the atoms of the tetrahedral cluster. The ground-state energy and the wave function are obtained exactly using the numerical diagonalization method. Results demonstrate that for low electron concentration, the tetrahedral cluster shows antiferromagnetic order due to the fact that the electrons prefer to stay in the host metal to avoid the double occupations. However, when the number of the electrons is large, the tetrahedral cluster exhibits a ferromagnetic ground-state.