On the ferromagnetism of high-spin states

The possibility of ferromagnetic ordering in a generalized Hubbard model and with infinite Hubbard energy is studied. The phase diagram of the ferromagnetism existence as a function of the degree of filling of d-shell is constructed. The calculation of the critical density points, between which ferromagnetic instability arises, was performed in a model of the semi-elliptic primer density of state. On the base of the deduced criterion, the ferromagnetic instability region was observed inside each integer interval of variation of the d-electron density. The separate region appearance of the ferromagnetic instability is due to the possibility of the change of the exchange scattering amplitude sign when the Fermi excitation energy is increased. (C) 2002 Elsevier Science B.V. All rights reserved.