ITINERANT FERROMAGNETISM IN NICKEL

To study the origin of the ferromagnetism in metallic nickel, triply-degenerate bands with 0.6 hole per site are treated in the Gutzwiller procedure, where experimentally deduced values for the on-site effective interaction energies are used. We adopt the mechanism that the Hund's-rule coupling effect combined with the hole migration process works for alighning their spin moments ferromagnetically. Owing to the screening effect of conduction electrons, the energy of the triplet configuration of the d(8) polar state is reduced to be buried in the d-bands. So the triplet state can be realized more frequency than the singlets. As a result, it is found, the itinerant ferromegnetism in nickel originates from the hopping process which involves the polarization. In the paramagnetic stste, this process is restricted more by the intraatomic correlation effect than in the ferromagnetic state. The condition requisit for realizing the ferromagnetic ground state is shown. Given also are the band-width narrowing factor and the weight of doubly occupied sites for the ferromagnetic ground state.