Effect of Electron Correlation in a Narrow Band

Gutzwiller's variational method is used to investigate the Pauli spin susceptibility and the spin waves in a degenerate narrow band. It is found that the susceptibility tends to become negative for sufficiently strong correlation if the number of holes is small and if large density of states occurs at the top of the band near the Fermi energy. For Ni, a numerical analysis is performed using the simplified density-of-states curve proposed by Kanamori. The conditions for the occurrence of ferromagnetic Ni agree with those obtained by Kanamori. The energies of spin waves in ferromagnetic metals are obtained by examining the normal modes of spin excitations in the correlated ground state. Only the improvement upon the random-phase-approximation (RPA) result which is due to correlated electron hoppings is considered. In the long-wavelength limit, the coefficient $C$ in the expression $\hslash {\omega }_q=C{q}^{ 2}$ is reduced from the RPA value by this correlation effect, in agreement with the predictions of other theories.