Localization and correlation effects in itinerant ferromagnets

The effects of disorder, in particular of localization, have been studied in the vicinity of the ferromagnetic transition by making use of a generalized N-orbital model within a 1/N expansion technique. Fermi-liquid behavior is obtained in the N→∞ limit with two separate diffusion constants for spin- and charge-density fluctuations. The spin-diffusion constant associated with spin fluctuations and Stoner excitations is found to acquire a localization correction. While the dc conductivity in the ferromagnetic phase also acquires the same localization correction, the spin-wave stiffness constant does not. This indicates the system can exist in an insulating state and exhibit long-range magnetic order—a ferromagnetic Anderson insulating state.