Quasispin model for itinerant magnetism—effects of short-range order

Abstract

The cluster—Bethe-lattice method has been used to study the short-range-ordered state of an itinerant magnetic system. We assume a local moment on each lattice site, but the moments may point up or down and have long- or short-range order. The electronic structure is solved, and the size of the local moments is determined self-consistently. It is found that the Friedel criterion for local moments in the disordered state is different from the Stoner criterion for ferromagnetic state. The phase transition from the ordered state to the paramagnetic state is, in most cases, described by a transition to the local-moment state with short-range order. In the disordered state the energy bands remain spin split over a large part of the wave-vector space. The wave vectors are complex due to spin disorder, and the electron wave function is a mixture of majority and minority band states.