Theory of Itinerant Ferromagnets Exhibiting Localized-Moment Behavior above the Curie Point

Abstract

By using a functional integral formulation of the theory of itinerant ferromagnets above the Curie point, we show that for strong Coulomb interaction $U$, there are localized moments exhibiting a characteristic Curie-law susceptibility with the correct free spin-\textonehalf{} limiting value of the Curie constant. For weak $U$ the same formulation gives a Pauli-like susceptibility, again with the proper limit, while for intermediate values the theory gives a smooth interpolation between the extreme cases.