Sinusoidal and Helical Structures in Tiny-Moment Magnets

Abstract

The crossover between itinerant-electron magnetism and local-moment magnetism is investigated using the Hubbard moderson model.Intersite spin fluctuations are considered by the 1/d-expansion method, with d being the spatial dimensionality. When there is substantial nesting of the Fermi surface, the staggered susceptibility shows a Curie-Weiss-like temperature dependence.This Curie-Weiss law is of leading order in 1/d or O [ (1/d)⁰ ].When the Néel temperature T_N is so low that T_N << T_K, with T_K being the local Kondo temperature, ordered magnetic moments are tiny.The ratio of the specific heat jump to the totalspecific heat at T_N is approximately proportional to the ratio of the nested area of the Fermi surfaceto the total Fermi surface.When there is strong quenching of magnetic moments by local quantum spin fluctuationsand nesting of the Fermi surface is substantial enough, a sinusoidal magnetic structure stabilizes.Otherwise, a helical magnetic structure stabilizes.