Effect of spin fluctuations on itinerant electron antiferromagnetism

The effect of spin fluctuations on itinerant electron antiferromagnetism is discussed by extending the theory of Moriya and Kawabata for itinerant ferromagnetism. The correction to the Hartree-Fock free energy as a function of the sublattice magnetization is expressed in terms of the transversal dynamical susceptibilities, which are approximated by the modified random phase approximation. Numerical calculations are made for the free electron model with Umklapp processes. It is shown that the contribution from spin fluctuations can be quite important in describing the magnetic properties of itinerant antiferromagnets. The Néel temperature is generally lowered from its Hartree-Fock value and the staggered susceptibility above the Néel temperature shows an approximate Curie-Weiss behavior even when the uniform susceptibility has a weak temperature dependence.