Dynamical Correlated-Effective-Field Approximation. II

Abstract

The dynamical correlated-effective-field approximation (CEFA) developed by the present author is extended to the helical spin structure specified by a general wave vector Q. The advantage of the dynamical CEFA is that it can correctly take into account the single-ion energy term and the term of sin (Q·R_ij)(S_i^ζS_j^ξ−S_i^ξS_j^ζ) characteristic to the helical spin structure, where ζ and ξ denote the rotating coordinate axis in the plane of the spin rotation. As an example the approximation is applied to the isotropic Heisenberg system, and the Néel temperature and the magnetization are calculated for the helical spin structures in the hexagonal lattice.