Spin correlations for a classical linear magnet with exchange and single-site anisotropy energies

Abstract

Spin-correlation functions are calculated for the exactly soluble model of a one-dimensional array of classical spins interacting via a Heisenberg exchange and a single-site anisotropy of the form B(S^z)². Analytic results are obtained in the limit low temperatures, and numerical results presented for general temperatures. For B positive, the spins align in the xy plane at low temperatures, with the inverse correlation length k_z tending to a value proportional to B¹2/. For B negative, alignment occurs along the z direction at low temperatures. The divergence of the susceptibility chi _z is of the form exp (constant/temperature).