Modified Spin-Wave Theory of Quasi-Two-Dimensional Heisenberg Antiferromagnet

Abstract

The thermodynamic properties of quasi-two-dimensional Heisenberg antiferromagnet have been investigated in the framework of the modified spin-wave theory. A set of self-consistent equations is derived for chemical potential µ and two mean-field parameters, characterizing the nearest-neighbor spin correlations. Solving these equations under the condition µ=0, we derive a formula determining the Néel temperature T N as a function of the coupling ratio ε ≡ J ⊥ / J // between the interplane and intraplane exchange couplings. In the region above T N , the self-consistent equations have been solved numerically, to discuss the temperature dependence of the correlation length.