A Study of Anisotropic Heisenberg Antiferromagnet with S = 1/2 on a Square Lattice by Monte-Carlo Method

Abstract

The two-dimensional (2D) Heisenberg model (J < 0) with anisotropic exchange Δ = 1 — Jx/Jz ≥ 0 and with S = 1/2 is studied by the quantum Monte-Carlo method. Energy, susceptibility, specific heat, spin–spin correlation functions, and correlation radius are calculated. The dependence of the Néel temperature TN/J = 2/ln(11/Δ) on the exchange anisotropy is determined. The static magnetic factor is very slowly decreased for T/J < 0.4. It is assumed to realize topological excitations in the range of these temperatures. The correlation radius of the isotropic Heisenberg model is fitted by the dependence 1/ξ = 2.05T1.0(6)/exp (1.0(4)/T).The temperature behavior of the static structural magnetic factor in La2CuO4 and Er2CuO4 for T > TN is in agreement with the MC calculations.