Impurity Effects on Two-Dimensional Anisotropic Heisenberg Antiferromagnets

Abstract

We study magnetic behavior of a completely random dilute S=1/2 anisotropic Heisenberg antiferromagnet on the two-dimensional square lattice by using the coherent potential approximation. In the anisotropic Heisenberg model, the xy-anisotropy defined by J_p^(z)/J_p^(xy) is enhanced with increasing nonmagnetic impurities, where J_p^(z) and J_p^(xy) are the z and xy components of the coherent exchange constant, respectively. On the other hand, the isotropic Heisenberg model retains the isotropic nature for any impurity concentration. The critical concentration at the percolation threshold is obtained. The Néel temperature and the magnitude of the coherent exchange constant are calculated as a function of the impurity concentration.