IMPURITY EFFECTS ON 2-DIMENSIONAL ANISOTROPIC HEISENBERG ANTIFERROMAGNETS

We study magnetic behavior of a completely random dilute S = 1/2 aniso tropic Heisenberg antiferromagnet on the two-dimensional square lattic e by using the coherent potential approximation. In the anisotropic He isenberg model, the xy-anisotropy defined fy J(p)(z)/J(p)(xy) is encha nced with increasing nonmagnetic impurities, where J(p)(z) and J(p)(xy ) are the z and xy components of the coherent exchange constant, respe ctively. On the other hand, the isotropic Heisenberg model retains the isotropic nature for any impurity concentration. The critical concent ration at the percolation threshold is obtained. The Neel temperature and the magnitude of the coherent exchange constant are calculated as a function of the impurity concentration.