Universality of the ratio of the critical amplitudes of the magnetic susceptibility in a two-dimensional Ising model with nonmagnetic impurities

The behavior of the magnetic susceptibility of a two-dimensional Ising mode l with nonmagnetic impurities is investigated numerically. A new method for determining the critical amplitudes and critical temperature is developed. The results of a numerical investigation of the ratio of the critical ampl itudes of the magnetic susceptibility are presented. It is shown that the r atio of the critical amplitudes is universal right up to impurity concentra tions q less than or equal to 0.25 (the percolation point of a square latti ce is q(c) = 0.407254). The behavior of the effective critical exponent gam ma(q) of the magnetic susceptibility is discussed. Apparently, a transition from Ising-type universal behavior to percolation behavior should occur in a quite narrow concentration range near the percolation point of the latti ce. (C) 2000 MAIK "Nauka / Interperiodica".