NUMERICAL-SIMULATION OF THE CRITICAL-DYNAMICS OF DISORDERED 2D ISING SYSTEMS

Critical relaxation of the magnetization has been studied by numerical simulation in the 2D Ising model with nonmagnetic impurity atoms froz en in lattice sites. A square lattice with dimensions of 400(2) was st udied at spin concentrations p = 1.0, 0.95, 0.9, 0.85, 0.8, 0.75, and 0.7. The dynamic critical exponent z was determined by the Monte Carlo method and the dynamic renormalization-group method. The following va lues were found for z(p): z(1) = 2.24 +/- 0.07, z(0.95) = 2.24 +/- 0.0 6, z(0.9) = 2.24 +/- 0.06, z(0.85) = 2.38 +/- 0.05, z(0.8) = 2.51 +/- 0.06, z(0.75) = 2.66 +/- 0.07, and z(0.7) = 2.88 +/- 0.06. A singular scaling of the exponent was found: z = A' .\ln(p - p(c))\ + B' with th e constants A' = 0.56 +/- 0.07 and B' = 1.62 +/- 0.07.