Two-Dimensional Dilute Ising Models: Critical Behavior near Defect Lines

We consider two-dimensional Ising models with randomly distributed ferromagnetic bonds and study the local critical behavior at defect lines by extensive Monte Carlo simulations. Both for ladder- and chain-type defects, nonuniversal critical behavior is observed: the critical exponent of the defect magnetization is found to be a continuous function of the strength of the defect coupling. Analyzing corresponding stability conditions, we obtain new evidence that the critical exponent of the bulk correlation length of the random Ising model does not depend on dilution, i.e., =1.