WEAK VERSUS STRONG UNIVERSALITY IN THE 2-DIMENSIONAL RANDOM-BOND ISING FERROMAGNET

We address the issue of universality in two-dimensional disordered Isi ng systems, by considering long, finite-width strips of ferromagnetic Ising spins with randomly distributed couplings. We calculate the free energy and spin-spin correlation functions (from which averaged corre lation lengths, xi(av), are computed) by transfer-matrix methods. An a nsatz for the size dependence of logarithmic corrections to xi(av) is proposed. Data for both random-bond and site-diluted systems show that purr system behavior (with nu=1) is recovered if these corrections ar e incorporated, discarding the weak-universality scenario.