Strong-disorder paramagnetic-ferromagnetic fixed point in the square-lattice ±j Ising model

Abstract

We consider the random-bond ±J Ising model on a square lattice as a function of the temperature T and of the disorder parameter p (p=1 corresponds to the pure Ising model). We investigate the critical behavior along the paramagnetic-ferromagnetic transition line at low temperatures, below the temperature of the multicritical Nishimori point at T *=0. 9527(1), p *=0.89083(3). We present finite-size scaling analyses of Monte Carlo results at two temperature values, T≈0.645 and T=0.5. The results show that the paramagnetic-ferromagnetic transition line is reentrant for T T *. Our results for the critical exponents are consistent with the hyperscaling relation 2β/ν-η=d-2=0. © 2009 Springer Science+Business Media, LLC.