THE 2-DIMENSIONAL RANDOM BOND ISING-MODEL AT CRITICALITY - A MONTE-CARLO STUDY

The two-dimensional random bond Ising model with two distinct ferromagnetic nearest-neighbour couplings, J and J', distributed randomly over the lattice with concentration 112 is studied for various ratios J'N at criticality. The critical temperature is exactly known from self-duality. The size-dependent specific heat shows a crossover from the perfect Ising to the randomnessdominated critical behaviour of doubly logarithmic form. In the latter region, our estimates for the critical exponents of the sizedependent magnetization and susceptibility are in very good agreement with analytic results suggesting. © 1990 The Japan Society of Applied Physics.