Critical Behavior of the Three-Dimensional Dilute Ising Antiferromagnet in a Field

We report results of large Monte Carlo simulations of an experimentally realizable random-field system: the three-dimensional dilute Ising antiferromagnetic in a field. We find that the correlation time diverges dramatically as T→Tc; the results are consistent with a proposed new type of activated dynamic scaling. The transition appears to be continuous, with effective critical exponents η=0.5±0.1 and ̃ \~η=-1.0±0.3 for strong fields, away from the weak-field regime where crossover effects distort exponent estimates. These strong-field exponents satisfy recently derived inequalities.