Dynamical Effects and the Critical Behavior of Random-Field Systems (Invited)

摘要

A variety of phemonena is observed experimentally in random-field (RF) systems realized by the application of an external field to diluted antiferromagnets. At low temperatures, infinitely long hysteric effects are manifested by the history dependence of the final states: long-range order is observed if the field is applied after final states, while domain-states are reached when field-cooled. While no indications for critical fluctuations are detected in 2d systems, scaling behavior, for both the correlation length and the specific-heat, is observed in 3d systems over an intermediate range of temperatures. The related critical properties seem to be well described by the corresponding ones in the 2d pure Ising model. The renormalization-group approach, which yields for the equilibrium critical exponents their values of the pure model in d-2 dimensions, is reviewed. A generalization of the dimensional-reduction approach, which accounts self-consistently for renormalized responses of the RF system, is presented. The dynamical effects are implicitly incorporated through the variation in the critical response between the local and the global regimes, associated with short and long time scales, respectively. In both regimes the lower critical dimension is found to be d = 2 in accordance with stability arguments. The short-time critical behavior indicates a dimensional-reduction by one for the 3d thermal exponents, in agreement with the experimental results. 36 references. (ERA citation 10:007894)