Hysteresis and avalanches: phase transitions and critical phenomena in driven disordered systems

We discuss Barkhausen noise in magnetic systems in terms of avalanches near a disorder-induced critical point, using the hysteretic zero-temperature r andom-field Ising model and recent variants. As the disorder is decreased, one finds a transition from smooth hysteresis loops to loops with a sharp j ump in magnetization (corresponding to an infinite avalanche). In a large r egion near the transition point the model exhibits power-law distributions of noise (avalanches), universal behavior and a diverging length scale. Uni versal properties of this critical point are reported that were obtained us ing renormalization group methods and numerical simulations. Connections to other experimental systems such as athermal martensitic phase transitions (with and without 'bursts') and front propagation are also discussed. (C) 2 001 Elsevier Science B.V. All rights reserved.