History-induced critical behavior in disordered systems

Barkhausen noise as found in magnets is studied both with and without long-range (LR) demagnetizing fields using the nonequilibrium, zero-temperature random-field Ising model. Two distinct subloop behaviors arise and are shown to qualitatively agree with experiments on thin film magnets and soft ferromagnets. With LR fields present subloops resemble a self-organized critical system, while their absence results in subloops that reflect the critical point seen in the saturation loop as the system disorder is changed. In the former case, power law distributions of noise appear in subloops, while in the latter case history-induced critical scaling is studied in avalanche size distributions and their second moments as well as spin-flip correlation functions.