Avalanches, Barkhausen Noise, and Plain Old Criticality

We explain Barkhausen noise in magnetic systems in terms of avalanches of domains near a plain old critical point in the hysteretic zero-temperature random-field Ising model. The avalanche size distribution has a universal scaling function, making nontrivial predictions of the shape of the distribution up to 50% above the critical point, where two decades of scaling are still observed. We simulate systems with up to 1000^3 domains, extract critical exponents in 2, 3, 4, and 5 dimensions, compare with our 2D and 6- predictions, and compare to a variety of experiments.