Barkhausen noise and critical scaling in the demagnetization curve

The demagnetization curve, or initial magnetization curve, is studied by examining the embedded Barkhausen noise using the nonequilibrium, zero temperature random-field Ising model. The demagnetization curve is found to reflect the critical point seen as the system's disorder is changed. Critical scaling is found for avalanche sizes and the size and number of spanning avalanches. The critical exponents are derived from those related to subloops. Finally, the behavior in the presence of long range demagnetizing fields is discussed. Results are presented for simulations of up to one million spins.