Universality and size effects in the Barkhausen noise

We show that the Barkhausen avalanches exhibit power law distributions and scaling exponents belonging to two distinct universality classes. We explain these results in terms of the critical behavior of the domain wall at the depinning transition, with exponents set by the long-range dipolar interactions arising from local magnetostatic fields, and by the elastic curvature of the wall. We are also able to predict the precise dependence of the cutoff on the demagnetizing factor k due to sample size. These predictions are experimentally confirmed on three samples (two polycrystalline 6.5 wt % Si-Fe and an amorphous Fe21Co64B15 under applied tensile stress) which are progressively cut in order to increase k. All these results allow us to link the material microstructure and the sample geometry to the macroscopic noise properties