Correlations of triggering noise in driven magnetic clusters

We show that the temporal fluctuations ΔH(t) of the threshold driving field H(t), which triggers an avalanche in slowly driven disordered ferromagnets with many domains, exhibit long-range correlations in space and time. The probability distribution of the distance between successive avalanches as well as the distribution of trapping times of domain wall at a given point in space have fractal properties with the universal scaling exponents. We show how these correlations are related to the scaling behavior of Barkhausen avalanches occurring by magnetization reversal. We also suggest a transport equation which takes into account the observed noise correlations.