Interface Depinning, Self-Organized Criticality, and the Barkhausen Effect

We report measurements of magnetic avalanches in a Fe-Ni-Co alloy. The distribution of avalanche sizes is given by $P\left(A\right)\propto A^{-\alpha }\exp \left({-A/A}_0\right)$, with $\alpha =1.33\mathrm{}\pm 0.10$. The role of demagnetizing effects in the avalanche statistics is demonstrated. We analyze a simple model of interface growth and find a power law distribution of avalanche sizes over a wide range of parameters when an infinite-range demagnetization field is included. The exponents agree with those found at the critical field in the absence of demagnetization effects.