Hysteresis and avalanches in disordered systems

Abstract

Rate-independent hysteresis is studied in magnetic systems driven by an external field for which the influence of thermal fluctuations is negligible. In such systems, the hysteresis cycles are not continuous, but rather are composed of a sequence of magnetisation jumps or avalanches between metastable states; the so-called Barkhausen noise. The study of the statistical distribution of such avalanches provides an alternative description to the more common procedure of measuring properties of the loop shape. We focus on four different zero-temperature 3d lattice models: the random field Ising model, the random bond Ising model, the site-diluted Ising model and the random anisotropy Ising model. By defining appropriate local dynamics, we have studied the metastable evolution by numerical simulations. We analyse the avalanche size distribution as a function of the degree of quenched disorder in these systems. For specific amounts of disorder, the distributions exhibit critical behaviour that can be characterised by universal exponents.