Crackling noise and complexity in natural systems

Gianfranco Durin

Istituto Nazionale di Ricerca Metrologica (I.N.Ri.M), Torino, Italy

Is there any relation between a devastating earthquake, a snow avalanche, some drops of water in a sponge, or a ferromagnet along an hysteresis loop? Despite huge differences, all these natural systems respond to external perturbations by a burst of events on a broad range of sizes. This random response is commonly termed as 'crackling noise', and represents a common feature of many complex systems. After a general introduction of the main features of this noise, we aim to present the most recent results in the particular crackling noise produced in soft magnetic materials, known as Barkhausen noise. Many of the theoretical and experimental results obtained in ferromagnets can in fact be applied with success to the study of other complex systems. This helps us to understand complexity within a more general theoretical framework, and focus the role of criticality and universality to set the noise properties.