Barkhausen noise and size effects in magnetic microstructures

The properties of the Barkhausen noise in a series of permalloy squares have been measured with a magneto-optical hysteresigraph. The magnetic structures have been litographically defined in a permalloy film (thickness 160 nm) as squares having a size from 20 to 320 mum. The statistical distributions of the most significant parameters of the Barkhausen jumps have been extracted from the original data. At variance with respect to bulk and thin films, the jump amplitude distribution does not follow a well-defined power-law behavior. This observation is explained in terms of a transition between a discrete magnetization regime typical of small magnetic structures and the more usual regime observed in extended samples. (C) 2001 American Institute of Physics.