Magnetic flux propagation in 3%Si-Fe single crystals

The magnetization process has been investigated by means of a space-time analysis of the Barkhausen signal associated with domain-wall motion. The microscopic phenomenology of flux propagation has been elucidated from local measurements and suitable time averaging, performed as a function of actual permeability μ of the sample. Magnetization reversals, whose nucleation corresponds to a given cross-section, are propagated along the sample in a diffusive fashion, and their final size appears to be controlled essentially by the demagnetizing field. In particular, the average reversal amplitude is found to decay with distance from the nucleation site, according to a μ^1/2 law. A general stochastic equation for the Barkhausen effect, describing the behavior in space and time of the magnetic flux derivative associated with domain-wall motion, is presented. An analytical expression for the average Barkhausen avalanche is derived from which the dependence on time, distance from nucleation cross-section, and permeability can be predicted accurately