  Many systems crackle, from earthquakes and financial market to Barkhausen
effect in ferromagnetic materials. Despite the diversity in essence, the noise
emitted in these dynamical systems consists of avalanche-like events with broad
range of sizes and durations, characterized by power-law avalanche
distributions and typical average avalanche shape that are signatures dependent
on the universality class of the underlying dynamics. Here we focus on the
crackling noise in ferromagnets and scrutinize the traditional statistics of
Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films
having different thicknesses. We show how scaling exponents and average shape
of the avalanches evolve with the structural character of the materials and
film thickness. We find quantitative agreement between experiment and
theoretical predictions of models for the magnetic domain wall dynamics, and
then elucidate the universality classes of Barkhausen avalanches in
ferromagnetic films. Thereby, we observe for the first time the dimensional
crossover in the domain wall dynamics, and the outcomes of the interplay
between system dimensionality and range of interactions governing the domain
wall dynamics on Barkhausen avalanches.
