Abstract
Many systems crackle, from earthquakes and financial markets 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 fingerprints describing the universality class of the underlying avalanche 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.
Highlights
Crackling noise arises in many systems; when driven slowly, they respond with the emission of a noise consisting of series of sudden avalanche-like events with broad range of sizes and durations[1,2,3,4]
By comparing our experiments with theoretical predictions of models for the domain walls (DW) dynamics, we find that polycrystalline and amorphous films with distinct thicknesses assume values consistent with three well-defined universality classes
The films split into the following classes of materials: (i) Polycrystalline films thicker than 100 nm presenting three-dimensional DW dynamics governed by long-range dipolar interactions; (ii) Amorphous films thicker than 100 nm having three-dimensional magnetic behavior with short-range DW surface tension governing the DW dynamics; (iii) Polycrystalline and amorphous films thinner than 50 nm with a two-dimensional DW dynamics dominated by strong long-range dipolar interactions
Summary
Crackling noise arises in many systems; when driven slowly, they respond with the emission of a noise consisting of series of sudden avalanche-like events with broad range of sizes and durations[1,2,3,4]. The Barkhausen avalanches have been investigated primarily through magneto-optical techniques[32,33,34,35,36,37,38,39,40,41,42] and, just more recently, with the inductive technique[43,44,45,46,47,48,49] These first reliable magneto-optical experiments have shown that the magnetic behavior in thin films typically differs from that found for bulk materials, a characteristic entirely devoted to the dimensionality of the system. The results of this wide statistical treatment of Barkhausen avalanches, besides corroborating the universality classes found for bulk materials, suggest that the two-dimensional DW dynamics is not shared among films in all thickness ranges. Experimental investigations confronted to theoretical predictions and simulations have uncovered that scaling exponents and average shape of Barkhausen avalanches reflect fundamental features
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