Signature of effective mass in crackling-noise asymmetry

Abstract

C rackling noise is a common feature in many dynamic systems 1-9 , the most familiar instance of which is the sound made by a sheet of paper when crumpled into a ball. Although seemingly random, this noise contains fundamental information about the properties of the system in which it occurs. One potential source of such information lies in the asymmetric shape of noise pulses emitted by a diverse range of noisy systems [8][9][10][11][12] , but the cause of this asymmetry has lacked explanation 1 . Here we show that the leftward asymmetry observed in the Barkhausen effect 2 -the noise generated by the jerky motion of domain walls as they interact with impurities in a soft magnet-is a direct consequence of a magnetic domain wall's negative effective mass. As well as providing a means of determining domain-wall effective mass from a magnet's Barkhausen noise, our work suggests an inertial explanation for the origin of avalanche asymmetries in crackling-noise phenomena more generally.Crackling noise is the response of many physical systems to a slow external driving force, characterized by outbursts of activity (avalanches or pulses) spanning a broad range of sizes, separated by quiescent intervals 1 . In condensed matter, notable examples are the magnetization noise emitted along the hysteresis loop in ferromagnets (that is, the Barkhausen effect 2 ), the noise from magnetic vortices in type-II superconductors 3 , ferroelectric materials 4 and driven ionic crystals 5 . In the context of mechanics, examples are the acoustic emission signal in fracture 6 and plasticity 7 and, on a larger scale, seismic activity corresponding to an earthquake 8,9 . Quantitative understanding of crackling noise is of fundamental importance in different applications, from non-destructive material testing to hazard prediction. This goal can be achieved only through the identification of general universal properties common to these systems, irrespective of their differences in the internal dynamics and microstructural details. In this context, the average shape of the individual pulses of which the signal is composed has been proposed as the best tool to characterize these universal features of crackling noise 1 . In analogy with critical phenomena, it is expected that pulses of different durations can be rescaled on a universal function, whose shape would only depend on general features of the physical process underlying the noise. This scenario is supported by the analysis of a variety of models, where pulse shapes are described by universal symmetric scaling functions [12][13][14] . In most experimental data, however, the pulse shape is markedly asymmetric with respect to its midpoint, that is, avalanches start quickly but return to zero more slowly 1,[8][9][10][11][12] . These results are puzzling because the models accurately reproduce several other universal quantities, such as avalanche distributions and power spectra 11,15 .One of the most studied examples of crackling noise is the Barkhausen effect recorded in soft magnetic mate...

Crackling noise in fractional percolation

“…While only a caricature of the intricate processes in ferromagnets 6,7 , it nonetheless explains multiple randomly distributed discontinuous jumps in the total magnetization MðtÞ: ¼ …”

“…Magnification of the hysteresis curve of a magnetic material in a changing external field, for instance, reveals that the magnetization curve is not smooth but exhibits small discontinuities. This series of correlated jumps is called the Barkhausen effect, which is a standard example for crackling noise in physics [6][7][8] . Despite its importance, crackling noise is far from being understood.…”

Statistical properties of Barkhausen noise in amorphous ferromagnetic films

“…Moreover, we also focus the analysis on the measurement of the average avalanche shape, a sharper tool for comparison between theory and experiments, going far beyond power laws, and being more informative than slopes [1,2,5,22,29,[66][67][68]. The average avalanche shape has been estimated for a wide variety of systems, as planar crack front propagation experiments [69,70], plastically deforming crystals [71], earthquakes [11] and Barkhausen noise [6,29,68].…”

“…Experimentally, the asymmetry is dependent on the material parameters, as the magnetic permeability µ conductivity σ, as well as geometrical dimensions of the sample, as the thickness. Here, by employing films with intermediate thickness, the characteristic timescale for relaxation [68] is of ∼ns, value smaller than the range of the avalanche durations, above ∼ µs. For this reason, the domain wall dynamics seems to be not affected by eddy current effects, resulting in symmetric average shapes, undistorted by eddy currents.…”

Complex networks and waveforms from acoustic emissions in laboratory earthquakes

“…The average skewness of Q profiles as an asymmetry measure can be quantified by (Eq. 1 in Zapperi et al, 2005) …”