Universal properties of magnetization dynamics in polycrystalline ferromagnetic films

Abstract

We investigate the scaling behavior in the statistical properties of Barkhausen noise in ferromagnetic films. We apply the statistical treatment usually employed for bulk materials in experimental Barkhausen noise time series measured with the traditional inductive technique in polycrystalline ferromagnetic films having different thickness from 100 to 1000 nm and determine the scaling exponents. Based on this procedure, we group the samples in a single universality class, since the scaling behavior of Barkhausen avalanches is characterized by exponents τ∼1.5, α∼2.0, and 1/σνz∼ϑ∼2.0 for all the films. We interpret these results in terms of theoretical models and provide experimental evidence that a well-known mean-field model for the dynamics of a ferromagnetic domain wall in three-dimensional ferromagnets can be extended for films. We identify that the films present an universal three-dimensional magnetization dynamics, governed by long-range dipolar interactions, even at the smallest thicknesses, indicating that the two-dimensional magnetic behavior commonly verified for films cannot be generalized for all thickness ranges.

Statistical properties of Barkhausen noise in amorphous ferromagnetic films

“…[8], provide a further insight on the DWs dynamics in ferromagnetic films and the role of structural character on the scaling behavior in the BN statistical properties. In particular, we verify that materials can be classified in different universality classes, and confirm that the classes proposed in Ref.…”

“…[6,8,30,31,62]. For each experimental run, the statistical properties are obtained from 150 measured Barkhausen noise time series, by averaging the distributions over a 10 5 − 10 6 avalanches.…”

“…In mean-field systems, such as polycrystalline films with intermediate thicknesses [6,8], with 1/σνz ∼ 2.0, the average temporal avalanche shape is known to be given by an inverted parabola, while the average shape for different sizes is given by a semicircle. Here, the average avalanche shapes are in quantitative agreement with theoretical predictions proposed in Ref.…”

“…Moreover, as a fundamental signature of the avalanches, the average temporal avalanche shape has been estimated and shown to be given by a symmetric inverted parabola, providing strong indications of the underlying physics, such as the system dimensionality and kind and range of interactions governing the avalanche dynamics. More recently, we have obtained the same wide statistical analysis for Permalloy polycrystalline ferromagnetic films with thicknesses between 100 and 1000 nm [8]. In that case, we grouped the films in a single universality class since all films irrespective on the thickness are characterized by the scaling exponents τ ∼ 1.5, α ∼ 2.0 and 1/σνz ∼ ϑ ∼ 2.0 at the smallest magnetic field rate.…”

“…Experimentally, several interesting results have been obtained for different ferromagnetic films through both magneto-optical [42][43][44][45][46][47][48][49][50][51][52] and inductive [6,8,53] [44], both results obtained through measurements performed using a magneto-optical elipsometer. D.-H. Kim et al [45] have presented τ ∼ 1.33 for Co polycrystalline films, with thicknesses varying from 5 to 50 nm, and S.-C. Shin et al [46] have found τ ∼ 1.33 for Co and MnAs films, with the same thicknesses, by measurements using a magneto-optical microscope magnetometer, capable of observing directly the motion of the DWs and the Barkhausen avalanches [47].…”