Navegando por Autor "Sommer, Rubem Luis"
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Artigo Angular dependence of asymmetric magnetoimpedance in exchange biased NiFe/IrMn multilayers(AIP Publishing LLC, 2014-03-11) Silva, Ricardo Barreto da Silva; Corrêa, Marcio Assolin; Silva, Edimilson Felix da; Mori, Thiago José de Almeida; Della Pace, Rafael Domingues; Pinto, Roberta Dutra de Oliveira; Viegas, Alexandre Da Cas; Bohn, Felipe; Sommer, Rubem LuisWe investigate the angular dependence of asymmetric magnetoimpedance of NiFe/IrMn multilayers and explore the possibility of tuning the linear region of the magnetoimpedance curves by modifying the angle between the applied external magnetic field and exchange bias field, and probe current frequency. We quantify the sensitivity by calculating the ratio jDZj=jDHj at low magnetic fields as a function of the frequency for samples cut with different orientations and show that considerable values in the linear region around zero field can be reached. The results extend the possibilities for application of exchange biased magnetoimpedance multilayers as probe element for the development and improvement of auto-biased linear magnetic field sensorsArtigo Annealing effects on the microwave linewidth broadening of FeCuNbSiB ferromagnetic films(AIP Publishing LLC, 2015-03-26) Alves, Marcos José Pereira; Gonzalez-Chavez, Diego Ernesto; Bohn, Felipe; Sommer, Rubem LuisWe systematically investigate the annealing effects on the microwave linewidth broadening of FeCuNbSiB ferromagnetic films with thickness of 100 nm. We correlate the non-uniform residual stress obtained from grazing incidence x-ray diffraction measurements with the ferromagnetic resonance (FMR) linewidth due to effective field inhomogeneities measured from broadband ferromagnetic resonance absorption measurements. We also estimate the annealing temperature effect on the Gilbert and two-magnon scattering contributions to the total ferromagnetic resonance FMR linewidth. We show that the effective field inhomogeneities constitute the main contribution to the microwave linewidth, while this contribution is related to the non-uniform residual stress in the films which is reduced by thermal annealingArtigo Magnetization dynamics in nanostructures with weak/strong anisotropy(AIP Publishing LLC, 2014-03-13) Andrade, Antonio Marcos Helgueira de; Corrêa, Marcio Assolin; Viegas, Alexandre Da Cas; Bohn, Felipe; Sommer, Rubem LuisWe investigate the high-frequency response of magnetization dynamics through magnetoimpedance (MI) effect in Permalloy-based multilayered thin films produced with two different non-magnetic metallic spacers: Cu and Ag. Due to the nature of the spacer materials, we are able to play with magnetic properties and to study both systems with weak/strong magnetic anisotropy. We verify very rich features in the magnetoimpedance behavior and high magnetoimpedance ratios, with values above 200%. We compare the MI results obtained in multilayered thin films with distinct spacers and number of bilayers, and discuss them in terms of the different mechanisms that govern the MI changes observed at distinct frequency ranges, intensity of the magnetic anisotropy, alignment between dc magnetic field and anisotropy direction. Besides, by considering a theoretical approach that takes into account two single models together and calculate the transverse magnetic permeability and the MI effect, we support our interpretation via numerical calculations modeling the effect of weak/strong magnetic anisotropy on the MI response. Thus, we confirm that these features are very important for the use of multilayered films in sensor applications and, both the frequency and field response can be tailored to fulfill the requirements of a given deviceArtigo Magnetoimpedance effect at the high frequency range for the thin film geometry: numerical calculation and experiment(AIP Publishing LLC, 2014-12-24) Bohn, Felipe; Corrêa, Marcio Assolin; Silva, Ricardo Barreto da; Sommer, Rubem LuisThe magnetoimpedance effect is a versatile tool to investigate ferromagnetic materials, revealing aspects on the fundamental physics associated to magnetization dynamics, broadband magnetic properties, important issues for current and emerging technological applications for magnetic sensors, as well as insights on ferromagnetic resonance effect at saturated and even unsaturated samples. Here, we perform a theoretical and experimental investigation of the magnetoimpedance effect for the thin film geometry at the high frequency range. We calculate the longitudinal magnetoimpedance for single layered, multilayered, or exchange biased systems from an approach that considers a magnetic permeability model for planar geometry and the appropriate magnetic free energy density for each structure. From numerical calculations and experimental results found in literature, we analyze the magnetoimpedance behavior and discuss the main features and advantages of each structure. To test the robustness of the approach, we directly compare theoretical results with experimental magnetoimpedance measurements obtained at the range of high frequencies for an exchange biased multilayered film. Thus, we provide experimental evidence to confirm the validity of the theoretical approach employed to describe the magnetoimpedance in ferromagnetic films, revealed by the good agreement between numerical calculations and experimental resultsArtigo Multifractality in domain wall dynamics of a ferromagnetic film(American Physical Society, 2012-12-27) Lima, Gustavo Zampier dos Santos; Corrêa, Marcio Assolin; Sommer, Rubem Luis; Bohn, FelipeWe investigate the multifractal properties in the dynamics of domain walls of a ferromagnetic film. We apply the Multifractal Detrended Fluctuation Analysis method in experimental Barkhausen noise time series measured in a 1000-nm-thick Permalloy film under different drivingmagnetic field frequencies, and calculate the fluctuation function Fq (s), generalized Hurst exponent h(q), multifractal scaling exponent τ (q), and the multifractal spectrum f (α). Based on this procedure, we provide experimental evidence of multifractality in the dynamics of domain walls in ferromagnetic films and identify a rich and strong multifractal behavior, revealed by the changes of the scaling properties of over the entire Barkhausen noise signal, independently of the driving magnetic field rate employed in the experimentArtigo Quantitative Scaling of Magnetic Avalanches(American Physical Society, 2016-08-15) Durin, Gianfranco; Bohn, Felipe; Corrêa, Marcio Assolin; Sommer, Rubem Luis; Doussal, P. Le; Wiese, K. J.We provide the first quantitative comparison between Barkhausen noise experiments and recent predictions from the theory of avalanches for pinned interfaces, both in and beyond mean field. We study different classes of soft magnetic materials, including polycrystals and amorphous samples—which are characterized by long-range and short-range elasticity, respectively—both for thick and thin samples, i.e., with and without eddy currents. The temporal avalanche shape at fixed size as well as observables related to the joint distribution of sizes and durations are analyzed in detail. Both long-range and short-range samples with no eddy currents are fitted extremely well by the theoretical predictions. In particular, the short-range samples provide the first reliable test of the theory beyond mean field. The thick samples show systematic deviations from the scaling theory, providing unambiguous signatures for the presence of eddy currentsArtigo Statistical properties of Barkhausen noise in amorphous ferromagnetic films(American Physical Society, 2014-09-29) Bohn, Felipe; Corrêa, Marcio Assolin; Carara, M.; Papanikolaou, Stefanos; Durin, G.; Sommer, Rubem LuisWe investigate the statistical properties of the Barkhausen noise in amorphous ferromagnetic films with thicknesses in the range between 100 and 1000 nm. From Barkhausen noise time series measured with the traditional inductive technique, we perform a wide statistical analysis and establish the scaling exponents τ , α, 1/σ νz, and ϑ. We also focus on the average shape of the avalanches, which gives further indications on the domain-wall dynamics. Based on experimental results, we group the amorphous films in a single universality class, characterized by scaling exponents τ = 1.28 ± 0.02, α = 1.52 ± 0.3, and 1/σ νz = ϑ = 1.83 ± 0.03, values compatible with that obtained for several bulk amorphous magnetic materials. Besides, we verify that the avalanche shape depends on the universality class. By considering the theoretical models for the dynamics of a ferromagnetic domain wall driven by an external magnetic field through a disordered medium found in literature, we interpret the results and identify an experimental evidence that these amorphous films, within this thickness range, present a typical three-dimensional magnetic behavior with predominant short-range elastic interactions governing the domain-wall dynamics. Moreover, we provide experimental support for the validity of a general scaling form for the average avalanche shape for non-mean-field systemsArtigo Universal properties of magnetization dynamics in polycrystalline ferromagnetic films(American Physical Society, 2013-09-23) Bohn, Felipe; Corrêa, Marcio Assolin; Viegas, Alexandre da Cas; Papanikolaou, Stefanos; Durin, Gianfranco; Sommer, Rubem LuisWe 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/σ νz ∼ 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 domainwall 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 rangesArtigo Waiting-time statistics in magnetic systems(Nature Research, 2020-06-16) Sousa, Ivandson Praeiro de; Lima, Gustavo Zampier dos Santos; Corrêa, Marcio Assolin; Sommer, Rubem Luis; Corso, Gilberto; Bohn, FelipeMany complex systems, from earthquakes and financial markets to Barkhausen effect in ferromagnetic materials, respond with a noise consisting of discrete avalanche-like events with broad range of sizes and durations, separated by waiting times. Here we focus on the waiting-time statistics in magnetic systems. By investigating the Barkhausen noise in amorphous and polycrystalline ferromagnetic films having different thicknesses, we uncover the form of the waiting-time distribution in time series recorded from the irregular and irreversible motion of magnetic domain walls. Further, we address the question of if the waiting-time distribution evolves with the threshold level, as well as with the film thickness and structural character of the materials. Our results, besides informing on the temporal avalanche correlations, disclose the waiting-time statistics in magnetic systems also bring fingerprints of the universality classes of Barkhausen avalanches and a dimensional crossover in the domain wall dynamics