Navegando por Autor "Carara, M."
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Artigo 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 Thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films(IOP Publishing, 2017-04-03) Silva, Edimilson Félix da; Corrêa, Marcio Assolin; Pace, R. D. Della; Cid, C. C. Plá; Kern, P. R.; Carara, M.; Feitosa, Carlos Chesman de Araújo; Santos, O. Alves; Rodríguez-Suárez, R. L.; Azevedo, A.; Rezende, S. M.; Bohn, FelipeWe investigate the thickness dependence of the magnetic anisotropy and dynamic magnetic response of ferromagnetic NiFe films. We go beyond quasi-static measurements and focus on the dynamic magnetic response by considering three complementary techniques: the ferromagnetic resonance, magnetoimpedance and magnetic permeability measurements. We verify remarkable modifications in the magnetic anisotropy, i.e. the well-known behavior of in-plane uniaxial magnetic anisotropy systems gives place to a complex magnetic behavior as the thickness increases, and splits the films in two groups according to the magnetic properties. We identify magnetoimpedance and magnetic permeability curves with multiple resonance peaks, as well as the evolution of the ferromagnetic resonance absorption spectra, as fingerprints of strong changes of the magnetic properties associated to the vanishing of the in-plane magnetic anisotropy and to the emergence of non-homogeneous magnetization configuration, local anisotropies and out-of-plane anisotropy contribution arisen as a consequence of the non-uniformities of the stress stored in the film as the thickness is increased and/or to the columnar growth of the film. We interpret the experimental results in terms of the structural and morphological properties, quasi-static magnetic behavior, magnetic domain structure and different mechanisms governing the magnetization dynamics at distinct frequency ranges