Navegando por Autor "Sommer, R. L."
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Artigo Effects of second order surface anisotropy in YIG sputtered onto GGG (1 0 0) oriented substrate(Elsevier B.V., 2018-08-17) Oliveira, Alexandre Barbosa de; Feitosa, Carlos Chesman de Araújo; Rodríguez-suárez, R. L.; Costa, R. B.; Silva, U. C.; Costa, N. P.; Silva, B. G.; Sommer, R. L.; Bohn, Felipe; Correa, M. A.In this work, we produced Y3Fe5O12 textured films, with thicknesses between 50 nm and 500 nm, onto (1 0 0) Gd3Ga5O12 by magnetron sputtering and post annealing, and investigated the first and second order surface and cubic anisotropy constants using the ferromagnetic resonance technique. The surface anisotropy constants exhibited different behaviors with film thickness, with the first order presenting the usual inverse of ferromagnetic layer thickness. Besides this inverse of thickness behavior, the second order also came up with a constant value. In the frame of spin reorientation transition phenomenon, we evaluated volume and surface contribution to the surface anisotropy. Although the second order cubic anisotropy constant is one order of magnitude stronger than the first order, they did not show any explicit thickness dependence. The second order terms of surface and cubic anisotropy appeared to be essential to allow simultaneous fit of in-plane and out-of-plane angular dependence of resonance field. Moreover, they had to be negative to describe the out-of-plane results correctly. Our results raised critical issues that shall be taken into account when explaining the new and recent spintronics and caloritronics effects in YIG.Artigo Exploring the magnetization dynamics of NiFe/Pt multilayers in flexible substrates(Elsevier, 2016-09-29) Corrêa, Marcio Assolin; Dutra, Roberta; Marcondes, Tatiana Lisboa; Mori, T. J. A.; Bohn, Felipe; Sommer, R. L.We investigate the structural and magnetic properties, and the magnetization dynamics in Ni81Fe19/Pt multilayer systems grown onto rigid and flexible substrates. The structural characterization shows evidence of a superlattice behavior, while the quasi-static magnetization characterization reveal a weak magnetic anisotropy induced in the multilayers. The magnetization dynamics is investigated through the magnetoimpedance effect. We employ a theoretical approach to describe the experimental magnetoimpedance effect and verify the influence of the effective damping parameter on the magnetization dynamics. Experimental data and theoretical results are in agreement and suggest that the multilayers present high effective damping parameter. Moreover, our experiments raise an interesting issue on the possibility of achieving considerable MI% values, even for systems with weak magnetic anisotropy and high damping parameter grown onto flexible substratesArtigo Universal temporal characteristics and vanishing of multifractality in Barkhausen avalanches(American Physical Society, 2017-08-31) Lima, Gustavo Zampier dos Santos; Corso, Gilberto; Corrêa, Marcio Assolin; Sommer, R. L.; Ivanov, P. Ch.; Bohn, FelipeBarkhausen effect in ferromagnetic materials provides an excellent area for investigating scaling phenomena found in disordered systems exhibiting crackling noise. The critical dynamics is characterized by random pulses or avalanches with scale-invariant properties, power-law distributions, and universal features. However, the traditional Barkhausen avalanches statistics may not be sufficient to fully characterize the complex temporal correlation of the magnetic domain walls dynamics. Here we focus on the multifractal scenario to quantify the temporal scaling characteristics of Barkhausen avalanches in polycrystalline and amorphous ferromagnetic films with thicknesses from 50 to 1000 nm. We show that the multifractal properties are dependent on film thickness, although they seem to be insensitive to the structural character of the materials. Moreover, we observe for the first time the vanishing of the multifractality in the domain walls dynamics. As the thickness is reduced, the multifractal behavior gives place to a monofractal one over the entire range of time scales. This reorganization in the temporal scaling characteristics of Barkhausen avalanches is understood as a universal restructuring associated to the dimensional crossover, from three- to two-dimensional magnetization dynamicsArtigo Wide frequency range magnetoimpedance in tri-layered thin NiFe/Ag/NiFe films: experiment and numerical calculation(AIP Publishing, 2011-11-08) Corrêa, Marcio Assolin; Bohn, Felipe; Escobar, Vivian Montardo; Marques, M. S.; Viegas, A. D. C.; Schelp, L. F.; Sommer, R. L.Given that the magnetoinductive effect (MI), skin effect and ferromagnetic resonance influence magnetic permeability behavior at different frequency ranges, the description of the magnetoimpedance effect over a wide range of frequency becomes a difficult task. To that end, we perform an experimental investigation of the magnetoimpedance effect in a tri-layered thin film over a wide frequency range. We compare the experimental results for a tri-layered thin film with numerical calculus performed using an approach that considers a magnetic transverse susceptibility model for planar systems and an appropriate magnetoimpedance model for a tri-layered system together. The results show remarkably good agreement between numerical calculus and experimental measurements. Thus, we discuss the experimental results in terms of different mechanisms that govern the MI changes observed in distinct frequency ranges and provide experimental support to confirm the validity of the theoretical approach