Navegando por Autor "Agra, Kennedy Leite"
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Artigo Dynamic magnetic behavior in non-magnetostrictive multilayered films grown on glass and flexible substrates(Elsevier, 2013-12-12) Agra, Kennedy Leite; Mori, Thiago José de Almeida; Dorneles, Lucio Strazzabosco; Escobar, Vivian Montardo; Silva, Ubiratan Correia; Feitosa, Carlos Chesman de Araújo; Bohn, Felipe; Corrêa, Marcio AssolinDynamic magnetic behavior, through magnetoimpedance effect, is investigated in non-magnetostrictive multilayered films of Ni81Fe19/(Ag,Ta) grown on glass and flexible substrates. The magnetoimpedance measurements are performed in a wide range of frequencies (from 0.01 GHz up to 3.0 GHz) and are interpreted in terms of the structural and quasi-static magnetic properties of the films. In particular, Ni81Fe19/Ag multilayered films grown on glass and flexible substrates present very similar results, with MImax values of 40% at around 0.5 GHz. For the Ni81Fe19/Ta multilayered film on glass substrate, higher MImax value is observed, 60% at around 0.45 GHz, whereas for the one produced on flexible substrate, 28% at around 0.3 GHz. Thus, the fact that the produced multilayered films present good MI performance, irrespective of the employed substrate, opens new possibilities for technological applications, making easier the integration of these samples as a sensor element in MI based electronic devices, where flexible substrates can be used with the same efficiencyTese Estudo da dinâmica da magnetização em multicamadas magnetostrictivas(Universidade Federal do Rio Grande do Norte, 2015-09-10) Agra, Kennedy Leite; Correa, Márcio Assolin; Bohn, Felipe; ; http://lattes.cnpq.br/9522788035526763; ; http://lattes.cnpq.br/2531075321550052; ; http://lattes.cnpq.br/3439888539159944; Bezerra, Claudionor Gomes; ; http://lattes.cnpq.br/5085046065890176; Medeiros, Suzana Nóbrega de; ; http://lattes.cnpq.br/2148858591663240; Silva, Ricardo Barreto da; ; http://lattes.cnpq.br/8538297526477728; Suarez, Roberto Lázaro Rodriguez; ; http://lattes.cnpq.br/3693365352022151Multicamadas magnéticas têm uma grande importância no desenvolvimento de elementos sensores baseados no efeito magnetoimpedância (MI). O advento de dispositivos usando substrato flexível orgânico têm aberto novas fronteiras para o desenvolvimento da tecnologia nas mais diversas áreas. Diante disso torna-se necessário a produção e estudo das propriedades magnéticas e mecânicas em filmes ferromagnéticos crescidos em substrato flexível. Neste trabalho, foram produzidas multicamadas ferromagnéticas de Py, Co e FeCuNbSiB em substratos flexível e rígido, utilizando a técnica de magnetron sputtering. Na ocasião utilizou-se de uma metodologia para caracterizar as propriedades estruturais, magnéticas e mecânicas. Para isso foram utilizados os seguentes instrumentos de medida: difratômetro de Raios-X, magnetômetro de amostra vibrante, analisador de impedância, instrumentos de medida de dimensões e software de elementos finitos. Através de uma análise meticulosa, foi possível observar e correlacionar o comportamento do efeito MI com as propriedades magnéticas quase-estáticas, estruturais e mecânicas. Observando-se uma forte dependência da MI com a magnetostricção de saturação, quando são introduzidas anisotropias magnetoelásticas, através de tensões mecânicas. As propriedades magnéticas das multicamadas de Py mostram-se insensíveis as tensões aplicadas. Já, nas multicamadas ferromagnéticas de Co, teve como principal resultado, um aumento da dispersão de MI atrelado à elevação das tensões mecânicas. No caso, das multicamadas de FeCuNbSiB, a inversão do eixo de anisotropia é o resultado mais interessante, provocando modificações na configuração do efeito MI, trazendo informações muito ricas da dinâmica da magnetização, quando tensões mecânicas são aplicadas ao sistema.Artigo Giant magnetoimpedance effect in Co2FeAl single layered and Co2FeAl/Ag multilayered films in amorphous substrates(Elsevier, 2015-05-08) Silva, Anderson Max Cirilo da; Escobar, Vivian Montarddo; Callegari, G.L.; Agra, Kennedy Leite; Feitosa, Carlos Chesman de Araújo; Bohn, Felipe; Corrêa, Marcio AssolinWe investigate the structural, quasi-static and dynamic magnetic properties of a Co2FeAl single layered film and a Co2FeAl/Ag multilayer, both grown onto amorphous substrate. We verify that both films have A2 structure and anisotropic magnetic behavior, as well as present the well-known magnetoimpedance behavior of anisotropic systems. The magnetization dynamics is discussed in terms of the mechanisms that govern the magnetoimpedance effect in a wide range of frequencies, as well as of the orientation between the external magnetic field and electrical current with respect to the magnetic anisotropy. The single layer has the largest magnetoimpedance variations values of 50% for 3.0 GHz, while the multilayer present considerable higher values, reaching to 200% at the same frequency. The association of kind of sample structure, anisotropic magnetic behavior and low damping parameter α of the CFA alloy opens possibilities to reach higher magnetoimpedance performances. The results place the CFA full-Heusler alloy as a promising candidate for applications in magnetoimpedance-based sensors and radio frequency range devicesArtigo Handling magnetic anisotropy and magnetoimpedance effect in flexible multilayers under external stress(Elsevier, 2016-12-15) Agra, Kennedy Leite; Bohn, Felipe; Mori, T. J. A.; Callegari, Gustavo Luiz; Dorneles, Lúcio S.; Corrêa, Marcio AssolinWe investigate the dynamic magnetic response though magnetoimpedance effect of ferromagnetic flexible NiFe/Ta and FeCuNbSiB/Ta multilayers under external stress. We explore the possibility of handling magnetic anisotropy, and consequently the magnetoimpedance effect, of magnetostrictive multilayers deposited onto flexible substrates. We quantify the sensitivity of the multilayers under external stress by calculating the ratio between impedance variations and external stress changes, and show that considerable values can be reached by tuning the magnetic field, frequency, magnetostriction constant, and external stress. The results extend possibilities of application of magnetostrictive multilayers deposited onto flexible substrates when under external stress and place them as very attractive candidates as element sensor for the development of sensitive smart touch sensorsArtigo Mirroring the dynamic magnetic behavior of magnetostrictive Co/(Ag,Cu,Ta) multilayers grown onto rigid and flexible substrates(Elsevier, 2015-06-19) Agra, Kennedy Leite; Gomes, Reben Rudson Mendes; Della Pace, Rafael Domingues; Dorneles, Lucio Strazzabosco; Bohn, Felipe; Corrêa, Marcio AssolinWe investigate the magnetoimpedance effect in a wide frequency range in magnetostrictive Co/(Ag,Cu,Ta) multilayers grown onto rigid and flexible substrates. We observe a direct correlation between structural and quasi-static magnetic properties and the magnetoimpedance effect, since they are directly dependent on the nature of the spacer material. Moreover, we verify that all these properties are insensitive to the kind of employed substrate. We compare the magnetoimpedance results measured for multilayers in rigid and flexible substrates and discuss them in terms of different mechanisms that govern the impedances changes, magnetic anisotropy, structural character, and of numerical calculation results found in the literature. The fact that magnetostrictive multilayers can be reproduced in distinct kinds of substrates corresponds to an important advance for their applicability. The results place multilayers grown onto flexible substrates as attractive candidates for application as probe element in the development of MI-based sensor device