Navegando por Autor "Lima, U. R."
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Artigo Ni Zn nanoferrite for radar-absorbing material. Journal of Magnetism and Magnetic Materials(Elsevier, 2008-05) Araujo, José Humberto de; Lima, U. R.; Nasar, Marivalva Cerqueira; Nasar, Ricardo Silveira; Rezende, M. C.Nanoparticles of nickel–zinc ferrite have been prepared by using the citrate precursor method. According to scanning electron microscopy (SEM), the particle size is nanometric for the powder calcined at 350 °C/3.5 h. The phase formation has been studied by applying different calcining atmospheres, such as air and argon. Pure Ni–Zn ferrite has been observed when calcined in argon at the temperature of 350 °C. Hysteresis analyses have been done with magnetization of 53.01 emu/g at 350 °C and obtaining 84.62 emu/g at 1100 °C due to an optimization of domains formation at high temperature. Measures of reflectivity of Ni–Zn ferrite/epoxy composite have been obtained below 21% at 350 °C and above 96% at 1100 °C with a coercive field of 26.61 Oe. Low value of coercive field increased the mobilization of domains wall and increased the radiation absorptionArtigo Synthesis of NiCuZn ferrite nanoparticles and microwave absorption characterization(Elsevier, 2008-07-25) Araújo, José Humberto de; Lima, U. R.; Nasar, Marinalva Cerqueira; Nasar, Ricardo Silveira; Rezende, M. C.; Oliveira, José F.This study aimed at the low temperature synthesis of NixCu0.5−xZn0.5Fe2O4 ferrite nanoparticles using the citrate precursor method and the reflectivity characterization of Radar absorbing materials. The NiCuZn phase obtained at 350 °C by the Rietveld method showed homogeneous nanoparticle formation. The analysis of particle size and the critical diameter of the domains indicated monodomain formation on nanometric scale. Vibrating sample magnetometry showed that adding copper to NiZn ferrite decreases magnetization saturation and the calcining temperature. Reflectivity measures taken by the wave guide method, obtained absorption radiation of 96.6% for x = 0.3 at 12 GHz.