D.R. Cornejo

Avaliação da microestrutura e das propriedades magnéticas de ferritas Ni-Zn dopadas com cobre

An evaluation was made of the microstructure and magnetic properties of Ni0.5-xCuxZn0,5Fe2O4 ferrites with x = 0.1, 0.2, 0.3 and 0.4 prepared by combustion reaction with particle sizes 23 to 29 nm. The resulting powders were uniaxially compacted at 385 MPa into pellets and sintered at 1000 oC/2 h. The samples were characterized by apparent density and porosity measurements, X-ray diffraction, scanning electron microscopy and M-H magnetic measurements. The X-ray diffraction revealed crystalline inverse spinel as the major phase in all the specimens and a small amount of hematite (a-Fe2O3) as the secondary phase in the x = 0.1 and 0.4 samples. An increase in the amount of copper caused a slight increase in grain size (0.65 to 0.68 µm), a decrease in the apparent porosity (33.7% to 6.6%) and a reduction in saturation magnetization from 69 to 54 emu/g.

Síntese, por reação de combustão em forno de microondas, de nanoferritas de níquel dopadas com cromo

Chromium-doped nickel nanoferrite powder was prepared by combustion reaction, using microwave energy as the external heating source, and the influence of the Cr3+concentration on the NiCrxFe2-xO4 system was investigated. The powder, which was prepared according to the concept of propellant chemistry, was heated in a microwave oven under a power of 980 W. The resulting material was characterized by XRD, BET, SEM, helium picnometry and magnetic measurements. The results indicate that it was possible to obtain chromium-doped nickel ferrite nanopowders and that raising the chromium concentration caused an increase in particle size (from 15 nm to 55 nm), and a reduction in the magnetic parameters.

Estudo do efeito da diluição nas propriedades microestruturais e magnéticas de ferritas Mn0,65Zn0,35Fe2O4 por reação de combustão

As ferritas Mn-Zn vem sendo utilizadas em diversas areas tecnologicas por apresentarem propriedades atrativas no âmbito tecnico-cientifico. Este trabalho teve como objetivo sintetizar ferritas Mn0,65Zn0,35Fe2O4 por reacao de combustao e avaliar o efeito da diluicao dos reagentes em agua destilada sobre as caracteristicas microestruturais e magneticas. As amostras foram caracterizadas por difracao de raios X, microscopia eletronica de varredura e transmissao, temperatura de Curie e por medidas magneticas. Foi observado que o aumento da diluicao em agua durante a sintese por reacao de combustao foi favoravel para obtencao da ferrita Mn0,65Zn0,35Fe2O4 monofasica. Tambem favoreceu a diminuicao do tamanho de aglomerado e aumento da temperatura de Curie com valor maximo de magnetizacao de saturacao de 62 emu/g para a amostra diluida na proporcao 1:10.

Influência do teor de Zn2+ nas características morfológicas e magnéticas de ferritas Mn1-xZnxFe2O4 sintetizados em grande escala por reação de combustão

This study aimed to evaluate the influence of Zn2+ in the morphological and magnetic characteristics of ferrites Mn1-xZnxFe2O4 (where x= 0.0, 0.35, 0.5 and 0.65 mol of Zn) synthesized by combustion reaction in a pilot scale with batches of 200 g/reaction. The samples were characterized by X-ray diffraction, scanning/transmission electron microscopy, and magnetic measurements. The results indicated that all compositions were single phase of ferrite; morphologically the addition of Zn to MnFe2O4 system caused a slight reduction in size of the agglomerates, and reduced the particle size, but this behavior was not linear with the Zn2+ content. The samples had characteristic magnetic behavior of soft magnetic materials, maximum saturation magnetization of 62 emu/g for the sample with lower zinc content in its composition.

Avaliação microestrutural e magnética de Fe3O4 sintetizada pelo método de reação de combustão

The magnetite nanoparticles have been the subject of numerous scientific researches in various fields such as in biomedicine because of their spontaneous magnetization, chemical stability and non-toxicity. This work aims to evaluate the microstructural and magnetic properties of magnetite nanoparticles (Fe3O4) synthesized by combustion reaction induced in a microwave oven under an atmosphere of nitrogen (N2). The influence of N2 flow for synthesis in the structure, morphology and magnetic characteristics of the synthesized product was investigated. The samples were characterized by X-ray diffraction, scanning electron microscopy and magnetic measurements. The results show that it was possible to obtain the magnetite phase (Fe3O4) with traces of hematite (Fe2O3). The N2 flow and the exposure time modified the magnetic structure and the characteristic of the synthesized product. All samples showed small clusters of irregular shapes and sizes ranging from about 20 μm and saturation magnetization between 31 and 70 emu/g, being promising materials for application in biomedicine.

Magnetization and AC Susceptibility Study of Nb/Ni/Nb Thin Films

A study on the behavior of the magnetization and the ac susceptibility in Nb(40 nm)/Ni(x nm)/Nb(40 nm) thin films was carried out. It was observed that the hysteresis loops of these heterostructures show oscillations of the magnetization in regions of magnetic field where the irreversible reversal of the magnetization of the ferromagnet occurs. This behavior appears to show a coupling between the magnetic fields generated by the vortex in the Nb and the magnetization of the Ni nanograins. The analysis of the real and imaginary components of the ac susceptibility in the tri-layers shows no uniform results in relation to Ni layer thickness. However, the critical temperatures calculated from both components at zero applied field show an oscillation with respect to the Ni layer thickness.

Analysis Of Magnetic Behavior Of Exchange enhanced SmFeCo magnets

A series of densified exchange-enhanced SmFeCo magnets was produced by mechanical alloying,followed by a heat treatment. The nanocrystalline phases and the grain size distribution of thesamples were characterized from x-ray diffraction patterns. Magnetic measurements in terms ofdifferent models were analyzed for the temperature behavior of the magnetization and coercivity.One analytical formulation was derived from the random anisotropy model predicting that withincreasing M