Examinando por Autor "Urquijo, J.P."
Mostrando 1 - 3 de 3
Resultados por página
Opciones de ordenación
Ítem Growth of magnetite films by a hydrogel method(Elsevier B.V., 2017-06-15) Velásquez, A.A.; Marín, C.C.; Urquijo, J.P.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)Magnetite (Fe3O4) films were grown on glass substrates by formation and condensation of complex of iron oxides in an agarose hydrogel. The obtained films were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Room Temperature Mössbauer Spectroscopy (TMS), Vibrating Sample Magnetometry (VSM), Atomic Force Microscopy (AFM) and Voltage vs. Current measurements by the four-point method. FTIR and TGA measurements showed that some polymer chains of agarose remain linked to the surface of the magnetic particles of the films after heat treatment. SEM measurements showed that the films are composed by quasi spherical particles with sizes around 55 nm. Mössbauer spectroscopy measurements showed two sextets with broaden lines, which were assigned to magnetite with a distributed particle size, and two doublets, which were assigned to superparamagnetic phases of magnetite. For the specific dimensions of the films prepared, measurements of Voltage vs. Current showed an ohmic behavior for currents between 0 and 200 nA, with a resistance of 355 kO. © 2017 Elsevier B.V.Ítem Implementation and automation of a Faraday experiment for the magneto-optical characterization of ferrofluids(Institute of Physics Publishing, 2016-01-01) Velásquez, A.A.; Urquijo, J.P.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)This work presents the design, assembly and automation of a Faraday experiment for use in characterization of the magneto-optical response of fluids and ferrofluids. The magnetooptical Faraday experiment was automated using programmable equipment, controlled through the IEEE-488 port via Standard Commands for Programmable Instruments executed from a graphical interface developed in LabVIEW software. To calibrate the system the Verdet constants of distilled water and isopropyl alcohol were measured, obtaining an error percentage less than 2% for both fluids. Subsequently we used the system for measuring the Verdet constant of a ferrofluid of iron oxide nanoparticles diluted in distilled water, which was synthesized and, before its dilution, characterized by scanning electron microscopy, room temperature Mossbauer spectroscopy and vibrating sample magnetometry. We found that the Verdet constant of the diluted ferrofluid was smaller than that of distilled water, indicating opposite contributions of the effects of the diamagnetic and paramagnetic phases present in the ferrofluid to the magneto-optical effect. Details of the assembly, control of the experiment and development of the measurements are presented in this paper.Ítem Influence of Co2+ on the structural and magnetic properties of substituted magnetites obtained by the coprecipitation method(SPRINGER, 2015-01-01) Velásquez, A.A.; Urquijo, J.P.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)In this paper we report the effect of divalent cobalt on the structural and magnetic properties of substituted magnetites, Fe 3-xCo xO4, with ?=Co 2+/Fe = 0, 5, 10, 15, 20 and 30 % wt, synthesized by the coprecipitation method. The samples were characterized by Atomic Absorption Spectroscopy, X-ray Diffraction, room temperature Mössbauer Spectroscopy and Vibrating Sample Magnetometry. The effect of Co 2+ was found to depend strongly of the concentration employed in the synthesis process. For ?=15 % the Co 2+ promotes the formation of particles more crystalline and with higher saturation magnetization, remanence and coercivity than those obtained in absence of this cation. A sequential increasing of the lattice parameter is observed, as well as a reduction in the hyperfine magnetic field of the Fe 2.5+sub spectrum, while the hyperfine magnetic field of the Fe 3+sub spectrum keeps almost constant. For ?=20 % and 30 % the crystallinity of the samples decreases, particle size distribution effects are evidenced and the saturation magnetization decreases drastically. The results suggest that for low Co 2+ contents the substitution of Fe 3+by Co 2+ at octahedral sites of the inverse spinel system is the dominant effect, while for the highest concentrations used the substitution of Fe 2+ by Co 2+ and the increasing of the particle size distribution are the dominant effects. © 2015, Springer International Publishing Switzerland.