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Izquierdo J.L.,Laboratorio Of Materiales Ceramicos Y Vitreos | Montoya J.F.,Laboratorio Of Materiales Ceramicos Y Vitreos | Moran O.,Laboratorio Of Materiales Ceramicos Y Vitreos | Arnache O.,University of Antioquia | Saldarriaga W.,Laboratorio Of Materiales Ceramicos Y Vitreos
Journal of Superconductivity and Novel Magnetism | Year: 2013

YBaCo4O7+δ thin films with thicknesses of 180 nm were grown by means of magnetron sputtering technique onto (100)-SrTiO 3,(100)-LaAlO3,(100)-MgO, and (0001)-Al2O 3 substrates. The structural characterization performed by X-ray diffraction shows that films deposited on MgO, SrTiO3, and c-Al 2O3 substrates grow with preferential orientation in the (203) direction. For LaAlO3 substrates, the preferred growth direction is the (212). The coupling between the lattice parameter of the compound and those of the substrates seems to determine the preferred orientation for the growth onto the different substrates. We carry out measurements of the resistivity as a function of the temperature in the standard four-terminal configuration, and analyze the results in the framework of some transport models such as simple thermal activation, small polaron hopping, and Mott's variable range hopping (VRH). A better agreement with the experimental data is observed by applying the latter model. The fitting of this model to the experimental data allows for determining important physical parameters related to the electrical conduction in these materials such as the density of states at the Fermi level. © 2012 Springer Science+Business Media, LLC. Source


Moran O.,Laboratorio Of Materiales Ceramicos Y Vitreos
Journal of Superconductivity and Novel Magnetism | Year: 2013

In this paper, we report the preparation of La0.7Sr 0.3MnO3 colossal magnetoresistance nanoparticles by means of the polymeric precursor method, at a temperature of 650 C. Rietveld refinement of the X-ray powder diffraction spectra shows that the chemically-synthesized manganite is single-phase with the space group R3C. By using the peak broadening technique and Scherrer's formula, a grain size of ∼15 nm was estimated. The ferromagnetic to paramagnetic transition is sharp with a Curie temperature of TC ∼360 K. In spite of the low annealing temperature, the insulator-metal-like transition temperature (T p) is close to TC. Transport measurements on the prepared samples show a magnetoresistance change of ∼10 % at room temperature in a field of 2 T. This high-field MR is probably due to grain-boundary effects. © 2012 Springer Science+Business Media, LLC. Source

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