Abstract In the present research, the synthesis of cobalt oxide Co3O4 was carried out using the sol-gel technique with subsequent heat treatment at 225 and 235 °C. The final product obtained was characterized by X-ray diffraction (XRD), showing a pure crystalline phase of Co3O4, cell parameters a=b=c=8.071 Å, and a volume of 525.7 Å3. The particle size was between 2.37 and 2.77 µm, which indicated that structural transformations from Co to Co3O4 induced an increase in the particle size. Through Rietveld refinement, the interatomic distances and inclination angles of the Co1, Co2, and Co3 polyhedra were analyzed in order to establish the structural behavior of cobalt oxide (II, III) at 235 °C. The UV-vis analysis allowed determining band gap (Eg) with values of 1.6 eV in the first region and 0.97 eV in the second. Scanning electron microscopy images showed that the particles agglomerated with increasing calcination temperature and exhibited larger particles. This work presents a detailed analysis of structural parameters of Co3O4 using the Vesta software with Rietveld refinement data.

Es bien conocido que la teoría de Ginzburg-Landau es una herramienta teórica confiable para investigar el estado de Shubnikov en muestras superconductoras en presencia de campos magnéticos aplicados. En este trabajo resolvemos el sistema de ecuaciones Ginzburg Landau en dos y tres dimensiones en dos casos particulares: para un paralelepípedo de volumen Vp; con área transversal Sp = 9ξ ²(0), 36ξ ²(0) y altura hp = 1ξ (0),6ξ (0), donde ξ (0) es la longitud de coherencia y por otra parte, para un disco fino con un defecto circular y triangular centrado con topología punto/anti-punto. En ambos casos las muestran estan submersas en un campo magnético homogeneo. Los efectos de las fuerzas de anclaje/anti-anclaje debido a los defectos en el disco y los efectos de demagnetización debido al tamaño finito del paralelepipedo sobre la configuración de vortices y campos críticos son discutidos. En el caso tridimensional, el campo magnético y el parámetro de orden no son invariantes a lo largo de la dirección z.

It is well-known that the time dependent Ginzburg-Landau theory is a reliable theoretical tool to investigate the Shubnikov state in a superconductor sample in presence of an external applied magnetic field. In this work, we solved the system of the Ginzburg-Landau equations in two and three dimensions for two particular cases: For a parallelepiped with volume Vp; with transversal area Sp = 9ξ ²(0), 36ξ ²(0) and height hp = 1ξ (0),6ξ (0), where ξ (0) is the coherence length. In the other hand, for a thin disk with a centered circular and triangular defect, with topology of dot/anti-dot. In both cases are immersed into a homogeneous magnetic field. The effects of pinning/anti-pinning forces due to defects in the disk and demagnetization effects due to the finite size of the parallelepiped on configuring vortices and critical fields are discussed. In the tridimensional case, the magnetic field and the order parameter are not invariant along the direction z.

In this work we investigate the vortex dynamics in a square mesoscopic superconducting cylinder in the presence of an applied magnetic field parallel to its axis. The rectangular cross-section of the sample is L² and an engineered columnar defect of area d² at the center is taken into account; L = 12ξ(0) for all simulations while d varies discretely from 1ξ(0) to 10ξ(0). We study the magnetization and the vortex configuration, increasing the magnetic field from zero to the normal state field. We found that for d > 7ξ(0) no vortices in the superconductor area are possible. Also, if the size of the defect is reduced, the nucleation fields decrease.