Estudo da microestrutura e da relaxação magnética em supercondutores de YBa2Cu3O7-δ texturizado

Abstract

In this work we report an experimental study about the Field Cooled (FC) magnetic relaxation in melt-textured YBa2Cu3O7-δ (Y123) samples, growing by Top Seeding Melt-Texturing (TSMT) and Bridgman techniques, correlating the magnetization effects with morphological and structural aspects obtained by electronic microscopy. Magnetic fields were applied parallel and perpendicular to the ab plane with different temperatures and cooling rates. The FC magnetization measurements showed a paramagnetic response associated to the paramagnetic Meissner effect (PME). The appearance of the paramagnetic response in magnetic relaxation measurements suggests a magnetic flux compression scenario into the sample, with two different regimes, corresponding to different vortex dynamics. The time effects are correlated to the experimental results obtained by microscopy techniques. By scanning electron microscopy technique (SEM) it was possible to observe the occurrence of secondary phases dispersed into the superconducting matrix related to Y2BaCuO5 (Y211) phase added during the preparation of the samples. By transmission electron microscopy technique (TEM) it was possible to observe structural defects into the Y2BaCuO5 grains, which shows a complex microstructure acting as a strong pinning center into the superconducting material. Our results suggest that a magnetic relaxation associated with the PME might be explained by the magnetic flux compression scenario into the superconducting sample, and the different regimes of magnetic relaxation can be attributed to an intra and extragranular vortex dynamic inside the Y2BaCuO5 grain. More investigation is need in order to clarify and confirm our results.