Comportamento da irreversibilidade magnética e da resistência elétrica em supercondutores de YBa 2 Cu 3 O 7-δ texturizado mediante campos magnéticos pulsados

Abstract

In this work the electrical and magnetic behavior in a textured sample of the YBa 2 Cu 3 O 7-δ superconductor through pulsed magnetic fields up to 60T was investigated. The sample was grown by the Bridgman technique and with the addition of 30% by weight of the Y211 phase, obtained from the Department of Materials Science and Metallurgical Engineering of the Universitat Politécnica de Catalunya in Barcelona, Spain. Electrical and magnetic measurements with pulsed fields were performed at Dresden Magnetic Field Laboratory located at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Dresden, Germany. The sample was morphologically characterized using a scanning electron microscope from the Electron Microscopy Center (CEME-Sul) of the Federal University of Rio Grande (FURG), where it was possible to observe the presence of a crystallographic alignment characteristic of the texturing process, besides the presence of the Y211 phase grains distributed in the superconducting matrix. The magnetic moment measurements were performed in two applied magnetic field configurations, H // ab e H // c. By means of these measurements it was possible to determine the field of magnetic irreversibility, Hirr (T), and obtain the magnetic irreversibility line for the two configurations of the applied magnetic field, which were adjusted by the giant flux creep model until a certain magnetic field region. The measurements of electrical magnetoconductivity were performed by applying magnetic field and electric current in 4 different field-current configurations and for each applied magnetic field pulse the respective magnetic field associated to the zero resistance temperature was determined. The results showed that for measurements with applied magnetic field parallel to the ab plane, the superconducting transition was less affected with the increase of the applied magnetic field, since larger values of magnetic field were obtained, associated to the coherence temperature in comparison with the results of the measurements made with application of magnetic field parallel to axis c, whose values of magnetic field were smaller. From the results of H irr (T) e H (T c0 ) a correlation was made between the magnetic irreversibility and the null resistance lines, where we can observe that the null resistance occurs below the limit of magnetic irreversibility in all field-current configurations. The zero resistance values of this work were also obtained only at temperatures below or close to the limit of magnetic irreversibility. The anisotropy of magnetic irreversibility and zero resistance can be observed, as expected for a textured sample of good quality. The results of electrical magnetoconductivity that were influenced by the Lorentz force presented lower values of H (T c0 ) leading to the assumption of a change in the vortex dynamics in the sample.