Correlação entre a irreversibilidade magnética e a resistência nula em supercondutores de YBa2Cu3O7-d

• Ano de defesa: 2013
• Autor(a) principal: Nunes, Sabrina Esperança
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Pelotas; Instituto de Física e Matemática; Programa de Pós-Graduação em Física; UFPel; Brasil
• Palavras-chave em Português: Física; Estudo experimental; YBa2Cu3O7-d; Propriedades elétricas; Propriedades magnéticas; CNPQ::CIENCIAS EXATAS E DA TERRA::FISICA
• Link de acesso: http://guaiaca.ufpel.edu.br/handle/prefix/9749

This work consists in an experimental study concerning electric and magnetic properties in two melt-textured YBaCuO samples grown by Bridgman and top-seeding techniques with different contents of the Y211 phase added during the growth. The samples were characterized by electron microscopy, which was verified the presence of the Y211 phase into the superconducting matrix besides the crystallographic orientation. Electric magnetoresistance measurements were performed with the magnetic field applied along the ab plane and the c-axis in five different field-current configurations. The results showed a narrow transition moderately affected by magnetic field. Magnetic measurements were performed based on ZFC and FC procedures with the magnetic field applied along the ab plane and the c-axis. The ZFC measurements showed a decrease of the shielding effect when the magnetic field is augmented and the FC measurements showed the paramagnetic Meissner effect. The irreversibility line was determined in both samples. The irreversibility line for Bridgman sample was described by flux creep model, and for top-seeding sample it was described by superconducting glass model, pointing out to a granular behavior in relation to this sample. The correlation between the irreversibility line (Tirr) and the zero resistance line (Tc0) showed the zero resistance state occurring into the reversible region for all field-current configurations. The results also showed a strong anisotropy concerning the irreversibility lines and the zero resistance lines for both samples. In our results, the Lorentz force influence apparently was not decisive in the vortex dynamics observed. Were performed additional experiments in order to verify the influence of the oscillating amplitude of the sample into the magnetometer during magnetic measurements. The results pointed out to a strong influence of this parameter to the determination of the irreversibility temperature.