O Efeito da Dopagem Química sobre Propriedades Magnéticas e Elétricas dos Estados Supercondutor e Normal de Monocristais de YBa2Cu3O7-δ

• Ano de defesa: 2021
• Autor(a) principal: Jaeckel, Sandra Teixeira
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Pelotas; Programa de Pós-Graduação em Física; UFPel; Brasil
• Palavras-chave em Português: YBa2Cu3O7-δ; Substituições químicas; Propriedades elétricas; Propriedades magnéticas; Chemical substitutions; Eletrical properties; Magnetic properties; CIENCIAS EXATAS E DA TERRA; FISICA
• Link de acesso: http://guaiaca.ufpel.edu.br/xmlui/handle/prefix/12971

Experimental results of DC magnetization and AC electrical magnetoresistivity were obtained and analyzed in order to understand the effects of substitutions of 1% of Cu by Au, Ni, Zn and Mg and of up to 10% of Y by Ca on some properties, both in superconducting [diamagnetic thermodynamic fluctuations, DTF and kinetic energy density of Cooper pairs condensation, EK] and normal states [thermodynamic fluctuations in electrical magnetoconductivity, TFEM and Hall coefficient, RH] of do YBa2Cu3O7-δ. The DC magnetization results of samples do YBa2Cu3O7-δ and YBa2Cu2,97M0,03O7-δ (M= Au, Ni, Zn and Mg) show that the behavior of DTF is characterized by a 3D-XY to 3d-LLL crossover depending on the applied magnetic field (μ0H), showing the clear distinction between the correlated (μ0H < 2,5kOe) and the uncorrelated (μ0H >2,5kOe) character by the DTF of the superconducting order parameter (Ψ). All Cu-doped samples showed a reduction in the magnitude of EK, in the magnetically reversible regime. Such behavior is possible due to the fact that the chemical substitutions employed act as scattering centers for the Cooper pairs. In the samples, the profile presented by EK versus T is mildly affected by the application of μ0H, which may possibly be associated with the 3d character and the low planar anisotropy of the system. In the longitudinal configuration in the normal state of the Y0,95Ca0,05Ba2Cu3O7-δ (MCa5) and YBa2Cu2,97Au0,03O7-δ (MAu) samples, the AC electrical magnetoresistivity measurements show that the behavior of the TFEM, near the critical transition temperature (T>TC), is marked by the occurrence of genuinely critical 3D-XY regimes (λCR≈0,33 and λSCR< 0,33). In the MCa5 sample, the lowest value observed was λSCR=0,07, suggesting that the N-S transition is classified as weakly first order (λ ≈ 0). The characterization of DTF, superconducting state and TFEM, normal state of the MAu sample, in T ≈ TC, in terms of the 3D-XY formalism, indicates that the behavior of TF of Ψ near the TC tends to be symmetrical. In the cross-sectional configuration, AC electrical magnetoresistivity measurements performed in the normal state of the Y1-xCaxBa2Cu3O7-δ (x = 0,01; 0,05 and 0,10) samples provided that the behavior of RH(T) was investigated in the overdoped region in carriers (p > 0,16) of the T versus p diagram of do YBa2Cu3O7-δ. The analyzes identified the coexistence of the ordinary R0 and anomalous (χRS) contributions due to the behavior of RH(T). The R0 behavior was strongly dependent on p, while that presented by χRS as a function of p was strongly influenced by the pseudogap state up to p < 0,19. The origin of the anomalous contribution to RH(T) is probably related to scattering of magnetic nature, arising from magnetic fluctuations from the establishment of chiralities in the coupling between spontaneous orbital currents and spins located in Cu atoms.