Excess conductivity and magnetization of CoFe2O4 combined with Y1Ba2Cu3O7-δ as a superconductor

Abstract

In this study, we determined the direct current DC isothermal magnetization (M − H and M-T), global critical current density (Jc), intra-grain critical current density (Jcintra), and excess conductivity for samples of CoFe2O4 (CFO; 1.0, 2.0, and 3.0 wt%) combined with Y1Ba2Cu3O7-δ (YBCO). X-ray diffraction analysis and Rietveld refinement suggested that all of the composite samples belonged to the Pmmm space group. No significant variations in the lattice parameters were observed after the inclusion of CFO in the YBCO matrix. The crystallite size decreased after CFO was added to the YBCO matrix according to field emission scanning electron microscopy. The addition of CFO to the YBCO matrix changed the flux pinning ability, thereby reducing the global critical current densities (Jc) and intra-grain critical current density (Jcintra) as the CFO concentration increased, but Jc and Jcintra both increased at the higher concentration., Jc and Jcintra were obtained from DC isothermal magnetization measurements (M − H) using Bean's critical state model. The critical temperature (TC) decreased and the residual resistivity (ρ0) increased as the wt.% of CFO increased, thereby indicating that the trapping of charge carriers occurred as well as grain boundary resistivity enhancement. Excess conductivity analysis was performed to investigate the thermal fluctuations near the critical temperature and various crossover temperatures were obtained using the Aslamazov–Larkin model.