Investigation of Temperature Dependence of the Irreversibility Line of GdBa2Cu3O7-delta Added with Nanosized Ferrite ZnFe2O4

摘要

Superconducting samples of the type (ZnFe2O4) (x) GdBa2Cu3O7-delta were synthesized by the conventional solid-state reaction technique. The nanosized (ZnFe2O4) content x varied from 0 to 0.1 wt% of the samples' total mass. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning and transmission electron microscopes (SEM and TEM). The effect of ZnFe2O4 addition, which acts as flux pinning centers, was investigated using ac magnetization at different applied dc magnetic fields. It was found that addition of the nanosized (ZnFe2O4) up to 0.06 wt% enhances the critical current density J (c) and the superconducting transition temperature T (c). On the other hand, the superconducting properties of these samples are deteriorated for x > 0.06 wt%. The irreversibility line was thermally activated. The logarithmic plot of H (irr) versus (1 - T (irr)/ T (c)(0)) shows a crossover at about 500 Oe, reflecting the transition from two- to three-dimensional vortex fluctuations. The B (irr)-T curves are well fitted according to Matsushita's model, which is based on the de-pinning mechanism caused by thermally activated flux creep.