Abstract
Superconductor samples of type (CoFe2O4)(x)GdBa2Cu3O7-delta (0 <= x <= 0.1) were synthesized by the conventional solid-state reaction technique, whereas nanosized CoFe2O4 was prepared by co-precipitation method with grain size of about 8.5 nm. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE). The temperature dependence of real (chi') and imaginary (chi '') components of AC magnetic susceptibility (ACMS) at different magnetic field amplitude (3-15 Oe) was investigated. The analysis of the temperature dependence of ACMS was performed using Bean critical state model. The values of the critical current density J(c) at T > T-p (T-p is the inter-granular loss peak temperature) were calculated as a function of magnetic field and nanosized CoFe2O4 content. It was found that the low nanosized CoFe2O4 addition content (x = 0.01) improves the critical current density J(c) of Gd-123 superconducting phase. The observed variation of J(c) with temperature indicated that the weak links are changed from superconductor-normal metal-superconductor (SNS) for free sample to superconductor-insulator-superconductor (SIS) type of junctions for samples added with nanosized CoFe2O4 of x > 0.01. We also discussed the experimental results in the framework of the critical state model to estimate the effective volume fraction of the grains f(g) using Cole-Cole plots.