On the Impact of Magnetic Co-nanoparticles on the Activation Energy and Transport Critical Current Density in Multilayered Y\(_{3}\)Ba\(_{5}\)Cu\(_{8}\)O\(_{18-\delta }\) Superconductors

Addition of magnetic nanoparticles of cobalt in the inter-granular region of polycrystalline Y\(_{3}\)Ba\(_{5}\)Cu\(_{8}\)O\(_{18-\delta }\) (Y-358) affects both the superfluid phase stiffness (\(J\) \(_{s}\)) and the transport critical current density (\(J\) \(_{c}\)). We have studied the current-voltage (IV) characteristics of (i) the pure Y-358 and (ii) Co-mixed Y-358 superconductors. \(J_s\) via an exponent related to nonlinearity of the IV curves is obtained within the framework of Berezinskii-Kosterlitz-Thouless (BKT) transition. A distinct indication of the BKT transition has been observed in the Y-358+0.75 wt.% Co composite system. \(J_c\) (T) has also been extracted to understand the effectiveness of Co-nanoparticles. A suppression in the current induced activation energy (U) in zero magnetic field leads to the degradation in transport \(J\) \(_{c}\) in the composite Y-358 superconductors.