Role of Co nanoparticles in CuTl-1223 superconductor

Cobalt (Co) nanoparticles were added in Cu0.5Tl0.5Ba2Ca2Cu3O10−δ(CuTl-1223) superconducting matrix to obtain (Co)x/CuTl-1223 (x=0, 0.25, 0.50, 0.75, and 1.0 wt%) nanoparticles-superconductor composites. The crystal structure of host CuTl-1223 phase was not affected but superconducting transport properties were suppressed after the addition of these nanoparticles. Suppression of superconductivity was attributed to ferromagnetic nature of Co nanoparticles due to enhanced scattering cross-section of the carriers. The average crystallite size of Co nanoparticles was 50 nm, which were usually found in blocked state along their anisotropy axis below room temperature. The sharp suppression of diamagnetic signal could be due to two possible reasons (i) decrease in superconducting volume fraction and (ii) pair-breaking across ferromagnetic Co nanoparticles in blocked state.