Impact of Co2C nanoparticles on enhancing the critical current density of Bi-2223 superconductor

Abstract

We have investigated the superconducting properties of nanocomposite pellets made from Bi-2223 and Co2C powders. Our measurements reveal loss of superconducting fraction in the nanocomposites. However, the retained superconducting fraction exhibits robust bulk superconducting properties. The Tc of the retained superconducting fraction was 109 K, which was found to be comparable to that of the pure Bi-2223 pellet. We found that the composite’s net magnetization response is a superposition of the contributions of ferromagnetic and superconducting fractions. Analysis revealed that the surviving superconducting fraction exhibits a robust Meissner response. In the nanocomposite, the irreversibility field of the superconducting fraction at 77 K is found to increase by almost three times compared to the pristine material, thereby showing strong vortex pinning features. We also find a broadened magnetic field regime over which we observe that a single vortex pinning regime sustained in the nanocomposite. The critical current density, Jc, of the nanocomposite was found to be approximately five times higher than that of the pristine Bi-2223 pellet at low T. In fact, the enhancement in Jc is most significant in the high T regime, where at temperatures close to Tc in the nanocomposite, we see almost two orders of magnitude increase in Jc compared to the pristine Bi-2223 pellet. Our study suggests that larger sized agglomeration of magnetic nanoparticles of Co2C leads to loss of superconductivity in the nanocomposite. However, there are also unagglomerated Co2C nanoparticles distributed uniformly throughout the nanocomposite, which act as efficient pinning centers that allow for collective vortex pinning centers to be retained, even up to temperatures near Tc, and these nanoparticles also do not compromise the bulk Tc of the superconducting fraction. Our study shows that these nanocomposites that exhibit enhanced Jc especially in the high T regime are potentially useful for high current applications.