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Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Ag doping

We report the impact of silver addition on granularity of NdFeAsO0.8F0.2 superconductor. The ac susceptibility and electrical resistivity under magnetic field are measured to study the improvement in weak links of NdFeAsO0.8F0.2 with addition of Ag. The Ag free NdFeAsO0.8F0.2 compound shows superconductivity at around 51.8K. Typical two step superconducting transitions due to the inter and intra grain contributions, induced from the combined effect of superconducting grains and the inter-granular weak-coupled medium respectively are clearly seen in susceptibility plots. In comparison to the pure NdFeAsO0.8F0.2 compound, the coupling between the superconducting grains is significantly improved for 20Ag silver doped sample, and the same is deteriorated for higher Ag content i.e., for 30wt Ag sample. The magneto transport measurements R(T)H of polycrystalline 20Ag doped NdFeAsO0.8F0.2, exhibited the upper critical filed [Hc2(0)] of up to 334Tesla, which is slightly higher than the one observed for pure NdFeAsO0.8F0.2. The flux flow activation energy varies from 7143.38K to 454.77K with magnetic field ranging from 0Tesla to 14Tesla for 20wtAg doped NdFeAsO0.8F0.2. In this investigation, our results show that limited addition of Ag improves the granular coupling of superconducting grains of NdFeAsO0.8F0.2 compound.