Abstract
Doping effect of ZnO-nanoparticles on the superconducting properties of MgB2 has been studied. The 2% nano-ZnO doped MgB2 shows the excellent Jc and Hirr at all temperatures and magnetic fields amongst the doped and undoped sample. The lattice parameter-c shows the higher value for 2% ZnO doped MgB2 sample, which clearly demonstrates the presence of the lattice strain in doped samples. The residual resistivity ratio was increased as the nano-ZnO doping level increased. Very slight variation in Tc is observed from the temperature dependence of resistivity plot of nano-ZnO doped MgB2. In M (H) plot at low applied fields, we have observed large vortex instabilities (vortex-avalanches) associated with 2% and 4% doped samples. Vortex avalanche effect is diminishes with increasing temperature and disappears near 15 K. The results are discussed in terms of local-vortex instabilities caused by doping of ZnO nanoparticles. Scanning electron microscopy studies show that the synthesized samples are well adherent and grains are uniformly distributed with an average particle size of similar to 5-10 mu m.