Effect of nano ZnO doping on the nature of pinning of MgB₂ superconductors

The paper reports the J_C(H, T) of nano-ZnO doped MgB2 samples calculated from M–H loop measurements. Volume pinning forces at different temperatures have been evaluated as a function of the field from the J_C–H data. Two different scaling laws, one by Fietz and Webb and another one by M. Eisterer, are used here to analyze the pinning forces. All samples show the scaling behavior, which confirms the existence of grain boundary pinning. The XRD and R–T data show the substitution of Zn at Mg sites. The anisotropy in the sample is found to decrease with the doping of the nano-ZnO. The improvement in the J_C(H, T) of the sample with the nano-ZnO doping is due to decrease in the anisotropy and increase in the volume pinning forces. The 2% nano-ZnO doping is found to be the optimal value in order to achieve the highest J_C(H, T) in these samples.