Calculation of Normalized Pinning Force and Nature of Pinning Mechanism for Nano-Al Doped MgB2 Superconductor

The Jc(H) of nano-Al doped MgB2 samples has been calculated from M(H) loop measurements at different temperatures. Normalized volume pinning forces as a function of the reduced field have been analyzed at different temperatures and doping level which was taken from the Jc(H) data. The modified scaling law was used as discussed by the Eisterer to analyze the pinning forces. This law was compared with the scaling law used by the Fietz and co-worker. The grain boundary pinning is found the dominant pinning mechanism in all the doped samples and exhibit the scaling behavior. The XRD and temperature dependence of resistivity confirms the successful substitution of nano-Al at Mg sites. The results endorse that the magnetic anisotropy decreased from pure to the dirty limit with the doping of the nano-Al. The enhancement in the Jc(H) of the sample with the nano-Al doping is due to decrease in the anisotropy and increase in the volume pinning forces. The 2 % nano-Al doped sample between 15?30K shows the highest Jc(H) among all the samples.