Drastic enhancement of magnetic critical current density in Zn doped Bi-2212

At several temperatures (T) we have studied magnetization (M) as a function of magnetic field (H) in (i) the pure Bi-2212 and (ii) the Zn doped Bi-2212 below respective critical temperatures, Tc. An enhancement in Delta M(H) in Zn doped Bi-2212 has been observed. Based on the criterion, Delta M = constant the HT diagram is found. Shifting in the irreversibility line (IL) has also been investigated. An enormous enhancement of magnetic critical current density (Jcm) in the Zn doped Bi-2212 superconductor is observed. We have analysed Jcm(H) to understand the microscopic nature of vortex pinning. A possible crossover from the collective pinning regime at lower magnetic field to a single vortex pinning with the increase in H at several T is observed in both samples having almost similar granular nature. Pinning of pancake vortices is strongly affected by the localised magnetic moment induced by nonmagnetic Zn in Cu sites. Change in the pinning force density in doped Bi-2212 has been explained.