Vortex pinning and dynamics in high performance Sr_0.6K_0.4Fe₂As₂ superconductor

We have studied vortex pinning and dynamics in a Sr_0.6K_0.4Fe₂As₂ superconducting tape with critical current density J_c ∼ 0.1 MA/cm² at 4.2 K and 10 T. It is found that grain boundary pinning is dominant in the vortex pinning mechanism. Furthermore, we observe large density of dislocations which can also serve as effective pinning centers. We find that the temperature dependence of critical current density is in agreement with the model of vortices pinned via spatial fluctuation of charge carrier mean free path. Magnetic relaxation measurement indicates that the magnetization depends on time in a logarithmic way. The relaxation rate in the low and intermediate temperature region is small, and it exhibits a weak temperature and field dependence. A crossover from elastic creep to plastic creep regime is observed. Finally, we conclude a vortex phase diagram for the high performance Sr_0.6K_0.4Fe₂As₂ superconducting tape.