Evidence of δl pinning induced by citric acid doping in MgB2 superconductor

The critical current density (J(c)) and flux-pinning mechanism of MgB2 doped with citric acid (C6H8O7) from 0 to 30wt% have been investigated in detail by magnetic and resistive measurements. The temperature dependence of critical current density, J(c)(T), at particular field within the single vortex regime was analyzed. delta T-c pinning mechanism was found to be the only important pinning mechanism in pure MgB2 samples, while delta l pinning is dominant with little effect of delta T-c pinning for citric acid doped samples. It was observed that the contribution of delta l pinning enhances with the increasing doping level of critic acid, and it was also found that MgB2 doped with 15wt% critic acid shows the best performance in J(c)-B behavior.