Significant improvement of flux pinning and irreversibility field in nano-carbon-doped MgB2 superconductor

We report the synthesis and variation of superconductivity parameters such as transition temperature T c , upper critical field H c , critical current density J c , irreversibility field H irr and flux pinning parameter ( F p ) for the MgB2−xCx system with nano-carbon doping up to x = 0.20 . Carbon substitutes successfully on boron site and results in significant enhancement of H irr and J c ( H ) . Resistivity measurements reveal a continuous decrease in T c under zero applied field, while the same improves remarkably at higher fields with an increase in nano-carbon content for MgB2−xCx system. The irreversibility field value ( H irr ) is 7.6 and 6.6 T at 5 and 10 K respectively for the pristine sample, which is enhanced to 13.4 and 11.0 T for x = 0.08 sample at same temperatures. Compared to undoped sample, critical current density ( J c ) for the x = 0.08 nano-carbon-doped sample is increased by a factor of 24 at 10 K at 6 T field.