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 TcTc, upper critical field HcHc, critical current density JcJc, irreversibility field Hirr and flux pinning parameter (Fp)(Fp) for the MgB2−xCx system with nano  -carbon doping up to x=0.20x=0.20. Carbon substitutes successfully on boron site and results in significant enhancement of Hirr and Jc(H)Jc(H). Resistivity measurements reveal a continuous decrease in TcTc 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 (Hirr) 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=0.08x=0.08 sample at same temperatures. Compared to undoped sample, critical current density (Jc)(Jc) for the x=0.08x=0.08nano-carbon-doped sample is increased by a factor of 24 at 10 K at 6 T field.