Improving superconducting properties of MgB2 by graphene doping

We report the synthesis and characterization of MgB2 made from nano-boron and doped with graphene in the following mole percentages, x = 0, 3.0 and 12.0. The effect of graphene doping on the normal state resistivity (Ï), superconducting transition temperature (Tc), irreversibility and upper critical fields (Hirr and Hc2), and critical current density (Jc), as well as the pinning force (Fp) were evaluated. We found that the graphene doping has a positive impact on the above mentioned properties. In the case of the optimally doped (x = 3.0%) sample, the critical current density at 5 K corresponds to 1.4 × 105 A/cm2 for 2 T field, whereas the undoped sample showed 9.6 × 104 A/cm2 for the same field, i.e., 1.5 times improvement. Furthermore, the optimally doped sample showed a Jc of nearly 1 × 104 A/cm2 at 5 K, 8 T, which is a significantly high value. The upper critical field has been enhanced to 13 T at 20 K for the optimal doping level. The flux pinning behavior has been evaluated from the curve of flux pinning force against applied magnetic field, and it reveals that the maximum pinning has been improved by nearly 1.2 times at 20 K, due to the graphene doping.