Doping effect of nano-diamond on superconductivity and flux pinning in MgB₂

The doping effect of diamond nanoparticles on the superconducting properties of MgB₂ bulk material has been studied. It is found that the superconducting transition temperature T_c of MgB₂ is suppressed by the diamond doping, however, the irreversibility field H_irr and the critical current density J_c are systematically enhanced. Microstructural analysis shows that the diamond-doped MgB₂ superconductor consists of tightly-packed MgB₂ nano-grains (∼50-100 nm) with highly dispersed and uniformly distributed diamond nanoparticles (∼10-20 nm) inside the grains. The highly density of dislocations and diamond nanoparticles may be responsible for the enhanced flux pinning in the diamond-doped MgB₂.