Doping Effect and Flux Pinning Mechanism of Nano-SiC Additions in MgB2 Strands

Superconducting MgB2 strands with nanometer-scale SiC additions have been investigated systematically using transport and magnetic measurements. A comparative study of MgB2 strands with different nano-SiC addition levels has shown C-doping-enhanced critical current density Jc through enhancements in the upper critical field, Hc2, and decreased anisotropy. The critical current density and flux pinning force density obtained from magnetic measurements were found to greatly differ from the values obtained through transport measurements, particularly with regards to magnetic field dependence. The differences in magnetic and transport results are largely attributed to connectivity related effects. On the other hand, based on the scaling behavior of flux pinning force, there may be other effective pinning centers in MgB2 strands in addition to grain boundary pinning.