Evaluation of connectivity, flux pinning, and upper critical field contributions to the critical current density of bulk pure and SiC-alloyed Mg B 2

Measurement of critical current density J c , normal state resistivity ρ n , and upper critical field H c 2 on pure and 10% SiC-doped Mg B 2 bulks show systematic enhancement of H c 2 by SiC addition and by lowering reaction temperature. H c 2 ( 10 K ) exceeds 33 T , while the extrapolated zero temperature value exceeds 40 T . The Rowell [ Supercond. Sci. Technol. 16 , R17 ( 2003 ) ] analysis suggests that only 8%-17% of the Mg B 2 cross section actually carries current. Higher reaction temperature enhances the connectivity but degrades H c 2 and flux pinning, making the measured J c a complex balance between connectivity, H c 2 , and flux pinning induced by grain boundaries and precipitates.