Enhancement of flux pinning and high-field critical current density in carbon-alloyed Mg B2 thin films

We have studied flux pinning and critical current density in carbon-alloyed Mg B2 thin films prepared by hybrid physical-chemical vapor deposition. We found that carbon alloying significantly enhances flux pinning. The thermal activation energy of vortices U (H) and critical current density Jc (H) are much higher in carbon-alloyed films than in pure Mg B2 films at high fields. From the scaling behavior of the reduced pinning force with reduced field, we found that the dominant pinning mechanism changes from the grain boundary pinning in pure Mg B2 films to normal point pinning at low carbon content and back to grain boundary pinning at higher carbon contents for H ab. No dominant pinning mechanism exists when H ab.