Significant improvements of the high-field properties of carbon-dopedMgB2 films by hot-filament-assisted hybrid physical–chemical vapor deposition using methane asthe doping source

Abstract

We report a significant enhancement in upper critical fieldHc2 and irreversibilityfield Hirr incarbon-doped MgB2 films fabricated by hot-filament-assisted hybrid physical–chemical vapor deposition(HFA-HPCVD) using methane as the doping source. For the parallel field, a verylarge temperature derivative value of 3 T K−1 nearTc was achieved in aheavily doped film with Tc near 28 K. Carbon doping also enhanced flux pinning, resultingin a much higher critical current density in a magnetic fieldJc(H) than in undoped samples. The result suggests a more effective doping of carbon into theMgB2 structure and a better connectivity between the carbon-dopedMgB2 grainsthan in previous reports. A clear correlation between the decrease in grain size and the enhancementof Hc2 was observed.