Significant improvement of flux pinning and irreversibility field in nano-carbon-doped MgB2 superconductor

摘要

We report the synthesis and variation of superconductivity parameters such as transition temperature T-c, upper critical field He, critical current density J(c), irreversibility field H-irr and flux pinning parameter (F-p) for the MgB2-xCx system with nano-carbon doping up to x = 0.20. Carbon substitutes successfully on boron site and results in significant enhancement of H-irr and J(c)(H). Resistivity measurements reveal a continuous decrease in T-c under zero applied field, while the same improves remarkably at higher fields with an increase in nano-carbon content for MgB2-xCx system. The irreversibility field value (H-irr) is 7.6 and 6.6 T at 5 and 10 K respectively for the pristine sample, which is enhanced to 13.4 and 11.0 T for x = 0.08 sample at same temperatures. Compared to undoped sample, critical current density (J(c)) for the x = 0.08 nano-carbon-doped sample is increased by a factor of 24 at 10 K at 6 T field. (C) 2008 Elsevier Ltd. All rights reserved.