Enhancement of in-field Jc in MgB2/Fe wire using single and multi-walled nanotubes

We investigated the doping effects of SWCNTs and MWCNTs on the Tc, lattice parameters, Jc(B), microstructure, and Hc2 of MgB2/Fe wire. These effects systematically showed the following sequence for Tc and the a-axis: the SWCNT doped wire the MWshortCNT doped wire > the MWlongCNT doped wire > un-doped wire. A dominating mechanism behind all these findings is the level of C substitution for B in the lattice. The best Jc(B) and Hc2 were obtained on SWCNT doped wire because the level of C substitution for B in this wire is higher than all others.