Improved flux pinning and high critical current density in Fe-sheathed MgB2 wires and tapes by carbon nanotube doping

Carbon nanotube-doped Fe-sheathed MgB2 wires and tapes with different doping levels were fabricated by the in situ powder-in-tube method. The phases, microstructures and flux pinning were characterized by XRD, SEM/TEM, magnetic and transport-property measurements. It is found that carbon nanotubes (CNTs) doping resulted in a significant enhancement in the field dependence of critical current density Jc for all the added wires and tapes. The Jc in 13 T and 4.2 K for the CNTs doped tapes (optimal MgB1.9C0.1) increased by a factor of 11 compared to that of the undoped sample. The observed Jc(B) improvement in the added samples is attributable to the enhanced flux pinning caused by the CNTs doping.