Improvement of Upper Critical Field and Critical Current Density in Single Walled CNT Doped ${\hbox{MgB}}_{2}/{\hbox{Fe}}$ Wires

We evaluated the doping effect of single walled carbon nanotubes (SWCNT) on the phase formation, microstructure, critical current density (J
_c
), and upper critical field (H
_c2
) of MgB
₂
superconductor. All samples were sintered at temperatures ranging from 650 to 1000degC for 30 min. A typical high sintering temperature (900degC) sample was composed of well-consolidated MgB
₂
grain of 100 to 200 nm and nanosized particles, resulting in enhancement of J
_c
and H
_c2
. This indicates that lattice defects and microstructural change have occurred as a result of carbon (C) coming from SWCNT. On the other hand, a sample sintered at low temperature (700degC) contained relatively large grains. Specifically, SWCNT doped MgB
₂
wire sintered at 900degC exhibited excellent J
_c
> 10
⁴
Acm
^-2
up to 8 T at 4.2 K. This result indicates that flux pinning for sample produced at a high sintering temperature are enhanced by SWCNT doping. SWCNT is one of the promising C sources for MgB
₂
superconductor with excellent J
_c
.