Transport currents of two-axially rolled and post-annealed MgB2/Fe wires at 4.2 K

Single- and four-core MgB 2 wires have been made by the powder-in-tube (PIT) method using a commercial MgB 2 powder ( Alfa Aesar ) and two-axial rolling deformation in an Fe sheath. The deformed wires were subjected to annealing at temperatures from 950 °C up to 1100 °C for 30 minutes in argon. The interface layer thickness of 10–25.4 μm caused by inter-diffusion and reaction between the MgB 2 core and the Fe sheath has been observed in all annealed wires. Transport currents of as-deformed and post-annealed wires were measured at the temperature 4.2 K and external magnetic field B = 0–5.5 T. The presence of a ferromagnetic sheath in MgB 2 composite wire influences the I c ( B ) characteristics leading to I c hysteresis and I c anisotropy, which is more pronounced for those that have not been annealed (weakly linked grains) in comparison to well-connected MgB 2 grains after recrystallization. A comparison of the overall current densities versus the external magnetic field of NbTi, Nb 3 Sn and Bi-2223 superconductors with four-core MgB 2 wire is also presented.