Significant enhancement of flux pinning in MgB₂/Fe/Cu superconducting wires fabricated by in situ powder-in-tube method

Dense MgB₂/Fe/Cu wires with and without Zr doping were successfully prepared through the in situ powder-in-tube (PIT) method. MgB ₂/Fe/Cu wires were sintered at 650-850 °C for 2 h in argon. Critical current density (J_c) of the wires was measured at different temperatures in the magnetic field up to 8 T by standard four probe method. As shown by inductive measurements, the heat treatment temperature has an obvious influence on flux pinning of MgB₂ wire. Also it is found that the flux pinning in MgB₂ wire can be remarkably improved by Zr doping. The microstructure observation for MgB₂ wires shows that MgB ₂/Fe/Cu wire with Zr doping has better grain connectivity and higher density than other samples. The mechanism leading to high transport critical current densities of MgB₂/Fe/Cu wires based on MgB₂ grain size is discussed. The results indicate that the J_c can be further improved to meet the requirement for applications by optimizing the process conditions.