High critical current density in MgB2/Fe wires

Abstract

High-quality monofilamentary MgB2wires with Fe sheath were fabricated by the powder-in-tube (PIT) method at ambient pressure. The phase compositions, microstructure features and flux pinning properties are investigated by using x-ray diffractometer, SEM, TEM and a standard four-probe technique. It is found that MgB2 has no reaction with Fe. The results indicate that MgB2 wires are dense and only MgB2 and few MgO phases exist in the core area. MgB2/Fe wires exhibit very high transport critical current densities of 1.43 × 105 A cm−2 (4.2 K, 4 T), 2.8 × 104 A cm−2 (4.2 K, 6 T), 3.72 × 104 A cm−2 (15 K, 4 T) and 2.34 × 104 A cm−2 (25 K, 3 T). The maximum flux pinning force shows a peak at 4 T at 4.2 K, suggesting strong pinning at high fields. The reasons for the large Jc in the sample was also discussed.