High critical current density in MgB₂/Fe wires

High-quality monofilamentary MgB₂ wires 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 J_c in the sample was also discussed.