Superconducting properties of MgB₂ wires and tapes with different metal sheaths

We have successfully fabricated mono- and multifilamentary MgB₂ wires and tapes with different sheathed metals such as Cu, Ta, NbZr and Fe by the powder-in-tube method. The phase compositions, microstructure features and superconducting properties are investigated by X-ray diffractometer, optical microscopy, SEM, standard four-probe technique and SQUID magnetometer. The results indicate that there is no reaction between the sheathed metals used here except Cu. For the Cu/Ta/MgB₂ wire, the irreversibility field achieves 6.6 T at 5 K and J_c is higher than 10⁵ A/cm² at 5 K in self-field. By using NbZr as a buffer layer, 18-filamentary Cu/MgB₂ tapes show a transport high J_c of 8 × 10⁴ A/cm² (10 K self-field). Remarkably, we prepared the Fe/MgB₂ wire with high transport J_c of 5.6 × 10⁴ A/cm² (15 K, 3 T) and 5.1 × 10⁴ A/cm² (25 K, 2 T). The reasons for the improvement of J_c in high fields were briefly discussed.