Mono- and multifilamentary Fe/MgB2 tapes and wires with high transport critical current densities were prepared by using the powder-in-tube technique and fine powders. The influence of the initial MgB2 grain size upon critical current density, upper critical and irreversibility fields was studied. After reducing the MgB2 grains to μm-sized by ball milling, the critical current density, JC, was enhanced, while the upper critical field, μ0HC2, remained unchanged. The anisotropy ratio between the upper critical fields parallel and perpendicular to the tape surface was determined to be 1.3, reflecting a deformation induced texture. A good agreement was found between resistive and inductive JC values, measured at various temperatures between 4.2 and 25K. In monofilamentary tapes, JC values close to 105A/cm2 were measured at 25K/1T, while JC values of about 106A/cm2 were extrapolated for 4.2K/0T. Fe/MgB2 tapes exhibited high exponential n factors for the resistive transition: n values of 60 and 30 were found at 4 and 6T, respectively. Multifilamentary wires (with 7 filaments) exhibited slightly lower JC values, 1.1 x 105A/cm2 at 4.2K/2T.

Improved Transport Critical Current and Irreversibility Fields in Mono- and Multifilamentary Fe/MgB2 Tapes and Wires using Fine Powders. R.Flükiger, P.Lezza, C.Beneduce, N.Musolino, H.L.Suo: Superconductor Science and Technology, 2003, 16, 264-70