Influence of the sintering process on critical currents, irreversibility lines and pinning energies in multifilamentary MgB₂wires

We have investigated the electrical transport properties for two MgB 2 wires containing four MgB 2 filaments in an Fe matrix, made by an ex situ process. The two wires differed in their final treatment. While only the mechanical deformation steps were applied to one of them (wire A ), the other (wire B ) was annealed in an Ar atmosphere to perform sintering of the powder grains. Critical currents were measured by the transport method, at temperatures ranging from 4.2 K to 30 K, and in magnetic fields up to 8 T. Due to the sintering step, critical currents and pinning energies of the wire B strongly increased with respect to the wire A . The analysis of the R ( T ) curves and current–voltage characteristics revealed that the irreversibility line was affected by the sintering process. An explanation of the observed behaviours is given in terms of the different activation volumes for pinning energies.