Superconducting properties of multi-filamentary MgB2 wires

Full text: Many efforts are underway to produce multi-filamentary wires of MgB2, where the superconducting laments are embedded in good conducting material. Unfortunately strong chemical reactions between MgB2 and Cu deteriorate superconducting properties strongly. Therefore barrier sheaths between both materials are necessary. For these Nb and Ti are found to be useable. The important question is, how superconducting properties depend on the reduction of both lament diameter and barrier thickness. In this work we report on magnetic investigation of a series of MgB2 wires, with nineteen laments. All samples were prepared in the same way, but with lament diameters between 58.8 and 17.7 μm. With decreasing lament diameter the width of superconducting transition increases, although superconducting transition itself is not changed. Critical current density and irreversibility line also decrease. From magnetic relaxation measurements mean effective activation energies U are determined. They are also decreasing with decreasing lament diameter. The temperature dependence of U points to the existence of a pinning energy distribution, which broadens with decreasing lament diameter. (author)