Role of novel Mg-coating method on transport properties of MgB2/Fe wires

We report a comparative study which reveals the role of excess magnesium addition technique on transport properties of single-core in-situ MgB2/Fe wires. Transport measurements are performed on MgB2/Fe wires which initially contain different amounts of excess Mg with < 1 wt.%, 1 wt.%, and 5 wt.% of Mg + 2B precursor powder. The MgB2/Fe wire with <1 wt.% excess Mg is produced by using the Mg-coating technique, in which an excess amount of Mg is first coated into the initial iron tube by evaporation, then the stoichiometric Mg + 2B powder is filled into this Mg-coated iron tube. Transport properties of the Mg-coated wire are compared with those of the wires which are produced directly from the non-stoichiometric precursor powders having 1 wt.% and 5 wt.% excess-Mg. The highest J(c) (28 K) of 1.99 x 10(2)A/cm(2) and the biggest n-value (28 K) of 4.8 are obtained for the Mg-coated wire sample under B = 7T, despite its lowest initial excess-Mg ratio among the whole wires. We suggest that the results of the present work are expected to contribute to the existing debates on Mg stoichiometry which essentially affect the critical current density of MgB2 wires under low/moderate magnetic fields.