The effects of nano-scale iron doping on superconductivity and microstructure of MgB2 bulk

Mg_1-xFe_xB₂ superconductor was prepared by in situ solid state reaction to study the effects of nano-iron doping on the superconductivity of MgB₂. Two kinds of nano-iron sources were used: nano-iron particles and nano-iron wires. It was found that crystal structure was not affected by nano-iron doping for either form of dopant source. T_c, J_c, and H_irr were severely suppressed by iron nano-particles doping. In contrast, with iron nano-wires doping, T_c of the MgB₂ superconductors were not changed remarkably, while their J_c and H_irr were slightly enhanced at all the temperature ranges investigated in this work. Under 4 T field, the sample doped with 1% wt iron nano-wires reached the highest J_c of 1.1 times 10⁴ A/cm² at 10 K and 2.2 times10² A/cm² at 20 K, respectively. It was argued that the Fe nano-wires may be introduced into MgB₂ as external pinning centers in high field region.