Properties of MgB2 bulks after combined doping with Fe and C by adding Iron(II) lactate (C6H10FeO6)

Bulk MgB₂ doped with C and Fe was prepared by using the solid state sintering method with C₆H₁₀FeO₆ as dopant. The phase composition, microstructure, and superconducting properties were studied. X-ray diffraction (XRD) shows the presence of iron after the doping. The addition of C₆H₁₀FeO₆ increases the a- and c-axis parameters of MgB₂, as evidenced by the shifting of the (100) and (002) peaks to a lower angle on the XRD patterns. Fe atoms were distributed uniformly, as shown by the field emission scanning electron microscope images, while the magnetization of the sample was dominated by the signals from the MgB₂ superconductor, although the iron-containing materials also contributed a minor amount of magnetization. The residual resistivity ratio was decreased as the C₆H₁₀FeO₆ doping level increased. The critical temperature also decreased with increased doping level, as did the critical current density, J_c. The doping also caused decreases in the irreversibility field, H_irr, and the upper critical field, H_c2. The decrease in H_c2 and H_irr, together with the harmful effects from impurity phases such as MgO is the reason for the decrease in J_c.