The effect of impurity and the suppression of superconductivity in Na(Fe0.97−xCo0.03Tx)As (T = Cu, Mn)

We report the successful growth of and the effect of impurity scattering in single crystals of Na( ${\mbox{F}}{{{\mbox{e}}}_{0.97-x}}$ ${\mbox{C}}{{{\mbox{o}}}_{0.03}}$ ${{{\mbox{T}}}_{x}}$ )As (T = Cu, Mn). The temperature dependence of the DC magnetization at high magnetic fields is measured for different concentrations of Cu and Mn. Detailed analysis based on the Curie–Weiss law indicates that Cu doping weakens the average magnetic moments, while doping with Mn enhances the local magnetic moments greatly, suggesting that the former may produce nonmagnetic or very weak magnetic impurities, and that the latter may give rise to magnetic impurities. However, it is found that both doping with Cu and doping with Mn will enhance the residual resistivity and suppress the superconductivity, at similar rates, in the low doping region, which is consistent with the prediction of the S $^{\pm }$ model. For the Cu-doped system, the superconductivity is suppressed completely at a residual resistivity of ${{\rho }_{0}}=0.87$ m Ω cm, for which a strong localization effect is observed. However, in the case of Mn doping, the suppression of ${{T}_{c}}$ becomes much weaker beyond x = 0.03 and superconductivity is maintained even up to a residual resistivity of 2.86 m Ω cm. Clearly the magnetic Mn impurities may even be not as detrimental as the nonmagnetic or very weak magnetic Cu impurities to the superconductivity in the high doping regime.