Fluctuating magnetism of Co- and Cu-doped NaFeAs

Abstract

We report an x-ray emission spectroscopy (XES) study of the local fluctuating magnetic moment (µ bare ) in NaFe 1−x Co x As and NaFe 1−x Cu x As. In NaFeAs, the reduced height of the As ions induces a local magnetic moment higher than Ba 2 As 2 , despite lower T N and ordered magnetic moment.As NaFeAs is doped with Co µ bare is slightly reduced, whereas Cu doping leaves it unaffected, indicating a different doping mechanism: based on electron counting for Co whereas impurity scattering dominates in the case of Cu. Finally, we observe an increase of µ bare with temperature in all samples as observed in electron-and hole-doped BaFe 2 As 2 . Since both Co and Cu doping display superconductivity, our findings demonstrate that the formation of Cooper pairs is not connected with the complete loss of fluctuating paramagnetic moments.