Figure 1: Topographic STM images and characterizations of the related single crystals
(a,b) STM images of the Cu-doped and the Mn-doped samples with the a bias voltage of Vbias=15, 8 mV and tunneling current of It=100, 150 pA, respectively. The inset shows the rescanned data in a small area with much higher pixel, from which one can clearly see the Cu and Mn impurities. (a,b) Scale bars, 2 nm. (c) Temperature dependence of resistivity for the pristine sample and the doped ones. The superconductivity is suppressed clearly when the residual resistivity is enhanced. (d) The doping dependence of the critical transition temperature Tc for both the Cu- and Mn-doped samples. (e) The magnetization measured at μ0H=1T on the pristine sample (black open squares), the Cu-doped samples (blue symbols) and the Mn-doped samples (red symbols). One can see that the low temperature up-turn gets enhanced clearly by the Mn doping, but not enhanced by the Cu doping. (f) The average magnetic moment per Fe site calculated by the Curie–Weiss law for the Cu- and Mn-doped samples. Clearly, doping Mn induces strong averaged magnetic moments, whereas doping Cu seems to weaken the averaged local moments.
