Kondo effect and local disorder in ion irradiated AuFe

Polycrystalline Au films with thicknesses between 30 nm and 80 nm were stepwise implanted with Fe+ ions at liquid helium temperature up to a concentration of 130 ppm and the resulting Kondo behavior was determined in situ down to 1.4 K applying an ac-technique with a resistance resolution of 2×10-5. Combining the implantation with various annealing steps as well as further Ar+ ion irradiations, the degree of disorder within the samples could be systematically varied. From the results, it is concluded that different types of defects must be distinguished when discussing the effect of disorder on the Kondo behavior: Defects which are closely trapped by the Fe atoms and strongly influence the Kondo effect, while hardly affecting the value of the residual resistivity, and defects which are sufficiently far away from the Fe atoms to exclude any direct influence. This second type strongly contributes to the residual resistivity without a correspondingly large effect on the Kondo behavior.