Measurement of Tc suppression in tungsten using magnetic impurities

We have measured the effects of dilute magnetic-atom doping on the superconducting transition temperature of tungsten thin films. Our ‘‘Tc tuning’’ technique is accurate, precise, and simple. Experiments were performed using dc-magnetron-sputtered tungsten films with undoped values of Tc in the range of 70–150 mK. The magnetic-atom doping was achieved using ion implantation. Specific Tc suppressions of between 5% and 65% were targeted and observed in this study. The transition width of each undoped sample was '1 mK and the transition widths remained sharp after implantation with Fe ions. Our data are in good agreement with predictions of a linear dependence of Tc suppression with increasing magnetic-atom concentration, in the small concentration limit. At higher concentrations, antiferromagnetic coupling between the magnetic dopant atoms becomes important and the Tc-suppression effect is diminished. We use our Tc data to calculate the Abrikosov–Gor’kov ~AG! and Ruderman–Kittel–Kasuya–Yosida ~RKKY! spin– flip relaxation parameters tAG and tRKKY . We conclude with a brief discussion of applications of the Tc-tuning technique, and present our plans for future studies in this area. © 1999 American Institute of Physics. @S0021-8979~99!03624-5#