Measurement of T-c suppression in tungsten using magnetic impurities

We have measured the effects of dilute magnetic-atom doping on the supercon ducting transition temperature of tungsten thin films. Our "T-c tuning" tec hnique is accurate, precise, and simple. Experiments were performed using d c-magnetron-sputtered tungsten films with undoped values of T-c in the rang e of 70-150 mK. The magnetic-atom doping was achieved using ion implantatio n. Specific T-c suppressions of between 5% and 65% were targeted and observ ed in this study. The transition width of each undoped sample was approxima te to 1 mK and the transition widths remained sharp after implantation with Fe-56(+) ions. Our data are in good agreement with predictions of a linear dependence of T-c suppression with increasing magnetic-atom concentration, in the small concentration limit. At higher concentrations, antiferromagne tic coupling between the magnetic dopant atoms becomes important and the T- c-suppression effect is diminished. We use our T-c data to calculate the Ab rikosov-Gor'kov (AG) and Ruderman-Kittel-Kasuya-Yosida (RKKY) spin-flip rel axation parameters tau(AG) and tau(RKKY). We conclude with a brief discussi on of applications of the T-c-tuning technique, and present our plans for f uture studies in this area. (C) 1999 American Institute of Physics. [S0021- 8979(99)03624-5].