Effect of annealing on the anomalous electrical resistivity of dilute copper-iron alloys at low temperatures

Abstract

Electrical resistivity measurements in the temperature range 1.5–35 K on two copper alloys containing 115 and 380 atomic ppm iron are reported, in their unannealed state and also after annealing for 16 and 66 h in fore-vacuum at 530–550°C. Below the temperature of the resistivity minimum the impurity resistivity Δρ has the Kondo lnT behavior. However, in the liquid helium region the resistivity drops from its value atT=0, in proportion toT2, conforming to Nagaoka's theory forT<TK/5. The Kondo temperatureTK is evaluated from the Δρ versusT2 plots using Nagaoka's equation and is found to decrease with increasing concentration. Annealing is found to reduce the effective iron concentration and alsoTK. The impurity resistivity per atomic percent in our samples can be expressed as a universal function ofT/TK at the lowest temperatures underTK/4.