Disappearance of the kondo effect of Ce impurities in (La,Th) based alloys

We present an experimental study of the resistivity at low temperature of (La, Th) based alloys with Ce impurities. We observe a logarithmic behaviour of the resistivity vs temperature at low concentration of Th. When we increase the concentration of Th, the magnetic resistivity is no longer logarithmic but linear with T, and at still higher concentrations of Th, the anomaly in the resistivity disappears. Moreover, the curve of the slope of the logarithmic resistivity vs the concentration of Th goes through a maximum for 20% Th before vanishing for 50% Th.