Kondo Effect in Specific Heat of Cu-Au(Fe) Alloys

Abstract

The specific heats of a series of α‐phase Cu‐Au and dilute magnetic Cu‐Au(Fe) alloys with Fe concentrations near 0.04 at. % were measured over the temperature range 1–10 K. The alloys had Au concentrations of 2.4, 4.8 and 10 at. %. This work is a continuation of our program of studies on the Kondo effect due to dilute Fe in binary host alloys. In the case of binary host alloys it is necessary to take into account the possibility that the Kondo temperature TK will depend on the particular local environment of the impurity since local variations in the electronic properties will produce local variations in TK. Our previous specific heat results1 for the α‐phase Cu‐Al(Fe) system indicated such local environmental effects were important in that system. In contrast, resistivity results by other experimenters for Cu‐Au(Fe) suggested the absence of local effects since those results could be fit to a universal function of T/TK where TK decreased with increasing Au concentration. This contrasting result motivated the present specific heat investigation of Cu‐Au(Fe). The excess specific heat due to the Fe impurities in the Cu‐Au alloys showed the broad peak characteristic of the Kondo effect. A theoretical expression for the Kondo effect in the specific heat was used to fit the Cu‐Au(Fe) results and the Cu(Fe) results of other investigations. The excess resistivity for the various alloys had the same functional dependence on a scaled temperature T/TK in agreement with the resistivity results. In contrast, the Cu‐Al(Fe) results cannot be fit with this functional dependence. These results suggest that the Al atoms produce a significant local perturbation on the electronic properties in comparison with the Au atoms. This is not unexpected since Cu and Au are both noble metals while Cu and Al have appreciably different valances.