Specific heats of dilute magnetic α-phase Cu-Au(Fe) alloys

This study of the specific heats of dilute magnetic α-phase Cu-Au(Fe) alloys is a continuation of our work on dilute Fe in binary-host alloys. Our previous specific-heat results for the α-phase Cu-Al(Fe) system indicated that the Kondo effect depended on the particular local environment of the Fe impurity. The present study was motivated by resistivity experiments which suggested for Cu-Au(Fe) a contrasting picture where local-environment effects are not important. 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.%. The excess specific heat due to the Fe impurities show a broad peak characteristic of the Kondo effect. A recently derived theoretical expression for the Kondo effect in the specific heat was successful in fitting these Cu-Au(Fe) results and the Cu(Fe) results of other investigators. The contribution from the Fe impurities for the various alloys had the same functional dependence on a scaled temperature TTK, where the TK decreased with increasing Au concentration. This agreed with the existence of a universal resistance curve for Cu-Au(Fe) found by other experimenters. Comparisons are made with our previous specific-heat result for the Cu-Al(Fe) system which could not be fit with a universal curve. It is suggested that local-environment effects are important in the Cu-Al(Fe) system in contrast with the Cu-Au(Fe) system.