Kondo temperature and Heavy Fermion behavior in Yb1−xYxCuAl series of alloys

Results on x-ray diffraction, electrical resistivity, specific heat and magnetization on the Yb1−xYxCuAl series of compounds are reported. The analysis of the x-ray data shows the increase of the unit cell volume with the Y dilution. The electrical resistivity shows an evolution from Kondo lattice regime for x≤0.6 to single impurity behavior for x = 0.8 and 0.94. The electronic coefficient γ shows values of Heavy Fermion systems along the series for 0 ≤x<1. On the other hand, dc magnetic susceptibility measurements show typical curves of intermediate valence systems with a maximum around 25K. Below this maximum, the values of low temperature susceptibility (χ(0)) decrease with the increase of Y content. From the dependence of χ(0) and γ upon Y substitution, an increase of 12% of the Kondo temperature (TK) for x = 0.8 alloy respect to the reference YbCuAl (x = 0) is estimated. This is further supported by the evolution of the temperature of the maximum in the magnetic contribution of the specific heat. The overall results can be explained by the increase of the hybridization as consequence of negative pressure effects obtained by the chemical substitution of Yb by Y, thus leading to the increase of TK, in agreement with the Doniach's diagram.