Magnetic properties of the intermediate valence compounds YbIn${\mathrm{Au}}_2$ and Yb${\mathrm{Ni}}_2$${\mathrm{Ge}}_2$

Yb in YbIn${\mathrm{Au}}_2$ and Yb${\mathrm{Ni}}_2$ ${\mathrm{Ge}}_2$ is found via studies of magnetic susceptibility to be in a mixed-valence state. By including a diamagnetic susceptibility contribution and the effects of a small amount of trivalent impurity, an excellent fit of susceptibility versus temperature data can be obtained on a simple theoretical model. Thermal dependence of the activation parameters is found to be small.