  Quantum criticality has been considered to be specific to crystalline
materials such as heavy fermions. Very recently, however, the Tsai-type
quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical
behavior. To obtain a deeper understanding of this new material, we have
searched for other Tsai-type cluster materials. Here, we report that the metal
alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the
Tsai-type quasicrystal and that both possess no localized magnetic moment. We
suggest that the Au-Al-Yb system is located near the border of the divalent and
trivalent states of the Yb ion; we also discuss a possible origin of the
disappearance of magnetism, associated with the valence change, by the
substitution of the constituent elements.
