We performed electrical resistivity ρ, magnetic susceptibility χ, specific heat C and electron diffraction measurements on single-crystalline samples of PrT 2Zn 20 (T=Ru, Rh and Ir). The three compounds show the Van Vleck paramagnetic behavior, indicating the nonmagnetic crystalline electric field (CEF) ground states. A Schottky-type peak appears at around 14K, irrespective of the T element, which can be moderately reproduced by a doublet-triplet model. For T=Ru, a structural transition occurs at T s=138K, below which no phase transition appears down to 0.04K. On the other hand, for T=Ir, antiferroquadrupole (AFQ) ordering arising from the nonmagnetic Γ 3 doublet takes place at T Q=0.11K. For T=Rh, despite a structural transition between 170 and 470K, the CEF ground state is still the non-Kramers Γ 3 doublet. However, no phase transition due to the Γ 3 doublet was observed even down to 0.1K.
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