We have performed inelastic neutron scattering and magnetic susceptibility measurements on Pr(Ru1-xRhx)4P12 (0 ≤ x ≤ 0.15), in which the antiferro-multipole ordering of PrRu 4P12 is gradually suppressed with increasing x. The saturation of magnetic susceptibility at low temperature suggests that all the 4f-electron ground states are singlet for x ≥ 0.03, in contrast to the triplet and singlet ground states in the ordered phase of PrRu4P 12. Neutron experiments show the presence of two types of crystal field (CF) level schemes: a temperature-dependent one similar to one of those observed in PrRu4P12 as signatures of the ordering, and an additional temperature-independent one indicating the existence of Pr ions which do not contribute to the ordering. Rh-substitution seems to have two effects: a local effect causing temperature-independent CF levels of Pr ions, and a wide-range effect causing switch of ground state. The ordering in low Rh-content compounds arises from the inequivalent CF level schemes that allow conserving the antiferro-type ordering pattern of multipoles through thermal excitation, despite the common ground state in compounds with x ≥ 0.03.
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