We report inelastic neutron scattering results for single-crystalline samples of PrFe4P12, which undergoes a transition from the heavy-electron phase to the antiferro-type nonmagnetic ordered phase. In contrast to the quasielastic magnetic response observed in the heavy electron phase, the well-defined inelastic peaks located at 1.5 and 3meV are superimposed in the ordered phase. The maximum spectral intensity appears at the Brillouin zone center for the original Im3̄ structure, and the minimum spectral intensity appears at the zone boundaries including the ordering vector q 0 = (1,0.0). The evolution of the 1.5 meV peak with an applied magnetic field in the ordered phase is in agreement with excitations between 4f-electron crystalline-field- splitting levels, while the 3 meV peak is smeared out rapidly. The spectra are consistent with the recently proposed staggered ordering of a Pr site with well-localized f-electrons and that with a Kondo-singlet-like state, which are represented as the totally symmetric state accompanied by the charge modulation of carriers.
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