Magnetic Excitation in Totally Symmetric Staggered Ordered Phase of PrFe4P12

We report inelastic neutron scattering results for single-crystalline samples of PrFe 4 P 12 , 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 3 meV are superimposed in the ordered phase. The maximum spectral intensity appears at the Brillouin zone center for the original I m \bar3 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 4 f -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 tota...