On the Symmetry of Low-Field Ordered Phase of PrFe4P12 : 31P NMR

We have performed 31P nuclear magnetic resonance (NMR) experiments on the filled skutterudite compound PrFe4P12 to investigate the exotic ordered phase at low temperatures and low magnetic fields. Analysis of the NMR line splitting in the ordered phase indicates that totally symmetric (\Gamma_1-type) staggered magnetic multipoles are induced by magnetic fields. This is incompatible with any type of quadrupole order at zero field. We conclude that the ordered phase has broken translational symmetry with the wave vector Q=(1,0,0) but the Th point symmetry at the Pr sites is not broken by the non-magnetic \Gamma_1-type order parameter.