Physica B 359–361 (2005) 871–873 Neutronscatteringstudiesoforderparametersandexcitations in antiferro-quadrupolar phase of PrFe 4 P 12 L. Hao a ,K.Iwasa a,Ã , K. Kuwahara b ,M.Kohgi b , H. Sugawara c ,Y.Aoki b , H. Sato b , T.D. Matsuda d , J.-M. Mignot e , A. Gukasov e ,M.Nishi f a Department of Physics, Tohoku University, Aramaki-aza-aoba, Aoba-ku, Sendai 980-8578, Japan b Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan c Department of Mathematical and Natural Sciences, Tokushima University Tokushima 770-8502, Japan d Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai 319-119, Japan e Laboratoire Le´on Brillouin, CEA-CRNS, CEA/Saclay, 91191 Gif sur Yvette Cedex, France f Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan Abstract The order parameters in the antiferro-quadrupolar (AFQ) ordered phase of PrFe 4 P 12 have been investigated by polarized neutron diffraction measurement. By observing the interference effect of scattering amplitudes from the Fe- iondisplacementandtheantiferromagneticcomponentinducedbythemagneticfieldappliedalongthe[0,0,1]axis,we conclude that the dominant ordered quadrupole is O 0 2 in the low-temperature phase. By inelastic neutron scattering experiment for a single-crystal sample, we observed sharp magnetic excitations in the AFQ-ordered phase, whose maximum intensity appears at the Brillouin zone center and minimum at the zone boundary. This fact indicates the existence of ferromagnetic correlation between Pr ions in the AFQ-ordered phase. r 2005 Elsevier B.V. All rights reserved. PACS: 71.27.+a; 61.12.Ex; 75.90.+w Keywords: PrFe 4 P 12 ; Antiferro-quadrupolar ordering; Neutron scattering PrFe 4 P 12 crystallizing in a cubic structure (Im ¯ 3; T 5 h )hasrecentlyattractedmuchattentionduetoits heavy electron behavior which is novel for Pr- based compounds [1,2]. Specific heat, electrical resistivity and magnetic susceptibility show sharp anomalies at T A ¼ 6:5K which indicate a clear phase transition. However, no magnetic ordering was observed by power neutron diffraction mea- surement [2–4]. X-ray superlattice reflections characterized by the wave vector q ¼½1; 0; 0 were observedbelow T A andthescatteringpatternwere explained by the formation of crystal structure ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$-see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.01.328 Ã Corresponding author. Tel.: +81222176486; fax: +81222176489. E-mail address: iwasa@iiyo.phys.tohoku.ac.jp (K. Iwasa).