Paramagnetic Phase of a Heavy-Fermion Compound, CeFePO, Probed by 57Fe   M\"{o}ssbauer Spectroscopy
  57Fe M\"{o}ssbauer spectroscopy was applied to an iron-based layered compound CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed in the M\"ossbauer spectra of CeFePO indicating a paramagnetic phase of the Fe magnetic sublattice. All the spectra were fitted with a small quadrupole splitting, and the Debye temperature of CeFePO was found to be \sim448 K. The isomer shift at room temperature, 0.32 mm/s, was almost equal to those of LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts and unit cell volumes, it was found that the Fe of CeFePO has a similar valence state to other layered iron-based quaternary oxypnictides except LaFePO. 
Tetsuro Nakamura, Takashi Yamamoto, Masanori Matoba, Yasuaki Einaga,   and Yoichi Kamihara
cond-mat.str-el