Raman spectra in iron-based quaternary CeO<inf>1-x</inf>F<inf>x</inf>FeAs and LaO<inf>1-x</inf>F<inf>x</inf>FeAs

Abstract

Raman spectra have been measured on iron-based quaternary CeO 1-x F x FeAs and LaO 1-x F x FeAs with different amounts of fluorine doping at room temperatures. A group analysis has been made to clarify the optical modes. Based on first-principle calculations, the observed phonon modes can be assigned accordingly. In LaO 1-x F x FeAs, the E g and A 1g modes related to the vibrations of La are suppressed with increasing F doping. However, F doping only has a small effect on the E g and A 1g modes of Fe and As. The Raman modes of La and As are absent in rare-earth substituted CeO 1-x F x FeAs, and the E g mode of oxygen, corresponding to the in-plane vibration of oxygen, moves to around 450cm -1 and shows a very sharp peak. The electronic scattering background is low, and electron-phonon coupling is not evident for the observed phonon modes. Three features are found above 500cm -1 , which may be associated with multi-phonon processes. Nevertheless, it is also possibl e that they are related to magnetic fluctuations or interband transitions of d orbitals, considering their energies. © 2009 IOP Publishing Ltd.