Raman spectra in iron-based quaternary CeO1-xFxFeAs and LaO1-xFxFeAs
Abstract
Raman spectra have been measured on iron-based quaternary CeO1-xFxFeAs and LaO1-xFxFeAs with varying fluorine doping at room temperatures. A group analysis has been made to clarify the optical modes. Based on the first principle calculations, the observed phonon modes can be assigned accordingly. In LaO1-xFxFeAs, the Eg and A1g modes related to the vibrations of La, are suppressed with increasing F doping. However F doping only has a small effect on the Eg and A1g modes of Fe and As. The Raman modes of La and As are absent in rare-earth substituted CeO1-xFxFeAs, and the Eg mode of oxygen, corresponding to the in-plane vibration of oxygen, moves to around 450 cm-1 and shows a very sharp peak. Electronic scattering background is low and electron-phonon coupling is not evident for the observed phonon modes. Three features are found above 500 cm-1, which may be associated with multi-phonon process. Nevertheless it is also possible that they are related to magnetic fluctuations or interband transitions of d orbitals considering their energies.