Moessbauer spectroscopy of La0.87Ca0.13FePO and LaFeAsO0.93F0.07 under external magnetic field and nuclear resonant inelastic scattering of La0.87Ca0.13FePO

An 57Fe Moessbauer spectroscopic study of iron-based layered superconductors La0.87Ca0.13FePO and LaFeAsO0.93F0.07 under external magnetic fields of up to 14T was performed. Our results suggest that hyperfine fields induced by local magnetic moments are, if any, small and that the magnetic feature of Fe in La0.87Ca0.13FePO and LaFeAsO0.93F0.07 is most likely to be paramagnetism with itinerant electrons. This feature is confirmed both above and below the transition temperature for LaFeAsO0.93F0.07. Furthermore, the temperature dependence of the iron-specific phonon density of states in La0.87Ca0.13-FePO was measured by using the nuclear resonant inelastic scattering of synchrotron radiation. We have found that the temperature-dependent change in the iron-specific phonon density of states of La0.87Ca0.13FePO was smaller than that of LaFeAsO0.89F0.11. (author)