~(57)Fe M?ssbauer spectroscopy study of the 37 K superconductor Sm_(0.85)Ba_(0.15)FeAsO doped with fluorine

摘要

M?ssbauer spectroscopy investigation of superconducting Sm_(0. 85)Ba_(0. 15)FeAsO_(0.7)F_(0.3) (Tc = 37 K) has been performed. The spectra appear to be a singlet pattern throughout the temperature range of 20-290 K. The value of Debye temperature is obtained (θD ~ 390 K). Unusual behavior of the central shift as a function of temperature is observed below 60 K. Unlike cuprate superconductors, phonon softening is not observed near T_c of the iron pnictide.