Atomic vibrational dynamics of amorphous Fe–Mg alloy thin films

Abstract

Abstract The atomic vibrational dynamics of 57 Fe in 800-A thick amorphous Fe x Mg 1− x alloy thin films (0.3≤ x ≤0.7) has been investigated at room temperature by nuclear resonant inelastic X-ray scattering (NRIXS) of 14.4125 keV synchrotron radiation. The amorphous phase has been successfully stabilized by codeposition of Fe and Mg in ultrahigh vacuum onto a substrate held at −140 °C during deposition. The amorphous structure of the samples was confirmed by X-ray diffraction and conversion electron Mossbauer spectroscopy. The 57 Fe-projected partial vibrational density of states, g ( E ), has been obtained from the measured NRIXS vibrational excitation probability, together with thermodynamic quantities such as the probability of recoilless absorption ( f -factor), the average kinetic energy per Fe atom, the average force constant, and the vibrational entropy per Fe atom. A plot of g ( E )/ E 2 versus E proves the existence of non-Debye-like vibrational excitations with a peak at E bp ∼3–5 meV (boson peak). Both the boson peak height and E bp were found to depend linearly on the composition x . Above the boson peak, g ( E )/ E 2 exhibits an exponential decrease.