Atomic vibrational dynamics of amorphous Fe–Mg alloy thin films

• Published in: The Journal of physics and chemistry of solids Vol. 66; no. 12; pp. 2263 - 2270
• Main Authors: Sahoo, B., Keune, W., Sturhahn, W., Toellner, T.S., Alp, E.E.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 01.12.2005; Elsevier
• Subjects: advanced photon source; AMORPHOUS STATE; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; IRON ALLOYS; Lattice dynamics; MAGNESIUM ALLOYS; MATERIALS SCIENCE; Phonons in low-dimensional structures and small particles; Physics; THIN FILMS; VIBRATIONAL STATES; Vibrational states in disordered systems; Magnesium alloys; Force constants; Amorphous alloy; Phonon density of states; Iron alloys; Thin films; X-ray scattering; Inelastic scattering; Lattice dynamics; Phonon mode; Boson peak; Chemical composition; Codeposition; Synchrotron radiation
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2005.09.090

The atomic vibrational dynamics of 57Fe in 800-Å 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 Mössbauer spectroscopy. The 57Fe-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.