Atomic vibrational density of states in crystalline and amorphousTb1−xFex alloy thin films studied by nuclear resonant inelastic x-ray scattering (NRIXS)

Abstract

Nuclear resonant inelastic x-ray scattering of 14.4125 keV synchrotron radiation was employedto measure directly the partial (Fe projected) vibrational density of states (VDOS),g(E), of vapour-quenchedamorphous (a-)Tb1−x57Fex thin film alloys and epitaxial Tb57Fe2(110) thin films. A comparison of the VDOS measured at 300 and 10 K, respectively, demonstrates thatthe vibrational anharmonicity is small in these systems. The probability of recoilless absorption(f factor), the average kinetic energy per Fe atom and the average force constant were obtained. A plotof g(E)/E2 versus E proves the existence of non-Debye-like vibrational excitations at excitation energies belowabout 10 meV for the amorphous alloys. At a constant film thickness of 17.5 nm, theprobability of these excitations scales about linearly with the Tb concentration.