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Nuclear resonant inelastic x-ray scattering of 14.4125 keV synchrotron radiation was employed to measure directly the partial (Fe projected) vibrational density of states (VDOS), g(E), of vapour-quenched amorphous (a-)Tb 1−x 57 Fe x thin film alloys (0.20 x 0.82) and epitaxial Tb 57 Fe 2 (110) thin films. A comparison of the VDOS measured at 300 and 10 K, respectively, demonstrates that the 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 plot of g(E)/E 2 versus E proves the existence of non-Debye-like vibrational excitations at excitation energies below about 10 meV for the amorphous alloys. At a constant film thickness of 17.5 nm, the probability of these excitations scales about linearly with the Tb concentration.

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