Atomic Vibrational Dynamics of Thin Films Studied by Nuclear Resonant Inelastic X-Ray Scattering: Amorphous Tb1−x Fe x Alloys

Nuclear resonant inelastic X-ray scattering (NRIXS) of 14.4125 keV synchrotron radiation was used to measure directly the partial vibrational density of states (VDOS), g(E), of vapor-quenched amorphous Tb1−x 57Fe x thin film alloys (0.20 ⩽ x ≤ 0.82). The structure of the samples was characterized by X-ray diffraction and Mossbauer spectroscopy. The behavior of the Lamb-Mossbauer factor obtained from measured vibrational excitation probability densities indicates vibrational softening with increasing Tb content. A plot of g(E)/E 2 versus E 2 proves the existence of non-Debye-like vibrational excitations below about 10 meV, becoming more pronounced with rising Tb content.