Atomic vibrational dynamics of thin films studied by nuclear resonant inelastic X-ray scattering:: Amorphous Tb1-xFex 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-xFex)-Fe-57 thin film alloys (0.20 less than or equal to x less than or equal to 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 proves the existence of non-Debye-like vibrational excitations below about 10 meV, becoming more pronounced with rising Tb content.