Atomic vibrational density of states in crystalline and amorphous Tb_1 <i>x</i>Fe_<i>x</i>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 employed to measure directly the partial (Fe projected) vibrational density of states (VDOS), g(E), of vapour-quenched amorphous (a-)Tb 1-x 57Fe 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.