Phonon density of stales in Fe/Cr(001) superlattices and Tb-Fe thin-film alloys

Inelastic nuclear scattering of X-rays from the 14.413 keV nuclear resonance of (57)Fe was employed to measure directly the Fe-projected phonon density of states (DOS) in MBE-grown Fe/Cr(0 0 1) superlattices on MgO(0 0 1). The Mossbauer-inactive (56)Fe isotope was used in the Fe levers. A 1 Angstrom thick Mossbauer-active (57)Fe-probe layer (95% enriched) was placed at different locations within the Fe layers, This procedure permits to distinguish phonon density of states at the Fe-Cr-interface from that at the center of the Fe-film. Distinct differences have been observed in the DOS of our samples. The phonon DOS of an amorphous Tb(33)Fe(67) alloy film was found to be a broad and structureless hump, contrary to that of an epitaxial TbFe(2) film, which exhibits characteristic features. (C) 1999 Elsevier Science B.V. All rights reserved.