Local vibrational densities of states of dilute Fe atoms in Al and Cu metals

The local vibrational densities of states of highly dilute Fe (0.017 at. %) in Al metal and Fe (0.1 at. %) in Cu metal were measured by using nuclear resonant inelastic scattering of synchrotron radiation. The characteristic vibrational modes of Fe in Al were found to be modes of resonance with the host Al phonon spectrum. In the measured spectrum of Fe in Cu, in addition to resonance vibrational modes, just above the phonon cutoff energy of Cu metal a peak interpreted as being a localized mode predicted theoretically by the Green's-function method was found.