COLLECTIVE EXCITATIONS IN AMORPHOUS FE85B15

Measurements of the dynamic structure factor performed on the MARI spectrometer at ISIS on the metallic glass Fe85B15 are briefly discussed. The spectra were fitted by a sum of two Gaussian functions, one representing the elastic peak and one the inelastic part of the spectrum, and a linear background in order to obtain a 'dispersion curve' for the collective excitations at small Q. Several interesting features are noticeable. (i) At 295 K, the measured data at small Q are very well described by the sound velocity calculated from the Young modulus while at 20 K this is not the case. At this temperature, the data do not seem to extrapolate to the origin but to a finite energy. (ii) The 'dispersion curve' is asymmetric with regard to Q0/2.