Dispersion of acoustic-like and optic-like vibrational excitations in Ni{sub 2}B metallic glass

The dynamic structure factor S(Q, E) of Ni{sub 2}B metallic glass was studied by inelastic neutron scattering in the ranges of momentum transfers 0.7 < {Dirac_h}Q/A{sup -1} < 7, and energy, 2 < E/meV < 70, transfers. The measurements were performed with the IN4 spectrometer (Institut Laue-Langevin (ILL), Grenoble, France) on three samples of the same chemical composition but with different contents of Ni and B isotopes, as a result of which partial contributions were determined. The cuts through S(Q, E) for different values of E and Q demonstrated a characteristic behavior indicating that vibrational excitations, similar to acoustic and optical phonon excitations in crystals, propagate in an amorphous medium in a certain energy and momentum range.