BRILLOUIN-SCATTERING FROM SURFACE ACOUSTIC-WAVES IN NI AL MULTILAYER FILMS/

The surface acoustic wave velocities in Ni/Al multilayer films were de termined using Brillouin scattering for several modulation periods Lam bda ranging from 10.7 Angstrom to 84.9 Angstrom. The Rayleigh wave vel ocity shows a minimum around Lambda similar to 40 Angstrom. In order t o obtain more detailed information on the elastic properties of the mu ltilayer system, the effective elastic constants, C-11, C-33, C-44 and C-13, were determined for each multilayer. The C-13 constant increase s by about 50% below Lambda similar to 40 Angstrom and the C-33 consta nt decreases slightly below Lambda similar to 30 Angstrom as Lambda de creases. On the other hand, the C-11 constant is independent of Lambda . These elastic constants effect the Rayleigh wave velocity only sligh tly, while the minimum of the C-44 elastic constant is a major cause o f the minimum Rayleigh wave velocity.