Abstract
Attenuation and phase velocity change of ultrasonic waves have been measured in the amorphous metal Pd0.775Si0.165Cu0.06 as a function of the amplitude in the frequency range 370 to 1 080 MHz and for temperatures down to 0.05 K. The amplitude dependent attenuation, attributed to the resonant absorption by the two-level systems (T.L.S.), varies as the square of the frequency and the inverse of the temperature, in agreement with the standard theory of T.L.S. The attenuation at high amplitude depends linearly on the temperature and is frequency independent at the lowest temperatures. The velocity increases logarithmically with the temperature. The slope of Δv/v versus Ln T was found to be amplitude and frequency independent. Thus no confirmation of the behaviour observed at lower frequencies (10 to 90 MHz) by other workers in an alloy of the same composition could be provided