Low Temperature Elastic Properties of Icosahedral and Glassy PdUSi

We have measured the low-frequency elastic propertied of Pd58. 8 U20.6Si20.6 in both quasicrystal and glassy phases from 0.01K to 20K. Both materials show a large negative temperature coefficient of sound velocity over the entire temperature range. The slope in the icosahedral phase increases below 5K, the nominal spin-glass transition temperature, while the glassy sample show only a gradual increase in slope as the temperature is lowered. The damping in both samples decreases continuously as the temperature is lowered. Our results suggest that the magnetic behavior of this system may be important in interpreting the low temperature properties.