Temperature dependence of the sound attenuation at the spill glass transition of metallic spill glasses

We have measured the sound attenuation (Q(-1)) in the kHz-range of a re-entrant (Metglass 2826A) and a dilute spin glass (Pd(Fe)) with freezing temperatures (T-f) of 1.2 K and 1 mK. For the two samples Q(-1) shows a broad maximum at T-f. In spite of very different T-f and one order of magnitude difference in Q(max)(-1), the reduced curve Q(-1)(T)/Q(max)(-1) vs. T/T-f follows the same temperature dependence. We show that this dependence can be well described with a thermally activated phonon-spin relaxation time with a broad distribution of activation energies. The maximum activation energy of the distribution scales with the freezing temperature.