The Landau-Khalatnikov mechanism associated with the relaxation of the order-parameter amplitude gives a peak in the longitudinal ultrasonic attenuation $\alpha$ near $T_c$, which quantitatively accounts for the observed peak in U${\mathrm{Be}}_{13}$ and U${\mathrm{Pt}}_3$. At lower temperatures this mechanism gives a power-law attenuation.

• Received 11 March 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.1627