We have determined the magnetic response $S\left(\omega \right)$ of UCu ${}_{5-x}{\mathrm{Pd}}_x(x=1,1.5\mathrm{})$ for temperatures $T$ ranging from 12 to 300 K and energy transfers $\omega$ from 0.5 to 200 meV. $S\left(\omega \right)$ is virtually identical in the two compounds, displaying localized moment dynamics for $\omega \gtrsim 25$ meV. For $\omega <25\mathrm{}$ meV, temperature provides the only energy scale for the magnetic excitations with the dynamical susceptibility described by a universal scaling function ${\chi }^{\prime \prime }(\omega ,T)\sim {\omega }^{-1/3\mathrm{}}Z(\omega /T)$. We argue that $S\left(\omega \right)$ represents critical scattering associated with a $T=0\mathrm{}$ phase transition, whose origin lies with the magnetic screening of individual uranium ions.

• Received 21 November 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.725