Glassy spin dynamics in non-fermi-liquid UCu5-xPdx, x=1.0 and 1.5 -: art. no. 066402

Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCu5-xPdx, x = 1.0 and 1.5, have been studied using muon spin-lattice relaxation. The sample-averaged asymmetry function (G) over bar (t) indicates strongly inhomogeneous spin fluctuations and exhibits the scaling (G) over bar (t, H) = (G) over bar (t/H-gamma) expected from glassy dynamics. At 0.05 K gamma (x = 1.0) = 0.35 +/- 0.1, but gamma (x = 1.5) = 0.7 +/- 0.1. This is in contrast to inelastic neutron scattering results, which yield gamma = 0.33 for both concentrations. There is no sign of static magnetism greater than or similar to 10(-3) mu (B)/U ion in either material above 0.05 K. Our results strongly suggest that both alloys are quantum spin glasses.