NMR studies of two unusual f-electron metals

We present the results of nuclear magnetic resonance (NMR) studies down to very low temperatures for two U compounds, UCu_3.5Pd_1.5 and U_0.8Y_0.2Pd₃, where the conduction electrons experience strong interactions and for which the temperature dependences of the thermal and transport properties do not obey the expectations of a simple Fermi-liquid model. Also the temperature and field dependences of the nuclear magnetization recovery of UCu_3.5Pd_1.5 in Cu nuclear quadrupole resonance show unusual features that cannot be reconciled with common expectations for a simple metal, but they are well accounted for by the Kondo disorder model. For U_0.8Y_0.2Pd₃, our Y NMR results indicate a distribution of internal static magnetic fields at the Y sites and a small temperature-dependent enhancement of the spin-lattice relaxation rateT ₁ ^? with respect to YPd₃. The NMR spectra are consistent with the presence of very small frozen U moments, but the temperature dependence of the spin-lattice relaxation rate indicates a more complicated situation.