Kondo disorder and non-Fermi-liquid behavior in ${\mathrm{UCu}}_{5\mathrm{-}\mathit{x}}$${\mathrm{Pd}}_{\mathit{x}}$ and ${\mathrm{CeCu}}_{5.9}$${\mathrm{Au}}_{0.1}$

Muon spin rotation (μSR) has been used to probe non-Fermi-liquid (NFL) behavior in the heavy-fermion alloys ${\mathrm{UCu}}_{5\mathrm{-}\mathit{x}}$ ${\mathrm{Pd}}_{\mathit{x}}$, x=1.0 and 1.5, and ${\mathrm{CeCu}}_{5.9}$ ${\mathrm{Au}}_{0.1}$. Zero-field μSR puts an upper bound of ∼0.01${\mathrm{\mu }}_{\mathit{B}}$/U atom on any static magnetism in ${\mathrm{UCu}}_{5\mathrm{-}\mathit{x}}$ ${\mathrm{Pd}}_{\mathit{x}}$, which is too weak to affect the transverse-field μSR linewidth or to give rise to NFL behavior. In agreement with NMR results, μSR spectra in transverse fields suggest that a broad distribution of Kondo temperatures (‘‘Kondo disorder’’) is important in ${\mathrm{UCu}}_{5\mathrm{-}\mathit{x}}$ ${\mathrm{Pd}}_{\mathit{x}}$. NFL anomalies at temperature T then arise from ‘‘free’’ spins for which ${\mathit{T}}_{\mathit{K}}$≪T. Comparison of μSR and NMR linewidths also indicates short-range spatial correlation of the Kondo disorder in ${\mathrm{UCu}}_{5\mathrm{-}\mathit{x}}$ ${\mathrm{Pd}}_{\mathit{x}}$, in agreement with the local character of the dynamic susceptibility inferred from neutron scattering experiments. In ${\mathrm{CeCu}}_{5.9}$ ${\mathrm{Au}}_{0.1}$ the data suggest significant Kondo disorder only if the spatial correlation is long ranged, which is not indicated by other properties of this alloy. © 1996 The American Physical Society.