Susceptibility inhomogeneity and non-Fermi liquid behavior in UCu5-xPtx

Transverse-field μSR shifts and relaxation rates have been measured in the non-Fermi liquid (NFL) alloy system UCu5-xPtx, x=1.0, 1.5, and 2.5. At low temperatures the fractional spread in Knight shifts δK/K≈δχ/χ is ≳2 for x=1, but is only half this value for x=1.5 and 2.5. In a disorder-driven scenario where the NFL behavior is due to a broadly distributed (Kondo or Griffiths-phase cluster) characteristic energy E, our results indicate that δE/Eav≈(δK/K)T→0 is similar for UCu5-xPdx (x=1 and 1.5) and UCu4Pt, but is reduced for UCu5-xPtx, x=1.5 and 2.5. This reduction is due to a marked increase of E with increasing x; the spread δE is found to be roughly independent of x. Our results correlate with the observed suppression of other NFL anomalies for x>1 in UCu5-xPtx but not in UCu5-xPdx, and are further evidence for the importance of disorder in the NFL behavior of both these alloy systems.