Susceptibility inhomogeneity and non-Fermi liquid behavior in UCu_5-xPt_x

Transverse-field μSRμSR shifts and relaxation rates have been measured in the non-Fermi liquid (NFL) alloy system UCu5-xPtxUCu5-xPtx, x=1.0x=1.0, 1.5, and 2.5. At low temperatures the fractional spread in Knight shifts δK/K≈δχ/χδK/K≈δχ/χ is ≳2≳2 for x=1x=1, but is only half this value for x=1.5x=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 EE, our results indicate that δE/Eav≈(δK/K)T→0δE/Eav≈(δK/K)T→0 is similar for UCu5-xPdxUCu5-xPdx (x=1x=1 and 1.5) and UCu4UCu4Pt, but is reduced for UCu5-xPtxUCu5-xPtx, x=1.5x=1.5 and 2.5. This reduction is due to a marked increase of EE with increasing xx; the spread δEδE is found to be roughly independent of x . Our results correlate with the observed suppression of other NFL anomalies for x>1x>1 in UCu5-xPtxUCu5-xPtx but not in UCu5-xPdxUCu5-xPdx, and are further evidence for the importance of disorder in the NFL behavior of both these alloy systems.