Development ofinhomogeneous conduction electron spin polarization in the antiferroquadrupolar phase of UPd3

Abstract

We have measured the Knight shift and inhomogeneous linebroadening of positive muons implanted in monocrystallineUPd3 from 2 K up to 300 K. We find two components in thetransverse-field (Hext = 0.6 T) precession signal withamplitude ratio 2:1, which is independent of temperature up to300 K. The two signals are associated with two different muonsites with axial symmetry. Both the Knight shifts and therelaxation rates show pronounced anomalies at the criticaltemperatures of T2≃4.4 K, believed to reflect, inter alia, a magnetic transition, T1≃6.8 K and T0≃7.6 K, originating from antiferroquadrupolar ordering.Details depend on sample orientation and signal component. It isargued that the particular temperature dependence of both theKnight shift and the inhomogeneous line broadening of thestronger component below 10 K is associated with the contacthyperfine contribution to the Knight shift and reflects aninhomogeneous conduction electron spin polarization caused bythe antiferroquadrupolar order. Additional zero-field µSRmeasurements yield a very small temperature-independentrelaxation rate consistent with the field inhomogeneity arisingfrom the Pd nuclear dipole fields. In particular, below 4.5 Kthere is no evidence for additional static fields due to amagnetically ordered state.