Magnetism in heavy-fermion U(Pt,Pd)3 studied by μSR

We report μSR experiments carried out on a series of heavy-electron pseudobinary compounds U(Pt1-xPdx)3 (x≤0.05). For x≤0.005 the zero-field muon depolarization is described by the Kubo-Toyabe function. However the temperature variation of the Kubo-Toyabe relaxation rate ΔKT(T) does not show any sign of the small-moment antiferromagnetic phase with TN approx. 6 K (signalled by neutron diffraction), in contrast to previous reports. The failure to detect the small ordered moment suggests it has a fluctuating (>10 MHz) nature, which is consistent with the interpretation of NMR data. For 0.01≤x≤0.05 the muon depolarization in the ordered state is described by two terms of equal amplitude: an exponentially damped spontaneous oscillation and a Lorentzian Kubo-Toyabe function. These terms are associated with antiferromagnetic order with substantial moments. The Knight shift measured in a magnetic field of 0.6 T on single-crystalline U(Pt0.95Pd0.05)3 in the paramagnetic state shows two signals for B perpendicular c, while only one signal is observed for B parallel c. The observation of two signals for B perpendicular c, while there is only one muon localization site (0,0,0), points to the presence of two spatially distinct regions of different magnetic response. (author)