Muon Spin Rotation And Relaxation In Pr1-Xndxos4sb12: Magnetic And Superconducting Ground States

Muon spin rotation and relaxation (mu SR) experiments have been carried out to characterize magnetic and superconducting ground states in the Pr1-xNdxOs4Sb12 alloy series. In the ferromagnetic end compound NdOs4Sb12 the spontaneous local field at positive-muon (mu(+)) sites below the ordering temperature T-C is greater than expected from dipolar coupling to ferromagnetically aligned Nd3+ moments, indicating an additional indirect RKKY-like transferred hyperfine mechanism. For 0.45 <= x <= 0.75, mu(+) spin relaxation rates in zero and weak longitudinal applied fields indicate that static fields at mu(+) sites below T-C are reduced and strongly disordered. We argue this is unlikely to be due to reduction of Nd3+ moments, and speculate that the Nd3+-mu(+) interaction is suppressed and disordered by Pr doping. In an x = 0.25 sample, which is superconducting below T-C = 1.3 K, there is no sign of "spin freezing" ( static Nd3+ magnetism), ordered or disordered, down to 25 mK. Dynamic mu(+) spin relaxation is strong, indicating significant Nd- moment fluctuations. The mu(+) diamagnetic frequency shift and spin relaxation in the superconducting vortex-lattice phase decrease slowly below T-C, suggesting pair breaking and/or possible modification of Fermi-liquid renormalization by Nd spin fluctuations. For 0.25 <= x <= 0.75, the mu SR data provide evidence against phase separation; superconductivity and Nd3+ magnetism coexist on the atomic scale.