Muon spin rotation and relaxation in Pr1−xNdxOs4Sb12: Magnetic and superconducting ground states

Abstract

Muon spin rotation and relaxation (μSR) 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 (μ+) sites below the ordering temperature TC 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, μ+ spin relaxation rates in zero and weak longitudinal applied fields indicate that static fields at μ+ sites below TC are reduced and strongly disordered. We argue this is unlikely to be due to reduction of Nd3+ moments, and speculate that the Nd3+-μ+ interaction is suppressed and disordered by Pr doping. In an x=0.25 sample, which is superconducting below Tc=1.3 K, there is no sign of “spin freezing” (static Nd3+ magnetism), ordered or disordered, down to 25 mK. Dynamic μ+ spin relaxation is strong, indicating significant Nd-moment fluctuations. The μ+ diamagnetic frequency shift and spin relaxation in the superconducting vortex-lattice phase decrease slowly below Tc, suggesting pair breaking and/or possible modification of Fermi-liquid renormalization by Nd spin fluctuations. For 0.25≤x≤0.75, the μSR data provide evidence against phase separation; superconductivity and Nd3+ magnetism coexist on the atomic scale.

Source-reported materials — not catalogue approval

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