Muon spin rotation and relaxation inPr1−xNdxOs4

D. E. MacLaughlin

¹

,

P. C. Ho

²

,

Lei Shu

³

et al.

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 Nd 3+ 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 Nd 3+ moments, and speculate that the Nd 3+ -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 Nd 3+ 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 Nd 3+ magnetism coexist on the atomic scale.

Muon spin rotation and relaxation in Pr1−xNdxOs4Sb12 : Superconductivity and magnetism in Pr-rich alloys

“…As was previously observed for x = 0.25 [29], there is no oscillation or increase of KT at low temperatures that 1) to ZF data. Rates for x = 0 and x = 0.25 are from reanalysis of previously reported data [29,31]. Dashed line: normal-state rate for x = 0 from Ref.…”

“…Observation of temperature-dependent relaxation rates down to ∼100 mK is evidence for good thermalization of the samples to this temperature. Previously reported data for x = 0 [9,31] and 0.25 [29], obtained at ISIS and TRIUMF, Vancouver, Canada, have been reanalyzed and included here.…”

“…Phase diagram of Pr 1−x Nd x Os 4 Sb 12 . Superconducting and ferromagnetic transition temperatures (T c and T Curie , respectively) from electrical resistivity ρ, magnetic susceptibility χ , specific heat C [28], and μSR ( [29], this paper), onset of broken TRS, x = 0 from ZF μSR [11,30,31], and upper temperature limits for static Nd 3+ magnetism and/or broken TRS from ZF μSR (this paper).…”

“…In Results for x = 0 and 0.25 are from reanalysis of previously reported data (Refs. [31] and [29], respectively). contrast, no increase of KT below T c is observed for 0.05 x 0.20 down to the lowest temperatures of measurement [Fig.…”

“…The phase diagram of the superconducting and ferromagnetic transition temperatures (T c and T Curie , respectively) versus Nd concentration x is shown in Fig. 1 [28,29], together with the onset of broken TRS at T c for x = 0 [11,30,31]. One of the major features is the relative insensitivity of T c to Nd doping; the rate of decrease is comparable to that for nonmagnetic Ru doping [27] and much slower than for rare-earth doping of both conventional and unconventional superconductors.…”