Weak quasistatic magnetism in the frustrated Kondo lattice Pr2Ir2O7

Abstract Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr 2 Ir 2 O 7 for temperatures in the range 0.025–250 K. Kubo–Toyabe relaxation functions are observed up to ≳ 200 K , indicating static magnetism over this temperature range. The T → 0 static muon spin relaxation rate Δ ( 0 ) ≈ 8 μ s - 1 implies a weak quasistatic moment ( ∼ 0.1 μ B ) . The temperature dependence of Δ is highly nonmean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero for T T f . The data rule out ordering of the full Pr 3 + CEF ground-state moment ( 3.0 μ B ) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced 141 Pr nuclear magnetism. The dynamic relaxation rate λ increases markedly below ∼ 20 K , probably due to slowing down of spin fluctuations in the spin-liquid state. At low temperatures λ is strong and temperature-independent, indicative of a high density of low-lying spin excitations as is common in frustrated antiferromagnets.