Weak quasistatic magnetism in the frustrated Kondo lattice Pr2Ir2O7

Abstract Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr2Ir2O7 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 141Pr 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.