Weak quasistatic magnetism in the frustrated Kondo lattice Pr2Ir2O7

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 ∆(0) ≈ 8 μs implies a weak quasistatic moment (∼0.1μB). The temperature dependence of ∆ is highly non-mean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero for T < Tf . The data rule out ordering of the full Pr CEF ground-state moment (3.0 μB) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced 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.