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 greater than or similar to 200 K, indicating static magnetism over this temperature range. The T -> 0 static muon spin relaxation rate Delta(0) approximate to 8 mu s(-1) implies a weak quasistatic moment (similar to 0.1 mu(B)). The temperature dependence of A 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 Pr3+ CEF ground-state moment (3.0 mu(B)) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced Pr-141 nuclear magnetism. The dynamic relaxation rate A increases markedly below similar to 20 K probably due to slowing down of spin fluctuations in the spin-liquid state. At low temperatures lambda is strong and temperature-independent, indicative of a high density of low-lying spin excitations as is common in frustrated antiferromagnets. (C) 2008 Elsevier B.V. All rights reserved.