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 Delta(0) ~ 8 mus-1 implies a weak quasistatic moment (~0.1 muB). The temperature dependence of Delta is highly non-mean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero below ~150 K. The data rule out ordering of the full Pr3+ CEF ground-state moment (3.0 muB) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced 141Pr nuclear magnetism. The dynamic relaxation rate lambda increases markedly below ~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.