Weak quasistatic magnetism in the frustrated Kondo lattice Pr_2Ir_2O_7

TL;DR

This study reveals persistent weak static magnetism in Pr_2Ir_2O_7 over a wide temperature range, likely due to hyperfine-enhanced nuclear moments, and observes slow spin fluctuations characteristic of frustrated antiferromagnets.

Contribution

The paper provides the first muon spin relaxation evidence of weak quasistatic magnetism in Pr_2Ir_2O_7, highlighting its non-mean-field temperature dependence and ruling out full Pr^3+ moment ordering.

Findings

Weak static magnetism persists up to > 200 K

Static relaxation rate indicates tiny magnetic moments (~0.1 μ_B)

Slow spin fluctuations observed below 20 K

Abstract

Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr_2Ir_2O_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 Delta(0) ~ 8 mus^-1 implies a weak quasistatic moment (~0.1 mu_B). 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 Pr^3+ CEF ground-state moment (3.0 mu_B) 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.