Study of the ground state properties of $LiHo_xY_{1-x}F_4$ using $\mu$SR

TL;DR

This study investigates the ground state magnetic properties of LiHo_xY_{1-x}F_4 using muon spin relaxation, revealing persistent dynamics without spin glass signatures and highlighting the role of hyperfine interactions.

Contribution

It provides new insights into the low-temperature spin dynamics of LiHo_xY_{1-x}F_4, challenging previous spin glass interpretations and emphasizing hyperfine interactions.

Findings

No evidence of spin glass behavior down to 15mK.

Observed dynamic magnetism with a temperature-independent fluctuation rate below 300mK.

Fluctuation rate increases with x up to 0.08, then saturates.

Abstract

$LiHo_xY_{1-x}F_4$ is an insulating system where the magnetic Ho$^{3+}$ ions have an Ising character, and interact mainly through magnetic dipolar fields. We used the muon spin relaxation technique to study the nature of the ground state for samples with x=0.25, 0.12, 0.08, 0.045 and 0.018. In contrast with some previous works, we have not found any signature of canonical spin glass behavior down to $\approx$15mK. Instead, below $\approx$300mK we observed dynamic magnetism characterized by a single correlation time with a temperature independent fluctuation rate. We observed that this low temperature fluctuation rate increases with x up to 0.08, above which it levels off. The 300mK energy scale corresponds to the Ho3+ hyperfine interaction strength, suggesting that the hyperfine interaction may be intimately involved with the spin dynamics in this system.