Ground State of the Easy-Axis Rare-Earth Kagom\'e Langasite Pr$_3$Ga$_5$SiO$_{14}$

TL;DR

This study investigates the magnetic ground state of Pr$_3$Ga$_5$SiO$_{14}$ using muon spin relaxation and NQR, revealing a Van-Vleck paramagnetism rather than a spin-liquid state.

Contribution

It provides the first local-probe evidence that Pr$_3$Ga$_5$SiO$_{14}$ exhibits Van-Vleck paramagnetism, challenging previous spin-liquid hypotheses.

Findings

Quasi-static internal fields develop below 40 K.

Hyperfine-enhanced $^{141}$Pr nuclear magnetism is observed.

A broad maximum in relaxation rate at ~10 K indicates excited crystal-field levels.

Abstract

We report muon spin relaxation ($\mu$SR) and $^{69,71}$Ga nuclear quadrupolar resonance (NQR) local-probe investigations of the kagom\'e compound Pr$_3$Ga$_5$SiO$_{14}$. Small quasi-static random internal fields develop below 40 K and persist down to our base temperature of 21 mK. They originate from hyperfine-enhanced $^{141}$Pr nuclear magnetism which requires a non-magnetic Pr$^{3+}$ crystal-field (CF) ground state. Besides, we observe a broad maximum of the relaxation rate at $\simeq 10$ K which we attribute to the population of the first excited magnetic CF level. Our results yield a Van-Vleck paramagnet picture, at variance with the formerly proposed spin-liquid ground state.