Universal fluctuating regime in triangular chromate antiferromagnets

TL;DR

This study investigates the magnetic properties and fluctuating regimes in the frustrated triangular lattice antiferromagnet $ ext{α-HCrO}_2$, revealing persistent spin dynamics below the magnetic transition due to interlayer frustration, with implications for spin-liquid behavior.

Contribution

It provides comprehensive experimental and theoretical analysis of $ ext{α-HCrO}_2$, highlighting the role of interlayer frustration in sustaining spin fluctuations in triangular antiferromagnets.

Findings

Magnetic transition at $T_N \,\simeq\,22.5$ K observed.

Broad fluctuating regime with slow dynamics persists down to 0.7$T_N$.

Interlayer frustration leads to persistent spin dynamics below $T_N$.

Abstract

We report x-ray diffraction, magnetic susceptibility, heat capacity, $^{1}$H nuclear magnetic resonance (NMR), and muon spin relaxation ($\mu$SR) measurements, as well as density-functional band-structure calculations for the frustrated $S=3/2$ triangular lattice Heisenberg antiferromagnet (TLHAF) $\alpha$-HCrO$_{2}$ (trigonal, space group: $R\bar{3}m$). This compound undergoes a clear magnetic transition at $T_{\rm N} \simeq 22.5$~K, as seen from the drop in the muon paramagnetic fraction and concurrent anomalies in the magnetic susceptibility and specific heat. Local probes (NMR and $\mu$SR) reveal a broad regime with slow fluctuations down to $0.7\,T_{\rm N}$, this temperature corresponding to the maximum in the $\mu$SR relaxation rate and in the NMR wipe-out. From the comparison with NaCrO$_{2}$ and $\alpha$-KCrO$_{2}$, the fluctuating regime and slow dynamics below $T_{\rm N}$ appear to be hallmarks of the TLHAF with $ABC$ stacking that leads to a frustration of interlayer couplings between the triangular planes. This interlayer frustration is a powerful lever to generate spin states with persistent dynamics and may bear implications to spin-liquid candidates with the triangular geometry.