Spin Fluctuations from Hertz to Terahertz on a Triangular Lattice

TL;DR

This study investigates the magnetic fluctuation dynamics in NiGa$_2$S$_4$, revealing a significant slowdown near 8.5 K and persistent microsecond fluctuations indicating emergent phenomena within its short-range correlated state.

Contribution

It provides a detailed analysis of temporal magnetic correlations over thirteen decades, uncovering anomalous slow spin dynamics and emergent degrees of freedom in a triangular lattice antiferromagnet.

Findings

Spin fluctuation rate drops sharply near 8.5 K.

Persistent microsecond spin fluctuations above 8.5 K.

Emergent degrees of freedom within short-range correlations.

Abstract

The temporal magnetic correlations of the triangular lattice antiferromagnet NiGa$_2$S$_4$ are examined through thirteen decades ($10^{-13}-1$~sec) using ultra-high-resolution inelastic neutron scattering, muon spin relaxation, AC and nonlinear susceptibility measurements. Unlike the short-ranged {\it spatial} correlations, the temperature dependence of the {\it temporal} correlations show distinct anomalies. The spin fluctuation rate decreases precipitously upon cooling towards $T^{\ast}=8.5$~K, but fluctuations on the microsecond time scale then persist in an anomalous dynamical regime for 4 K $<T\le T^{\ast}$. As this time scale exceeds that of single site dynamics by six orders of magnitude, these fluctuations bear evidence of emergent degrees of freedom within the short-range correlated incommensurate state of NiGa$_2$S$_4$.