Unusual spin dynamics in the van der Waals antiferromagnet FeGa2S4

TL;DR

This study investigates the complex spin dynamics of the van der Waals antiferromagnet FeGa2S4, revealing unusual relaxation behaviors and challenging the conventional spin-glass transition interpretation through comprehensive experimental analysis.

Contribution

It provides detailed characterization of spin relaxation over thirteen orders of magnitude and uncovers non-diverging nonlinear susceptibilities, suggesting alternative mechanisms beyond a standard spin-glass transition.

Findings

Spin relaxation time spans thirteen orders of magnitude.

Nonlinear susceptibilities do not diverge at the anomalous temperature.

Above T* the spins fluctuate slowly (~10^-5 sec).

Abstract

Spin dynamics in the van der Waals antiferromagnet FeGa$_2$S$_4$ with triangular lattices are investigated using magnetometry, neutron scattering, and muon spin relaxation measurements. The characteristic spin relaxation time is thoroughly clarified over thirteen orders of magnitude. Although the temperature dependence of DC and AC susceptibilities recalls a conventional spin-glass transition, nonlinear susceptibilities showing no divergences at the anomalous temperature, $T^{\ast}=16.87(7)$~K, deny that and instead hint at other mechanisms. Elastic neutron scattering together with previously measured muon results depict a slowly fluctuated ($\sim 10^{-5}$~sec) spin state above $T^{\ast}$. In juxtaposing the underlying simplest structure among frustrated magnets with an intricate hierarchy of time scales, FeGa$_2$S$_4$ can be a playground for studying temporal spin correlations in the two-dimensional limit.