Magnetic correlations in triangular antiferromagnet FeGa$_2$S$_4$

TL;DR

This study investigates magnetic correlations in the triangular antiferromagnet FeGa$_2$S$_4$ using various experimental techniques and theoretical modeling, revealing complex static and dynamic magnetic behaviors and exchange interactions.

Contribution

It provides detailed experimental characterization and theoretical modeling of magnetic interactions in FeGa$_2$S$_4$, highlighting the roles of major and minor magnetic sites and exchange couplings.

Findings

Magnetic short-range correlations are static at low temperatures and become dynamic around 30-50 K.

Minor sites contribute to a magnetic peak that vanishes at 5.5 K.

Exchange couplings are estimated as J1=1.7 meV, J2=0.9 meV, J3=0.8 meV, but not all spectral features are explained.

Abstract

The crystal structure and magnetic correlations in triangular antiferromagnet FeGa$_2$S$_4$ are studied by x-ray diffraction, magnetic susceptibility, neutron diffraction and neutron inelastic scattering. We report significant mixing at the cation sites and disentangle magnetic properties dominated by major and minor magnetic sites. The magnetic short-range correlations at 0.77 \AA$^{-1}$ correspond to the major sites and being static at base temperature they evolve into dynamic correlations around 30 - 50 K. The minor sites contribute to the magnetic peak at 0.6 \AA$^{-1}$, which vanishes at 5.5 K. Our analytical studies of triangular lattice models with bilinear and biquadratic terms provide the ratios between exchanges for the proposed ordering vectors. The modelling of the inelastic neutron spectrum within linear spin wave theory results in the set of exchange couplings $J_1=1.7$\,meV, $J_2=0.9$\,meV, $J_3=0.8$\,meV for the bilinear Heisenberg Hamiltonian. However, not all features of the excitation spectrum are explained with this model.