Investigating the magneto-elastic properties in FeSn and Fe$_{3}$Sn$_{2}$ flat band metals

TL;DR

This study explores the magnetic, electronic, and lattice properties of FeSn and Fe3Sn2, revealing flat bands, magneto-elastic coupling in FeSn, and persistent spin correlations at high temperatures, advancing understanding of topological quantum magnets.

Contribution

It provides combined experimental and theoretical insights into the magneto-elastic and spin dynamics in FeSn and Fe3Sn2, highlighting differences in lattice responses and spin correlations.

Findings

FeSn exhibits magneto-elastic coupling and spin-phonon interactions.

Fe3Sn2 shows no lattice anomaly across T_N.

Spin waves persist above T_N, indicating high-temperature ferromagnetic correlations.

Abstract

Topological quantum magnets FeSn and Fe$_{3}$Sn$_{2}$ were studied using neutron scattering and first-principles calculations. Both materials are metallic but host dispersionless flat bands with Dirac nodes at the $K$ point in reciprocal space. The local structure determined from the pair density function analysis of the neutron diffraction data provided no evidence for electron localization in both compounds, consistent with their metallic nature. At the same time, in FeSn, an anomalous suppression in the $c$-axis lattice constant coupled with changes in the phonon spectra were observed across T$_{N}$ indicating the presence of magneto-elastic coupling and spin-phonon interactions. In addition, it was observed that spin waves persisted well above T$_{N}$, suggesting that the in-plane ferromagnetic spin correlations survive at high temperatures. In contrast, no lattice anomaly was observed in Fe$_{3}$Sn$_{2}$. The inelastic signal could be mostly accounted for by phonons, determined from density functional theory, showing typical softening on warming.