Magnetic excitations and absence of charge order in the van der Waals ferromagnet Fe$_{4.75}$GeTe$_2$

TL;DR

This study investigates magnetic excitations in Fe$_{4.75}$GeTe$_2$, revealing a dual nature of magnons and a lack of charge order, indicating enhanced three-dimensional magnetic correlations in this van der Waals ferromagnet.

Contribution

The paper provides the first detailed analysis of magnetic excitations in Fe$_{4.75}$GeTe$_2$, showing a dual magnon continuum and clarifying the absence of charge order, thus advancing understanding of its magnetic ground state.

Findings

Dual magnetic excitations with a magnon and a broad continuum

Enhanced out-of-plane magnetic correlation length compared to similar compounds

No evidence of charge order in the crystal structure

Abstract

Understanding the ground state of van der Waals (vdW) magnets is crucial for designing devices leveraging these platforms. Here, we investigate the magnetic excitations and charge order in Fe$_{4.75}$GeTe$_2$, a vdW ferromagnet with $\approx$ 315 K Curie temperature. Using Fe $L_3 - $edge resonant inelastic x-ray scattering, we observe a dual nature of magnetic excitations, comprising a coherent magnon and a broad non-dispersive continuum extending up to 150 meV, 50$\%$ higher than in Fe$_{2.72}$GeTe$_2$. The continuum intensity is sinusoidally modulated along the stacking direction $L$, with a period matching the inter-slab distance. Our results indicate that while the dual character of the magnetic excitations is generic to Fe-Ge-Te vdW magnets, Fe$_{4.75}$GeTe$_2$ exhibits a longer out-of-plane magnetic correlation length, suggesting enhanced 3D magnetic character. Furthermore, resonant x-ray diffraction reveals that previously reported $\pm$(1/3, 1/3, $L$) peaks originate from crystal structure rather than from charge order.