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

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.

17 pages, 3 figures, supplementary file