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arXiv · 2411.12887

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

V. K. Bhartiya·T. Kim·J. Li·T. P. Darlington·D. J. Rizzo·Y. Gu.·S. Fan·C. Nelson·J. W. Freeland·X. Xu·D. N. Basov·J. Pelliciari·A. F. May·C. Mazzoli·V. Bisogni
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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.

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V. K. Bhartiya, T. Kim, J. Li, T. P. Darlington, D. J. Rizzo, Y. Gu., S. Fan, C. Nelson, J. W. Freeland, X. Xu, D. N. Basov, J. Pelliciari, A. F. May, C. Mazzoli, V. Bisogni. 2024-11-19. Magnetic excitations and absence of charge order in the van der Waals ferromagnet Fe$_{4.75}$GeTe$_2$. https://doi.org/10.1038/s41535-025-00803-1

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