Spectroscopic signature of 3D magnetism in the itinerant van der Waals ferromagnet Fe₅GeTe₂

Recently discovered family of high-temperature itinerant van der Waals ferromagnets Fe_5-xGeTe_2. Moreover, Fe₅GeTe₂ displays the highest T_c ~ 315 K and has the potential for magnonic devices operating at room temperature [4,5]. However, it is not yet known whether magnons in Fe₅GeTe₂ are confined to 2D or propagate in 3D. Investigation of dispersing magnons via inelastic neutron scattering is not feasible due to the small size of available single crystals. In this study, we overcome this issue by employing a complimentary probe, resonant inelastic x-ray scattering (RIXS), on a high-quality mm-size single crystal of Fe₅GeTe₂ [5]. A broad magnetic continuum stretching up to 150 meV and displaying a strong intensity modulation along (00L) is observed [6]. We show that this intensity modulation is compatible with a dominant inter-slab magnetic interaction enabling 3D propagation of magnons in the room-temperature ferromagnet Fe₅GeTe₂ [6].

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2. X. Wu, et al., Phys. Rev. B 104, 165101 (2021).

3. K. Yamagami, et al., Phys. Rev. B 106, 045137 (2022).

4. L. Alahmed, et al., 2D Mat 8, 045030 (2021).

5. A. May, et al., ACS Nano 13, 4436 (2019).

6. V. K. Bhartiya, et al., unpublished.