Spectroscopic Signature of 3D Magnetism in a Van der Waals Ferromagnet Fe₅GeTe₂

The recently discovered family of van der Waals itinerant ferromagnets Fe_5-xGeTe₂ (0&lt;x&lt;2) are strongly correlated electronic systems and realize intriguing ground states i.e. heavy fermions and charge density wave [1-3]. Moreover, the <i>cleavable</i> Fe₅GeTe₂displays the highest <i>T_c</i> ~ 315 K and has the potential for miniaturized spintronic devices operating at room temperature [4-5]. However, it is not yet known if the magnons in Fe₅GeTe₂ are confined in 2D or propagate in 3D. To date, investigation of magnons via inelastic neutron scattering is not feasible due to the small size of the available single crystals. In this study, we overcome this issue by employing a high-resolution resonant inelastic X-ray scattering (RIXS) on a mm-size single crystal of Fe₅GeTe₂[5]. A broad magnetic continuum stretching up to 150 meV and displaying a strong intensity modulation along (0 0 <i>L</i>) 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].<br/><br/>[1] Y. Zhang, et al., Sci. Adv. <b>4</b>, eaao6791 (2018).<br/>[2] X. Wu, et al., Phys. Rev. B <b>104</b>, 165101 (2021).<br/>[3] K. Yamagami, et al., Phys. Rev. B <b>106</b>, 045137 (2022).<br/>[4] L. Alahmed, et al., 2D Mat <b>8</b>, 045030 (2021).<br/>[5] A. May, et al., ACS Nano <b>13</b>, 4436 (2019).<br/>[6] V. K. Bhartiya, et al., unpublished.