${\text{Fe}}_{3-x}{\text{GeTe}}_2$ is a layered magnetic van der Waals material of interest for both fundamental and applied research. Despite the observation of intriguing physical properties, open questions exist even on the basic features related to magnetism: is it a simple ferromagnet or are there antiferromagnetic regimes, and are the moments local or itinerant. Here, we demonstrate that antiferromagnetic spin fluctuations coexist with the ferromagnetism through comprehensive elastic and inelastic neutron scattering and thermodynamic measurements. Our realistic dynamical mean-field theory calculations reveal that the competing magnetic fluctuations are driven by an orbital selective Mott transition (OSMT), where only the plane-perpendicular $a_{1g}$ orbital of the $\mathrm{Fe}\left(3d\right)$ manifold remains itinerant. Our results highlight the multi-orbital character in ${\text{Fe}}_{3-x}{\text{GeTe}}_2$ that supports a rare coexistence of local and itinerant physics within this material.

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• Magnetism
• Spin dynamics
• Ferromagnets
• van der Waals systems
• DFT+DMFT
• Inelastic neutron scattering
• Neutron diffraction
• Neutron scattering