Suppression of local magnetic moment formation and paramagnetic exchange interactions in monolayer Fe${}_3$GeTe${}_2$

Abstract

We study the electronic and magnetic properties of monolayer Fe${}_3$GeTe${}_2$ within the DFT+DMFT approach in the paramagnetic phase. We argue that this compound is sufficiently far from the local magnetic moment limit, demonstrating non-linear temperature dependencies of the partial inverse local and uniform magnetic susceptibilities in a broad temperature range. We find that in the regime of moderate Coulomb interactions ($U=3-4$ eV), the iron atoms located above and below the Ge plane carry a substantial local magnetic moment ($\mu \gtrsim 4.5{\mu }_B$), while the iron atom located within the Ge plane does not exhibit any pronounced magnetic moment. At the same time, the RKKY-type exchange interactions between these two symmetry-nonequivalent types of atoms turn out to be crucial for stabilizing long-range ferromagnetic order in Fe${}_3$GeTe${}_2$. The estimated spin-wave stiffness and Curie temperature are in good agreement with the experimental data, indicating that a dynamical treatment of electron correlations in Fe${}_3$GeTe${}_2$ is essential to properly describe its partially itinerant magnetic behavior.

10 pages, 8 figures