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

TL;DR

This study uses advanced computational methods to analyze the magnetic properties of monolayer Fe$_3$GeTe$_2$, revealing suppressed local magnetic moments and the importance of exchange interactions for its ferromagnetism.

Contribution

It demonstrates the significance of dynamical electron correlations and RKKY exchange interactions in understanding the magnetic behavior of monolayer Fe$_3$GeTe$_2$, a novel insight into its magnetic properties.

Findings

Iron atoms above/below Ge plane have large magnetic moments

Iron atom within Ge plane shows negligible magnetic moment

Calculated Curie temperature matches experimental data

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.