Unraveling effects of electron correlation in two-dimensional Fe${}_n$GeTe${}_2$ (n=3, 4, 5) by dynamical mean field theory

The Fe${}_n$GeTe${}_2$ systems are newly discovered two-dimensional van-der-Waals materials, exhibiting magnetism at room temperature. The sub-systems belonging to Fe${}_n$GeTe${}_2$ class are special because they show site-dependent magnetic behavior. We focus on the critical evaluation of magnetic properties and electron correlation effects in Fe${}_n$GeTe${}_2$ ($n$= 3, 4, 5) (FGT) systems performing first-principles calculations. Three different ab-initio approaches have been used, viz., i) standard density functional theory (DFT), ii) incorporating static electron correlation (DFT+U) and iii) inclusion of dynamic electron correlation effect (DFT+DMFT). Our results show that DFT+DMFT is the most accurate technique to correctly reproduce the magnetic interactions and experimentally observed transition temperatures. The inaccurate values of structural parameters, magnetic moments and exchange interactions obtained from DFT+U make this method inapplicable for the FGT family. Correct determination of magnetic properties for this class of materials is important since they are promising candidates for spin transport and spintronic applications at room temperature.