Microscopic Insights for Beyond Room-Temperature Ferromagnetism in Ni doped Two-Dimensional Fe${}_5$GeTe${}_2$

Abstract

Enhancement of Curie temperature ($T_{\mathrm{C}}$) of two-dimensional (2D) magnets is immensely desirable for room temperature spintronic applications. Fe${}_5$GeTe${}_2$ is an exceptional van der Waals metallic ferromagnet due to its tunable physical properties and relatively higher $T_{\mathrm{C}}$ than other 2D magnets. Using density functional theory combined with dynamical mean field theory and Monte Carlo simulations, we show that the $T_{\mathrm{C}}$ of Fe${}_5$GeTe${}_2$ monolayer can increase well-above room temperature by substitutional doping with Ni. It is found that two specific sublattices (Fe1 and Fe4) are the first and second most energetically preferred occupation sites for Ni. $T_{\mathrm{C}}$ of Fe${}_{5-\delta }$Ni${}_{\delta }$GeTe${}_2$ increases up to $\sim$ 400 K at $\delta \sim$20\%. Exchange interactions between particular Fe5-Fe4 pairs play a dominating role in tuning the transition temperature, influenced by doping-induced structural distortions. Finally, we highlight the effect of dynamical electron correlation in site-specific electronic structure and quasi-particle mass of Fe-$d$ orbitals with varying Ni dopi

10 pages, 4 figures