Emerging 2D ferromagnetism and charge transport in silicene, germanene and graphene compounds

Recent years have witnessed remarkable progress in engineering two-dimensional (2D) magnetism via defects, edges, adatoms or magnetic proximity. However, intrinsic 2D ferromagnetism remained elusive until recent discovery of magneto-optical response in Cr-based layers, stimulating the search for novel 2D magnets with tunable properties. We discovered a class of 2D ferromagnets based on 2D-Xenes, elemental analogues of graphene – layered structures of silicene [1] or germanene [2] functionalized by rare-earth atoms. We track the evolution from the antiferromagnetism of the bulk to intrinsic 2D ferromagnetism of a few monolayers of MSi₂ [1,3] and MGe₂ [2,3]. The magnets are compatible with the mature Si and Ge technologies, which is instrumental for engineering new spintronic devices. The lateral charge transport is found to be layer-dependent once the MSi₂ structures are scaled down to a few monolayers limit [4]. A similar approach is applied to graphene: By analogy with MSi₂ and MGe₂ , we synthesized a monolayer of EuC₆ .The system demonstrates the anomalous Hall effect and negative magnetoresistance [5]. EuC₆ monolayer exhibits ferromagnetism: its magnetic transition temperature is controlled by low magnetic fields – a fingerprint of 2D ferromagnetism [5]. In proximity with EuO, graphene becomes ferromagnetic at 220 K, well above the Curie temperature of EuO [6]. This work is supported by NRC "Kurchatov Institute" (No. 1055) and the Russian Science Foundation (grants 20-79-10028 and 19-19-00009).