2D Ferromagnetism in Silicene Materials*

The appeal of ultra-compact spintronics drives intense research on magnetism in low-dimensional materials. Recent years have witnessed remarkable progress in engineering two-dimensional (2D) magnetism via defects, edges, adatoms and magnetic proximity. However, intrinsic 2D ferromagnetism remained elusive until recent discovery of magneto-optical response in Cr-based layers[1,2], stimulating the search for novel 2D magnets with tunable properties. We employ a bottom-up approach to produce layered structures of silicene (a Si counterpart of graphene) functionalized by rare-earth atoms, ranging from the bulk down to one monolayer. We track the evolution from the antiferromagnetism of the bulk to intrinsic 2D ferromagnetism of ultrathin layers of GdSi₂ and EuSi₂ [3]. Remarkably, the charge transport is found to be layer-dependent once silicene structures are scaled to a few-monolayers limit: it evolves from a Kondo-like trend to an insulating behavior once a gap opens up in its charge excitation spectrum. The discovery of a class of robust 2D magnets, compatible with the mature Si technology, is instrumental for engineering new spintronic devices.

[1] Gong, C. et al. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals. Nature 546, 265 (2017).
[2] Huang, B. et al. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit. Nature 546, 270 (2017).
[3] Tokmachev A.et al. Emerging two-dimensional ferromagnetism in silicene materials”, Nature Communications 9, 1672 (2018).