FeSi₂: a two-dimensional ferromagnet containing planar hexacoordinate Fe atoms

Abstract

As an unconventional bonding pattern different from conventional chemistry, the concept of planar hypercoordinate atom was first proposed in the molecular system, and it has been recently extended to 2D...

Two-Dimensional Iron Silicide (FeSix) Alloys with Above-Room-Temperature Ferromagnetism

“…Table summarizes the calculated energies of 2D FeSi x alloys under different magnetic states with reference to the FM state. Four 2D FeSi x alloys are FM at their ground state with the energy difference between AFM and FM varying from 143.04 to 546.51 meV/Fe, similar to previously reported FM Fe 2 Si (205 meV/Fe) and FeSi 2 (36 meV/Fe), , suggesting that the FM ground state is solid for 2D FeSi x alloys, which is independent of the value of x in the current study. Additionally, for Fe 3 Si 2 , Fe 4 Si 2 -hex, and Fe 4 Si 2 -orth, the FM ground state is consistent with their bulk counterparts, while 2D FeSi 2 exhibits ferromagnetism different from its nonmagnetic bulk counterpart after dimensional reduction …”

“…The easy axis (EA) of Fe 3 Si 2 and Fe 4 Si 2 -orth are along the out-of-plane (001) direction, while that of FeSi 2 and Fe 4 Si 2 -hex is along the in-plane direction. As summarized in Table S3, the MAE of Fe 3 Si 2 , Fe 4 Si 2 -hex, FeSi 2 , and Fe 4 Si 2 -orth are 627, 58, 936, and 529 μeV/Fe, respectively, which are about one to two orders larger than those of cubic Fe (1.4 μeV per atom), Co (65 μeV per atom), and Ni (2.7 μeV per atom). , In addition, the MAE values of Fe 3 Si 2 and FeSi 2 are higher than those of previously reported 2D Fe 2 Si (560 μeV/Fe) and FeSi 2 (56 μeV/Fe). , The large MAE value makes 2D FeSi x suitable for magnetoelectronic applications.…”

“…Binary iron silicide (Fe–Si) alloys, as a class of non-vdW compounds, host a rich phase diagram, such as Fe 3 Si, Fe 2 Si, Fe 5 Si 3 , FeSi, and α-FeSi 2 , which showcases a plethora of exotic magnetic phenomena ranging from excellent soft magnetic properties and half-metallicity to unusual temperature-dependent magnetic characteristics for fundamental physics and technological applications. − Recently, room-temperature ferromagnetism together with a high spin-polarization ratio has been observed in 2D iron silicide, indicating that the designation of high-temperature ferromagnets via downsizing the thickness of the iron silicide film to the atomic scale is feasible. − For example, a 2D Fe 2 Si nanosheet with room-temperature ferromagnetism and enhanced spin polarization has been theoretically predicted by reducing the dimension of the Fe 2 Si bulk, which has been confirmed experimentally. , However, the variety of 2D iron silicides is still limited, inspiring the exploration of new 2D iron silicides with intrinsic and room-temperature magnetism.…”

Two-dimensional Be2Al and Be2Ga monolayer: anti-van’t Hoff/Le Bel planar hexacoordinate bonding and superconductivity

“…[36][37][38][39][40][41][42] Besides isolated clusters, planar hypercoordinate motifs can also be embedded on a two-dimensional (2D) scale owing to the electronic-stabilization induced steric force and good electron delocalization. 43 Recently, a set of anti-van't Hoff and Le Bel 2D nanostructures have been found as global minima, [44][45][46][47][48][49][50][51][52][53][54][55][56] giving rise to the great possibility of potential physical and chemical applications for anti-van't Hoff and Le Bel structures. In the case of the 2D scale with planar hexacoordinate motifs, the global-minimum Be 2 C monolayer was predicted to be a semiconductor with a moderate band gap in 2014.…”

“…The stable FeSi 2 was also recently found to be an intriguing 2D ferromagnet. 55 As discussed above, most of the reported 2D materials with planar hexacoordination are related to transition metals, 43 while a triangular network with planar hexacoordination entirely composed of main-group metals is relatively rare. Through a systematic search, herein, we present evidence that the Be 2 M (M = group 13 atoms) monolayer possesses planar hexacoordinate bonding, where a Be 6 hexagon encompasses a planar hexacoordinate M center.…”