FeSi 2 : a two-dimensional ferromagnet containing planar hexacoordinate Fe atoms.

As an unconventional bonding pattern different from conventional chemistry, the concept of planar hypercoordinate atoms was first proposed in the molecular system, and it has been recently extended to 2D periodic systems. Using first-principles calculations, herein we predict a stable FeSi 2 monolayer with planar hexacoordinate Fe atoms. Due to its abundant multicenter bonds, the FeSi 2 monolayer shows excellent thermal and kinetic stability, anisotropic mechanical properties and room-temperature ferromagnetism ( T C ∼360 K). Furthermore, we have demonstrated the feasibility of directly growing an FeSi 2 monolayer on a Si (110) substrate while maintaining the novel electronic and magnetic properties of the freestanding monolayer. The FeSi 2 monolayer synthesized in this way would be compatible with the mature silicon semiconductor technology and could be utilized for spintronic devices.