Room-Temperature Ferromagnetism in Two-Dimensional Fe₂Si Nanosheet with Enhanced Spin-Polarization Ratio

Searching experimental feasible two-dimensional (2D) ferromagnetic crystals with large spin-polarization ratio, high Curie temperature and large magnetic anisotropic energy is one key to develop next-generation spintronic nanodevices. Here, 2D Fe₂Si nanosheet, one counterpart of Hapkeite mineral discovered in meteorite with novel magnetism is proposed on the basis of first-principles calculations. The 2D Fe₂Si crystal has a slightly buckled triangular lattice with planar hexacoordinated Si and Fe atoms. The spin-polarized calculations with hybrid HSE06 function method indicate that 2D Fe₂Si is a ferromagnetic half metal at its ground state with 100% spin-polarization ratio at Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamic simulation shows that 2D Fe₂Si crystal has a high thermodynamic stability and its 2D lattice can be retained at the temperature up to 1200 K. Monte Carlo simulations based on the Ising model predict a Curie temperature over 780 K in 2D Fe₂Si crystal, which can be further tuned by applying a biaxial strain. Moreover, 2D structure and strong in-plane Fe-Fe interaction endow Fe₂Si nanosheet sizable magnetocrystalline anisotropy energy with the magnitude of at least two orders larger than those of Fe, Co and Ni bulks. These novel magnetic properties render the 2D Fe₂Si crystal a very promising material for developing practical spintronic nanodevices.