Room-Temperature Ferromagnetism in Two-Dimensional FeSi 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 FeSi nanosheet, one counterpart of Hapkeite mineral discovered in meteorite with novel magnetism is proposed on the basis of first-principles calculations. The 2D FeSi 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 FeSi 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 FeSi 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 FeSi crystal, which can be further tuned by applying a biaxial strain. Moreover, 2D structure and strong in-plane Fe-Fe interaction endow FeSi 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 FeSi crystal a very promising material for developing practical spintronic nanodevices.