High Curie temperature and carrier mobility of novel Fe, Co and Ni carbide MXenes.

Two-dimensional (2D) magnets with room temperature ferromagnetism and semiconductors with moderate band gap and high carrier mobility are highly desired for applications in nanoscale electronics and spintronics. By performing the first-principles calculations, we investigate novel Fe, Co, Ni carbide based pristine (MC) and functionalized (MCT, T: F, O, OH) MXenes. Our calculations show that FeC, CoC, NiC, FeCF, FeCO, FeC(OH), CoCF, CoC(OH) and NiCF are dynamically and mechanically stable. More importantly, FeC, CoC, FeCF and FeC(OH) exhibit intrinsic ferromagnetism (magnetic moments 2-5μ per unit cell). Monte Carlo simulations suggest high Curie temperatures of 590 and 920 K for FeC and FeCF, respectively, at the HSE06 level owing to the large spin magnetic moments and strong ferromagnetic coupling. Based on the deformation potential theory, we predict high and anisotropic hole mobility (0.2-1.4 × 10 cm V s) for semiconducting FeCO and CoC(OH). Additionally, NiCF demonstrates highly anisotropic electron mobility together with a direct band gap. Our results further show the effectiveness of surface functionalization in modulating the electronic and magnetic properties and broadening the properties of MXenes to achieve long-range intrinsic ferromagnetism well above room temperature and high carrier mobility.