Intriguing p-orbital magnetic semiconductors and carrier induced half-metallicity in surface oxygen-functionalized two-dimensional [formula omitted] ([formula omitted]) crystals

Abstract

Two-dimensional (2D) ferromagnetic semiconductors with robust magnetism are urgently desired for nanoscale spintronics applications. However, it remains a challenge to realize them experimentally. In this work, we proposed intriguing 2D p-orbital ferromagnetic semiconductors X2NO2 (X=Ca,Sr) monolayer with 3μB magnet per unit under O surface termination using first-principles calculations. The Ca2NO2 monolayer is bipolar magnetic material (BMS) with spin-flip gap 0.24 eV, and the Sr2NO2 is half-semiconductor (HSC) with spin-flip gap 0.31 eV, which is large enough to prevent the spin-flip transition. The Curie temperature can reach to 206 and 239 K, respectively, due to the superexchange interaction between N- ions. The values are much higher than the boiling point of liquid nitrogen (77 K) and comparable to that of the reported ScCl monolayer. Moreover, the half metals are obtained via carrier doping for both the Ca2NO2 and Sr2NO2 monolayers. In addition, the half-metallic completely spin-polarized direction of BMS Ca2NO2 monolayer can be controlled by carrier doping type. Furthermore, the magnetism of X2NO2 monolayer is derived from p orbital, without the involvement of conventional transition metals or rare earth atoms. This is advantageous for high-speed and long-distance spin-polarization transport. These results suggest that the X2NO2 monolayer can develop spin field effect transistor for information processing and storage, and open opportunities for designing new ferromagnetic semiconductors.