B4CN3and B3CN4monolayers as the promising candidates for metal-free spintronic materials

The search for candidates of spintronic materials, especially among the two-dimensional (2D) materials, has attracted tremendous attentions over the past decades. By using a particle swarm optimization structure searching method combined with density functional calculations, two kinds of boron carbonitride monolayer structures (B4CN3 and B3CN4) are proposed and confirmed to be dynamically and kinetically stable. Intriguingly, we demonstrate that the magnetic ground states of the two BxCyNz systems are ferromagnetic ordering with a high Curie temperature of respectively 337 K for B4CN3 and 309 K for B3CN4. Furthermore, based on their respective band structures, the B4CN3 is found to be a bipolar magnetic semiconductor (BMS), while the B3CN4 is identified to be a type of spin gapless semiconductor (SGS), both of which are potential spintronic materials. In particular, carrier doping in the B4CN3 can induce a transition from BMS to half-metal, and its spin polarization direction is switchable depending on the doped carrier type. The BMS property of B4CN3 is very robust under an external strain or even a strong electric field. By contrast, as a SGS, the electronic structure of B3CN4 is relatively sensitive to external influences. Our findings successfully disclose two promising materials toward 2D metal-free spintronic applications.