First-principles study on the p-orbital multiferroicity of single-layer XN (X = Ge, Sn, Pb)

Two-dimensional (2D) multiferroic materials have triggered a burst of interest owing to their wide applications in nanoelectronics. Specifically, p-orbital multiferroicity is strongly desired but has been very few reported. Here, based on first-principles calculations, we unveil a new type of 2D multiferroic material: the single-layer (SL) XN (X = Ge, Sn, Pb). Our findings show these materials are ferromagnetic semiconductors with strong magnetoelectric coupling and wide bandgaps. The multiferroicity is related to the unpaired p-orbital electrons of N atoms and the buckled crystal structure. All the single layers show easy-plane magnetocrystalline anisotropy, and the magnetic anisotropy energy increases significantly with the atomic number increasing. Our Monte Carlo simulations suggest the Curie temperature TC is 205.44 K, 200.45 K, and 287.88 K for SL GeN, SnN, and PbN, respectively. By applying tensile strain, the TC can be further increased to 225.39 K, 245.35 K, 369.99 K, respectively. Additionally, biaxial strain can induce semiconductor-to-half-metal and ferroelectricity-to-paraelectricity transition in the single layers. We aspire that our work contributes to the exploration of room-temperature p-orbital multiferroicity.