p-orbital multiferroics in single-layer SiN

Multiferroics, coupling magnetism with electric polarization, provides special opportunities for both fundamental research and device applications. The current multiferroic research in a two-dimensional lattice is invariably focused on d-orbital based systems. We alternatively show by first-principles calculations that ideal multiferroics is present in a p-orbital based lattice of single-layer SiN. Single-layer SiN is a semiconductor exhibiting intrinsic ferromagnetism and ferroelectricity simultaneously. Its magnetism correlates with the extended p–p interaction between unpaired p orbitals of N atoms. The buckled symmetry guarantees the existence of an out-of-plane electric dipole, giving rise to the ferroelectric order. More remarkably, the ferroic orders in single-layer SiN display strongly coupled physics, i.e., the spatial distribution of magnetic moments can be well controlled by the reversal of electric polarization, thereby establishing the long-sought multiferroics with strong magnetoelectric coupling. These findings not only enrich a two-dimensional multiferroic family, but also enable a wide range of device applications.