Prediction of a monolayer spin-spiral semiconductor: CoO with a honeycomb lattice

The recent successful fabrication of two-dimensional (2D) CoO with nanometer-thickness motivates us to investigate monolayer CoO due to possible magnetic properties induced by Co atoms. Here, we employ first-principles calculations to show that monolayer CoO is a 2D spin-spiral semiconductor with a honeycomb lattice. The calculated phonon dispersion reveals the monolayer's dynamical stability. Monolayer CoO exhibits a type-I spin-spiral magnetic ground state. The spin-spiral state and the direct bandgap character are both robust under biaxial compressive strain (−5%) to tensile strain (5%). The bandgap varies only slightly under either compressive or tensile strain up to 5%. These results suggest a potential for applications in spintronic devices and offer a new platform to explore magnetism in the 2D limit.