Although the interlayer interaction is weak, it exhibits an important influence on the electronic behaviors in two-dimensional layered semiconductors. Using first-principles calculations, we find that tuning of lone-pair electron properties by carrier injection breaks time symmetry in SnO nanosheets, which is responsible for the ferromagnetic (FM) phase transition. Upon hole doping, the most stable FM state of monolayer SnO occurs at $3.2\times {10}^{14}/{\mathrm{cm}}^2$ with an average magnetic moment of $1.0{\mu }_B/\text{carrier}$. In multilayer SnO nanosheets, lone-pair electrons are redistributed due to the interaction of Sn atoms in adjacent layers, which cancels out the FM coupling mediated by holes. A half-metallic FM ground state is recovered when the interlayer lone-pair electron interaction is weakened. The itinerant magnetism originates from an exchange splitting of lone-pair electron states at the top of the valence band where the density of states exhibits a sharp van Hove singularity in this system.

• Received 18 May 2017

DOI:https://doi.org/10.1103/PhysRevApplied.8.064019