Magnetism and piezoelectricity in stable transition metal silicate monolayers

Two-dimensional van der Waals (2D vdW) single layered materials with ferromagnetism and piezoelectricity have been a subject of recent attention. Despite numerous reports of 2D ferromagnetic materials, developing an air stable and transferable vdW material has been challenging. To address this problem, we studied layered transition metal silicates that are derivatives of kaolinites and lizardites with transition metals substituting on ${\mathrm{Al}}^{3+}$ and ${\mathrm{Mg}}^{2+}$ sites using ab initio density functional theory calculations. This class of materials is appealing because they meet the symmetry requirements for piezoelectricity and can host a range of transition metal cations. As oxides, these materials are inherently stable in air. Following our previous experimental work, we predict that these compounds are stable under varying ${\mathrm{O}}_{2}$ partial pressure and can be synthesized using a surface-assisted method. We also show that the oxidation states of the substituted transition metal ions can be tuned through the level of hydrogenation.