Double transition metal MXenes with wide band gaps and novel magnetic properties.

Novel wide band gaps and magnetism in ordered titanium-vanadium, titanium-chromium, and titanium-manganese carbide and nitride based MXenes are predicted using density functional theory. Based on the recent synthesis of Ti centred double transition metal MXenes, we study MXenes with a central Ti layer and different surface early 3d metals, and various terminations, TiM2X2T (M = V, Cr, Mn; X = C, N; T = H, F, O, OH). While previously studied MXenes are strongly metallic, we predict surface metal and termination dependent metal-insulator transitions in the Cr-N and Mn-N series. A uniquely wide band gap over 1 eV is predicted for TiMn2N2F2 using the HSE06 density functional while the unterminated TiMn2N2 remains metallic. The entire TiCr2C2T series is predicted to be semiconducting. Distinct from the more common Ti-C MXenes, not all combinations of metals and terminations are predicted to be stable. Within the examined sets of materials, anti-ferromagnetic orders are generally most favorable. The new MXenes further extend the range of properties accessible in this family of two-dimensional nanomaterials.