Ordered double-M elements MXenes TiMC: Large in-plane stiffness and ferromagnetism

By performing the density functional theory type of first-principles calculations, we investigate four ordered double-M elements MXenes, TiMC (M = Zr, Hf, Cr and Mo) which contain one more element than Ti₂C and may offer new physical properties. Our calculation results show that these monolayers are not only dynamically stable, but also have large in-plane stiffness. We demonstrate the intrinsic ferromagnetism of metallic TiZrC and TiHfC whose Curie temperatures are higher than that of Ti₂C. And, differing from Cr₂C in which the four 3d electrons of the divalent Cr atoms are fully polarized, the partially polarized Cr atoms in TiCrC are anti-ferromagnetic coupling with each other. Additionally, we predict that the 1%–3% compressive strain turns TiZrC and TiHfC into ferromagnetic half-metals with 100% spin-polarization at Fermi level. More importantly, our calculations show that TiZrC, TiHfC and TiMoC with surface terminated by O atoms all convert into semiconducting with direct band gap around 1.40 eV, while TiCrCF₂ is ferromagnetic half-metal with large energy gap of 3.14 eV for the semiconducting spin channel.