Electronic and Magnetic Properties of Ordered Double Transition-Metal MXenes: Ti ₂ MC ₂ T ₂ (M = Cr, Mo, and W; T = F, O, OH, and Cl)

Here, we use a GFN-xTB (Geometries, Frequencies, and Noncovalent interactions Tight Binding) Hamiltonian of the density functional tight binding (DFTB) method to study the structural, electronic, and magnetic properties of Ti₂MC₂ (M = Cr, Mo, and W) and Ti₂MC₂T₂ (T = -F, -O, -OH, and -Cl). By investigating the magnetic ordering, we found that the bare, F, -OH, and Cl-terminated Ti₂MC₂ MXenes prefer an antiferromagnetic (AFM) alignment and show a metallic character. However, the magnetism is suppressed by O termination. This result suggests that magnetism can be enhanced in the presence of F-, OH-, and Cl-surface functional groups. We also investigated the Ti and M vacancy defects. We remark that the M-defect maintains the AFM ordering, whereas a magnetic transition from AFM to ferromagnetic (FM) ordering is shown by the creation of a Ti vacancy. Among the studied double transition-metal MXenes, the Ti-defected systems show the highest magnetic moments, and the magnetism is mainly due to the Ti atoms. Our DFTB investigations allow for efficient exploration of the magnetism in double metal MXenes and the effect of functionalization on the electronic and magnetic properties of the studied materials. The obtained electronic properties suggest that the Ti₂MC₂T₂ monolayers are metals, the same behavior as compared to the majority of monotransition-metal MXenes. These findings can serve as a guide for comprehending the electronic and magnetic properties of double metal MXenes.