Interplay of electronic structure, magnetism, strain, and defects in carbide MXenes

Abstract

The two-dimensional (2D) magnetic and semiconducting materials, including carbide MXenes, are in high demand for magneto-electronic devices and applications. Here, we report a first-principles study of electronic structure and magnetism of a Ti2C MXene, its derivatives Ti2CT2 (T = -F, -O, -OH, -H), and the effect of single vacancy defects (25% C, 12.5% O, and 12.5% and 5.5% Ti) and transition metal (V, Cr, Mn, and Co) dopings. The MAX phase Ti2AlC is a non-magnetic (NM) metal which upon removal of Al layer forms a pristine Ti2C MXene with A-type antiferromagnetic (AFM) semiconductor having reliable transition temperature (TN=41K) predicted by the Heisenberg model. All the functionalized MXenes are stable as NM metal except for Ti2CO2 which remains semiconducting with NM ground state. The significant effect of spin–orbit coupling (SOC) is evident in the band structure forming Dirac-like cones and band inversions near the Fermi level. Depending upon the type of vacancy defects Ti2CO2 is NM metal and ferromagnetic (FM) metal. The transition metal (TM) doped MXenes fulfill FM Stoner criterion. The V- and Co-doped MXenes are metals, whereas Cr- and Mn-doped are half-metal and semiconductor.