Theoretical Characterization of the Magnetic Properties of Vanadium-doped Ti2C MXenes

Abstract

MXenes are two-dimensional materials composed of transition metals and light elements, known for their high conductivity and versatile surface chemistry. The introduction of spin centers via doping can lead to promising materials for spintronics, magnetic sensing, and data storage. We study the effect of V doping in Ti2C using first principle and Monte-Carlo simulations. Our results show that pristine Ti2C exhibits ferromagnetic intralayer and antiferromagnetic interlayer exchange interactions, yielding an antiferromagnetic ground state. Vanadium incorporation alters these couplings, yet all doped configurations - Ti7VC4 and three Ti6V2C4 variants - retain predominantly antiferromagnetic order. Despite the preserved ground state, V doping enhances the magnetic response, most notably in the p-Ti6V2C4 configuration, which displays increased low-field susceptibility and partial spin alignment across layers. As experimentally isolating individual doped phases is unlikely, samples will consist of mixed configurations whose collective behavior nonetheless exhibits clear signatures of V-induced magnetic modification. These results reveal how transition-metal substitution tunes exchange interactions in MXenes and offer guidance for engineering their magnetic functionalities.

Figures (6)

• Figure 1: Representation of the 8 magnetic centers in the Ti$_8$C$_4$ supercell and considering the magnetic coupling. Left: top view, right: front view in the direction of the arrows. Titanium atoms are represented in blue, carbon in brown.
• Figure 2: Substitution patterns and new coupling constants in vanadium doped titanium carbide. Vanadium atoms are represented in red. The nomenclature of Ti6V2C4 is adapted from organic chemistry, classifying double substitution in a hexagonal arrangement as ortho (1,2), meta (1,3) or para (1,4).
• Figure 3: Angle-dependence of the MAE with respect to the rotation of the spin in the yz plane, while 0$^\circ$ represents the (001) direction, values in $\mu$eV/atom.
• Figure 4: Magnetic configuration in the ground state of the unitary cell for the five configurations studied: a) Ti8C4, b) Ti7VC4, c) m-Ti6 V2C4, d) o-Ti6V2C4, and e) p-Ti6V2C4. The figures on the left correspond to a semi-lateral perspective, and the figures on the right to a top perspective. For each case, the total moment of the supercell normalized to the saturated case is reported. Note: The figure shows that the spin orientations do not coincide with the out-of-plane direction indicated by the effective anisotropy; this is because the anisotropy is at least two orders of magnitude smaller than the exchange interactions, which, from a dynamic point of view, only leads to the minimization of the exchange energy.
• Figure 5: Hysteresis curves for the four vanadium-doped cases: a) Ti7VC4, b) m-Ti6V2C4, c) o-Ti6V2C4, and d) p-Ti6V2C4. Simulations were performed considering $30\times30\times2$ metal atoms (Ti and V) with periodic boundary conditions.