Ultrafast spin manipulation in low-dimensional magnetic materials is essential for next-generation spintronic devices, yet the microscopic mechanisms governing spin dynamics, especially the role of surface termination, remain unclear. Here, TiCrCT 2 (T = O, F) MXenes are systematically investigated using real-time time-dependent density functional theory and nonadiabatic molecular dynamics. The results reveal that surface termination governs distinct magnetic responses, including a ferrimagnetic-to-ferromagnetic transition in TiCrCF 2 driven by Ti spin reversal, while TiCrCO 2 preserves its ferrimagnetic order. This behavior originates from spin-conserving, spin-selective charge transfer between Ti and Cr sublattices, followed by asymmetric relaxation of spin carriers determined by the spin-resolved band-edge structure. Electron–phonon coupling dominates over spin–orbit coupling, enabling rapid same-spin transitions, whereas spin-flip processes occur on longer time scales. These findings establish a unified mechanism linking electronic structure, carrier relaxation, and magnetization dynamics, and highlight surface termination as an effective route to tailor ultrafast spin responses in MXenes.
Yu et al. (Tue,) studied this question.