Tailoring Spin Relaxation Pathways in Monolayer Black Phosphorus via Transition Metal Doping.

Controlling spin dynamics in two-dimensional (2D) materials is critical for advancing quantum computing and spintronic technologies. Here, we systematically investigate the spin relaxation and flip dynamics in black phosphorus (BP) monolayers doped with transition metal atoms (Ti, V, Cr, and Ni) using time-domain nonadiabatic dynamics simulations. Compared with the pristine BP, doping of magnetic atom introduces magnetic moments (0.56-3.62 μB) and significantly alters the spin polarization of conduction band minimum, establishing two distinct pathways for spin relaxation: spin-down dominated (Ti@BP, Ni@BP) and spin-up dominated (V@BP, Cr@BP). These two categories exhibit contrasting magnetic responses upon photoexcitation─either enhancing or reducing the net magnetic moment. Crucially, the scale of relaxation time is governed by dopant-specific electron-phonon coupling and spin-orbit coupling strengths. Our findings highlight an effective strategy for tuning spin dynamics and magnetic lifetimes in 2D semiconductors through single-atom doping, offering valuable insights for the rational design of spintronic devices.