Light-Induced Ultrafast Enhancement of Magnetic Orders in Monolayer CrX₃

The recent discovery of light-tunable intrinsic ferromagnetism in two-dimensional (2D) van der Waals crystals has opened up a new arena for spintronics. However, the underlying mechanism is still under debate. Here, we performed excited-state density functional theory (DFT) calculations for optical manipulation of magnetism in monolayered CrX₃ (X = Cl, Br, I). By applying the real-time time-dependent DFT method, we found that the laser pulses can directly induce ultrafast spin-selective charge transfer from X atoms to Cr atoms and further generate a dramatic magnetic moment of Cr atom changes. The microscopic mechanisms for ultrafast changing of magnetic order are discussed based on the p-d electron transition and electron-phonon coupling. Combined with constrained DFT and Monte Carlo simulations, we further theorized the light-excited effects on exchange interaction and found that the Curie temperature of CrX₃ under light excitation (>150 K) is significantly higher than that in the ground state (<70 K). Our results open new opportunities to manipulate the spin in 2D magnets as well as the potential applications in spintronics.