Laser-Induced Ultrafast Magnetic Phase Transition in 2D Van Der Waals Antiferromagnetic Heterostructures.

Light offers the fastest route to controlling magnetization, yet the microscopic mechanisms in 2D magnets have been less explored. Here, using real-time time-dependent density functional theory combined with ab initio nonadiabatic molecular dynamics, ultrafast laser-induced spin transfer and spin relaxation dynamics in 2D van der Waals antiferromagnetic CrI3/CrGeTe3 heterostructures are investigated. Laser excitation is found to induce pronounced interlayer nonequilibrium spin dynamics and ultrafast magnetic moment reconstruction, driving a transition from an antiferromagnetic (AFM) state to a ferrimagnetic (FiM) state. This transition is governed by two key factors: i) asymmetric ultrafast demagnetization of magnetic atoms in the two ferromagnetic layers, leading to substantial changes in interlayer exchange interactions, and ii) a compensatory contribution from the magnetic moments of nonmagnetic atoms, which enhances the stability of the FiM state. Moreover, spin relaxation analysis reveals distinct relaxation mechanisms in the CrI3 and CrGeTe3 layers, where asymmetric interlayer relaxation dynamics significantly extend the FiM lifetime. These findings provide a comprehensive physical picture of laser-induced magnetization transitions in 2D magnets, offering critical theoretical insights for the development of light-controlled magnetic storage and ultrafast spintronic switches.