Controlling\nUltrafast Magnetization Dynamics via Coherent\nPhonon Excitation in a Ferromagnet Monolayer

Exploring ultrafast magnetization control in 2D magnets\nvia laser\npulses is established, yet the interplay between spin dynamics and\nthe lattice remains underexplored. Utilizing real-time time-dependent\ndensity functional theory (rt-TDDFT) coupled with Ehrenfest dynamics\nand nonadiabatic molecular dynamics (NAMD) simulations, we systematically\ninvestigate the laser-induced spin-nuclei dynamics with pre-excited\nA<sub>1g</sub> and E<sub>2g</sub> coherent phonons in the 2D ferromagnet\nFe<sub>3</sub>GeTe<sub>2</sub> (FGT) monolayer. Selective pre-excitation\nof coherent phonons under ultrafast laser irradiation significantly\nalters the local spin moment of FGT, consequently inducing additional\nspin loss attributed to the nuclear motion-induced asymmetric interatomic\ncharge transfer. Excited spin-resolved charge undergoes a bidirectional\nspin-flip between spin-down and spin-up states, characterized by a\nsubtle change in the spin moment within approximately 100 fs, followed\nby unidirectional spin-flip, which will further contribute to the\nspin moment loss of FGT within tens of picoseconds. Our results shed\nlight on the coupling of coherent phonons with magnetization dynamics\nin 2D limit.