Chiral phonon-driven spin dynamics across van der Waals interface

The coupling between chiral phonons and magnetization dynamics has gained significant attention recently with the help of new ultrafast techniques. Experimental evidence showed that the spin-phonon coupling may occur in thin-film heterostructures, where the phonons are excited in one material and spins are generated in another material, but the exact coupling mechanisms are still under debate. Here, we measured the spin dynamics of a van der Waals magnetic thin film in proximity with an ionic insulator with chiral phonon excitations. We found clear evidence of fast magnetization transfer induced by the phonons. We were able to distinguish various mechanisms, including ultrafast thermal demagnetization, phonon transport through the interface, and spin exchange interactions. Our results may provide guidelines for realizing ultrafast magnetization and non-equilibrium states with time-reversal symmetry breaking in a broader range of materials for spintronics.