Chiral Phonons Enable Ultrafast Magnetization Switching via Magnetoelastic Coupling

Phonons are desirable for current-free energy-efficient spin manipulation and harnessing their chirality to achieve ultrafast magnetization switching remains actively pursued. Here we demonstrate that terahertz-driven chiral phonons enable faster magnetization switching than linear phonons through the purely magnetoelastic coupling that transfers both energy and angular momentum. Only one phonon handedness efficiently transfers angular momentum to the spin system, which we explain by a large fictitious kinematic Barnett-like field at THz frequencies that destabilizes spin precession for the opposite chirality. Considering different regions of the spinwave spectrum, we find that switching conditions can be realized near the {\Gamma}-point where strong energy transfer and spinwave excitation dominate, and near the P-point which offers minimal energy loss. Our results establish phonon chirality as a decisive and previously overlooked parameter in spin-lattice dynamics within the magnetoelastic coupling mechanism, offering a promising avenue for ultrafast low-energy spintronic devices.