Generalized Helicity-Dependent Magnetization Switching via Substrate Phonons

Coherent excitation of circularly-polarized substrate phonons can drive deterministic reversal of magnetization in an adjacent magnetic layer. However, the extent to which this substrate-mediated mechanism can be generalized across different materials remains unresolved. Here, we measure and compare the spectral dependence of helicity-dependent magnetization reversal in magnetic GdFeCo layers grown on a diverse set of diamagnetic substrates. Switching is observed for all investigated substrates, spanning six point groups and several infrared-active transverse-optical phonon symmetries. While the switching spectra broadly overlap with the Reststrahlen bands, their maxima are systematically shifted to wavelengths shorter than the corresponding transverse-optical phonon resonances. This spectral mismatch shows that substrate absorption alone does not determine the switching efficiency. Transfer-matrix calculations show that strong absorption concentrates energy deposition near the substrate interface, providing a possible source of local heating that could suppress magnetization reversal. Our results reveal the broad applicability of substrate-mediated phononic switching while showing that its efficiency is governed by the full optical response of the heterostructure rather than substrate absorption alone.