Magnon-phonon interactions from first principles

In spintronic and magnon-based devices, the lattice vibrations (phonons) of the host material limit the coherence time of electron spins and their ability to carry energy and information. In this talk, we present a first-principles approach to investigate magnon-phonon (mag-ph) interactions and the associated magnon relaxation times and mean free paths. Our method combines the ab initio Bethe-Salpeter equation with modern electron-phonon calculations.



We show results for mag-ph coupling matrices and magnon dynamics in two-dimensional ferromagnetic semiconductors, focusing on monolayer chromium halides. Our method identifies phonon modes strongly coupled to magnons, providing useful microscopic insights for engineering magnetic materials. For example, our results reveals magnon mean-free paths as long as 25 nm in CrI₃ at low temperature, highlighting the potential for future studies in magnon transport. The ability to describe coupled excitons and magnons in our formalism will also be discussed.