Direct observation of magnon-phonon coupling in yttrium iron garnet

The ferrimagnetic insulator yttrium iron garnet (YIG) has been widely used in microwave and spintronic devices. Anomalous features in spin Seeback effect voltages have been observed in Pt/YIG and attributed to magnon-phonon coupling. Using inelastic neutron scattering to map out low-energy spin waves and acoustic phonons in YIG as a function of increasing magnetic field, the authors find that the magnon-phonon interaction enhances the hybridized scattering intensity at the magnon-phonon dispersion crossing points in zero field. These results go against the expectations of conventional spin-lattice coupling, calling for a different explanation of the magnon-phonon interactions and the resulting magnon polarons in YIG.