Long-Range Phonon Spin Transport in Ferromagnet-Nonmagnetic Insulator Heterostructures

We investigate phonon spin transport in an insulating ferromagnet–nonmagnet–ferromagnet heterostructure. We show that the magnetoelastic interaction between the spins and the phonons leads to nonlocal spin transfer between the magnets. This transfer is mediated by a local phonon spin current and accompanied by a phonon spin accumulation. The spin conductance depends nontrivially on the system size, and decays over millimeter length scales for realistic material parameters, far exceeding the decay lengths of magnonic spin currents.