Helicity-Selective Phonon Absorption and Phonon-Induced Spin Torque from Interfacial Spin-Lattice Coupling

TL;DR

This paper uncovers how interfacial spin-lattice coupling in magnetic heterostructures causes helicity-dependent phonon absorption and enables phonon-induced spin torque, emphasizing the importance of interface effects in spin-lattice interactions.

Contribution

It introduces a novel helicity-helicity coupling mechanism at interfaces that does not depend on lattice deformation gradients, advancing understanding of spin-lattice interactions in magnetic heterostructures.

Findings

Helicity-dependent phonon absorption observed in magnetic heterostructures.

In-plane acoustic waves can exert spin torque via interfacial coupling.

Interface effects play a crucial role in angular-momentum transfer between spin and lattice.

Abstract

In magnetic heterostructures with broken inversion symmetry, the Rashba effect gives rise to a gradient-free interaction between magnons and phonons, which we term interfacial spin-lattice coupling. Here, we investigate the dynamic consequences of this interfacial coupling in ferromagnetic heterostructures. By expressing the interaction in terms of circular variables for magnetization and lattice displacement, we reveal a direct interface-induced helicity-helicity coupling hat does not rely on lattice deformation gradients. Consequently, it leads to helicity-dependent phonon absorption, enabling in-plane acoustic waves to exert a spin torque on the magnetization, which becomes dominant in thin magnetic films. Our findings highlight the crucial, yet overlooked, role of inversion-asymmetric interfaces in angular-momentum conversion between spin and lattice, opening up possibilities for efficient phonon-driven magnetic devices that are enabled by interface engineering.