Acoustic spin rotation in heavy-metal-ferromagnet bilayers.

Through pumping a spin current from ferromagnet into heavy metal (HM) via magnetization precession, parts of the injected spins are in-plane rotated by the lattice vibration, namely acoustic spin rotation (ASR), which manifests itself as an inverse spin Hall voltage in HM with an additional 90° difference in angular dependency. When reversing the stacking order of bilayer with a counter-propagating spin current or using HMs with an opposite spin Hall angle, such ASR voltage shows the same sign, strongly suggesting that ASR changes the rotation direction due to interface spin-orbit interaction. With the drift-diffusion model of spin transport, we quantify the efficiency of ASR up to 30%. The finding of ASR endows the acoustic device with an ability to manipulate spin, and further reveals a new spin-orbit coupling between spin current and lattice vibration. Controlling spin direction is the key for spintronic devices as it induces efficient and field-free switching. Herein, the authors propose using lattice vibrations in acoustic devices to replace the charge motion in conventional spintronic devices to realize the rotation of spin direction, that is, acoustic spin rotation. Acoustic spin rotation offers higher efficiency than spin rotation in conventional charge-current based spintronic devices. [ABSTRACT FROM AUTHOR]