Theory of the acoustic spin pumping

• Acoustically driven spin pumping in a ferromagnet/normal-metal bilayer is discussed.
• Landau–Lifshitz–Gilbert equation combined with Bloch equation is solved by linear response.
• Ferromagnet and normal-metal are modeled to interact via s–d exchange coupling.
• Sounds and magnetization are modeled to interact via exchange magnetostriction.
• Spin pumping signal is shown to be proportional to the input acoustic power.

Spin pumping refers to the spin current injection driven by magnetization dynamics from a ferromagnet into adjacent nonmagnetic conductors. Conventionally, ferromagnetic resonance is used to drive the magnetization dynamics and the spin pumping. Recently a new type of spin pumping driven by acoustic waves, i.e., the acoustic spin pumping, has been reported. We present a linear-response theory of the acoustic spin pumping.