Spin accumulation in acoustically excited Ni/GaAs/Ni trilayers

In this paper, we report the first theoretical results on the acoustic generation of spin accumulation in ferromagnet-semiconductor-ferromagnet trilayers. As a representative material system, we consider a Ni/GaAs/Ni trilayer coupled to a piezoelectric transducer, which injects a planar acoustic wave into the adjoining Ni film. By combining an analytical solution of the spin diffusion equation in the GaAs spacer with results of numerical simulations of the coupled elastic and magnetic dynamics in the Ni films, we quantify an oscillating inhomogeneous spin accumulation in GaAs. It is found that both dc and ac parts of the mean spin accumulation vary nonmonotonically with the spacer thickness tS, reaching maximal values at tS mostly close to 0.25 or 0.75 of the wavelength of the injected monochromatic acoustic wave. Remarkably, the transverse wave generates the spin accumulation much more efficiently than the longitudinal one. Our theoretical predictions provide guidelines for the development and optimization of energy-efficient acoustic spin injectors into semiconductors, which should have much lower power consumption than injectors driven by the microwave magnetic field.