Detection of spin current generated by the acoustic spin–rotation coupling mechanism via acoustic voltage

The method of combining surface acoustic waves (SAWs) with electrical detection has promoted the study of phonon–spin coupling and spintronics. Aiming at problems of difficult detection of DC voltage and unknown origin of spin current caused by SAW in ferromagnetic/light metal systems, we constructed the Ni/Cu/Ta on LiNbO3 substrate and measured acoustic voltages directly, which are used to analyze the spin current induced by SAW. By analyzing the angular dependence of acoustic voltages and estimating the maximum spin current, it is determined that acoustic voltages originate from the acoustic spin–rotation (ASR) coupling and the acoustic spin pumping (ASP) effects. The angular dependence shows that for the longitudinal voltage, the contribution of ASR to ASP is in the ratio of 3.22/3.77, while the transverse voltage is mainly contributed by the ASR. The maximum spin current due to ASR is 0.97 × 105 A/m2, while that due to ASP is 1.47 × 105 A/m2. This work provides ideas for the design of phonon–spin coupled devices.