Spin current modulation of the magnetically non-resonant acoustic voltage

Surface acoustic waves (SAWs) offer a low-power route for manipulating spin transport in magnetic films due to the coupling between magnons and phonons. In general, this strong magnon-phonon coupling occurs near the magnetic resonance frequency of the magnetic thin film, which limits the bandwidth and device flexibility. Therefore, it is very necessary to study the manipulation of spins using SAWs under magnetically non-resonant conditions. Here, we investigate the spin current modulation in FeGa/Cu/Ta film using SAWs with a frequency far from the resonance of the magnetic film. By measuring the dependence of the acoustic voltage on the magnetic film, we analyzed the generation of the spin current and the origin of the acoustic voltage. The relationship between the acoustic voltage components and the magnetic field angle reveals that the acoustic voltage mainly arises from three contributions: the spin rectification effect (SRE) in the magnetically non-resonant region, acoustic spin pumping, and acoustic spin-rotation, among which the non-resonant SRE is the dominant contribution (>90%). The SRE voltage exhibits a nonmonotonic dependence on Cu thickness, which is governed by the competition between enhanced magnetoelastic driving at small thicknesses and the combined suppression by mass loading and reduced anisotropic magnetoresistance at large thicknesses. Our findings break the bandwidth limitation of resonant excitation and achieve separation and synergistic control of multiple spin-current mechanisms under magnetically non-resonant conditions, providing a new design strategy for broadband, low-power, and contactless acoustic spintronic devices.