Voltage Signals Caused by Surface Acoustic Wave Driven Ferromagnetic Resonance Under Out-of-Plane External Fields

Under an external magnetic field, surface acoustic waves (SAWs) propagating onto a ferromagnetic thin film can excite ferromagnetic resonance (FMR). The magnetization precessional motion in resonance pumps spin current into the Rashba interface across an adjacent non-magnetic layer, which can be converted to charge current via the inverse Edelstein effect (IEE). Here, the SAW-driven FMR and the IEE voltage signals under in- and out-of-plane external magnetic fields are reported. When the external magnetic field has only an in-plane component, the SAW-driven FMR for positive and negative resonant fields have the same sign (even), while the spin-conversion due to IEE results in voltage signals with opposite signs for positive and negative fields (odd). However, when the out-of-plane component of the external magnetic field increases, the acoustic ferromagnetic resonance signal remains even. In contrast, the IEE voltage signal exhibits a sum of even and odd signal contributions. It is discussed that the appearance of the even contribution to the voltage signal does not correspond to well-known spin rectification mechanisms. The result may constitute a novel resonant spin rectification mechanism under SAW excitations.