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.