Observation of High Spin-to-Charge Conversion by Sputtered Bismuth Selenide Thin Films at Room Temperature

We investigated spin-to-charge conversion in sputtered Bi₄₃Se₅₇/Co₂₀Fe₆₀B₂₀ heterostructures with in-plane magnetization at room temperature. High spin-to-charge conversion voltage signals have been observed at room temperature. The transmission electron microscope images show that the sputtered bismuth selenide thin films are nanogranular in structure. The spin-pumping voltage decreases with an increase in the size of the grains. The inverse Edelstein effect length (λ_IEE) is estimated to be as large as 0.32 nm. The large λ_IEE is due to the spin-momentum locking and is further enhanced by quantum confinement in the nanosized grains of the sputtered bismuth selenide films. We also investigated the effect on spin-pumping voltage due to the insertion of layers of MgO and Ag. The MgO insertion layer has almost completely suppressed the spin-pumping voltage, whereas the Ag insertion layer has enhanced the λ_IEE by 43%.