Room-temperature spin-to-charge conversion in sputtered bismuth selenide thin films via spin pumping from yttrium iron garnet

We investigated spin-to-charge current conversion in sputtered Y₃Fe₅O₁₂ (YIG)/granular bismuth selenide (GBS) bi-layers at room temperature. The spin current is pumped to the GBS layer by the precession of magnetization at ferromagnetic resonance in the YIG layer. The spin-mixing conductance is determined to be as large as (13.64 ± 1.32) × 10¹⁸ m^-2, which is larger than that of YIG/Pt and comparable or better than that of YIG/crystalline bismuth selenide indicating that GBS is a good spin-sink. The figure of merit of spin-to-charge conversion, the inverse Edelstein effect length (λIEE), is estimated to be as large as (0.11 ± 0.03) nm. λIEE shows GBS film thickness dependence, and its value is three times as large as in crystalline bismuth selenide. The λIEE value larger than that of crystalline bismuth selenide and other topological insulators indicates that the spin-to-charge conversion is due to the spin-momentum locking. As the thickness of GBS increases, λIEE decreases, which means the figure-of-merit of spin-to-charge conversion is influenced by grain size.