The inverse Rashba-Edelstein effect (IREE) is a spin conversion mechanism that recently attracts attention in spintronics and condensed matter physics. In this letter, we report an investigation of the IREE in Bi/Ag by using ferrimagnetic insulator yttrium iron garnet (YIG). We prepared two types of samples with opposite directions of the Rashba field by changing a stacking order of Bi andAg. An electric current generated by the IREE was observed from both stacks, and an efficiency of spin conversion-characterized by the IREE length-was estimated by taking into account a number of contributions left out in previous studies. This study provides a further insight into the IREE spin conversion mechanism: important step towards achieving efficient spin-charge conversion devices. 2The conversion from a spin current to a charge current and vice versa, has been attracting growing interest over the last few years. One of the main mechanisms for conversion is the intrinsic spin-orbit interaction of the material, which is roughly proportional to Z 4 (Z is the atomic number). ) and magnonic charge pumping [19]. The electric current generated by these unwanted effects is detected together with the current generated by the IREE, which hinders precise estimation of the spin conversion efficiency of the IREE, i.e., the IREE length. To avoid these spurious effects superposing the IREE, an introduction of insulating spin source is indispensable.Furthermore, spin current dissipation in both Bi and Ag due to the ISHE and transparency of spin current at the Bi/Ag interface were not fully considered in previous IREE studies, which can also impede precise estimation of the IREE length.In this letter, we introduce ferrimagnetic insulator yttrium iron garnet (YIG) as a spin injector instead of conductive ferromagnet, which eliminates spurious electromotive forces from the ferromagnet layer. In addition, two types of samples with different stacking orders-Bi/Ag/YIG and Ag/Bi/YIG-were studied to understand an effect of the sign reversal of the Rashba field. To estimate the IREE length, we also took into account spin current dissipation in Bi and Ag layers due to the ISHE.We prepared two types of samples with different directions of the Rashba fields:Bi/Ag/YIG and Ag/Bi/YIG. Bi (7-nm-thick) and Ag (5-nm-thick) were deposited on single crystal YIG (10-µm-thick layer) by a resistance heating method (see Fig. 1(a)). Whereas the direction of the Rashba field with respect to the spin direction determines the sign of the IREE current, onlyPy/Ag/Bi/SiO 2 stacking order was investigated in the previous study of the IREE at the interface between Bi and Ag [11]. The samples with opposite directions of the Rashba field in this study 4 allowed further understanding of its role in the IREE. We used spin pumping to inject a pure spin current from the YIG into the Bi/Ag and the Ag/Bi. Spin pumping is a method of spin injection from a ferromagnet (or ferrimagnet) to an adjacent layer under the FMR of the ferromagnet. Under the FMR, a part of the ...