Figure 1: Schematic illustration of spin current valve.

(a) The transmission of spin current is switched on. Magnetization (M) of magnetic insulator (MI) oriented collinearly with the spin polarization σ (//y) of the pure spin current in the bottom normal metal (NM) layer generated by the spin Hall effect with an electric current J_injected. The spin-flip scattering of conduction electrons at the bottom NM/MI interface can create (M || −σ) or annihilate (M || σ) magnons. A non-equilibrium magnon population extends to the top MI/NM interface, and the spin angular momentum carried by magnons is transferred to conduction electrons in the top NM layer. The pure spin current flowing perpendicular to the NM layer is then converted to a charge current (J_induced) via the inverse spin Hall effect. (b) The transmission of spin current is switched off. M is perpendicular to the spin polarization σ of the spin current. In this geometry, the s–d exchange interaction between conduction electrons and local magnetic moments does not excite magnons in the MI. Consequently, there is no spin accumulation at the top MI/NM interface or induced charge current in the top NM layer.