Determination of spin pumping effect in CoFeB/Ir bilayer

Abstract

The spin pumping effect of CoFeB/Ir bilayers has been investigated via the broadband ferromagnetic resonance measurement. With increasing the thickness of heavy metal Ir layer, the Gilbert damping factor of 8 nm CoFeB film increases from 7 × 10−3 to 1.1 × 10−2, and the additional damping factors induced by the spin pumping effect quickly reaches its saturation value. According to the spin pumping theory, the spin mixing conductance of CoFeB/Ir and the spin diffusion length of Ir were obtained. The spin mixing conductance is 2.14 × 1019 m−2. Furtherly, the spin diffusion length is only 1.34 nm, which is quite shorter compared with the heavy metal Pt. Our results reveal the existence of the strong spin-orbit coupling in the heavy metal Ir, which can be a potential material for the application in spintronic devices.