Giant damping enhancement induced by exchange coupling in Y3Fe5O12/Co2FeAl0.5Si0.5 bilayers

Highlights: • The Gilbert damping in YIG capped by CFAS increased significantly. • The damping derived from exchange coupling and spin pumping effect between the YIG film and CFAS layer. • The spin inject efficiency in YIG/CFAS interface is higher than YIG/Pt bilayers. Gilbert damping enhancement induced by the spin pumping effect is investigated in Y₃Fe₅O₁₂(YIG)/heavy metal bilayers. Because its spin polarization is high and Gilbert damping is low, Co₂FeAl_0.5Si_0.5 (CFAS) is deemed a promising ferromagnetic material in spintronics devices. We studied microwave dynamic magnetizations in YIG/CFAS bilayers combined with ferromagnetic resonance measurement using a vector network analyzer to reveal a 5-fold giant damping enhancement compared with that for the YIG/Pt bilayers. This phenomenon was attributed to both the exchange coupling effect and spin pumping effect. By inserting a 10-nm Cu spacer, direct exchange coupling can be suppressed. A spin mixing conductance $g_{eff}^{\uparrow \downarrow }$ of 7.75 × 10¹⁸m⁻² generated by spin pumping was obtained. The study provides an effective approach to tailor the damping in magnetic thin films.