Role of Ta buffer layer in thickness-dependent Gilbert damping of sputtered FeAl thin films

Abstract

To address the technological perspective of FeAl alloy thin films in spintronic applications, we investigate how a 4 nm non-magnetic Ta buffer layer affects the ferromagnetic relaxation (damping) in FeAl for varying thicknesses (7–24 nm) using ferromagnetic resonance spectroscopy (FMR). It is found that the presence of a Ta buffer layer leads to the enhancement of Gilbert damping (α) from 0.0111 ± 0.0002 to 0.0236 ± 0.0007 (i.e., ∼112.6% increment) compared to a bare 7 nm FeAl film. However, effective magnetization and saturation magnetization in the Ta/FeAl (7 nm) film shows comparatively less increment in their values, i.e., ∼4.4% and ∼6.6%, respectively, compared to the 7 nm FeAl film as obtained from FMR and vibrating sample magnetometry techniques. We observed a significant increase in α due to the spin pumping effect at the interface of the heavy metal Ta layer and ferromagnetic FeAl layer. From first-principles density functional theory, the rise in α is qualitatively demonstrated by the enhanced density of states at the Fermi level. Intrinsic α calculated from the Kambersky torque–torque correlation model shows about six time rise in α with buffer layer compared to the bare 4.5 nm FeAl film, a similar trend as obtained experimentally. This research provides guidance to tailor α of FeAl through a heavy metal Ta buffer layer for application in economical spintronic devices.