Anomalous anti-damping in sputtered β-Ta/Py bilayer system

Anomalous decrease in effective damping parameter α(eff) in sputtered Ni(81)Fe(19) (Py) thin films in contact with a very thin β-Ta layer without necessitating the flow of DC-current is observed. This reduction in α(eff), which is also referred to as anti-damping effect, is found to be critically dependent on the thickness of β-Ta layer; α(eff) being highest, i.e., 0.0093 ± 0.0003 for bare Ni(81)Fe(19)(18 nm)/SiO(2)/Si compared to the smallest value of 0.0077 ± 0.0001 for β-Ta(6 nm)/Py(18 nm)/SiO(2)/Si. This anomalous anti-damping effect is understood in terms of interfacial Rashba effect associated with the formation of a thin protective Ta(2)O(5) barrier layer and also the spin pumping induced non-equilibrium diffusive spin-accumulation effect in β-Ta layer near the Ta/Py interface which induces additional spin orbit torque (SOT) on the moments in Py leading to reduction in [Image: see text]. The fitting of [Image: see text] (t(Ta)) revealed an anomalous negative interfacial spin mixing conductance, [Image: see text]and spin diffusion length,[Image: see text]. The increase in α(eff) observed above t(Ta) = 6 nm is attributed to the weakening of SOT at higher t(Ta). The study highlights the potential of employing β-Ta based nanostructures in developing low power spintronic devices having tunable as well as low value of α.