All-Optical study of Gilbert damping and spin orbit torque in Ta/CoFeB/SiO2 heterostructures

Abstract

Pure spin-current induced spin–orbit torque in a magnetic layer can externally control its magnetization dynamics including Gilbert damping. Here, we demonstrate control over Gilbert damping (Δα) in Substrate/β-Ta(t)/CoFeB(3 nm)/SiO2(2 nm) heterostructures with widely varying Ta thickness (3 ≤ t ≤ 20 nm) having stable β-phase using all-optical time-resolved magneto-optical Kerr effect. The pure spin-current due to the spin Hall effect in β-Ta exerts both damping-like and field-like spin–orbit torque to the CoFeB layer. We estimate the damping-like-torque efficiency over a wide range of t with and without Joule heating. In both cases, we obtained a remarkably high-value of damping-like-torque efficiency (ξDL) ∼ 0.40, suggesting that Joule heating has a negligible effect on the Δα. However, the modulation of precession frequency mainly originates from the Joule heating where contributions from field-like-torque and Oersted field are negligible. The high-value of ξDL and its stability over a wide-range of t will be key ingredients for future energy-efficient spintronic and magnonic devices.