Detection of torque effects in Co/Pt via ferromagnetic resonance

Abstract

Charge-current-induced torque effects on the magnetization dynamics of ferromagnetic/metal bilayer is interesting from the aspect of fundamental physics as well as the applications in spintronic devices. The torque-induced variation of damping constant of magnetization can be foreseen from the change of the linewidth of ferromagnetic resonance spectrum. The Oersted torque (τOe) and current-induced torque (τC) are induced by charge current; while the spin-orbit torque (τSO) and field-like torque (τFL) are induced by spin current. However, the torque effects often were hindered due to the heating-induced artifacts. In this work, we particularly pay attention to minimize the Joule heating effects in order to investigate the intrinsic torque effects in cobalt (Co)/platinum (Pt) bilayer with an applied charge current ranging from −60 to 60 mA. In this range, the Oersted field is estimated as 0.25 Oe which is much smaller than the experimental result of ΔHr (∼0.7 Oe), implying some contribution from the spin-current induced field like torque. The current-polarization-induced asymmetry of linewidth ΔW, ΔW≡W+Jc−W−Jc, increases from 0 to 0.15 with Jc changing from 0 to 60 mA, which is attributed to the spin-orbit torque.