Spin-orbit torque from a ferromagnetic metal

Abstract

The switching of magnetization by current-induced spin-orbit torque (SOT) has potential applications for energy-efficient spintronic devices. In the past, most conventional works have been focused on SOT in heavy metals. Here the SOT from a ferromagnetic metal is investigated, and two mechanisms of the field-free SOT induced magnetization switching are demonstrated to be from the interlayer exchange coupling and the tilted perpendicular magnetic anisotropy. We exclude the spin torque contribution from the anomalous Hall effect and the interfacial Rashba effect combined with spin precession. A spin Hall angle ${\ensuremath{\theta}}_{\mathrm{SH}}=\ensuremath{-}0.022$ of CoFeB is obtained by the current-induced hysteresis loop shift method, and the obtained ${\ensuremath{\theta}}_{\mathrm{SH}}$ is comparable with heavy metals. This work demonstrates that a considerable SOT can come from a ferromagnetic metal, and indicates the unconventional origin of spin-orbit coupling.