Spin-Orbit Torque Efficiency in Compensated Ferrimagnetic Cobalt-Terbium Alloys

We report spin-orbit torque induced magnetization switching of ferrimagnetic Co$_{\mathrm{1-x}}$Tb$_{\mathrm{x}}$ films with perpendicular magnetic anisotropy. Current induced switching is demonstrated in all studied film compositions, including those near the magnetization compensation point. A divergent behavior that scales with the inverse of magnetic moment is confirmed for the spin-orbit torque efficiency, which is consistent with angular momentum conservation. Moreover, we also quantified the Dzyaloshinskii-Moriya interaction energy in the Ta/Co$_{\mathrm{1-x}}$Tb$_{\mathrm{x}}$ system and found that the energy density increases with Tb concentration. The large effective spin-orbit torque, the previously demonstrated fast dynamic, and the minimal net magnetization in these ferrimagnetic systems promise spintronic devices that are faster and with higher density than traditional ferromagnetic systems.