Enhancement of current to spin-current conversion and spin torque efficiencies in a synthetic antiferromagnetic layer based on a Pt/Ir/Pt spacer layer

We investigated the current-induced spin-orbit torque (SOT) originating from the spin Hall effect in stack systems with perpendicularly magnetized Co/Pt/Ir/Pt/Co synthetic antiferromagnetic (AFM) structures which exhibit nearly compensated magnetization and interlayer exchange coupling of ${J}_{\mathrm{ex}}=0.11\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$. The results were compared with ferromagnetic stack systems with perpendicularly magnetized Pt/Co and (Ir/Pt)-multilayer/Co structures. The magnetizations of the two Co layers in the Co/Pt/Ir/Pt/Co synthetic AFMs can be switched between two antiparallel states simultaneously by SOT. By this switching mechanism, the current to spin-current conversion and spin-torque efficiencies in a synthetic AFM layer stack based on a Pt/Ir/Pt spacer layer are about twice as high as those of a ferromagnetic stack using a Pt heavy metal electrode. The efficient switching of compensated synthetic AFMs would advance magnetic memory devices with high density, high speed, and low power consumption. We expect the Pt/Ir/Pt spacer layer paves the way to AFM spintronics based on multilayer systems.