Antiferromagnetic interlayer exchange coupling and large spin Hall effect in multilayer systems with Pt/Ir/Pt and Pt/Ir layers

We investigated Pt/Ir/Pt and Pt/Ir multilayers as candidates of nonmagnetic spacer layers in synthetic antiferromagnetic (AF) layers, which are available for the systematic study on AF spintronics. In these systems, we observed (i) AF interlayer exchange coupling in Pt/Ir/Pt and Pt/Ir nonmagnetic spacer layers sandwiched by Co layers and (ii) large spin Hall conductivity in Pt/Ir multilayer heavy-metal systems which is essential to achieve low power consumption spin-orbit torque switching. We found that total nonmagnetic spacer layer thickness $[{t}_{\mathrm{total}}={t}_{\mathrm{Pt}}(\mathrm{Pt}\phantom{\rule{0.16em}{0ex}}\mathrm{thickness})+{t}_{\mathrm{Ir}}(\mathrm{Ir}\phantom{\rule{0.16em}{0ex}}\mathrm{thickness})]$ range in which AF interlayer exchange coupling is observed is wide in Co/nonmagnetic spacer layer/Co with Pt/Ir/Pt and Pt/Ir nonmagnetic spacer layers. Moreover, the large spin Hall angle of ${\ensuremath{\theta}}_{\mathrm{SH}}=10.3%$ and low resistivity of ${\ensuremath{\rho}}_{xx}=35\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ in Pt/Ir multilayer heavy metal are observed. These results indicate that Pt/Ir/Pt and Pt/Ir are nonmagnetic spacer layers allowing us to achieve the AF interlayer exchange coupling and generation of large spin-orbit torque via spin Hall effect in synthetic AF coupling layer system.