Field-free spin-orbit torque switching and large dampinglike spin-orbit torque efficiency in synthetic antiferromagnetic systems using interfacial Dzyaloshinskii-Moriya interaction

Deterministic switching of perpendicularly magnetized systems using spin-orbit torque (SOT) usually requires an in-plane auxiliary magnetic field, which limits its practical applications. Here, an interfacial Dzyaloshinskii-Moriya interaction is introduced into perpendicularly magnetized synthetic antiferromagnetic (AFM) systems by changing the type of capping or underlayer in the [capping layer]/Co/[Pt/Ir/Pt spacer layer]/Co/[underlayer] synthetic AFM system. Field-free switching in the synthetic AFM system is observed in the cases of W, Ta, ${\mathrm{Ir}}₂₂{\mathrm{Mn}}₇₈$ capping layers or ${\mathrm{Ir}}₂₂{\mathrm{Mn}}₇₈$ underlayer. Among the synthetic AFM systems with field-free switching, the synthetic AFM system with ${\mathrm{Ir}}₂₂{\mathrm{Mn}}₇₈$ capping layer shows the largest dampinglike SOT efficiency, ${\ensuremath{\xi}}_{\mathrm{DL}}=28.1%$. We also found observed large ${\ensuremath{\xi}}_{\mathrm{DL}}$ is related to the enhancement of spin absorption in antiferromagnetic Co magnetization configuration in synthetic AFM system compared to that in ferromagnetic Co magnetization configuration and the degree of enhancement increases with increasing the magnitude of interlayer exchange coupling between Co layers in synthetic AFM system. These results suggest that the synthetic AFM system is a promising building block for future nonvolatile high-speed memories and logic circuits using the spin Hall effect.