Investigation on spin-orbit torque induced perpendicular switching through voltage controlled magnetism*

Spin-orbit torques are shown to induce perpendicular magnetic switching in ultrathin ferromagnets (FMs) adjacent to heavy metals (HMs). Here, we demonstrated that the critical current density ($J_{c})$ for such perpendicular switching in HM/FM/oxide structures can be dramatically modulated by gate voltage induced reversible oxidation at FM/oxide interfaces [1]. Through controlling perpendicular anisotropy and saturation magnetization ($M_{s})$ of FM layer, respectively, we show $M_{s}$, rather than anisotropy field as suggested in macrospin model [2], dominates $J_{c}$. Moreover, the measured external field dependent $J_{c}$ results indicate that the spin-orbit torques have either a bulk or interface origin under different magnetization states. These results not only provide a promising means toward energy-efficient switching, but also offer further insights in understanding the reversal mechanism of the ferromagnetic layer. This work was supported in part by NSF (ECCS-1310338) and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.[1] C. Bi et al, submitted, [2] L. Liu et al. Phys. Rev. Lett. 109, 096602 (2012).