Terahertz spectrum in SHNO driven by the pure spin current

We studied the auto-oscillation spectrum of spin Hall nano-oscillators (SHNO) based on synthetic antiferromagnets (SAFs) by micromagnetic simulations. In our model, Py/Ru/Py is used as the SAF, and the typical heavy metal Pt is used to generate the pure spin current via spin Hall effect (SHE). The pure spin current perpendicularly flows into SAF and drive the magnetizations in SAF to precession. We found that the oscillation frequency of the nano-gap SHNO driven by the pure spin current can reach terahertz once the Ruderman-Kittel-Kasuya-Yosida (RKKY) intensity of SAF and current density are reasonably strong. This terahertz spectrum can be excited even without any external magnetic field. The competition between RKKY interaction and SHE definitely boost up the dynamics of magnetization in SAF. Moreover, the terahertz spectrum can be tuned by DC current and/or RKKY intensity. We also studied the influence of the thickness of SAF on the terahertz spectrum. Finally, the nonreciprocity of the generated terahertz spectrum is demonstrated by introducing DMI between HM and SAF. Our results suggest a possible way to exploit terahertz spintronics devices.