Deterministic Spin-Orbit Torque Switching of Mn3Sn with the Interplay between Spin Polarization and Kagome Plane

Previous studies have demonstrated spin-orbit torque (SOT) switching of Mn3Sn where the spin polarization lies in the kagome plane (configuration I). However, the critical current density ($ J_{crit}$) is unrealistically large ($ J_{crit}$=$ 10^{14}$ A/$ m^2$) and independent on the external field ($ H_{ext}$). The stabilized magnetic state also depends on the initial state. These features conflict with the ferromagnet (FM) switching scheme as claimed in those studies, and thus call for other explanations. Alternatively, the system with the spin polarization perpendicular to the kagome plane (configuration II) is more like the FM based system since the spin polarization is orthogonal to all magnetic moments. In this work, we show SOT switching of Mn3Sn in configuration II. Similar to the FM, Jcrit and Hext are in the order of $ 10^{10}$ A/$ m^2$ and hundreds of Oersted, respectively. The switching result is also independent of the initial state. Interestingly, the unique spin structure of Mn3Sn also leads to distinct features from FM systems. We demonstrate that Jcrit increases linearly with Hext, and extrapolation gives ultralow $ J_{crit}$ for the field-free switching system. In addition, the switching polarity is opposite to the FM. We also provide the switching phase diagram as a guideline for experimental demonstration. Our work provides comprehensive understanding for the switching mechanism in both configurations. The switching protocol proposed in this work is more advantageous in realistic spintronic applications. We also clearly reveal the fundamental difference between FM and noncollinear antiferromagnetic switching.