Efficient spin-orbit torques in Mn3Sn/Pt/ferromagnet multilayers induced by interfacial spin-orbit scattering

An important goal of spintronics research is to discover efficient methods of spin current generation. The symmetry conditions generally restrict spin polarizations to be orthogonal to both charge and spin flows in heavy metals. In contrast, the combination of time-reversal and specific structural symmetries breaking in noncollinear antiferromagnets with chiral spin structures represented by ${\mathrm{Mn}}_{3}\mathrm{Sn}$ permits the generation of spin currents with different orientations. Furthermore, the interfacial-generated spin current has proven to have strengths similar to those generated by bulk heavy metals. Here, we report efficient spin-orbit torques (SOT) in the ${\mathrm{Mn}}_{3}\mathrm{Sn}/\mathrm{Pt}/$ferromagnets multilayers, in which the ${\mathrm{Mn}}_{3}\mathrm{Sn}/\mathrm{Pt}$ bilayer system acts as an efficient spin current source due to giant interfacial spin-orbit scattering. Through SOT-induced magnetization switching, spin-torque ferromagnetic resonance, and second harmonic Hall resistance measurements, a robust spin current with x- and y-polarizations (${\ensuremath{\sigma}}_{x}$ and ${\ensuremath{\sigma}}_{y}$, respectively) generated in the ${\mathrm{Mn}}_{3}\mathrm{Sn}/\mathrm{Pt}/$ferromagnets multilayers is confirmed. Furthermore, all the results reveal magnetic octupole-dependent characteristics. As the current is applied along the magnetic octupole direction of the ${\mathrm{Mn}}_{3}\mathrm{Sn}$ layer, the robust ${\ensuremath{\sigma}}_{x}$ spin current results in a zero-field partial magnetization switching in the ${\mathrm{Mn}}_{3}\mathrm{Sn}/\mathrm{Pt}/\mathrm{Co}$ multilayers. Compared with the single ${\mathrm{Mn}}_{3}\mathrm{Sn}$ layer, the spin Hall angle (SHA) dramatically changes in the ${\mathrm{Mn}}_{3}\mathrm{Sn}/\mathrm{Pt}$ bilayers. The temperature-dependent SHA indicates that the large spin current generation efficiency in the ${\mathrm{Mn}}_{3}\mathrm{Sn}/\mathrm{Pt}$ bilayers is much larger than the single $\mathrm{Pt}$ layer, which is determined by the combination of magnetic order and giant interfacial spin-orbit scattering. Our work illustrates that the noncollinear antiferromagnet/heavy metal bilayer systems present an ideal spin current source characteristic.