Spin Torque Control of Magnetic Multiples in Topological Antiferromagnets*

Electrical manipulation of spin textures inside antiferromagnets represents a new opportunity for developing spintronics with superior speed and high device density. Different from ferromagnet where the magnetic ordering is described by a magnetic dipole moment, the magnetic ordering in antiferromagnet needs to be characterized by higher order magnetic multipole moment like quadrupoles or octupoles. It remains an interesting question how to  realize efficient control of the magnetic multipoles through the spin torque effect, which in nature reflects the transfer of dipolar angular momentum. In some of the existing reports on antiferromagnetic switching, because of the diminishing magnetic susceptibility, the nature and the magnitude of current-induced magnetic dynamics remain poorly characterized, whereas spurious effects further complicate experimental interpretations [1].

In this talk, I will discuss our recent experimental studies on controlling magnetic multipoles of antiferromagnets using spin orbit torque. First, by growing a thin film antiferromagnetic insulator, α-Fe₂O₃, along its non-basal plane orientation, we realize a configuration where an injected spin current can robustly rotate the quadrupole moment – the Neel vector within the tilted easy plane, with an efficiency comparable to that of classical ferromagnets [2]. Secondly, we also studied the spin torque induced magnetic dynamics in a non-collinear topological antiferromagnetic semimetal, where the spin orbit torque induces distinct dynamics on magnetic octupole moment compared with the well known magnetization dynamics in regular ferromagnets. By enabling efficient spin-orbit torque control on the antiferromagnetic ordering, our studies introduce new platforms for quantitatively understanding switching and oscillation dynamics in antiferromagnets.