Speaker
Description
Recently, current-induced spin-orbit torques(SOT) switching have been demonstrated in ferromagnet(FM) / antiferromagnet(AFM) multilayers with perpendicular anisotropy [1,2]. The use of an AFM results in multiple nonvolatile (memristive) states, akin to neural networks [3]. Past experiments suggest that the non-uniform exchange bias from the AFM causes separate switching of domains, leading to this behavior [4]. This description differs from conventional SOT switching in FM/nonmagnet (NM) cases [5]. A deeper understanding of the switching in FM/AFM structures is thus relevant for SOT research and for AFM applications in spintronic devices. Here we use x-ray photoemission electron microscopy to image the FM domains of [Co/Ni]2/PtMn layers, at intermediate switching states with injected currents. We find that the Co/Ni domains are shaped irregularly and are of the order of 300 nm. Sequential current pulses gradually switch domains by nucleation & expansion, reproducibly; commensurate with electrical measurements. As a 1st visualization of field-free SOT switching, this opens new avenues to understand and optimize this behavior for FM/AFM spintronics devices.
(Work supported by CSTI-ImPACT, JST-OPERA & the Swiss NSF)
[1] S.Fukami et al., Nat.Mater. 15,535 (2016).
[2] A.van den Brink et al., Nat.Comm. 7,10854 (2016).
[3] W. A. Borders et. al., Appl.Phys.Express 10,013007 (2017).
[4] A. Kurenkov et al., Appl.Phys.Lett. 110,092410 (2017).
[5] M.Baumgartner et al., Nat.Nanotech. 12,980 (2017).
