Multi-domain memristive magnetization switching in [Co/Ni]_X/PtMn heterostructures

Current-induced spin-orbit torques (SOT) enable the switching of ferromagnet (FM)/ antiferromagnet (AFM) multilayers for memory applications and potential use in neuromorphic computing [1]. We use x-ray photoemission electron microscopy to image the FM and AFM domains of [Co/Ni]_X/PtMn layers at intermediate switching states as a function of injected currents. The AFM PtMn layer has a granular texture, with majority of the domains smaller than 100 nm, whereas the FM domains in Co/Ni are typically larger than 200 nm. We find no strict correlation between the current-induced switching of FM domains and the underlying AFM domains. Imaging of Co/Ni domains shows that switching occurs by the incremental domain expansion driven by SOTs starting from the edges of blocked domains and proceeding by domain wall displacements rather than grain-by-grain [2]. Highly reproducible domain patterns are found between consecutive switching cycles. Together, the step-wise expansion of the domains and the domain pattern reproducibility determine the memristive properties of the bilayer.
[1] Fukami et al., Nat. Mater. 15,535 (2016); Kurenkov et al., Adv. Mater. 31, 1900636 (2019)
[2] Krishnaswamy et al., Phys. Rev. Applied 14, 044036 (2020).