Multidomain Memristive Switching of Pt38Mn62/[Co/Ni]n Multilayers

We investigate the mechanism of analoglike switching of ${\mathrm{Pt}}_{38}{\mathrm{Mn}}_{62}$/[$\mathrm{Co}$/$\mathrm{Ni}$] multilayers induced by spin-orbit torques. X-ray photoemission microscopy performed during magnetization reversal driven by current pulses shows that sequential switching of reproducible domain patterns can be achieved. Switching proceeds by domain-wall displacement starting from the edges of blocked ferromagnetic domains, which do not switch for either direction of the current and represent up to 24% of the total ferromagnetic area. The antiferromagnetic ${\mathrm{Pt}}_{38}{\mathrm{Mn}}_{62}$ layer has a granular texture, with the majority of the domains being smaller than 100 nm, whereas the ferromagnetic domains in $\mathrm{Co}$/$\mathrm{Ni}$ are typically larger than 200 nm. The blocked domains and the granular distribution of exchange bias constrain the origin as well as the displacement of the domain walls, thus leading to highly reproducible switching patterns as a function of the applied current pulses. These measurements clarify the origin of the memristive behavior in antiferromagnet-ferromagnet structures and provide clues for further optimization of spin-orbit torque switching and memristivity in these systems.