Control of the magnetic anisotropy in multirepeat Pt/Co/Al heterostructures using magnetoionic gating

Controlling magnetic properties through the application of an electric field is a significant challenge in modern nanomagnetism. In this study, we investigate the magnetoionic control of magnetic anisotropy in the topmost Co layer in $\mathrm{Ta}$/$\mathrm{Pt}$/[$\mathrm{Co}$/$\mathrm{Al}$/$\mathrm{Pt}$]${}_{n}$/$\mathrm{Co}$/$\mathrm{Al}$/$\mathrm{Al}\mathrm{O}$${}_{x}$ multilayer stacks comprising $n+1$ Co layers and its impact on the magnetic properties of the multilayers. We demonstrate that the perpendicular magnetic anisotropy can be reversibly quenched through gate-driven oxidation of the intermediary $\mathrm{Al}$ layer between $\mathrm{Co}$ and ${\mathrm{Al}\mathrm{O}}_{x}$, enabling dynamic control of the magnetic layers contributing to the out-of-plane remanence---varying between $n$ and $n+1$. For multilayer configurations with $n=2$ and $n=4$, we observe reversible and nonvolatile additions of 1/3 and 1/5, respectively, to the anomalous Hall-effect amplitude based on the applied gate voltage. Magnetic imaging reveals that the gate-induced spin-reorientation transition occurs through the propagation of a single ${90}^{\ensuremath{\circ}}$ magnetic domain wall separating the perpendicular and in-plane anisotropy states. In the five-repetition multilayer, the modification leads to a doubling of the period of the magnetic domains at remanence. These results demonstrate that the magnetoionic control of the anisotropy of a single magnetic layer can be used to control the magnetic properties of coupled multilayer systems, extending beyond the gating effects on a single magnetic layer.