The voltage control of magnetism is a promising path to the development of low‐power spintronic devices. Magneto‐ionics—exploiting voltage‐driven ion migration to control magnetism—has attracted interest because it can generate large magnetoelectric effects at low voltage. Here, the use of the solid‐state lithium‐ion battery technology for reversible voltage‐controlled switching between perpendicular and in‐plane magnetization states in a Co–Pt bilayer is demonstrated. Due to the small size and high mobility of lithium ions, small voltages produce an exceptionally high magnetoelectric coupling efficiency of at least 7700 fJ V–1 m–1 at room temperature. The magnetic switching effect is attributed to the modulation of spin‐orbit coupling at the Co–Pt interface when lithium ions migrate between a lithium storage layer (LiCoO2) and the magnetic interface across a lithium phosphorous oxynitride (LiPON) solid‐state electrolyte, which is corroborated by density functional theory calculations. Voltage control of magnetism in the battery structure does not show degradation over more than 500 voltage cycles, demonstrating promise for solid‐state lithium‐based magneto‐ionic devices.

Placing a suitable spacer layer between two magnetic layers can lead to an interaction between the magnetic layers known as Ruderman–Kittel–Kasuya–Yosida (RKKY) coupling. Controlling RKKY coupling, particularly the ability to switch between ferromagnetic and antiferromagnetic coupling, would enable novel magnetic data storage devices. By combining solid-state Li ion battery technology with an out-of-plane magnetized Co/Pt-based stack coupled through a Ru interlayer, we investigate the effects of the insertion of Li ions on the magnetic properties of the stack. The RKKY coupling and its voltage dependence are measured as a function of the Ru interlayer thickness, along with the effects of repeated voltage cycling. The Li ions both change the amplitude of the RKKY coupling and its phase, leading to the ability to switch the RKKY coupling between ferromagnetic and antiferromagnetic with applied voltages.

Ionic control of magnetism gives rise to high magnetoelectric coupling efficiencies at low voltages, which is essential for low-power magnetism-based nonconventional computing technologies. However, for on-chip applications, magnetoionic devices typically suffer from slow kinetics, poor cyclability, impractical liquid architectures, or strong ambient effects. As a route to overcoming these problems, we demonstrate a LiPON-based solid-state ionic supercapacitor with a magnetic Pt/Co40Fe40B20/Pt thin-film electrode which enables voltage control of a magnetic skyrmion state. Skyrmion nucleation and annihilation are caused by Li ion accumulation and depletion at the magnetic interface under an applied voltage. The skyrmion density can be controlled through dc applied voltages or through voltage pulses. The skyrmions are nucleated by single 60 μs voltage pulses, and devices are cycled 750000 times without loss of electrical performance. Our results demonstrate a simple and robust approach to ionic control of magnetism in spin-based devices.