Lithium-Ion Battery Technology for Voltage Control of Perpendicular Magnetization

Abstract

Voltage control of magnetism provides a promising path toward the development of low-power spintronic devices. Magneto-ionics exploiting voltage-driven ion migration as a control mechanism has attracted interest because it can generate large magnetoelectric effects at low voltage. Here, we demonstrate the use of all-solid-state lithium-ion battery technology for reversible voltage-controlled switching between perpendicular and in-plane magnetization states in a Co/Pt bilayer. The magneto-ionic battery structure consists of a 2 nm Ta/5 nm Pt/20 nm LiCoO2/70 nm LiPON/3 nm Co/5 nm Pt crossbar junction (Fig. 1a,b). Here, the LiPON film functions as a solid-state electrolyte and the LiCoO2 acts as the Li+ storage layer. Using magneto-optical Kerr effect (MOKE) microscopy, we show that the magnetization of the Co film switches between in-plane and perpendicular directions when voltages of +2.5 V and –2 V are applied (Fig. 1c,d). The magneto-ionic switching effect is reliably reproduced over multiple cycles (Fig. 2a,b) and switching takes less than 0.5 s at room temperature (Fig. 2c). Our structure can be cycled for >500 times without degradation. The magnetoelectric coupling efficiency is estimated to be 7,700 fJ/Vm at room temperature, which is the strongest magnetoelectric effect reported to date. We attribute the effect to changes in the hybridization of electron orbitals at the Co/Pt interface upon voltage-controlled insertion and deinsertion of Li+ ions. Our work sets a new benchmark for lithium-based magneto-ionics and demonstrates the relevance of battery design principles for the development of low-power spintronic devices.  Fig. 1 (a) Schematic of the magneto-ionic battery structure. (b) Optical microscopy image of a single crossbar junction. (c) Polar and (d) longitudinal MOKE hystersis curves recorded at –2.0 and +2.5 V.  Fig. 2 Reversible voltage-controlled switching of (a) the perpendicular magnetization and (b) the in-plane magnetization in zero magnetic field. (c) Time-resolved modulation of the longitudinal MOKE signal at room temperature recorded while toggling the voltage between –2.0 V and +2.5V in 0.5 s intervals.