Li-ionic control of magnetism through spin capacitance and conversion

Magnetoelectric (ME) coupling has gradually developed into one of the core means of advancing ultralow-power memory, logic, and sensor technologies. Among various strategies, magneto-ionic control of magnetism based on mechanisms such as redox, intercalation/deintercalation, and charge accumulation can be achieved in ion battery or capacitor systems. In this work, we demonstrate an ME effect originating from the spin capacitance, combining the advantages of intercalation batteries and supercapacitors. Giant, fast, and reversible modulations on the saturation magnetization of ferromagnets are achieved by Li ion motion across the ferromagnet/lithionic conductor interfaces at no more than 1 V. Furthermore, the magnetic evolution driven by the conversion reaction between FeO and Fe over a larger voltage range demonstrates ferromagnetic ordering of the FeO surface. These findings not only open new perspectives for developing high-performance magneto-ionic devices but also are crucial to designing spintronic devices composed of iron and oxide multilayer structures.