Reversible control of magnetism: on the conversion of hydrated FeF3 with Li to Fe and LiF

Conversion-type electrode materials are prominent examples of potential Li-ion battery cathodes and/or anodes with large specific capacities. Conversion reactions often rely on complete reduction or oxidation of a transition metal, leading to multi-electron redox processes per formula unit, accompanied by changes of crystal structure and electronic configuration and, consequently, of materials properties such as magnetization. Here, we report on the utilization of the FeF3/Fe conversion reaction to reversibly control the magnetization. Hydrated FeF3 was chosen as electrode material and the changes in magnetization upon reversible redox reaction against Li counter electrode monitored by means of Superconducting Quantum Interference Device magnetometry. In situ measurements provide insights into the changes in magnetization occurring during the conversion reaction, specifically revealing the transition from paramagnetism to ferromagnetism.