Robust magneto-ionic effect in Fe/FeOx thin films in electrolytes with different cations

Electrochemical reactions offer an elegant way to influence the magnetic properties of nanoscaled materials by applying a small voltage. The present study focuses on such magneto-ionic changes in thin Fe/FeOx films induced by interfacial electrochemical reactions in liquid electrolytes. The films are prepared by inclined sputter deposition and exhibit a uniaxial in-plane anisotropy. LiOH, NaOH and KOH in aqueous solution are used as electrolytes. The changes in the hysteresis loops and the magnetic microstructure are observed by in situ Kerr microscopy. Upon low voltage application, the electrochemical reduction reaction leads to the transformation of the FeOx-layer into the metallic Fe. Simultaneously, a strong decrease of coercivity and remanence together with an increase of domain size occur. These observations are in line with a previously reported magnetic de-blocking mechanism caused by the variation of Neel wall interactions during the oxide-metal transformation. When applying the oxidation potential, the coercivity, remanence, and domain size is re-established. The changes occur in a similar manner for all studied electrolytes and can be repeatedly achieved for multiple voltage switching steps. This evidences that the electrochemical reaction mechanism responsible for the magneto-ionic switching is very robust and dictated by the anion (OH-) rather than the type of cation.