Robust Magneto-Ionic Effect in Fe/FeO x Thin Films in Electrolytes With Different Cations

Abstract

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/FeO_<i>x</i> 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 an aqueous solution are used as electrolytes. The changes in the hysteresis loops and the magnetic microstructure are observed by <i>in-situ</i> Kerr microscopy. Upon low voltage application, the electrochemical reduction reaction leads to the transformation of the FeO_<i>x</i>-layer into the metallic Fe. Simultaneously, a strong decrease of coercivity and remanence together with an increase of domain size occurs. These observations are in line with a previously reported magnetic de-blocking mechanism caused by the variation of N&#x00E9;el wall interactions during the oxide&#x2013;metal transformation. When applying the oxidation potential, the coercivity, remanence, and domain size are 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^&#x2212;) rather than the type of cation.