Interfacial electrochemical effects on magnetism, often also named magneto-ionic effects, are an emerging room-temperature and low-voltage approach in the research area of voltage control of magnetism [1]. In magneto-ionic systems, the magnetic layer is gated via a solid or liquid electrolyte and the applied voltage triggers ion migration and interfacial redox reactions, which impact the magnetic properties. In contrast to multiferroic systems and capacitive electronic charging, magneto-ionic concepts make significant magnetic property changes possible at room temperature and without the need for strain mediation [2], [3]. Since the mechanism is based on electrochemical charge transfer at the electrode/electrolyte interface, the morphology and the composition may be key to the magneto-ionic efficiency. We report magneto-ionic manipulation of ultrathin films in extended and stripe geometry and 3D nanoplatelet structures. In situ magnetic transport measurements are used in this study to determine and analyze the magneto-ionic effect. For FeOOH nanoplatelets, the application of a low voltage via liquid electrolyte gating yields an ON switching of magnetization (deduced from changes of the anomalous Hall resistance, see Figure 1a) [4]. The transformation proceeds via voltage-induced dissolution/redeposition, with the initially paramagnetic FeOOH structure as iron ion reservoir. The time-dependency of the reduction reaction enables the non-volatile setting of magnetic layers with different total magnetic moments. A large reversible magneto-ionic change of magnetization of up to 15% is achieved in the resulting iron films, which is explained by the enhanced roughness of the iron films obtained from the nanoplatelet structure. For thin Fe3O4/Fe films in stripe geometry, we achieved a tunable magnetoresistance by electrolytic gating (Figure 1b) [5]. Here, the tuning mechanism relies on voltage-triggered redox reactions, which locally affect the Fe3O4 regions. In the low-magnetic-field region (&lt;1 T), a crossover from positive to negative magnetoresistance is achieved by a voltage change of only 1.72 V. We will further present first results on the impact of the composition in iron triad magneto-ionic systems on magnetic properties by going beyond iron structures. The proposed approach is promising for the development of energy-efficient magnetic switches, sensors, and magnetic actuation, and may offer new avenues in magnetoelectronic devices.

**References:**

[1] K. Leistner, Current Opinion in Electrochemistry Vol. 25, p. 100636 (2021) [2] C. Navarro-Senent et al., APL Materials, Vol. 7, p. 030701 (2019) [3] K. Duschek et al., J. Mater. Chem. C, Vol. 6, p. 8411 (2018) [4] M. Nichterwitz et al., J. Phys. D: Appl. Phys., Vol. 53, p. 084001 (2020) [5] M. Nichterwitz et al., ACS Appl. Electron. Mater., Vol. 2, p. 2543 (2020)

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/e678a85b2d151bfa98d2f7b3f748549d.jpg)
Fig. 1 (a) electric “ON” switching of magnetism via electrolytic gating of FeOOH nanoplatelets. Magnetization curves as measured by anomalous Hall effect (AHE) after reduction at −1.27 V for different reduction times. The inset shows the cross-sectional REM image of a FeOOH pristine sample. (Adapted from [4]). (b) Voltage-control of the magnitude and the sign of magnetoresistance (MR) of FeOx/Fe nanocomposite thin films by electrolytic gating in LiOH. The inset shows a cross-sectional HR-TEM image of the pristine iron oxide-iron nanocomposite film. (Adapted from [5]).

 Magneto-ionic effect in iron triad nanostructures with different shapes and composition

*Session Chair: Pan He, Fudan University*

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