Fig. 1: Device and set-up schematics for voltage-induced ferromagnetism in FeCoN nanodots.

a Schematic representation of FeCoN nanodots preparation by electron-beam lithography and sputtering. b Schematics of the electrochemical cell, custom-made in our lab, used for the in-situ measurements of voltage-induced magnetism within FeCoN nanodots by MOKE (see Section “Methods”). A zoomed-in panel depicts electric-double layer formation at the FeCoN/propylene carbonate (PC) electrolyte interface and N^3– migration out of and into the FeCoN layer when negative or positive gate voltage (V_G) is applied between working and counter electrode, respectively. c 3D topography of FeCoN nanodots measured by AFM in tapping mode. d EDX analysis of as-grown FeCoN nanodots. The inset shows an SEM image of the nanodots array. Evolution of hysteresis loops measured by MOKE during negative (e) and positive (f) voltage actuation of FeCoN nanodots. Starting from the paramagnetic state (purple curve in e), Kerr amplitude progressively increases over time. Simultaneously, the measured hysteresis loops undergo a transition in shape, evolving from square-like to constricted (see Supplementary Fig. 2). The opposite happens when positive voltage is applied, whereby the initial paramagnetic state can be reversibly restored.