Voltage control of magnetism via magneto‐ionics, where ion transport and/or redox processes drive magnetic modulation, holds great promise for next‐generation memories and computing. This stems from its non‐volatility and ability to precisely tune both the magnitude and speed of magnetic properties in a potential energy‐efficient manner. However, expanding magneto‐ionics to incorporate novel mobile ions or even multiple ion species is crucial for unlocking new phenomena and enabling multifunctional capabilities. Here, we demonstrate voltage‐driven multi‐ion transport in an FeBO system with increasing oxygen content, progressively transitioning from an electrostatic‐like response to a more pronounced electrochemical (magneto‐ionic) behavior. The voltage‐driven transport of both B and Fe is activated by oxidation state tuning, owing to the larger electronegativity of oxygen. Such charge‐transfer effects allow multi‐ion magneto‐ionics, where O ions move oppositely to Fe and B ions. These results pave the way for programmable functionalities by leveraging elements with different electron affinities through charge‐transfer engineering.
