Enhanced Magnetization in CoFe ₂ O ₄ Through Hydrogen Doping

Abstract Magnetic spinel oxides have attracted extensive research interest due to their rich physics and wide range of applications. However, these materials invariably suffer suppressed magnetization, due to structural imperfections (e.g., disorder, anti‐site defects, etc.). Herein, a dramatic enhanced magnetization is obtained with an increasement of 5 µ B /u.c in CoFe 2 O 4 (CFO) through ionic liquid gating induced hydrogen doping. The intercalated hydrogen ions lead to both distinct lattice expansion of ≈0.7% and notable Fe valence state reduction through electron doping, in which ≈17% Fe 3+ is reduced into Fe 2+ . These facts collectively trigger a site‐specific spin‐flip on tetrahedrally coordinated Co 2+ sites that enhances the net ferrimagnetic moment nearly to its theoretical maximum for perfect CFO.