Strong Enhancement of Room Temperature Ferrimagnetism in Insulating CoFe 2 O 4 by Site‐Specific Hydrogen Intercalation

ABSTRACT Strong enhancement of magnetization is highly desirable for increasing device efficiency, improving temperature stability, enhancing sensitivity, and enabling device miniaturization. Here, we demonstrate a 2.6−4.7 times higher room temperature ferrimagnetic moment (730−770 emu cc −1 ) compared to 170−260 emu cc −1 in as‐grown CoFe 2 O 4 films, achieved by site‐specifically intercalating hydrogen ions near the Fe 3+ in tetrahedral sites. While the spin moments of the Fe 3 + at octahedral and tetrahedral sites cancel each other out in as‐grown films, X‐ray spectroscopy of hydrogenated films reveals that both Fe 3+ and Co 2+ at octahedral sites can contribute to the enhanced total magnetic moment. This robust enhancement in insulating CoFe 2 O 4 , exhibiting high reproducibility over ≈10 cycles and long‐term stability over ≈10 d, suggests that hydrogenic‐ferrimagnetic coupling holds great promise for ultralow power electronics operating at high frequencies.