Above 400 K robust ferromagnetic insulating phase in hydrogenated brownmillerite iron oxide films with distinct coordinate

Ferromagnetic insulators (FMIs) with excellent optical transparency are highly appealing materials for advanced magneto-optical and spintronic devices. However, their applications have been substantially hindered for decades due to the limited availability of FMIs with low Curie temperature Tc and frustrated optical transparency. Herein, we reported that hydrogenated BaFeO2.5 films via facile and effective hydrogen plasma treatment exhibit consecutive structural transformations, accompanying with robust ferromagnetic insulating states with Tc > 400 K and desirable optical transparency with spectral range from visible to infrared. We elucidate the effect of reconfigurations of Fe-O coordinate geometry with distinct crystal structures on the emergent electronic properties of hydrogenated BaFeO2.5 films by combining experimental measurements and theoretical calculations. These findings underscore the importance of engineering polyhedral coordinate of perovskite-derived oxides in surmounting the inherent trade-off between ferromagnetism and electric insulation and open up opportunities for manipulating multifunctional electronic materials.