Multiferroic co-enhancement mechanism in double perovskite thin films through inequivalent chemical modulation

Single-phase multiferroics, which are driven by magnetic structures, are considered as an ideal material platform for realizing next-generation multi-field coupled spintronic devices. However, their Curie temperatures remain far below room temperature and/or the ferroelectric polarization is nearly vanishing. Here, an inequivalent charge strategy is reported that simultaneously enhances the ferroelectric and ferromagnetic ordering in Bi2FeMnO6 double perovskite thin films, effectively exploiting the tunability of chemical strain and valence. Abnormal lattice distortion and differential charge compensation ensure robust ferroelectricity (16.6–29.2 μC/cm2) and approximately sevenfold enhancement from 8.3 to 60 emu/cm3 in ferromagnetism, with Curie temperatures of both ferroic orderings exceeding 800 K, which is the best high-temperature metrics for existing multiferroic systems. Since ferroelectricity originates from Bi ions and octahedral distortions, this effectively avoids small polarization and weak A–B site coupling. This mechanism is expected to reignite interest in type I multiferroics and prompt a reexamination of current schemes for overcoming the incompatibility of the multiple ferroic orderings. Our work provides an important technological path and experimental insight for the development of room-temperature multiferroics by leveraging the tunability of double perovskites.