Defect-engineered ferroelectricity and magnetoelectric coupling in LaFeO₃ thin films

The pursuit of single-phase multiferroics that operate at room temperature remains a significant challenge due to the mutual exclusiveness of ferroelectricity and magnetism in most materials. LaFeO₃ (LFO), a classic antiferromagnet, is non-ferroelectric in its bulk form. Herein, we demonstrate the creation of room-temperature ferroelectricity in epitaxial LFO thin films via a defect-engineering strategy. By modulating the oxygen partial pressure during growth, we deliberately introduce cationic off-stoichiometry, leading to the formation of La_Fe and Fe_La antisite defects. A combination of scanning transmission electron microscopy, positive-up-negative-down measurements, and density functional theory calculations confirms that these antisite defects are the microscopic origin of a polar R3c phase, which gives rise to intrinsic switchable ferroelectricity. Furthermore, piezoresponse force microscopy under applied magnetic fields reveals a noticeable magnetoelectric coupling. This work not only unveils a novel mechanism for activating multiferroicity in LFO but also establishes cationic antisite engineering as a general paradigm for designing multifunctional properties in the rare earth orthoferrite family.