Atomic‐Scale Engineering of Coupled Ferroic States in BiFeO ₃ via Spin–Orbit Selective Implantation for Nonvolatile Memory

Abstract The relentless scaling of neuromorphic architectures and edge AI processors necessitates environmentally stable multiferroics capable of overcoming the intrinsic speed‐endurance‐scalability trade‐offs that constrain conventional nonvolatile memories. Although bismuth ferrite (BiFeO₃) exhibits promising room‐temperature multiferroic properties, its technological deployment remains impeded by excessive oxygen vacancy concentrations that induce irreversible polarization fatigue and leakage currents exceeding practical thresholds. Here, it is achieved atomic‐scale reconstruction of strain‐polarization coupling in bulk‐like BiFeO₃ thin films through spin‐orbit selective implantation of Zr⁴⁺/Ti⁴⁺ ions, thereby decoupling ferroelectric dynamics from defect‐mediated degradation mechanisms. A quantized collision model, validated by aberration‐corrected scanning transmission electron microscopy, reveals that ion implantation induces anisotropic lattice shear, which triggers collective Fe 3 ⁺ off‐centering displacement and polarization rotation via dynamic octahedral coupling. The engineered BiFeO₃ thin film demonstrates enhanced electrical characteristics, achieving a 92% enhancement in remanent polarization along with a three‐order‐of‐magnitude reduction in leakage current density compared to pristine BiFeO₃. Through the synergistic integration of a scalable sol‐gel deposition method utilizing environmentally benign precursors with ion‐implantation engineering, this work establishes a universal strain‐engineering paradigm for lead‐free multiferroics, effectively bridging atomic‐scale order manipulation with neuromorphic circuit functionality.