Atomic-Scale Visualization of Epitaxial Antiferromagnetic Coupling by Multislice Electron Ptychography

Controlling the anisotropic magnetism in epitaxial antiferromagnets is crucial for developing energy-efficient spintronic thin-film devices [1-3]. However, the mechanism connecting macroscopic magnetic order to underlying atomic-scale structure has remained poorly understood. Here, we elucidate the dual nature of epitaxial coupling in antiferromagnetic LaFeO₃/BiFeO₃/LaFeO₃ heterostructures by employing multislice electron ptychography (MEP). First, we demonstrate that epitaxy aligns the Néel vector of the top and bottom LaFeO₃ layers, thereby establishing a long-range, coherent antiferromagnetic order. Second, we reveal a localized magnetic coupling mechanism at the heterostructure interface. Precise mapping of atomic-scale oxygen octahedral tilt identifies a two-unit-cell-thick reconstruction layer wherein the tilt pattern abruptly reorients in response to the interfacial octahedral modulation. The sharp tilt gradient modifies the local Fe-O-Fe superexchange pathways, consequently altering the magnetic properties of the interfacial layers. These findings reveal a concerted antiferromagnetic coupling mechanism where both long-range crystallographic constraints and short-range octahedral reconstructions control magnetism, providing multiscale structural insights for the design of epitaxial thin film heterostructures for spintronics.