Atomistic geometry and bonding characteristics at the Sr ₂FeTaO₆/SrTiO₃ interface

Oxide heterointerfaces with broken translational symmetry offer a fertile ground for exploring fascinating physical properties that are absent in bulk constituents. Here, we apply advanced transmission electron microscopy to the Sr₂FeTaO₆/SrTiO₃ interface and elucidate that the deposited Sr₂FeTaO₆ thin film bonds directly to the SrTiO₃ substrate in an epitaxial, coherent, and atomically abrupt way. Combined with density-functional-theory calculations, we determine the explicit interface atomistic structure, the exact valence state of transition metals, the covalent interfacial bonding nature, and identify the antiferromagnetic superexchange magnetic coupling path between Fe ions as Fe-O-Ta-O-Fe.