Origin of anomalous magnetite properties in crystallographic matched heterostructures: Fe₃O₄(111)/MgAl₂O ₄(111)

Magnetite films grown on crystallographically matched substrates such as MgAl₂O₄ are not expected to show anomalous properties such as negative magnetoresistance and high saturation fields. By atomic resolution imaging using scanning transmission electron microscopy we show direct evidence of anti-phase domain boundaries (APB) present in these heterostructures. Experimentally identified shifts determine the atomic structure of the observed APBs. The dominant non-bulk superexchange interactions are between 180° octahedral-Fe/O/octahedral-Fe sites which provide strong antiferromagnetic coupling across the defect interface resulting in non-bulk magnetic and magnetotransport properties.