thin films*

Exchange bias that occurs from a magnetic/non-magnetic interface, called intrinsic exchange bias, is an intriguing topic for the nominal simplicity and potential applications. We have studied the epitaxial NiCo₂O₄ (111) films grown on Al₂O₃ (0001) substrates and discovered intrinsic exchange bias up to ≈ 1 kOe; the magnetization can even be pinned along only one direction. Thickness-resolved reflection high energy electron diffraction (RHEED) indicates an interfacial reconstruction that mimics CoO, which can serve as the antiferromagnetic layer for the exchange bias. The thickness of the interfacial layer is sensitive to the O₂ background pressure of the thin film growth, which in turn changes the exchange bias. These results suggest highly tunable interfacial structures and magnetic properties in NiCo₂O₄ films.