Exotic exchange bias at epitaxial ferroelectric-ferromagnetic interfaces

Multiferroics in spintronics have opened up opportunities for future technological developments, particularly in the field of ferroelectric (FE)-ferromagnetic (FM) oxide interfaces with functionalities. We find strong exchange bias shifts (up to 84 Oe) upon field cooling in metal-oxide (Fe/BaTiO₃) films combining FM and FE layers. The saturation magnetic moment of the FM layer is also significantly higher than in bulk (3.0 ± 0.2 μ_B/atom) and the reversal mechanism occurs via a domain nucleation process. X-ray absorption spectroscopy at the Fe K-edge and Ba L3-edge indicate presence of few monolayers of antiferromagnetic FeO at the interface without the formation of any BaFeO₃ layer. Polarized neutron reflectometry corroborates with our magnetization data as we perform depth profiling of the magnetic and structural densities in these bilayers. Our first principles density functional calculations support the formation of antiferromagnetic FeO layers at the interface along with an enhancement of Fe magnetic moments in the inner ferromagnetic layers.