Strain-driven exchange interaction and interface magnetism in LaNiO3/La0.67Sr0.33MnO3 heterostructures

The influence of strain and stacking sequence on interfacial ferromagnetism and exchange coupling in correlated oxide ${\mathrm{LaNiO}}_3\text{/}{\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_3$ (LNO/LSMO) heterostructures is investigated. LNO/LSMO heterostructures are grown on two different substrates [MgO and ${\mathrm{SrTiO}}_3$ (STO)] yielding different strains for the oxide layers that lead to different interfacial properties. Polarized neutron reflectivity (PNR) results indicate the emergence of a ferromagnetic interfacial LNO layer and exchange bias for LNO/LSMO heterostructures grown on MgO substrate. In contrast, no such phenomenon was observed for LNO/LSMO heterostructures grown on an STO substrate. Combining magnetometry, PNR, x-ray scattering, and soft x-ray absorption spectroscopy measurements, we found an enhanced magnetic moment and exchange coupling at interfaces that arises from charge transfer and orbital reconstruction via strain engineering in these complex oxide heterostructures. First-principles calculations suggest a possible orbital reconstruction as a result of different strains at interfaces which results from different interfacial magnetic phase behaviors. The study helps understand the manipulation of the exotic states with the aid of strain in oxide-based electronics.