Controlling magnetism and spin structures in strongly correlated systems by using electric field is of fundamental importance but challenging. Here, a high-spin ruthenate phase is achieved via a solid ionic chemical junction at SrRuO3/SrTiO3 interface with distinct formation energies and diffusion barriers of oxygen vacancies, analogue to electronic band alignment in semiconductor heterojunction.Oxygen vacancies trapped within this interfacial SrRuO3 reconstruct Ru-4d electronic structure and orbital occupancy, leading to an enhanced magnetic moment. Furthermore, an interfacial magnetic phase can be switched reversibly by electric-field-rectifying oxygen migration in a solid-state ionic gating device, providing a framework for atomic design of functionalities in strongly correlated oxides using a way of solid chemistry.

In recent decades, magnetoelectric effect in multiferroic materials has attracted extensive attention owing to the upcoming demands for new-generation multi-functional magnetoelectronic devices, such as transducer, sensor and so on. This gives people a strong push to explore the multiferroic materials with a reduced dimension and effective coupling between electric and magnetic orderings, especially at room temperature. Due to the weak magnetoelectric coupling strength in sing-phase multiferroic materials, scientists start to design nanocomposites and artificial nanostructures with strong coupling among order parameters (lattice, charge, spin and orbital). In this review, we will introduce recent major progresses of magnetoelectric coupling in multiferroic nanocomposites across their interfaces from the following four aspects: strain effect, charge transfer, magnetic exchange interaction and orbital hybridization, based on their coupling mechanisms. Through a full understanding of the above coupling among these orderings, it is possible to achieve the nanoscale modulation of magnetization (ferroelectric polarization) by external electric (magnetic) field. Apart from the magnetoelectric coupling, those artificially functional nanocomposites provide us a platform to explore and study the emerging physical phenomena so that we can design self-assembled nanostructures to tailor novel functionalities in future applications.