Electric field controllable high-spin SrRu O3 driven by a solid ionic junction

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