Creation of rare earth monoxides and exploration of new functionalities in 4f–5d electron systems

Abstract

Simple rare earth oxides are usually sesquioxides with stable trivalent rare earth ions, exhibiting highly insulating state. On the other hand, several rare earth monoxides with metastable divalent rare earth ions have been synthesized under high pressure only in 1980s, with the exception of chemically stable EuO and YbO. Recently, we demonstrated that rare earth monoxides can be synthesized by using thin film epitaxy. Thus, it is possible to obtain their first single crystalline or new solid phase materials, enabling to unveil their fundamental properties. In this article, we review recent progress on the synthesis and properties of rare earth monoxides.