Review of progress in the materials development of Re, Os, and Ir-based double perovskite oxides

In this review, we examine the latest experimental advances in materials science, focusing primarily on 5d transition metal-based double perovskite oxides, particularly rhenium (Re), osmium (Os), and iridium (Ir). These materials have attracted considerable attention because of their unique properties compared to conventional perovskite oxides, including high-TC ferrimagnetism, half-metallicity, insulating ferromagnetism, polar ferro-electricity, and multipolar magnetism. We have shown through many experiments that the high-temperature and high-pressure synthesis method is effective for introducing 5d transition metals such as Re, Os, and Ir into the B site of perovskite oxides. Here, we mainly discuss the high-pressure synthesis of novel double perovskite oxides and their properties. This process leads to characteristic relativistic effects and properties not observed in con-ventional perovskites. The adaptable nature of the double perovskite structure allows for significant modification of both A-and B-site elements, resulting in a wide range of physical properties. In this review, we will organize our understanding of Re-, Os-, and Ir-based double perovskites, highlight the influence of crystal structure on various properties, and explore potential applications across multiple technical and scientific domains. The goal is to provide a comprehensive overview that will enhance understanding and facilitate advances in the field of double perovskite materials research.