Recent advances in Re-based double perovskites: Synthesis, structural characterization, physical properties, advanced applications, and theoretical studies

Recently, double perovskite (DP) oxides denoted A2B′B″O6 (A being divalent or trivalent metals, B′ and B″ being heterovalent transition metals) have been attracting much attention owing to their wide range of electrical and magnetic properties. Among them, rhenium (Re)-based DP oxides such as A2FeReO6 (A = Ba, Sr, Ca) are a particularly intriguing class due to their high magnetic Curie temperatures, metallic-like, half-metallic, or insulating behaviors, and large carrier spin polarizations. In addition, the Re-based DP compounds with heterovalent transition metals B′ and B″ occupying B sites have a potential to exhibit rich electronic structures and complex magnetic structures owing to the strong interplays between strongly localized 3d electrons and more delocalized 5d electrons with strong spin–orbit coupling. Thus, the involved physics in the Re-based DP compounds is much richer than expected. Therefore, there are many issues related to the couplings among the charge, spin, and orbitals, which need to be addressed in the Re-based DP compounds. In the past decade, much effort has been made to synthesize Re-based DP compounds and to investigate their crystal structures, structural chemistry, and metal–insulator transitions via orbital ordering, cationic ordering, and electrical, magnetic, and magneto-transport properties, leading to rich literature in the experimental and theoretical investigations. This Review focuses on recent advances in Re-based DP oxides, which include their synthesis methods, physical and structural characterizations, and advanced applications of Re-based DP oxides. Theoretical investigations of the electronic and structural aspects of Re-based DP oxides are also summarized. Finally, future perspectives of Re-based DP oxides are also addressed.