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.

Double perovskite Sr2FeReO6 (SFRO) powders were synthesized by so‐gel process and annealed in argon atmosphere. Their structural, dielectric, magnetic, electrical, and optical properties were comprehensively investigated. It was found that the SFRO powders possessed a tetragonal crystal structure with I4/m space group and exhibited spherical shapes with some agglomeration due to the magnetic interactions between particles of the powders. Quantitative energy dispersive X‐ray spectrometer data revealed the atomic ratio of Sr, Fe, Re, and O elements close to the nominal values of 2:1:1:6. X‐ray photoemission spectroscopy spectra reveal two species of Re5+ and Re6‐7+ coexist in the SFRO powders. Sr, Fe, and O elements are present as Sr2+, Fe3+, and lattice oxygen, respectively. Dielectric property measurements revealed a Maxwell–Wagner type dielectric dispersion in the SFRO ceramics. Ferromagnetic behavior was verified by the observed magnetic hysteresis loops in the SFRO powders at 2 K and 300 K. The remanent magnetization and coercive field at 2 K were 8.23 emu/g and 3152 Oe, respectively, and the saturated magnetization was estimated to be 21.8 emu/g (or 2.0 μB/f.u.), smaller than the theoretical value of 3.0 μB/f.u. owing to the presence of the anti‐site defects. Magnetic Curie temperature (TC) was estimated to be 432.3 K. Intergranular tunneling magnetoresistance and hysteresis phenomena were observed in the SFRO powders at low temperatures, and the MR (2 K, 6 T) was measured to be −15% and −10% for MR (100 K, 6 T). Electrical transport and optical absorption measurements demonstrate the semiconducting nature of the SFRO with optical band gap of 1.39 eV. The electrical transport process follows the small polaron variable range hopping theory. The unique combination of high TC ferromagnetism with the semiconductivity enables the SFRO to be a promising candidate for spintronic devices.

The continuous miniaturization of the charge-based electronic devices and overcoming the bottleneck of Moore's law, have driven the rapid growth of spintronics, which operates the freedom of electronic spin rather...