Double perovskite Sr 2 FeReO 6 oxides: Structural, dielectric, magnetic, electrical, and optical properties

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.