Feng, H.L.; Adler, P.; Reehuis, M.; Schnelle, W.; Pattison, P.; Hoser, A.; Felser, C.; Jansen, M.: High-Temperature Ferrimagnetism with Large Coercivity and Exchange Bias in the Partially Ordered 3d/5d Hexagonal Perovskite Ba2Fe1.12O0s0.88O6. Chemistry of Materials 29 (2017), p. 886-895

Double perovskite oxides A2BB′O6 combining 3d- and 4d- or 5d- transition-metal ions at the B and B′ sites feature a variety of magnetic and magneto-electric properties. Targeting Ba2 FeOsO6, we synthesized powder samples of nonstoichiometric Ba2Fe1.12Os0.88O6 by solid-state reaction from the oxides. The crystal structure was investigated by using synchrotron powder X-ray and powder neutron diffraction. In contrast to Ca2FeOsO6 and Sr2FeOsO6, the compound adopts the hexagonal 6L perovskite structure (space group P3m1) with partial Fe−Os order at both the face-sharing B2O9-dimer and the corner sharing BO6-transition-metal sites. Magnetization, neutron diffraction, and 57Fe-Mössbauer spectroscopy results show that Ba2Fe1.12Os0.88O6 develops ferrimagnetic order well above room temperature at TC ≈ 370 K. The nonsaturated magnetization curve at 2 K features a magnetic moment of 0.4 μB per formula unit at 7 T and a pronounced hysteresis with a coercive field of about 2 T. Large exchange bias effects are observed when the magnetization curves are measured after field cooling. The peculiar magnetic properties of Ba2Fe1.12Os0.88O6 are attributed to an inhomogeneous magnetic state formed as a consequence of the atomic disorder. Our results indicate that hexagonal double-perovskite-related oxides are a promising class of compounds for finding new materials with potential applications as hard magnets or in the area of spintronics.