Crystal Structures of Ternary Ruthenium Ferrites SrM2±xRu4±xO11 with M = Fe, Co and Magnetic and Transport Properties of Al-doped Single Crystals
Résumé
Single crystals of SrM2±xRu4±xO11 with M = Fe, Co with maximum width 2 mm and thickness around 0.05 mm were grown from a chloride flux. Sample compositions were determined from refinements of X-ray diffraction data and microprobe analysis. The hexagonal crystal structure (space group P63/mmc, Z = 2) consists of basal-plane layers of edge-sharing octahedra (M,Ru)O6, which are connected along [001] by face-sharing pairs of octahedra (M,Ru)2O9 and trigonal bipyramids MO5. A significant homogeneity range is generated by variable occupation of the octahedral sites by 3d and 4d elements. Al is also found to substitute for transition elements in the octahedral sites. The title compounds are narrow-gap semiconductors and soft ferromagnets with Curie temperatures that can substantially exceed room-temperature, depending on composition. Al doping significantly modifies the transport properties, but magnetic properties such as the Curie temperature, magnetization and anisotropy are less affected. Hall coefficient measurements reveal the predominant charge carriers are holes. The structural, electronic and magnetic properties suggest that these solid solutions are promising candidates for spin-injection devices.
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