Abstract
The system Sr 3Fe 2O 6.00–6.90 forms a single phase of unusual structure, derived from that of perovskite by interleaving nonmagnetic layers of strontium-oxygen ions between pairs of perovskite layers composed of strontium-iron-oxygen ions. It exhibits a broad range of oxygen stoichiometry. As a consequence of this structure and the variable valence of the iron, a variety of magnetic interactions are possible. Between 1.4 and 300°K specimens of higher oxygen concentration are antiferromagnetic. The Neél temperature (130°K for Sr 3Fe 2O 6.90) approaches O°K at the composition Sr 3Fe 2O 6.50. Specimens in this range have positive paramagnetic Curie temperatures, indicative of a ferromagnetic type interaction. Specimens with oxygen content lower than Sr 3Fe 2O 6.50 exhibit strongly negative Fe 3+O =Fe 3+ exchange. At the lower oxygen limit, Sr 3Fe 2O 6.00, strongly antiferromagnetic ordering appears stable to above room temperature.
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