Abstract

We report the synthesis of SrMn 1− x Ga x O 3− δ perovskite compounds and describe the dependence of their phase stability and structural and physical properties over extended cation and oxygen composition ranges. Using special synthesis techniques, we have extended the solubility limit of Ga 3+ in the cubic perovskite phase to x≈0.33. Higher Ga concentrations lead to mixed phases until a single-phase ordered double-perovskite structure is obtained at x=0.5, i.e., Sr 2MnGaO 6− δ . In the cubic perovskite phase the maximum oxygen content is 3− x/2, which corresponds to 100% Mn 4+. All maximally oxygenated solid solution compounds are found to order antiferromagnetically, with the transition temperature linearly decreasing as Ga content increases. Reducing the oxygen content introduces frustration into the magnetic system and a spin-glass state is observed for SrMn 0.7Ga 0.3O 2.5 below 30 K. The brownmillerite phase at low oxygen content, Sr 2MnGaO 5, is found to have Icmm crystallographic symmetry. At 12 K its magnetic structure is found to order in the Icm′m′ magnetic symmetry corresponding to a G-type antiferromagnetic structure of Mn 3+ ions. At higher oxygen content, Sr 2MnGaO 5.5 is found to have Cmmm crystallographic symmetry with disordered oxygen vacancies. At 12 K two competing long-range magnetic structures are found for the Mn 4+ sublattice having C I m′m′m symmetry (G-type), and C P m′m′m symmetry (C-type), together with a G-type short-range magnetic correlations.

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