Flux growth of magnetoplumbite-type strontium ferrite single crystals with La-Co co-substitution

The Na2O flux method was successfully applied in the single crystal synthesis of the magnetoplumbite-type strontium ferrite with La-Co co-substitution (Sr1-xLaxFe12-yCoyO19), which is a familiar base material for commercial permanent magnets. The initial amount of Na2O flux was fixed in the molar ratio of Na/(Sr+La) = 5.17. Composition analysis revealed discordance between La and Co concentrations (x > y) in the obtained crystals, indicating that the extra charge introduced by the Co2+ substitution for Fe3+ is not compensated by La3+ for Sr2+. In the present growth condition, the necessary amount of La is nearly twice that of Co (y/x similar or equal to 0.55), suggesting valence instability of an appreciable amount of Fe3+ to Fe2+. Single crystalline magnetization measurements showed that the substitution markedly enhances the magnetic anisotropy and slightly raises the saturation magnetization. Remaining problems, which should be resolved before the experimental determination of the Co site occupation, are also discussed. (C) 2016 Elsevier Inc. All rights reserved.