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

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• 作者：A. Shimoda ; K. Takao ; K. Uji ; T. Waki ; Y. Tabata ; H. Nakamura ; ^{nakamura.hiroyuki.2w@kyoto-u.ac.jp" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Magnetoplumbite-type strontium ferrite ; Single crystal ; Magnetic anisotropy ; La&ndash ; Co co-substitution
• 刊名：Journal of Solid State Chemistry
• 出版年：2016
• 出版时间：July 2016
• 年：2016
• 卷：239
• 期：Complete
• 页码：153-158
• 全文大小：542 K

文摘

The Na₂O flux method was successfully applied in the single crystal synthesis of the magnetoplumbite-type strontium ferrite with La–Co co-substitution (Sr_1−xLa_xFe_12−yCo_yO₁₉)$\left({\mathrm{Sr}}_{1-x}{\mathrm{La}}_x{\mathrm{Fe}}_{12-\mathrm{<font\; color="red">y</font>}}{\mathrm{Co}}_{\mathrm{<font\; color="red">y</font>}}{\mathrm{O}}_{19}\right)$, 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)$(x>\mathrm{<font\; color="red">y</font>})$ in the obtained crystals, indicating that the extra charge introduced by the Co²⁺${\mathrm{Co}}^{2+}$ substitution for Fe³⁺${\mathrm{Fe}}^{3+}$ is not compensated by La³⁺${\mathrm{La}}^{3+}$ for Sr²⁺${\mathrm{Sr}}^{2+}$. In the present growth condition, the necessary amount of La is nearly twice that of Co (y/x≃0.55)$(\mathrm{<font\; color="red">y</font>}/x\simeq 0.55)$, suggesting valence instability of an appreciable amount of Fe³⁺${\mathrm{Fe}}^{3+}$ to Fe²⁺${\mathrm{Fe}}^{2+}$. 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.