Variations in the multiferroic properties of BiFeO₃ (BFO) powders were investigated with respect to the crystallite size and Gd-doping. Nanoscale BFO powders with an average particle size range of ~ 30–80 nm were synthesized by a solid-state reaction using microwave-assisted heat treatment with Bi(NO₃)₃·5H₂0, FeC₂O₄·2H₂O and Gd(NO₃)₃·6H₂O as source precursors supplying Bi, Fe, and Gd, respectively. These were heat-treated at temperatures ranging from 200 to 700 °C. The reaction led to the formation of crystallite powders with a particle size of a few tens of nanometers. It was confirmed that these samples had multiferroic properties at room temperature, and the value of M_s varied significantly from ferromagnetic to antiferromagnetic and vice versa with the size of the powders. In particular, ferromagnetic and ferroelectric features were observed when the size of the BFO powder was < ~ 30 nm (half of the spin-canted cycle). As the crystallite size was reduced to that corresponding to half of the spin canted cycle, the value of Ms increased by 8.8 times from 1.41 to 12.46 memu/g. Compared to pure BFO, when Gd was doped, Ms values increased by ~ 60% and 240% in ~ 30 nm and ~ 60 nm particle-sized powders.

Graphical Abstract

中文翻译：

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微波辅助固相反应合成纳米级 BiFeO3 粉末多铁性特征的精细控制

 研究了关于微晶尺寸和 Gd 掺杂的BiFeO ₃ (BFO) 粉末的多铁性特性的变化。平均粒度范围为 ~ 30–80 nm 的纳米级 BFO 粉末是通过固态反应合成的，使用微波辅助热处理，使用 Bi(NO 3 ₎ 3 _· 5H ₂ 0、FeC ₂ O ₄ ·2H ₂ O 和Gd(NO ₃ ) ₃ ·6H ₂O 作为源前体，分别提供 Bi、Fe 和 Gd。这些材料在 200 至 700 °C 的温度范围内进行热处理。该反应导致形成粒径为几十纳米的微晶粉末。证实这些样品在室温下具有多铁性，M _s的值从铁磁到反铁磁，反之亦然随粉末的大小而显着变化。特别是，当 BFO 粉末的尺寸 < ~ 30 nm（自旋倾斜周期的一半）时，观察到铁磁和铁电特征。随着微晶尺寸减小到对应于旋转倾斜周期的一半，Ms 值从 1.41 增加到 12.46 memu/g，增加了 8.8 倍。与纯 BFO 相比，掺杂 Gd 后，~ 30 nm 和 ~ 60 nm 粒径粉末的 Ms 值增加了 ~ 60% 和 240%。

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