School of Materials Science and Engineering, Beihang University, Beijing 100191, P. R. China.
Nanoscale. 2019 Sep 19;11(36):16962-16967. doi: 10.1039/c9nr06653e.
It is difficult to obtain dispersed particles of SmCo5 by calciothermic reduction because of sintering during the high-temperature reaction. This study presents a new strategy to synthesize dispersible SmCo5 particles by co-precipitating a precursor containing amorphous Sm(OH)3 and coherent nanoscale Co(OH)2 and Ca(OH)2 crystallites. The Ca(OH)2 dehydrates into CaO which forms an isolation shell around the SmCo5 particles that prevents them sintering during the reaction at 860 °C. A magnetization of 90 Am2 kg-1, a remanence ratio of 0.96 and a huge coercivity of 6.6-7.2 T were achieved at room temperature after dissolving the CaO and orienting a dispersion of the particles in epoxy in a 0.8 T external field. Based on its scan-rate dependence in high quasi-static and pulsed magnetic fields, the coercivity mechanism is identified as nucleation and growth of 88 nm3 nucleation volumes in a low-anisotropy surface region about 15 nm thick. The coercivity is the highest yet reported for nanoparticles of any permanent magnet and it opens the prospect of new high-temperature magnet composites.
由于高温反应过程中的烧结，通过钙热还原很难获得分散的 SmCo5 颗粒。本研究提出了一种通过共沉淀制备含有非晶态 Sm(OH)3 和相干纳米 Co(OH)2 和 Ca(OH)2 微晶的前体制备可分散 SmCo5 颗粒的新策略。在 860°C 的反应温度下，Ca(OH)2 脱水形成 CaO，在 SmCo5 颗粒周围形成隔离壳，防止颗粒在反应过程中烧结。在溶解 CaO 后，将颗粒在 0.8 T 外磁场中的环氧树脂分散体取向，在室温下获得了 90 Am2 kg-1 的磁化强度、0.96 的剩磁比和 6.6-7.2 T 的巨大矫顽力。基于其在高准静态和脉冲磁场中的扫描速率依赖性，矫顽力机制被确定为在约 15nm 厚的低各向异性表面区域中具有 88nm3 成核体积的成核和生长。该矫顽力是迄今为止报道的任何永磁体纳米颗粒中的最高矫顽力，为新型高温磁复合材料的开发开辟了前景。
