Twins - A weak link in the magnetic hardening of ThMn12-type permanent magnets
Twins - A weak link in the magnetic hardening of ThMn12-type permanent magnets
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DOI：
10.1016/j.actamat.2021.116968
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发表时间：
2021-06-02
期刊：
影响因子：
9.4
通讯作者：
Gutfleisch, Oliver
中科院分区：
文献类型：
--
作者：
Ener, Semih;Skokov, Konstantin P.;Gutfleisch, Oliver
Nd 2Fe 14 B型材料在室温附近表现出最高的能量积，因此主导了高性能永磁体市场。密集的研究工作旨在替代材料系统，其中包含具有类似或更好磁性的不太重要的元素。具有ThMn 12型结构的Nd和Sm基化合物表现出与Nd 2Fe 14 B相当甚至上级的本征性质。然而，在基于ThMn 12的块体烧结磁体中不可能实现技术上相关的磁化率和剩磁。使用SmFe 11 Ti作为原型代表，我们证明了性能差的一个重要原因是在微晶晶粒内形成孪晶。SmFe 11 Ti中的孪晶的性质进行了研究，在孪晶的“单晶”和散装和薄膜多晶样品，使用先进的电子显微镜和原子探针断层扫描以及模拟和基准Nd 2Fe 14 B相比。微孪晶和纳米孪晶都显示出57 +/- 2度的孪晶取向和Sm的富集，这可能影响该材料中的畴壁运动。微磁学模拟表明，孪晶作为成核中心，代表微观结构中磁性最弱的环节。利用分子动力学模拟方法，简要讨论了孪晶形成能与几何特征之间的关系。(C)2021 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Nd2Fe14B-type materials exhibit the highest energy product around room temperature and hence dominate the high-performance permanent magnet market. Intensive research efforts aim at alternative material systems containing less critical elements with similar or better magnetic properties. Nd- and Sm-based compounds with a ThMn12-type structure exhibit intrinsic properties comparable or even superior to Nd2Fe14B. However, it has not been possible to achieve technically relevant coercivity and remanent magnetization in ThMn12-based bulk sintered magnets. Using SmFe11 Ti as a prototypical representative, we demonstrate that one important reason for the poor performance is the formation of twins inside micro-crystalline grains. The nature of the twins in SmFe11 Ti was investigated in twinned "single crystals" and both bulk and thin film poly-crystalline samples, using advanced electron microscopy and atom probe tomography as well as simulations and compared with benchmark Nd2Fe14B. Both micro-twins and nano-twins show a twin orientation of 57 +/- 2 degrees and an enrichment in Sm, which could affect domain wall motion in this material. Micromagnetic simulations indicate that twins act as nucleation centers, representing the magnetically weakest link in the microstructure. The relation between twin formation energies and geometrical features are briefly discussed using molecular dynamic simulations. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.