npj: 磁性材料——化学无序和热磁波动的调控

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磁性随机固溶体代表了一大类从因瓦合金到多组分磁性高熵合金等重要晶体材料。他们同时存在化学无序和热磁波动，并与晶格振动耦合，在很大程度上调控了材料的热力学性质和相位稳定性，是新材料计算设计的关键参数。因此模拟磁性随机固溶体中的晶格振动时，有必要同时考虑磁波动和化学无序两个因素的影响，但目前还没有这样的晶格振动计算模拟。来自日本、德国和荷兰的Yuji Ikeda及其同事，基于第一原理，将有序磁系统方法与已有无序材料近似方法结合起来，同时考虑了由磁激发和由化学无序两种因素引起的力常数波动；开发了一种数值方法预测零上温区无序磁性固溶体的原子振动。准确地预测了温度升高时Fe-Pd和Fe-Pt 因瓦两种合金中横向声学模式的异常声子硬化。他们发现这种在传统谐波图像中无法解释的奇特行为，竟然是热磁波动的结果。这一方法既可直接为已有材料的物理行为提供新解释，也可为新材料的计算设计提供新方法。该文近期发表于npj Computational Materials 4:7 (2018)； doi: 10.1038/s41524-018-0063-1。英文标题与摘要如下，点击阅读原文可以自由获取论文PDF。

Temperature-dependent phonon spectra of magnetic random solid solutions

Yuji Ikeda, Fritz Körmann, Biswanath Dutta, Abel Carreras, Atsuto Seko, Jörg Neugebauer & Isao Tanaka

Abstract A first-principles-based computational tool for simulating phonons of magnetic random solid solutions including thermal magnetic fluctuations is developed. The method takes fluctuations of force constants due to magnetic excitations as well as due to chemical disorder into account. The developed approach correctly predicts the experimentally observed unusual phonon hardening of a transverse acoustic mode in Fe–Pd an Fe–Pt Invar alloys with increasing temperature. This peculiar behavior, which cannot be explained within a conventional harmonic picture, turns out to be a consequence of thermal magnetic fluctuations. The proposed methodology can be straightforwardly applied to a wide range of materials to reveal new insights into physical behaviors and to design materials through computation, which were not accessible so far.

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