Co和Cu共掺杂NiMnIn合金的磁-结构转变特性及机理研究

NiMnIn alloys have attracted great attention as a novel class of smart materials recently. However, the magnetic field to drive magnetostructural transition in these alloys is relative high and the hysteresis loss is relative large, which has become a bottleneck to limit the development of these materials. Based on the significant influences of the substitutions of Ni by Co and Mn by Cu on the magnetic interaction and hysteresis in NiMnIn alloys, in this project, we propose the Co and Cu co-doping to tailor the features of magnetostructural transition of NiMnIn alloys. First, the influences of the Co and Cu co-doping amount on the magnetization difference and the hysteresis during magnetostructural transition will be clarified. Then, based on superspace theory and first-principles calculations, the crystal structures of austenite and modulated martensite, the geometrical compatibility between these two phases and the atomic sites of doped atoms will be determined. Moreover, the mechanisms of Co and Cu co-doping on the spatial charge distribution, the atomic bond, the magnetic interaction and the features of magnetostructural transition will be revealed. Based on the above investigations, we will further optimize the amount of doped Co and Cu elements to develop NiCoMnCuIn prototype alloys with the excellent features of magnetostructural transition. This project may offer guidance for the design and property optimization of NiMnIn alloys.

NiMnIn合金是近年来备受关注的一类新型磁控智能材料。然而，驱动该合金磁-结构转变所需磁场以及磁-结构转变滞后相对较大，成为制约其发展和应用的瓶颈问题。基于Co取代Ni和Cu取代Mn对NiMnIn合金磁性能及滞后的显著影响，本项目提出Co、Cu共掺杂综合调节NiMnIn合金磁-结构转变特征的设计思想。拟借助现代材料结构与性能测试分析技术，结合基于超空间理论的复杂晶体结构解析方法和第一性原理计算，揭示Co、Cu共掺杂对该合金磁-结构转变磁化强度变化及滞后的影响规律，解析不同掺杂量下奥氏体相与调制马氏体相的晶体结构、几何兼容性以及掺杂元素的最优原子占位方式，阐明元素掺杂对NiMnIn合金空间电荷分布、化学键、磁交互作用和磁-结构转变的影响机制，开发出磁-结构转变性能优异的NiCoMnCuIn原型合金，为NiMnIn基合金磁控性能优化设计奠定基础。

NiMnIn合金是近年来备受关注的一类新型磁控智能材料。然而，驱动该合金磁-结构转变所需磁场以及磁-结构转变滞后相对较大，成为制约其发展和应用的瓶颈问题。针对该问题，本项目提出了Co & Cu共掺杂研究思路，旨在获得低磁场下优异磁控性能。经过实施，本项目完成了预期研究目标，成功地制备出了磁-结构转变驱动场及滞后较小的Ni45Mn36In13.3Co5Cu0.7（简称Cu0.7）和Ni45Mn36In13.2Co5Cu0.8（简称Cu0.8）原型合金。主要研究结果包括：1）随着Cu含量的增加，Co & Cu共掺杂NiMnInCoCu合金相变熵变逐渐升高、热滞后逐渐降低，其中热滞后降低的原因可归因于奥氏体和马氏体较好的几何兼容性；2）Cu0.7和Cu0.8合金磁-结构转变伴随磁性变化ΔM与已报道的Ni–Mn基合金相比具有最高的数值，其中Cu0.8合金在1.5 T低磁场下ΔM值甚至与部分Co掺杂Ni–Mn基合金在5 T磁场下的ΔM值相当；3）通过第一性原理计算发现，Co取代Ni后合金磁矩可从2.06 μB/f.u.增加到2.24 μB/f.u.；4）Cu0.7合金在5 T磁场下第一次磁场循环和第二次循环时最大等温磁熵变接近，这表明其磁热效应的可逆性较好。此外，Cu0.7合金的制冷能力和有效制冷能力分别为473.7和270.2 J kg−1，该数值在Ni–Mn基合金中均是最高值；5）Cu0.8合金在1.5和2 T磁场下等温磁熵变可达16.0和17.9 J kg−1 K−1，该数值高于大多数Ni–Mn基合金低磁场下的等温磁熵变。本项目的实施阐明了Co & Cu共掺杂对NiMnIn合金磁-结构转变的影响规律及机理，获得磁-结构转变性能优异的NiMnInCoCu原型合金，为NiMnIn基合金磁控性能优化设计奠定基础，也为其它磁控智能材料的元素掺杂改性研究提供借鉴。

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