磁驱动形状记忆合金结构转变与磁转变耦合及其与功能特性的关联性研究

Magnetic shape memory alloys (MSMAs) exhibit multifunctional properties (magnetic shape memory effect, giant magnetocaloric effect, giant magnetoresistance, etc.) based on the coupling between structural and magnetic transitions. As important scientific issues, the coupling mechanism of structural and magnetic transitions of MSMAs and the intrinsic correlation between the characteristic coupling parameters (coupling temperature, coupling temperature interval, coupling intensity, coupling entropy change, etc.) and the functional properties remain unclear and the clarification of these scientific issues is urgently needed. With NiMn-based MSMAs as the research object, the present project aims to explore the new thermodynamic and dynamic mechanisms responsible for structural and magnetic transitions and elucidate the origin and formation mechanisms for different structural and magnetic states, to reveal the coupling mechanism for structural and magnetic transitions and clarify the interaction laws for the microscopic magnetic and structural units (including the coupling laws for the multi-glassy state of strain glass and spin glass, and the interplay mechanisms for the nano-sized strain domains and magnetic clusters), and to disclose the intrinsic correlation between the characteristic coupling parameters and the functional properties and establish the effective and integrated physical model for optimizing functional properties based on tuning the characteristic coupling parameters. This study is of both great theoretical significance and practical interest for enriching and developing the theory on magnetically driven martensitic transformation and for designing novel high-performance magnetic shape memory materials.

磁驱动形状记忆合金能够产生基于结构转变与磁性转变耦合的多功能特性（磁致形状记忆效应、巨磁热效应、巨磁阻效应等）。作为重要的科学问题，磁驱动形状记忆合金结构转变与磁性转变的耦合机理以及耦合特征参数（耦合温度、耦合温区跨度、耦合强弱程度、耦合热效应等）与功能特性的内在关联性亟待澄清。本项目拟以NiMn基磁驱动形状记忆合金为研究对象，探索结构转变与磁性转变的热力学与动力学新机制，阐明不同结构和磁性状态的起源与形成机理；揭示结构转变与磁性转变的耦合机理，澄清微观磁性与结构基元的相互作用机制（包括应变玻璃与自旋玻璃的多玻璃态耦合规律、纳米应变畴和磁性团簇的交互作用机制）；揭示耦合特征参数与功能特性的内在关联性，建立基于耦合特征参数调控优化多功能特性的有效统一物理模型。本研究对丰富和发展磁驱动马氏体相变理论、研发新型高性能磁驱动形状记忆材料具有重要的理论意义和实际价值。

磁驱动形状记忆合金结构转变与磁性转变的耦合机理以及耦合特征参数与功能特性的内在关联是亟待解决的重要科学问题。本项目以Ni-(Co)-Mn-X (X=In，Sn，Sb)、Ni-(Co)-Fe-Ga和Fe-Mn-Ga磁驱动形状记忆合金为研究对象，以原位中子散射、同步辐射高能X射线衍射为特色技术手段，围绕结构转变与磁性转变耦合及其与功能特性的关联性，探索了磁驱动形状记忆合金结构转变和磁性转变的新机制，揭示了磁驱动形状记忆合金新型受限马氏体相变晶格动力学特征，发现了低场触发共存多重马氏体相互转变，澄清了具有动力学捕获的磁驱动形状记忆合金低温、高场下的异常磁化行为起源于磁场诱发的离散“雪崩式”相变。阐明了磁驱动形状记忆合金结构转变和磁性转变的耦合机理，查明了磁-结构转变耦合特征参数与功能特性的内在关联性。并在此基础上设计并研制出低场驱动巨磁热Ni-Co-Mn-Sn-Al合金（2T下磁熵变高达25J/kgK）、巨拉伸超弹性Ni-Mn-Sn-Fe磁驱动形状记忆微丝（拉伸可回复应变高达20%）和宽温域巨负热膨胀Fe-Mn-Ga磁性合金（温域81K、负热膨胀系数-0.0000502/K）。以上研究成果对深入理解磁驱动形状记忆合金磁-结构耦合相变机理和设计新型高性能磁驱动形状记忆材料具有重要的理论意义和实际价值。已发表高水平SCI论文15篇，其中包括金属材料领域权威期刊Acta Materialia 5篇，Applied Physics Letters 6篇，申请国家发明专利2项，做国际会议特邀报告2次，培养优秀青年科学基金获得者1人，博士研究生4人，硕士研究生4人。