Ni-Mn基哈斯勒合金变磁相变宽度的调控及其机理研究

Ni-Mn based Heusler alloys that show magnetic shape memory effect have potential applications as magnetic actuators and refrigerants, and has drawn researchers' wide attention. The characteristics such as meta-magnetic transformation interval has great influence on their properties. It has been found that a slight change in micro-structure could have great impact on the meta-magnetic transformation interval. However, the underlying mechanism remain unresolved. In this proposal, we will make systematic study of the regulation of meta-magnetic transformation interval induced by element doping and atomic order, we will utilize TEM to investigate the microstructures that may affect the transformation interval, and make direct observation of transformation process by using magnetic force microscopy. By analyzing the correlation between microstructures (such as twin structure, anti-phase domain, atomic order, etc.) and the characteristics of phase transition process (such as the nucleation, growth, and distribution of the new phase, etc.), we try to find the key factors and their way of affecting the transformation intervals, and provide guidance to real applications.

具有磁形状记忆效应的Ni-Mn基哈斯勒合金由于在磁驱动和磁制冷等方面具有潜在的应用前景，引起了研究者们的广泛关注。相变宽度作为合金变磁相变特征的主要参数之一，对合金性能有重要影响。研究表明，合金微结构的细小变化（如掺杂和原子有序度）会显著影响变磁相变的宽度。然而，对于微结构影响变磁相变宽度的机制并不清楚。本项目将系统研究掺杂和原子有序对变磁相变宽度的影响规律，采用透射电镜对影响变磁相变宽度的微结构特征进行系统研究，并采用磁力显微镜对马氏体相变过程进行直接观测。通过分析合金微结构（孪晶结构、反相畴、原子有序等）与相变行为特征（如形核、生长和分布规律等）的关联规律，提取影响合金变磁相变宽度的关键因素并分析其影响机制，最终为调控变磁相变宽度这一重要性质提供指导。

具有磁形状记忆效应的Ni-Mn基哈斯勒合金在磁驱动、磁传感、磁制冷等方面具有潜在的应用前景，调控马氏体相变宽对优化合金性能有重要影响。本项目通过宏观磁电特性测量、磁力显微镜测量、透射电镜表征等系统地研究了掺杂和原子有序等因素对变磁相变宽度的影响规律。首先，利用具有多物理场平台的扫描探针显微技术直接观测了变磁性相变材料NiCoMnIn合金中磁畴结构随温度场和磁场的演化过程，发现磁场作用下奥氏体首先从反铁磁马氏体孪晶界处形核，并随着磁场的增加逐步长大和扩张，表明马氏体孪晶界是控制相变过程的重要因素。进一步，研究了退火对NiCoMnIn合金的结构和马氏体相变的影响规律，发现退火并未明显改变合金的晶体结构，扫描探针显微镜测量结果表明退火使得马氏体相变的发生具有协同性；而在不退火的合金中，马氏体相变缓慢发生且相界面的演化基本呈现各向同性，因此不再具有协同性特征。透射电镜结果表明退火增强了合金的原子有序度，表明原子有序是影响马氏体相变宽度的重要因素。这些结果为深入理解和调控反铁磁马氏体与铁磁奥氏体之间的相转变提供了基础。