Ni(Fe,Co)MnAl合金中磁场诱导相变、磁电阻和磁致应变的研究

Ni-Mn-based ferromagnetic shape memory alloys have been a hot topic in the study of magnetic material research, owing to their abundant physical properties and wide application prospects. Particularly, Ni-Mn-Al alloys exhibit good mechanical performance, but the research and application of magnetic functional properties are limited by the fact that the martensitic transformation between two weakly magnetic states in these alloys cannot be induced by external magnetic field. In this project, we intend to focus on the transition element Fe or Co doped Ni-Mn-Al alloys; the magnetic-field-induced martensitic transformation will be achieved by adjusting the composition and the process parameters of sample preparation. The effect of Fe or Co doping on the electric configuration and magnetic properties will be studied in parallel with first-principle calculation. The mechanism and the experimental route for low-hysteresis and low-critical field in these alloys will be explored by tuning the composition, crystal structure, microstructure, and phase constituent. Furthermore, the magnetoresistance, magnetostrain will be investigated based on such magnetic-field-induced phase transitions. From the application point of view, the phase transition will be optimized in terms of large magnetoresistance and magnetostrain at low magnetic field as well as in wide temperature range. More importantly, the studies on these alloys will provide a possible experimental and theoretical route for the exploration of new multi-functional materials in future.

Ni-Mn基铁磁形状记忆合金因其丰富的物理内涵和广阔的应用前景成为当前磁性材料的研究热点。其中，Ni-Mn-Al合金具有较好的力学性能，然而其马氏体相变前后两相均为弱磁态，难以实现磁场诱导相变，影响了该类合金磁性功能性质的研究和开发。本项目拟以过渡元素Fe或Co掺杂的Ni-Mn-Al合金为研究对象，通过调节合金成分和制备工艺调控相变前后两相的磁性状态和相变类型，获得磁场诱导的马氏体相变。结合第一性原理计算研究Fe或Co掺杂对合金的电子结构、磁性状态等性质影响的物理机制。通过调整合金的成分、晶体结构、微结构、相组成等方法，探索实现低磁滞和低变磁性临界场的途径和机制。在相变调控的基础上，研究基于磁场诱导相变行为的磁电阻和磁致应变效应。从实际应用出发，优化相变行为并致力于探索在宽温区、低磁场下具有较大磁电阻和磁致应变的合金材料。为新型磁性功能材料的探索及其应用提供实验和理论依据。

Ni-Mn基铁磁形状记忆合金发生结构相变时耦合着磁相变，且该相变可以由外磁场驱动，因而人们在这类合金的马氏体相变附近发现了磁热、磁电阻和磁致应变等丰富的物理效应。由于这些特殊的物理现象对于探讨马氏体相变的机理及其潜在应用价值具有重要的科学意义，成为目前研究的热点。本项目以Ni(Fe,Co)MnAl合金为研究对象，通过Fe、Co元素掺杂、调节合金成分、改变制备工艺等方法在该类合金中获得了铁磁-弱磁型马氏体相变，并研究了相变附近的磁热、磁电阻和磁致应变等效应。主要工作成果包括：（1）通过Fe对Ni-Mn-Al合金掺杂，观察到Ni-Fe-Mn-Al合金奥氏体相的铁磁性得到明显增强，通过改变合金中Fe的含量能有效调节这类合金的马氏体相变温度及磁场诱导逆马氏体相变行为；在此基础上制备了Ni-Fe-Mn-Al合金条带，研究了相变附近的磁电阻效应；（2）在Co掺杂的Ni-Co-Mn-Al合金中实现了磁场诱导的逆马氏体相变，建立了合金成分、相变温度、磁场诱导的相变行为与相变附近磁电阻效应的内在联系；根据相变调控规律获得相变温度在室温附近的Ni42.8Co7.7Mn38.8Al10.7合金，发现了室温附近大的磁电阻和磁致应变效应，并利用磁场诱导相变机制进行了分析讨论；（3）发现Fe、Co共掺杂能有效调控Ni-Fe-Co-Mn-Al合金中的马氏体相变，获得了相变温度可以在较宽的温区内调整的共掺杂合金；Fe/Co掺杂的比例、合金的结构等因素是影响马氏体相变行为的关键因素，并在相变附近得到了大的磁热和磁电阻效应；（4）在Mn-Ni-Sn合金中通过改变Ni/Sn原子比例有效调控了马氏体相变；利用短时间退火处理有效调节了Ni-Mn-V-Sn和Ni-Mn-Sn-Sb条带的马氏体相变温度及相变附近的磁热效应；对比研究了Mn44.7Ni43.5Sn11.8合金及其条带在相变附近的电输运性质，在条带的相变附近获得了大的磁电阻效应；（5）利用Fe2Ga对MnNiSi合金进行掺杂成功制备出了Mn-Ni-Fe-Si-Ga合金，对其铁磁-顺磁型磁结构相变进行了有效调控，并在相变附近获得了大的磁热效应。本项目的研究丰富了铁磁形状记忆合金的研究内容，为Ni-Mn基系列合金的探索及应用提供了依据。