Ni-Mn-X(X=In,Sn,Sb)铁磁形状记忆合金的中间相及相关物理性质研究

A considerable attention has been paid to the intermediate phase (Premartensitic Phase) of Ni-Mn-Ga ferromagnetic shape memory alloys due to its abundant physical contents and potential application prospect. It is widely believed that the intermediate phase transition originates mainly from the strong magnetoelastic coupling between the magnetic and the structural degrees of freedom in Ni-Mn-Ga alloy system. In Ga-free Ni-Mn-X (X=In,Sn,Sb) Heusler alloys, however, almost no investigations about the intermediate phase are carried out by far. It is reported that application of the uniaxial stress can enhance the magnetoelastic coupling and increase the softening of anomalous phonon in Ni-Mn-Ga alloys, which could facilitate the intermediate phase transition to occur. Therefore, we intend to take Ni-Mn-X(X=In,Sn,Sb) slloys with the appropriate composition as the subject investigated and exert pressure to them by high pressure annealing, pre-deforming after annealing, and pre-stretching after annealing, which is aim to enhance the magnetoelastic interaction of these alloys. Our previous research results indicate that the intermediate phase has been observed in the Ni-Mn-X alloys after pressuring. We will study the law of the intermediate phase transition, the representation of intermediate phase, and the related physical properties and potential application in the vicinity of the intermediate phase transition. In addition, theoretical calculation about the intermediate phase in Ni-Mn-X alloys after pressuring will also be carried out according to the Landau theory. In the process of theoretical calculation, a enhancing term of the magnetoelastic coupling induced by the pressrue will be introduced to the free energy of system. By these calculations, we try to search for the exprimental and theoretical support for the physical mechanics about the occurrence of the intermediate phase transition and expanding the application area of Ni-Mn based ferromagnetic shape memory alloys.

Ni-Mn-Ga Heusler合金中间相（预马氏体相）以其丰富的物理内涵和潜在的应用前景受到广泛关注，其中强的磁弹耦合是中间相出现的主要原因。但在不含Ga的新型Ni-Mn-X (X=In,Sn,Sb)铁磁形状记忆合金中，中间相变却鲜有报道。研究发现，对Ni-Mn-Ga合金施加压力可以增大其磁弹耦合，使异常声子软化增强，有利于中间相的出现。因此本项目拟以新型Ni-Mn-X合金为研究对象，通过高压退火、退火后预压和退火后拉伸等手段对其施加压力，增强其磁弹耦合。前期预研结果表明，在施压后的新型Ni-Mn-X合金中观察到了中间相。我们将对中间相变规律，中间相表征和中间相变附近相关物理性质及潜在应用等进行研究。此外，根据Landau理论，在系统自由能中引入一项由压力所导致的磁弹耦合增强项，通过理论计算为理解Ni-Mn基铁磁形状记忆合金中间相变发生的物理机制和扩大其应用领域寻找实验和理论支持。

磁性相变合金以其丰富的物理性质，比如大的磁热效应、压热效应、弹热效应、磁电阻效应、磁致应变、交换偏置、巨霍尔效应等，在制冷、磁记录、人工智能等很多领域都具有潜在的应用前景，因此一直以来磁性合金相变调控都是人们研究的热点。在国家自然科学基金的资助下，我们开展了Ni-Mn基铁磁形状记忆合金相变调控、中间相变及相关物理性质的研究工作，并将相变调控相关工作进一步拓展到其他磁相变合金体系中。主要工作成果包括：（1）在高压退火的Ni43Mn41Co5Sn11合金中观察到由于中间相的存在所导致的特殊的磁热和磁电阻效应，即在一级磁相变材料中观察到由连续两个磁相变所导致的同号双磁熵变峰和双磁电阻峰；（2）发现快淬速度可以有效调控Ni-Co-Mn-Sn合金条带马氏体相变及相变附近磁热性能，在30m/s速度下甩出的条带中观察到γ沉淀相；（3）在Mn50.1Ni39.3Sn10.6合金条带和PMN-PT组成的复相材料中，利用应力驱动相变的机制实现了电场对合金交换偏置效应的有效调控，发现了电场作用下交换偏置场的减小，并利用应力驱动相变机制对相关物理现象进行了分析讨论；（4）制备出MnNiGe基和MnCoGe基新型铁磁形状记忆合金条带样品，对其磁相变进行调控，获得室温附近铁磁到顺磁磁结构相变及大的低场磁热效应；（5）对亚铁磁Mn2Sb基合金亚铁磁/反铁磁磁相变调控及相关磁功能性质进行了研究，在Mn1.9Co0.1Sb合金中观察到大的低场磁热效应和巨磁电阻效应；至结题时，我们已经在上述几个方面取得了很好的进展，共发表SCI论文14篇，其中Acta Materialia 1篇，Applied Physics Letters 3篇。我们的成果为磁性相变合金相变调控及相关物理性质研究提供了理论和实验依据。