具有磁弹耦合的亚铁磁Mn2Sb基合金磁致应变及各向异性磁电阻研究

A considerable attention has been paid to the ferrimagnetic Mn2Sb-based alloys due to their peculiar magnetic phase transition between the ferrimagnetic and antimagnetic states. Besides the mechanism of magnetic transition, magnetocaloric and magnetoresistance effect have also been investigated. But almost no magnetostriction of Mn2Sb-based alloys are noticed by far. It is reported that the sudden change of lattice parameters will be accompanied when the magnetic transition happens in the ferrimagnetic Mn2Sb-based alloys, which indicates the large magnetoelastic, and in turn suggests the large magnetostriction. In addition, owing to the natural layer structure, which is similar to the multilayer film, the magnetoresistance of Mn2Sb-based alloys should show the anisotropy. Therefore, the ferrimagnetic Mn2Sb-based slloys with the appropriate composition will be chosen as the investigated subject of this project. We intend to control the magnetic transition, enhance the magnetoelastic coupling, and make the alloys form the better texture by regulating the composition and adopting many sintering methods such as spark plasma sintering and microwave sintering, and directional solidification techniques including spray casting and hot-mold casting. Our previous research results indicate that the the large magnetostriction and anisotropic magnetoresistance has been observed in the ferrimagnetic Mn2Sb-based slloys with the appropriate composition. We will study the measurement, the representation, and potential application of the magnetostriction and anisotropic magnetoresistance. Finally, the first-principles calculations about the density of state, band structure, metallic ion sites, element hybridization, and the inter- or intra- interaction in Mn2Sb-based alloys will be carried out. By these calculations, we try to search for the exprimental and theoretical support for the physical mechanics about the regulation of the magnetic phase transition, the enhancement of magnetoelastic coupling, and the anisotropic magnetoresistance in Mn2Sb-based alloys, broadening their the practical application.

Mn2Sb基合金以其特有的亚铁磁/反铁磁相变备受关注。除相变机制外，部分研究也涉及到磁热效应和磁电阻，但合金的磁致应变目前还鲜有报道。研究发现，合金发生磁相变时伴随有大的晶格常数突变，具有强的磁弹耦合，预示着具有大的磁致应变；此外，由于合金天然的层状结构类似于多层膜，磁电阻应该会出现各向异性。因此本项目拟以Mn2Sb基合金为研究对象，探索通过调节成分和利用放电等离子体烧结、微波烧结等烧结方式以及喷铸、热模铸造等定向凝固技术调控磁相变，增强磁弹耦合，增加合金取向度。前期预研结果表明，我们在合适成分的合金中观察到大的磁致应变和各向异性磁电阻效应。我们将对合金磁致应变及各向异性磁电阻的测量、表征及其潜在应用等进行研究。最后通过第一性原理计算合金态密度、带结构、离子占位、元素杂化及层内层间相互作用，为理解合金相变调控机制、磁弹耦合增强机制、各向异性磁电阻机理和拓宽合金实际应用寻找实验和理论支持。

能够发生一级磁相变的Mn 基合金近些年备受关注，在温度、磁场、应力等诱导下，Mn基合金磁相变附近常伴随有巨磁热、压热、弹热、磁电阻、磁致应变、负热膨胀、交换偏置、霍尔效应等多种物理效应，在固态制冷、磁记录、人工智能、热传导、能量收集及存储等领域有着广阔的应用前景。在国家自然科学基金资助下，我们在Mn2Sb 基合金中进行了各向异性磁致应变、磁电阻、相变动力学囚禁、磁热效应和霍尔效应的研究工作，并将相关研究拓展到其他Mn基合金体系中，主要研究结果如下：（1）在Mn1.975Cr0.025Sb 合金中观察到磁弹相变的动力学囚禁现象，磁性和电阻测量支持了该现象的存在，磁场增大到8 T，磁弹相变完全消失，即，发生了完全的动力学囚禁。进一步研究发现，冻结的亚铁磁态在一定的温度和磁场范围内表现为玻璃转变行为，即囚禁的亚铁磁和反铁磁转变为磁玻璃态。（2）研究了Bi 掺杂(Mn2Sb)1-xBix 合金亚铁磁/反铁磁相变和相关物理效应，在Mn1.78Sb0.89Bi0.11 合金中发现目前报道的Mn2Sb 基合金中最大的磁电阻效应，同时也观察到动力学囚禁现象；（3）在电弧熔炼多晶Mn1.9Co0.1Sb 合金中发现由织构引起的各向异性的磁致应变效应，平行于织构方向应变值高达2500 ppm，此外在该合金中我们还发现拓扑霍尔效应，在室温附近低场下获得大的拓扑霍尔电阻；（4）通过调节Mn/Co比例的方法在MnCoGe合金中实现剧烈磁场驱动变磁性马氏体相变，获得巨室温磁热效应；（5）在非磁、大半径主族元素In 取代Mn的MnNiGe 合金中实现了磁场驱动的变磁性马氏体相变和成倍增加的磁熵变峰值，通过第一性原理计算和同步辐射测量对其机理进行了分析；（6）在球磨Mn0.965Co1.035Ge 合金粉末中获得了兼具大膨胀系数和包括室温在内的宽工作温区的优异负热膨胀性能；（7）在all-d Ni-Mn基Heusler合金的薄膜和条带样品中也观察到巨磁电阻、磁热效应、交换偏置等物理效应。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18 篇，其中Inorganic Chemistry 1 篇，Applied Physics Letters 2 篇，Scripta Materialia 1篇。我们的成果为Mn 基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。