基于外加多物理场实现Ni-Mn基变磁性Heusler合金中反磁热性能的优化

A new type of Ni-Mn based metamagnetic Heusler alloys has currently become one of researching hotspots in materials and condensed matter physics, because they usually perform a giant inverse magnetocaloric effect (MCE) by the magnetic-field-driven first-order magnetostructural martensitic transformation (MT). However, these alloys as a kind of inverse magnetocaloric materials still faces serious challenges in some respects inculuding reversibility and working temperature region. This is due to the interaction of relatively thermodynamical parametres and intrinsic hysteresis during metamagnetic MT. In the present project, we are going to use 3d/4d transitional elements appropriatelly doped in Ni-Mn-Z(Z=In, Sn, Sb) and prepared quaternary and quinary alloys. According to the occupied properties of each atom in the different cystal lattices, the correlatively thermodynamical parameters during metamagnetic transformation, such as the difference of magnetization between two phases (ΔM), the transition entropy change (ΔStr) and the driven-force of transition would be tailored. Through establishing the detailed phase diagram for the evolving trend between the aforementioned parameters and the chemical compositions of specimens, we will explore the optimal configuration among these key thermodynamical parametres. On this basis, both the hysteretic property and the driving force associated with tansformation would be systematically improved by the means of the external multi-physics fields (magnetic field and hydrostatic pressure), and thus expects realization of enhanced and reversible inverse magnetocaloric effect with a low energy consumption for such a kind of alloys.

新型Ni-Mn基变磁性哈斯勒合金通常在磁场驱动一级磁结构马氏体相变过程中展现出巨大的反磁热效应,现已成为材料科学和凝聚态物理的研究热点之一。然而，在变磁性马氏体相变过程中，由于相关热力学参数之间的相互制约以及本证的滞后性，导致这些合金作为一类反磁热材料在制冷可逆性和工作温区方面仍然面临着严峻的挑战。本项目将通过3d和4d过渡族元素的适量替代，制备以Ni-Mn-Z(Z=Sn,In,Sb)为母体的四元和五元合金。根据各原子在不同晶格中的占位性去调控变磁性马氏体相变过程中的相关热力学参数，如两相之间的磁化强度差异（ΔM）、转变熵变（ΔStr）以及相变驱动力。通过建立上述参数随试样化学组分之间变化趋势的翔实相图，去探寻这些关键热力学参数之间的最优配置。以此为基础，利用外加多物理场对相变滞后性和驱动力进行系统地优化，以期在低能耗下实现该类合金中增强及可逆的反磁热效应。

新型Ni-Mn基Heusler 合金作为一种磁智能材料具有潜在的应用前景，一直是当今凝聚态物理和材料科学的研究热点之一。本项目利用3d 和4d 过渡族元素的适量替代，制备以Ni-Mn-Z (Z=Sn, In, Ga)为母体的四元合金，通过澄清磁熵变、晶格熵变以及磁晶耦合效应之间的关联性问题，探索出三者之间的最优配置。与此同时，深入地探讨和掌握该类合金的热弹性马氏体相变在多物理场下（磁场和等静压）的演化规律，以此来显著降低它们的相变滞后性和驱动力。本项目以具有一级马氏体相变的Ni45Co5Mn35In15合金为例，采用一种多物理场方法实现了变磁性Ni-Mn基Heusler合金中其可逆的磁热效应。研究结果表明，由于该合金的晶格与自旋之间具有较强的耦合作用，该合金的马氏体相变对外加磁场与等静压均较为敏感，其相应速率分别为-6.4K/T和 4.24K/kbar。这使得外加1T的磁场便可以驱动该合金几乎完全相变，得到100%的总熵变。利用马氏体相变过程磁结构耦合较强的特性，构建了基于外加等静压辅以退磁场实现可逆退磁话过程，从而消除了磁滞现象，在很大程度上提高了磁热效应的可逆性。由此可在外加4kbar的等静压辅助下将马氏体相变过程中的本征热滞后从17.5K降低至0.5K。当外加磁场为1.8T时，可逆的最大等温熵变(ΔST)和绝热温变(ΔTad)值分别达到约±15J/kgK和约±3.5K，制冷量达到了160J/kg。这样的结果说明本项目的工作明显改善了该类合金在马氏体相变过程中的反磁热性能，提升该类材料在磁制冷技术上的应用前景。此外，本项目还对一些其它磁功能效应作了较为全面的研究，如压卡效应、磁热效应、磁电阻效应及交换偏置行为等，并对这些效应背后机理作了较为深入地探讨。上述的研究结果为凝聚态物理及材料科学领域的研究工作提供了十分有意义的基础研究资料。