双元素共掺杂Mn2Sb单晶中低滞后磁致伸缩及热膨胀效应研究

A first-order magnetoelastic phase transition is accompanied by a drastic variation of lattice parameters, and large magnetostriction and thermal expansion are expected to occur as well. As a consequence, the first-order magnetoelastic phase transition materials have becoming a hot topic in the areas of material science and condensed matter physics. However, the large saturation magnetic field and hysteresis limit its applications significantly. In this project, we will choose the Mn2Sb-based single crystals with intrinsic low hysteresis as our study object, and two elements will be codoped simultaneously. With the aid of first principles calculations, the evolutions of electronic structure and electronic density will be observed carefully with the changes of radius, valence electrons, electronegativity and site occupation of the doped elements. Their relationships with magnetism and the relative stability of the two magnetic ordering phases will be explored. The underlying mechanism of how the magnetoelastic coupling is influenced by the element doping will be also revealed, and the database of the linkage of composition-magnetism-lattice size is try to be established. The dynamical model of lattice parameter variation based on the first-order magnetoelastic transition will be improved. With the optimization of the key factors, abnormal (negative, near-zero) thermal expansion effect with wide operating temperature range and large magnetostriction with low driven field and high reversibility can be realized in this Mn2Sb based system.

一级磁弹相变材料在其磁相变过程中伴随着晶格尺寸变化从而产生巨大的磁致伸缩及热膨胀效应，目前已成为材料科学和凝聚态物理的研究热点之一，但其较高的饱和场和滞后性严重限制了其在相关领域的应用。本项目拟在具有较低相变热滞的Mn2Sb基单晶体系中，以双元素共掺杂为手段，以第一性原理计算为指导，系统地考察此体系的电子结构、电子密度等关键因素随掺杂原子半径、价电子数、电负性及占位情况的演化过程，探索其与磁性、两磁有序态相对稳定性的内在关联，揭示元素掺杂对磁弹耦合的调控机制，尝试构筑此体系的成分-磁性-晶格尺寸性能关联数据库，进一步完善一级磁弹相变过程中晶格尺寸演化的动力学模型并通过元素掺杂优化相关物理参数，以在此体系中实现宽温区奇异（负、近零）热膨胀和低场驱动、高可逆性的大磁致伸缩效应。

本项目系统地研究了具有四方、立方、正交以及单斜结构的Mn基金属间化合物中的磁相变现象，并详细地研究了其伴随的丰富物理现象，如热膨胀、磁热效应、压卡效应等。为快速制备单晶金属间化合物，研制了一台基于布里奇曼法的高通量单晶制备系统，可同时生长11个不同组分样品。且基于Labview软件开发出一种快速精修单晶XRD谱线的软件。通过不同半径的元素对Mn2Sb以及相关的金属间化合物的多晶/单晶体系的掺杂，以及多种物理场对其相变温度、相变前后自旋序进行了系统地研究。研究发现，小原子半径的Cr和大原子半径的Bi掺杂均对相变温度有提升作用，两种元素掺杂均在a轴方向显示了负热膨胀效应，而晶胞体积保持不变。通过计算和实验发现，多种元素掺杂样品具有较高的磁致伸缩效应，且滞后性较小，即既保持了一级相变的高输出特性，亦克服了一级相变滞后高的缺点。