X2MnZ基Heusler合金磁和相稳定性及力学性能的理论研究

L21-X2MnZ based alloys, under reasonable design, can possess good magnetic shape memory effect, which has become one of the hot fields of materials science research. Due to the different composition or preparation process, these alloys show different magnetic ordering, different phase stability, and they even occur the magnetic and structural phase transition at the same time. If we could have a good understanding and then reasonable control of the alloying effect on the magnetic and physical properties, as well as phase stability of X2MnZ based alloys, then we can realize the optimization of their magnetic shape memory performance. Since there are multitude choice of X and Z atoms and corresponding components, the experimental study of X2MnZ based alloys is very difficult. Moreover, both atomic and magnetic disordering situations make the first-principles calculation of these alloys to be impossible. Therefore, until now the true story of the alloying effect on the magnetic and physical properties and phase stability of X2MnZ based alloys still needs to be ascertained. In the present project, using the first-principles EMTO-CPA in combination with UppASD magnetic calculations, we will study systematically the magnetic ordering, crystal structure, elastic constants, and free energy including the vibrational and magnetic parts of X2MnZ based alloys; furthermore, we will try to analyze the composition and temperature dependence of the phase stability and then determine the phase boundary and critical temperature; we will try to explore the true story, as well as the mechanism of the alloying effect on the magnetic and physical properties and phase stability of X2MnZ based alloys; we will try to provide some theoretical basis for making a reasonable evaluation of the good performance of these alloys, and furthermore for realizing the optimization of their magnetic shape memory performance, by means of good controlling the alloying atoms and corresponding components.

合理设计的L21相X2MnZ基合金具有良好的磁形状记忆性能，是目前材料领域研究热点之一。随成分和制备工艺不同，合金磁有序方式可能发生改变，马氏体相变可能彻底消失，或同时伴随磁相变发生。了解合金化影响磁和相稳定性及力学性能的规律性并对其进行恰当控制，是实现X2MnZ基合金磁形状记忆性能优化的关键。众多X和Z合金原子及其组分很难用实验一一测量，且原子及其磁无序问题为第一原理计算造成极大困难。目前对合金化影响磁有序和马氏体相变及力学性能缺乏本质认识。本项目拟采用第一原理EMTO-CPA结合UppASD磁计算方法，系统研究X2MnZ基各合金奥氏体和马氏体相磁有序及转变温度、相稳定性、以及弹性力学性质；确定各组合金成分温度相图；探索合金化对磁和相稳定性及力学性能的影响规律及其物理机理；为解释L21相优异性能，并进一步合理控制合金化及组分，实现X2MnZ基合金磁和形状记忆性能的优化提供理论基础。

合理设计的L21相X2MnZ基合金具有良好的磁形状记忆性能，是目前材料领域研究热点之一。随成分和制备工艺不同，合金磁有序方式可能发生改变，马氏体相变可能彻底消失，或同时伴随磁相变发生。了解合金化影响磁和相稳定性及力学性能的规律性并对其进行恰当控制，是实现代表性X2MnZ基合金磁形状记忆性能优化的关键。众多X和Z合金原子及其组分很难用实验一一测量，且原子及其磁无序问题为第一原理计算造成极大困难。目前对合金化影响磁有序和马氏体相变及力学性能缺乏本质认识。本项目采用第一原理EMTO-CPA结合UppASD磁计算方法，系统研究X2MnZ基各合金奥氏体和马氏体相磁有序及转变温度、相稳定性、以及弹性力学性质；确定各组合金成分温度相图；探索合金化对磁和相稳定性及力学性能的影响规律及其物理机理；给出了X2Mn1+xSn1-x Heusler 合金体系磁有序结构的X原子成分依赖性规律，及其所产生的磁弹性效应对马氏体结构相变的影响规律；预测了(Ni1-xCox)2Mn1.60Sn0.40 Heusler合金的磁性质和马氏体结构相变的成分依赖性规律及其物理机理；揭示了Si，Ge和Sn掺杂的Co2MnGa合金的自旋极化和磁性随温度和成分变化的规律性和物理机制；揭示了Ni2(Mn1-xFex)Ga合金相变温度随成分变化的“反常”规律主要源于磁激发和声子振动的共同作用结果；理论验证了Co2YGa（Y=Sc，Ti，V，Cr，Mn）合金马氏体相变和磁性质随Y元素变化的实验规律性和物理机制。为解释X2MnZ基合金L21相优异性能，并进一步合理控制合金化及组分，实现X2MnZ基合金磁和形状记忆性能的优化设计提供了理论指导。