磁形状记忆合金Mn2NiGa的第一性原理计算

First-principles calculation of magnetic shape memory alloy Mn2NiGa

Mn 2NiGa磁形状记忆合金立方奥氏体相因在室温下具有可逆马氏体相变,同时居里温度高达588 K,在高温下具有优异的磁热效应,因而在相应的学术领域和应用领域中具有重要的研究价值。掌握Mn 2NiGa磁形状记忆合金的原子占位、结构相变、磁性质和弹性常数是实现Mn 2NiGa合金磁形状记忆性能优化的关键。采用目前国际上较为先进的第一性原理精确Muffin-Tin轨道方法,系统计算研究了0 K下Mn 2NiGa合金立方奥氏体相与四方马氏体相的晶格结构参数、磁矩、弹性常数、电子结构及总能。研究结果表明,Mn 2NiGa合金立方奥氏体相具有Hg 2CuTi型晶格结构,而非传统Ni 2MnGa的L 2 1结构;Mn原子是合金总磁矩的主要提供者,且2种Mn原子磁矩呈反平行排列;奥氏体相的剪切模量(C′=(C 11-C 12)/2)小于0,因而低温下立方结构不稳定,可以发生由立方相到四方相的马氏体相变;根据Jahn-Teller效应,低温下四方相相对于立方相的稳定性,主要源于2种Mn和Ni原子分别与Ga原子的共价结合作用。上述理论结果有望为Mn 2NiGa合金性能的进一步优化提供理论指导。

Mn 2NiGa magnetic shape memory alloy cubic austenitic phase factor has reversible martensite transformation at room temperature,and Curie temperature is up to 588 K.It has excellent magnetothermal effect at high temperature,so it has important research value in the corresponding academic field and application field.Understanding the atomic occupation,structural phase transition,magnetic properties and elastic constants of Mn 2NiGa magnetic shape memory alloy is the key to optimize the magnetic shape memory performance of Mn 2NiGa alloy.The lattice structure parameters,magnetic moment,elastic constant,electronic structure and total energy of Mn 2NiGa alloy cubic austenite phase and square martensite phase at 0 K have been systematically studied by using the currently advanced first-principles exact muffin-tin orbitals method.The results show that Mn 2NiGa alloy cubic austenitic phase has Hg 2CuTi lattice structure,while the traditional Ni 2MnGa has L 2 1 structure.The Mn atom is the main supplier of the total magnetic moment of the alloy,and the magnetic moments of the two Mn atoms are arranged in reverse parallel.The shear modulus(C′=(C 11-C 12)/2)of cubic austenitic Mn 2NiGa alloy is less than 0,so the cubic structure is unstable at low temperature and has martensitic transformation from cubic to tetragonal.According to the Jahn-Teller effect,the stability of tetragonal phase relative to cubic phase at low temperature is mainly due to the covalent bonding effect of Mn and Ni with Ga atoms,respectively.The theoretical results presented in this paper are expected to provide theoretical guidance for the optimization of the properties of Mn 2NiGa alloy.