Ni-Mn-Sn合金缺陷稳定性和磁性能的第一性原理研究

Defect stability and magnetic property of Ni-Mn-Sn alloys by first-principles calculations

Ni-Mn-Sn合金是一种极具工业应用潜力的新型铁磁形状记忆合金,化学成分对Ni_(2)Mn_(1+x)Sn_(1-x)合金的马氏体相变和磁性能影响重大,而在成分调整过程中势必会产生一系列的点缺陷.本文使用量子力学计算软件包VASP(Vienna ab-initio software package)研究了包含反位缺陷、空位和原子交换在内的点缺陷对Ni-Mn-Sn合金的结构稳定性、磁性能和电子结构的影响.通常借助第一性原理计算可以高效经济地对不同成分下合金的相变、磁性能和弹性性能展开研究,而且还可以得到不能直接用实验方法获得母相和产物相的基态能量、相变驱动力以及微观磁性能.研究结果表明,大多数点缺陷的形成能为负值,表明这些缺陷能够在Ni-Mn-Sn合金中形成并稳定存在.富Mn贫Sn是实验中常见的成分设计,势必会在合金中产生大量形成能相对较低的MnSn反位缺陷.Sn空位的形成大大降低了母相的稳定性,促进合金发生马氏体相变.当过量的Mn占据Sn位时,Mn-Mn间距减小30%,导致过量Mn的磁矩反平行于正常Mn原子的磁矩方向排列.本研究有助于更好地理解Ni-Mn-Sn合金的马氏体相变行为及其基础物理性能.

Ni-Mn-Sn alloy is a new type of ferromagnetic shape memory alloy with great potential for the industrial application.Chemical composition has a great influence on the martensitic transformation and magnetic properties for the nonstoichiometric Ni_(2)Mn_(1+x)Sn_(1-x) alloys.A large number of the point defects will be generated during the composition tuning process.In this work,the effects of point defects including antisites,vacancies,and atomic exchanges on the phase stability,magnetic property and electronic structure of the Ni-Mn-Sn alloy were investigated by using the first-principles calculations.Generally,the phase stability,magnetic and elastic properties of alloys with different compositions can be studied efficiently and economically by means of the first-principles calculations.Moreover,the ground state energy,driving force of phase transformation,and atomic magnetic moments of the parent phase and the product phase,which cannot be directly obtained by experiments,can be alternatively investigated through the first-principles calculations.The formation energy of most of the point defects is negative,indicating that these defects can form and stay stably in the parent phase of the non-stoichiometric Ni-Mn-Sn alloy.In particular,the Mn-rich and Sn-deficient Ni-Mn-Sn alloy is commonly used composition design during previous experimental studies.Martensite transition can be controlled effectively by adjusting the Mn and Sn contents.A large number of MnSnantisite defects with relatively lower formation energy would be generated in the parent phase of the Mn-rich and Sn-deficient Ni-Mn-Sn alloy.The formation of the Sn vacancy dramatically reduces the stability of the parent phase.This change will promote the martensitic transformation of the alloy.When the excess Mn atom occupies Sn site,the 30%decrease of the Mn-Mn distance leads the magnetic moment of the excess Mn antiparallel to that of the normal Mn.The smaller Ni-Mn distance causes a larger Ni moment.This study may provide a better understanding of the martensitic transition and physical properties for the Ni-Mn-Sn alloy.