Heusler合金Mn_2 NiGe磁性形状记忆效应的第一性原理预测

First-principle prediction of magnetic shape memory effect of Heusler alloy Mn_2 NiGe

运用基于密度泛函理论的第一性原理,对Hg2CuTi型Mn2NiGe的四方变形、晶体结构、磁性、电子结构、压力响应等进行了计算.计算结果表明:1)在由立方结构至四方结构的转变中,在c/a约为1.34处存在一个稳定的马氏体相;2)在奥氏体态和马氏体态下,Mn原子均是Mn2NiGe总磁矩的主要贡献者,但Mn(A),Mn(B)原子磁矩的值不等且呈反平行耦合,因而Mn2NiGe合金均表现为亚铁磁结构;3)在奥氏体态和马氏体态下,Mn(A),Mn(B)原子之间的亚铁磁耦合是由它们之间弱的d-d直接交换作用来维持.根据以上的计算结果,预测Mn2NiGe具有磁性形状记忆效应.

Tetragonal distortions,crystal structure,magnetism,electronic structure and pressure response of Hg2CuTi-type Mn2NiGe are calculated by the first-principles method based on the density functional theory.The calculations show that 1）in the process of transform from cubic to a tetragonal in structure,Mn2NiGe alloys exhibit a stable martensitic phase at c/ a ≈ 1.34;2 ） in austenite and martensite,Mn atoms are the main contributors to the magnetism in Mn2 NiGe,and Mn2NiGe alloys show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn（A） atom and Mn（B） atom;3）in austenite and martensite,the direct d-d exchange interaction between Mn（A） atom and Mn（B） atom is weak because of small overlap of d-projected DOS of Mn（A） atom and Mn（B） atom nearby the Fermi level.This is the reason why the Mn2NiGe alloys show ferrimagnetism.We can predict the magnetic shape memory effect （MSME） in Mn2NiGe alloys based on the the results of calculation above.