Heusler合金Mn2NiAl的电子结构、磁性质及四方变形的第一性原理

摘要

利用基于密度泛函理论的第一性原理,计算Mn2NiAl的晶体结构、四方变形、磁性、电子结构和压力响应.计算结果表明:Mn2NiAl在立方奥氏体相的平衡结构为铁磁态MnMnNiAl型结构,其中Mn原子占据A和B不等价晶位;在由立方结构向四方结构的变形中,在c/a≈1.24处存在一个稳定的马氏体相;在奥氏体相和马氏体相下,Mn原子对Mn2NiAl总磁矩的贡献最大,Mn(A)和Mn(B)原子磁矩的值不等并呈反平行耦合,且Mn(A)-d和Mn(B)-d的投影态密度在费米面附近交叠均较少,表明Mn(A)和Mn(B)原子间的d-d直接交换作用均较弱,而Mn原子内的交换作用较强,因此Mn2NiAl呈亚铁磁结构.%Crystal structure, tetragonal distortion, magnetism, electronic structure and pressure response of Mn2NiAl were calculated by means of first-principles method based on the density functional theory. The calculation results show the equilibrium structure of Mn2NiAl in the cubic austenitic phase is the MnMnNiAl structure with Mn atoms occupying A and B non-equivalent positions. In the process of transform from a cubic to a tetragonal structure, Mn2NiAl alloys exhibit a stable martensitic phase in c/a ≈ 1.24. In both the austenite and martensite phases, the contribution of Mn atoms to the total moments for Mn2 NiAl is the largest, the magnetic moments of Mn (A) and Mn ( B) atoms are inequality and antiparallel couple. The direct d-d exchange interactions between Mn(A) and Mn(B) atoms are weak because of the small overlap of ^-projected DOS of Mn(A) and Mn(B) atoms nearby the Fermi level, but the intra-atomic interactions in Mn atoms are strong, this is the reason why the Mn2NiAl alloys show ferrimagnetism.