磁性形状记忆合金Mn_2NiGa band Jahn-Teller效应的第一性原理研究

A first-principles study of band Jahn-Teller effect for magnetic shape memory alloy Mn_2NiGa

运用第一性原理的方法,研究了磁性形状记忆合金Mn_2NiGa在马氏体相变中晶格结构、磁结构、Mn原子d电子结构的变化.研究表明,伴随Mn_2NiGa马氏体相变的发生,形成了一个由两根长键及四根短键组成的拉长八面体结构,即产生了沿z轴拉长的Jahn-Teller畸变;在相变时,位于八面体中心的Mn原子的磁矩发生显著的变化,而作为配体的Ni、Ga原子的磁矩变化很微小;Jahn-Teller畸变的发生,是由于晶体的畸变使配住场产生变化,导致Mn原子d电子态密度重新分布,从而使e_g和t_(2g)能级分裂所致.

By means of the first-principles method, we investigate the change rule of crystal structure, magnetic structure and d electronic structure of Mn atom for magnetic shape memory alloy Mn2NiGa in the martensitic phase transition. The results show that in the martensitic phase transition for Mn2NiGa, a Jahn-Teller distortion is produced, which leads the z-axis to be longer, forming an elongated octahedral geometry. There is a significant change on magnetic moment for Mn atom in the center of octahedron, while those for the ligand atoms Ni and Ga are very little. The energy levels of eg and t2g are split by the redistribution of density of states for d electrons, and it is the reason of Jahn-Teller distortion.