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运用第一性原理的方法,计算磁性形状记忆合金Mn_2NiGe的晶体结构、磁结构、电子结构在马氏体相变中的变化.结果表明:Mn_2NiGe在发生马氏体相变时,产生了c轴拉长而a和b轴缩短的Jahn-Teller畸变,形成一个由两根长键和四根短键组成的拉长的八面体;伴随Jahn-Teller畸变,处于八面体中心的Mn离子的磁矩发生了显著的变化,而作为配体的Ni和Ge离子的磁矩基本不变;Jahn-Teller效应中Mn离子的e_g和t_(2g)能级的分裂,源自于晶体畸变所产生的配位场的改变,导致Mn离子d电子态密度的重新分布,从而在费米能级两侧打开一个赝能隙.
The first order principle is used to calculate the change of the crystal structure, magnetic structure and electronic structure of martensitic Mn_2NiGe during the martensite transformation.The results show that when the martensitic transformation occurs, the c axis Elongated Jahn-Teller distortion of the a and b axes to form an elongated octahedron consisting of two long and four short bonds; the magnetic moment of Mn ions in the octahedral center with Jahn-Teller distortion The magnetic moments of Ni and Ge ions as ligands are basically unchanged. The splitting of the e_g and t_ (2g) levels of Mn ions in the Jahn-Teller effect results from the distribution of the crystal distortion The change of the field will lead to the redistribution of the electronic density of states of Mn ions d, thus opening a pseudogap on both sides of the Fermi level.