单分子磁体磁学性质的理论研究

发布时间：2018-04-09 17:02

  本文选题：单分子磁体　切入点：量子化学理论　出处：《南京师范大学》2016年硕士论文

【摘要】：单分子磁体的慢磁驰豫效应和宏观的量子隧穿效应是90年代以来分子磁学领域的重大发现,由于其独特的磁学性质,有望被制作成高密度信息存储元件或被用于量子计算,现已经成为热门的研究领域。在本论文中,选择了近几年所报道的具有代表性的几种单分子磁体,使用量子化学理论及方法详细研究了它们磁各向异性来源和磁构效关系,希望能为实验上合成具有较高磁各向异性能垒和阻塞温度的单分子磁体提供理论指导。首先,研究了一个八配位Co单分子磁体的磁构效关系,计算并分析了两种结构变化对磁各向异性的影响。探索该分子磁体磁各向异性的来源和磁各向异性常数D绝对值最大时的可能结构。研究结果表明：扭转角φ偏离0度越大,dz2和dxy的混合β轨道沿着Co(Ⅱ)上磁轴的方向被拉伸的越厉害,这是该化合物具有较大磁各向异性的原因之一。此外,我们发现减小α或增大φ都可以增强化合物的磁各向异性,dz2和dxy混合β轨道的电子分布变化图也验证了这一结论。基于上述研究结果,我们推测磁各向异性常数D绝对值为最大值时的可能结构是a=52°且ψ=43°。其次,我们使用B3LYP和DDCI3方法研究了一系列带有不同配体NHC的二配位COⅠ-N~(-1)化合物[(NHC)CoNDmp](NHC=IPr(1)；cyIPr(2)；sIPr(3)),计算并研究了它们的交换耦合、磁各向异性和能级。从理论上探究基于CoⅠ-NⅠ化合物高能垒的来源。计算结果表明CoⅠ-N-Ⅰ化合物的Co和N间具超强的铁磁相互作用,同时我们计算得到的化合物基态和第一激发态的能级差(分别为275.6、292.9、314.7和383.1 cm~(-1))与实验上的测得能垒(分别为215、254和363 cm~(-1))吻合的很好。除此之外,[CoN]~+基团的自旋轨道耦合能级(351.0 cm~(-1))与化合物1-3能级相差不大,说明[CoN]~+固有的大的磁各向异性在化合物的磁各向异性中起着主要作用。这些结果表明这一系列CoⅠ-N-Ⅰ化合物可以被看成基于[CoN]~+基团的单分子磁体,它们较高的能垒主要来源于[CoN]~+基团大的磁各向异性。
[Abstract]:The slow magnetic relaxation effect and macroscopic quantum tunneling effect of monolayer magnets are important discoveries in the field of molecular magnetics since the 1990s. Due to their unique magnetic properties, they are expected to be made into high-density information storage devices or used in quantum computing.Now it has become a hot research field.In this paper, some representative monolayer magnets reported in recent years have been selected, and their magnetic anisotropy sources and magnetic structure-activity relationships have been studied in detail by using quantum chemistry theory and method.It is hoped that it will provide theoretical guidance for the experimental synthesis of monolayer magnets with high magnetic anisotropic barrier and blocking temperature.Firstly, the magnetic structure-activity relationship of an octahedral Co monolayer magnet is studied, and the effects of two structural changes on the magnetic anisotropy are calculated and analyzed.The source of the magnetic anisotropy of the molecular magnet and the possible structure when the absolute value of the magnetic anisotropy constant D is maximum is explored.The results show that the bigger the deviation of torsion angle 蠁 is, the more the mixed 尾 orbital of Dz2 and dxy is stretched along the direction of magnetic axis on Co (鈪，

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