低维纳米自旋电子材料的第一性原理研究

发布时间：2018-07-13 21:58

【摘要】：自旋电子学器件利用电子的自旋对信息进行存储、运输和处理,过去几十年中在科学领域以及工业领域都引起了广泛的关注。实用的自旋电子器件需要有较高的自旋极化率,居里温度以及大的磁晶各向异性能等特点。另外,纳米材料的研究及其应用是凝聚态物理和材料科学研究中的重要课题。在纳米尺度上实现自旋电子器件的关键是研究具有上述性质的低维铁磁晶体。随着石墨烯的快速发展,以及低维材料独特多样的电子结构,研究者对低维半金属材料的研究兴趣一直呈指数增长。但是由于碳材料中很难观察到明显的磁性,作为一种选择,二维类石墨烯结构的无机材料引起了人们的兴趣。金属有机框架材料(MOFs)是由金属和多齿有机单元通过配位键自组装成的一种多孔类沸石聚合物,它能够形成一维、二维和三维的结构,从而被广泛的研究。在设计MOFs材料时,根据所选择的金属种类,配体的尺寸和结构或者空间位组等特点将会产生多种多样的性质。近年来,随着密度泛函理论以及相关数值算法的发展,采用第一性原理的方法在原子尺度设计和研究磁性材料已经成为重要的研究手段。在本论文中,我们使用第一性原理计算的方法,研究了理论预测的低维纳米材料的基本电子结构和磁性。本论文分为六章,主要有三部分,第一部分即第一章简单地介绍了密度泛函理论。第二部分包括第二、三、四、五章,主要介绍了低维纳米材料的基本性质。第三部分介绍了金属甲酸盐框架[nH4][m(HCOO)3]的铁电和铁磁性。第一章主要介绍了密度泛函理论的发展。首先简单介绍了量子力学的绝热近似和Hartree-Fock近似,然后是Hohenberg-Kohn理论,Kohn-Sham方程,交换相关能量泛函以及儿个计算常见的软件包。在最后部分,我们对Berry Phase理论计算电极化的方法做了具体的介绍。第二章介绍了新的二维结构Fe2Si的电子性质和磁性。在这个工作中,基于第一性原理计算和分子动力学模拟(AIMD),我们构建了类石墨烯结构的Fe2Si材料,结果表明单层Fe2Si晶体是铁磁半金属,并且结构可以在高达1200K的高温下保持稳定。它具有约780K的居里温度和相当大的磁各项异性能,这些性质使单层Fe2Si在自旋电子学器件和电子设备方面有很好的应用前景。第三章主要使用杂化泛函HSE06计算了单层NbS2的电子结构和磁性;不同于PBE泛函计算的结果,HSE06的计算显示单层NbS2是窄带隙的双极磁性半导体,并且研究了不同类型的载流子掺杂以及施加应变对电子结构性质的改变。第四章简单计算了从CrOX(X=Cl,Br)体相结构中剥离出的单层CrOX的基本电子性质以及结构的稳定性。第五章主要计算了一维的金属有机框架结构金属-1,2,4,5苯四胺以及1,2,4,5苯酚的分子纳米线。使用第一性原理的方法研究了这些纳米线的稳定性以及电子结构性质。计算结果表明这些纳米线的结构是稳定的,并且都是半导体的性质。另外,我们也分析了载流子掺杂对电子结构的影响。第六章研究了金属甲酸盐框架[NH4][M(HCOO)3][M=Sc-Zn]的铁电极化以及磁性。首先,基于第一性原理的计算我们具体分析了[NH4][Zn(HCOO)3]铁电现象的起因以及在顺电相到铁电相转变过程中,电极化值和总能量的变化。紧接着,对各个结构的铁电极化值和电子结构性质以及磁性进行了计算和分析,除[NH4][Zn(HCOO)3]之外,其他的结构都是同时具有磁性和铁电性的材料。
[Abstract]:Spintronic devices use the spin of electrons to store, transport and deal with information. In the past few decades, a wide range of attention has been made in the field of science and industry. Practical spintronic devices require high spin polarization, Curie temperature and large magnetocrystalline anisotropy. Research and its application are an important subject in condensed matter physics and material science. The key to the realization of spintronic devices on nanoscale is the study of low dimensional ferromagnetic crystals with the above properties. With the rapid development of graphene and the unique and diverse electronic structure of low dimensional materials, the researchers have studied the low dimensional semi metal materials. Interest has been increasing exponentially. But because it is difficult to observe the apparent magnetism in the carbon material, as a choice, the inorganic material of the two-dimensional graphene structure has attracted people's interest. The metal organic frame material (MOFs) is a porous zeolite polymer assembled by the metal and multi tooth organic units through the coordination bond. It can form the form. A one-dimensional, two-dimensional and three-dimensional structure is widely studied. In the design of MOFs materials, a variety of properties will be produced according to the selected metal species, the size and structure of the ligand, or the spatial position. In recent years, with the development of the density functional theory and the related numerical algorithms, the method of first principle is adopted. The design and study of magnetic materials at atomic scale has become an important research method. In this paper, we use the method of first principle calculation to study the basic electronic structure and magnetic properties of the theoretically predicted low dimensional nanomaterials. This paper is divided into six chapters, including three parts. The first chapter, the first chapter, briefly introduces the density. Functional theory. The second part includes second, third, four, five chapters. The basic properties of low dimensional nanomaterials are mainly introduced. The third part introduces the ferroelectric and ferromagnetism of the formate [nH4][m (HCOO) 3]. The first chapter introduces the development of the density functional theory. First, the adiabatic approximation of quantum mechanics and the near Hartree-Fock are introduced. Yes, then the Hohenberg-Kohn theory, the Kohn-Sham equation, the exchange of the related energy functional and the common software package for computing. In the last part, we have made a specific introduction to the method of calculating the electrode of the Berry Phase theory. The second chapter introduces the electrical properties and magnetism of the new two-dimensional structure Fe2Si. In this work, the first character is based on the first nature. Principle calculation and molecular dynamics simulation (AIMD), we constructed the Fe2Si material of graphene like structure. The results show that the single layer Fe2Si crystal is ferromagnetic semi metal, and the structure can be stable at high temperature of up to 1200K. It has about 780K Curie temperature and considerable magnetic properties. These properties make the single layer Fe2Si in spin electricity. The third chapter mainly uses the hybrid functional HSE06 to calculate the electronic structure and magnetic properties of the single layer NbS2. Unlike the results of the PBE functional calculation, the calculation of HSE06 shows that the single layer NbS2 is a narrow band gap bipolar magnetic semiconductor, and the different types of carrier doping and application are studied. Changes in the properties of electronic structures. In the fourth chapter, the basic electronic properties and structural stability of the monolayer CrOX stripped from the CrOX (X=Cl, Br) body phase structure are simply calculated. The fifth chapter mainly calculates the one-dimensional metal organic frame structure metal -1,2,4,5 benzene four amine and the molecular nanowires of 1,2,4,5 phenol. The first principle is used. The stability of these nanowires and the properties of the electronic structure are studied. The results show that the structure of these nanowires is stable and the properties of semiconductors. In addition, we also analyze the effect of carrier doping on the electronic structure. In the sixth chapter, the ferroelectric polarization of the metal formate frame [NH4][M (HCOO) 3][M=Sc-Zn] is studied. First, based on the calculation of the first principle, we have analyzed the cause of the [NH4][Zn (HCOO) 3] ferroelectric phenomenon and the change of the electrode value and total energy during the phase to ferroelectric phase transition. Then, the ferroelectric polarization and the properties of the electronic structure and the magnetic properties of each structure are calculated and analyzed, except for the [NH4][Z. Besides n (HCOO) 3], other structures are materials with both magnetic and ferroelectric properties.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O641.4;TB383.1

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