低维材料的磁性和磁晶各向异性的第一性原理研究

发布时间：2018-04-30 15:10

本文选题：低维材料 + 替代掺杂　；参考：《吉林大学》2017年博士论文

【摘要】：目前,以石墨烯和MoS_2为代表的二维晶体材料由于其本身独特的优异性能和潜在的应用价值引起了广泛的关注,尝试用二维半导体材料作为自旋电子学材料的研究,近几年来获得高度重视和发展。另外,二维铁磁性材料可以看成是具有原子厚度的铁磁性薄膜,将具有大的磁晶各向异性的二维铁磁性材料用作磁记录介质将会有助于提高磁记录的存储密度。单层Cr S_2和单层Be_2C都是直接带隙半导体材料,具有良好的稳定性,可以作为制备纳米自旋电子器件的材料。单层Cr S_2和单层Be_2C是内禀非磁性的,为使它们有效地应用于纳米自旋电子器件,需要在其中引入可调控的磁性。有关研究发现,替代掺杂、施加应力以及裁剪纳米带等方法可以在二维材料中有效地引入磁性。另外,单层TaTe_2具有内秉铁磁性。更重要的是,Ta具有较强的自旋轨道耦合效应,这使得单层TaTe_2可能具有大的磁晶各向异性。本论文采用基于密度泛函理论的第一性原理分别计算研究了过渡金属元素和碱土金属元素的替代掺杂对单层Cr S_2的电子结构和磁学性质的影响,Be_2C纳米带的电子结构和磁学性质,单层TaTe_2的磁晶各向异性以及应变对单层TaTe_2磁晶各向异性的调控,阐明了其中的物理机制。本论文主要工作如下:1.系统研究了3d、4d过渡金属元素和碱土金属元素替代Cr掺杂对单层Cr S_2的电子结构和磁学性质的影响。这些元素包括Ca、Sc、Ti、V、Mn、Fe、Co、Ni、Cu、Zn、Ga、Sr、Y、Zr、Nb、Mo、Ru、Rh、Pd、Ag、Cd和In。结果表明,在富S的生长条件下更容易实现过渡金属和碱土金属原子对单层Cr S_2中Cr原子的替代掺杂。Nb、Mo、Ru和Rh掺杂不能在单层Cr S_2引入磁性,而Ca、Sc、Ti、V、Mn、Fe、Co、Ni、Cu、Zn、Ga、Sr、Y、Zr、Pd、Ag、Cd和In原子掺杂的单层Cr S_2的基态是磁性态。其中,V掺杂单层Cr S_2很容易被热激发到自旋非极化态。此外,计算显示掺杂系统的磁矩大小和磁矩分布不仅与掺杂原子的价电子数和d轨道占据数有关,而且与掺杂原子和它周围原子的杂化有关。2.系统研究了Be_2C纳米带的几何结构、稳定性、电子结构和磁学性质。研究的Be_2C纳米带包括N-b-Be_2C-NR-Be、N-a-Be_2C-NR、N-b-Be_2C-NR-Be-Be和N-b-Be_2C-NR-C。其中,N-b-Be_2C-NR-Be、N-a-Be_2C-NR和N-b-Be_2C-NR-Be-Be在室温下是热力学稳定的,并且有可能在实验上制备。氢化能够减少纳米带N-b-Be_2C-NR-C边界的C悬键,从而极大地提高N-b-Be_2C-NR-C的稳定性,计算表明N-b-Be_2C-NR-C-H在室温下也是热力学稳定的。纳米带N-b-Be_2C-NR-Be、N-a-Be_2C-NR和N-b-Be_2C-NR-Be-Be都是直接带隙的非磁性半导体,带隙值与边界结构和纳米带宽度密切相关。氢化的纳米带N-b-Be_2C-NR-C-H是半金属并且呈现铁磁性。N-b-Be_2C-NR-C-H具有较强的同一边界内的铁磁耦合相互作用,窄的纳米带5-b-Be_2C-NR-C-H具有边界间的铁磁相互作用。计算的态密度和自旋密度分布显示,N-b-Be_2C-NR-C-H在同一边界内和两边界间的铁磁耦合与极化电子的p-p杂化相互作用有关。3.系统研究了在-2%到8%的应变作用下单层TaTe_2的电子结构和磁学性质,特别是磁晶各向异性。结果显示单层TaTe_2是铁磁性金属,磁矩主要由Ta原子贡献。此外,无应变时单层TaTe_2的单胞磁晶各向异性能高达-4.72 me V。应变能够极大地增强单层TaTe_2的磁矩、Ta原子之间的铁磁耦合相互作用以及磁晶各向异性能。特别地,与无应变时相比,8%的拉伸应变能够使单层TaTe_2的磁晶各向异性能增加165%。通过分析态密度和Ta原子d轨道间的自旋轨道耦合相互作用对磁晶各向异性能的贡献,我们发现:单层TaTe_2大的面内磁晶各向异性能主要由Ta原子自旋相反的dxy和dx2-y2轨道间的自旋轨道耦合相互作用所贡献,并且在应变作用下这一贡献显著地增加,这就是应变能够提高单层TaTe_2磁晶各向异性能的主要原因。
[Abstract]:At present, two dimensional crystal materials, such as graphene and MoS_2, have attracted wide attention due to their unique excellent properties and potential application value. The study of two dimensional semiconductor materials as spintronics materials has been paid great attention and developed in recent years. Ferromagnetic thin films with atomic thickness, which will have large magnetocrystalline anisotropic two-dimensional ferromagnetic materials as magnetic recording medium, will help to improve the storage density of magnetic recording. Single layer Cr S_2 and single layer Be_2C are direct bandgap semiconductors, with good stability and can be used as materials for preparation of nano spintronic devices. Single layer C R S_2 and single layer Be_2C are intrinsic nonmagnetic. In order to effectively apply them to nano spintronic devices, it is necessary to introduce controllable magnetic properties in them. The study found that substitution, applied stress and trimming of nanometers can effectively induce magnetic properties in two-dimensional materials. In addition, the monolayer TaTe_2 has internal ferromagnetism. More importantly, Ta has a strong spin orbit coupling effect, which makes the monolayer TaTe_2 possibly have a large magnetocrystalline anisotropy. This paper uses the first principle based on the density functional theory to calculate the electronic structure and magnetic properties of the transition metal and alkaline earth metal elements to the single layer Cr S_2. The electronic structure and magnetic properties of Be_2C nanoribbons, the magnetocrystalline anisotropy of single layer TaTe_2 and the regulation of strain on the single TaTe_2 magnetocrystalline anisotropy are clarified. The main work of this thesis is as follows: 1. the 3D, 4D transition metal element and alkaline earth metal element instead of Cr doped to the single layer Cr S_2 have been studied in this paper. These elements, including Ca, Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, show that the transition metal and alkaline earth atoms are more likely to be substituted for the substitution of the transition metal and alkaline earth atoms on the monolayer. Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Y, and atoms are magnetically excited to the spin non polarizing state. Furthermore, the calculation shows that the magnetic moment and magnetic moment distribution of the doping system are not only related to the valence electrons and the occupancy of the orbital atoms of the doped atom, but also The.2. system studies the geometric structure, stability, electronic structure and magnetic properties of the Be_2C nanoribbons. The Be_2C nanbands of the study include N-b-Be_2C-NR-Be, N-a-Be_2C-NR, N-b-Be_2C-NR-Be-Be and N-b-Be_2C-NR-C., and N-b-Be_2C-NR-Be, N-a-Be_2C-NR and N-b-Be_2C-NR-Be-Be are at room temperature. It is thermodynamic stable and may be prepared experimentally. Hydrogenation can reduce the C suspension bond of the nanband N-b-Be_2C-NR-C boundary, thus greatly improving the stability of N-b-Be_2C-NR-C. The calculation shows that N-b-Be_2C-NR-C-H is also thermodynamically stable at room temperature. The nano band N-b-Be_2C-NR-Be, N-a-Be_2C-NR and N-b-Be_2C-NR-Be-Be are both direct bands. Nonmagnetic semiconductors with gap, the band gap is closely related to the boundary structure and the width of the nanoscale band. The hydrogenated nanoscale N-b-Be_2C-NR-C-H is semi metal and ferromagnetic.N-b-Be_2C-NR-C-H has a strong ferromagnetic coupling interaction within the same boundary, and the narrow nanoscale 5-b-Be_2C-NR-C-H has the ferromagnetic interaction between the boundary. The distribution of state density and spin density shows that the ferromagnetic coupling between N-b-Be_2C-NR-C-H in the same boundary and between the two sides of the.3. system is related to the P-P hybrid interaction of the polarized electrons. The.3. system has studied the electronic structure and magnetic properties of the monolayer TaTe_2 under the strain of -2% to 8%, especially the magnetocrystalline anisotropy. The results show that the monolayer TaTe_2 is ferromagnetic. In addition, the single cell magnetocrystalline anisotropy of a single layer of TaTe_2 in the absence of strain is up to -4.72 me V. strain, which can greatly enhance the magnetic moment of the single layer TaTe_2, the ferromagnetic coupling interaction between the Ta atoms and the magnetocrystalline anisotropy. In particular, the tensile strain of 8% can make the single strain of the single strain 8% The magnetocrystalline anisotropy of the layer TaTe_2 increases the contribution of 165%. to the magnetocrystalline anisotropy by the analysis of the density of States and the spin orbit coupling interaction between the Ta atom D orbits. We find that the magnetocrystalline anisotropy of the single layer TaTe_2 is mainly composed of the spin orbit coupling interaction between the Ta atoms spin opposite DXY and the dx2-y2 orbit. The contribution and contribution of strain increase significantly. This is the main reason why strain can enhance the anisotropy of single crystal TaTe_2.

【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O469

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