多铁性隧道结磁电输运的轨道效应

发布时间：2019-03-05 18:51

【摘要】：随着信息数据膨胀的加速发展,传统的只利用电子电荷属性的电子器件已经无法满足人们对元器件微型化、集成化等方面的迫切需求。因此,同时利用电子的电荷和自旋自由度来作为信息储存和传输载体的新兴学科——自旋电子学得到了科研工作者的广泛关注,其中基于巨磁阻效应(GMR)或隧穿磁电阻效应(TMR)的自旋电子学读头已经在信息存储方面取得了非常成功的应用。然而,这类元件数据的写入仍然需要通过外加磁场来实现。考虑到磁场作用范围的非局域化特点和产生磁场所需的高能耗的缺点,寻找超低能耗、精确局域化的非磁场有效控制就成为自旋电子学亟待研究解决的重要课题。多铁性材料,由于其中电性和磁性的共存并且相互耦合,为利用非磁场的方式控制磁性提供了物理可能。此外,考虑多铁性材料表界面处磁序非平庸的空间几何分布,我们可以获得额外的拓扑性自旋轨道相互作用;同时由于在两种材料界面处约束势阱空间反射对称性的破缺还会存在Rashba自旋轨道耦合,进而通过对轨道角动量的调制,我们也可以实现对材料磁性的非磁场控制。在本论文中,我们从理论上系统地研究了电场可调控的自旋轨道耦合(Rashba自旋轨道耦合和材料的磁拓扑性质诱导的自旋轨道耦合)对存在磁电相互作用的多铁性隧道结中输运性质的影响,并进一步讨论了输运性质关联的多种物理效应:如自旋霍尔效应,反常霍尔效应以及自旋弛豫之间的相互影响和调制。这些研究结果为未来基于自旋非磁调控的新型微纳自旋电子学器件的研发提供了必要的理论支持和现实的指导价值。在第一章我们回顾了多铁性系统的理论和实验方面的最新研究进展并且阐明了研究多铁性隧道结中磁电输运性质的重要意义以及优势所在。第二章我们分别从唯象角度和微观理论方面研究了界面处Rashba自旋轨道耦合和拓扑性自旋轨道耦合对多铁性隧道结中隧穿各向异性磁电阻效应的影响。由于这两项自旋轨道耦合的强度可以通过外电场来调控,因此最终隧穿磁电阻的各向异性大小是电场可控的。此外,磁电阻各向异性的幅度与之前已有结果相比也明显提高一个量级,这项研究对于未来生产多态数据存储器件提供了必要的理论指导。紧接着我们在第三章探讨了多铁性隧道结中的Seebeck和spin Seebeck效应。发现自旋轨道耦合的存在使得系统的热电系数表现出磁化方向依赖的各向异性,并且通过进一步计算可以得出系统具有比较高的品质因子(1),因此该结构有望被应用于生产高效率的热电和热自旋器件中。考虑到铁电/铁磁异质结界面处可能的磁电相互作用,在第四章我们研究了磁电效应对正常金属/铁电/铁磁隧道结的铁磁层中磁性耗散的影响。发现自旋轨道耦合的存在导致Gillbert阻尼呈现出C2v二重对称性,并且在铁电极化方向发生翻转时,Gillbert阻尼值的大小也会发生改变。第五章我们在不考虑任何杂质效应的前提下,分别研究了两种不同多铁性隧道结中内禀的自旋轨道耦合对隧穿自旋霍尔效应和反常霍尔效应的影响。最后一章我们对所有研究内容进行了总结并对下一步工作作出了展望。
[Abstract]:With the rapid development of the expansion of the information data, the traditional electronic device using the electronic charge property has not been able to meet the urgent need of the miniaturization and integration of the components. Therefore, at the same time, the electronic charge and the spin degree of freedom are used as the subject _ spin electronics of the information storage and transmission carrier to be widely concerned by the scientific research workers, In which a spin-electronics read head based on a giant magnetoresistive effect (gmr) or a tunneling magnetoresistance effect (tmr) has made a very successful application in information storage. However, writing of such element data still needs to be achieved by the addition of a magnetic field. In view of the non-localized characteristics of the magnetic field and the disadvantage of the high energy consumption required to generate the magnetic field, it is an important task to find the ultra-low energy consumption and the accurate localization of the non-magnetic field effective control. The multiferroic material is physically possible to control the magnetic properties in a non-magnetic field due to the coexistence and mutual coupling of electrical and magnetic properties. in addition, taking into account that non-ordinary spatial geometric distribution of the magnetic sequence at the interface of the multi-layer material, we can obtain additional topological spin-orbit interaction; at the same time, the Rashba spin-orbit coupling can exist due to the defect that the space reflection symmetry of the potential well is constrained at the interface of the two materials, Furthermore, by the modulation of the orbital angular momentum, we can also realize the non-magnetic field control of the magnetic properties of the material. In this paper, we have systematically studied the effect of the electric field-controlled spin-orbit coupling (spin-orbit coupling induced by the magnetic topological properties of the Rashba spin-track coupling and the material) on the transport properties of the multi-layer tunnel junction in which the magnetoelectric interaction exists, And further discusses the various physical effects associated with the transport properties, such as spin hall effect, abnormal hall effect and the interaction and modulation between spin relaxation. The results of these studies provide the necessary theoretical support and practical guidance value for the development of a new micro-nano-spin electronic device based on spin-non-magnetic control. In the first chapter, we review the latest research progress in the theory and experiment of the multi-channel system, and clarify the important significance and the advantage of the study of the magnetoelectric transport property in the multi-channel tunnel junction. In the second chapter, we study the effect of the Rashba spin-orbit coupling and the topological spin-orbit coupling on the tunneling anisotropic magnetoresistance effect in the multi-tunnel junction from the phenomenological angle and the micro-theory. Since the strength of the two spin-orbit coupling can be regulated by the external electric field, the anisotropic size of the final tunneling magnetic resistance is controllable by the electric field. In addition, the amplitude of the anisotropy of the magnetic resistance is obviously improved by a magnitude as compared with the prior art, which provides the necessary theoretical guidance for future production of the multi-state data memory device. Then we discussed the Seebeck and the spin Seebeck effect in the multi-tunnel junction in the third chapter. the presence of a spin-orbit coupling is found such that the thermoelectric coefficients of the system exhibit the anisotropy of the magnetization direction dependence and, by further calculation, the system has a relatively high quality factor (1), The structure is therefore expected to be applied to the production of high-efficiency thermoelectric and thermal spin devices. In the fourth chapter we study the effect of magnetoelectric effect on the magnetic dissipation in the ferromagnetic layer of the normal metal/ ferroelectric/ ferromagnetic tunnel junction, taking into account the possible magnetoelectric interaction at the ferroelectric/ ferromagnetic heterojunction interface. It was found that the presence of the spin-orbit coupling resulted in the Gillbert damping exhibiting a C2v double symmetry and the magnitude of the Gillbert damping value also changed when the direction of the ferroelectric polarization was reversed. In the fifth chapter, we studied the effect of the spin-orbit coupling on the tunneling spin-Hall effect and the abnormal Hall effect on the premise of not considering any impurity effect. In the last chapter, we sum up all the research contents and look forward to the next work.
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O469

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