Recent spinterfacial studies targeted to spin manipulation in molecular spintronic devices

Molecular spintronics is an emerging field which evoked wide research attention since the first molecule-based spintronic device has been reported at 2002. Due to the active study over the last few years, it is found that the interfaces in spintronic device, so called spinterface, is of critical importance for many key issues in molecular spintronics, such as enhancing spin injection, lengthening spin transport distance, as well as manipulating spin signals in molecular spintronic devices. Here in this review, recent studies regarding spinterface in molecular devices, especially those impressive efforts devoted on spin manipulation, have been systematically summarized and discussed.     

Large tunable Rashba spin splitting of a two-dimensional electron gas in Bi2Se3

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi(2)Se(3) from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.     

Ga vacancy induced ferromagnetism enhancement and electronic structures of RE-doped GaN

Because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors (DMSs) doped by rare-earth (RE) elements have attracted much attention since the high Curie temperature was obtained in RE-doped GaN DMSs and a colossal magnetic moment was observed in the Gd-doped GaN thin film. We have systemically studied the GaN DMSs doped by RE elements (La, Ce–Yb) using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. We have studied the electronic structures of DMSs, especially for the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. We found that, for materials containing f electrons, electronic correlation was usually strong and the spin–orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm are stabilized at antiferromagnetic phase, while GaN doped by other RE elements show strong ferromagnetism which is suitable materials for spintronic devices. Moreover, we have identified that the observed large enhancement of magnetic moment in GaN is mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the RE doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of RE-doped semiconductors in the third generation high efficiency photovoltaic devices.     

Co和Mn共掺杂ZnO铁磁性的第一性原理

基于密度泛函理论(DFT)的总体能量平面波超软赝势方法,结合广义梯度近似(GGA),对Co单独掺杂ZnO和(Co,Mn)共掺杂ZnO的32原子超原胞体系进行了几何结构优化,计算了纤锌矿结构ZnO、Co-ZnO及(Co,Mn)共掺杂ZnO的能带结构、电子态密度,并对此进行了详细的分析。计算结果表明,ZnO中单独掺杂Co元素显示出铁磁性行为,Mn的引入减弱了Co-ZnO的铁磁性。     

Proposal for a new class of materials: spin gapless semiconductors

The concept of the spin gapless semiconductor in which both electron and hole can be fully spin polarized is proposed, and its possibility is presented on the basis of first-principles electronic structure calculations. Possible new physics and potential applications in spintronic devices based on the spin gapless semiconductors are discussed.     

磁电子学器件应用原理

本文介绍几种重要的磁电子器件的基本结构和工作原理,包括巨磁电阻与隧穿磁电阻传感器、巨磁电阻隔离器、巨磁电阻与隧穿磁电阻硬盘读出磁头、磁电阻随机存取存储器、自旋转移磁化反转与微波振荡器。自旋晶体管作为未来磁电子学或自旋电子学时代的基本元素,目前大都还处在概念型阶段,本文也将对几种自旋晶体管的大致原理作简要介绍。     

石墨烯纳米片大自旋特性第一性原理研究

通过基于密度泛函理论的全电子数值轨道第一性原理电子结构计算,研究了各种形状有限石墨烯片段(石墨烯纳米片, GNF)的磁特性,证明GNF的自旋磁有序来源于由其形状决定的π键拓扑挫折(topological frustration)作用.锯齿形边缘的三角形GNF的净自旋不为零,如同一个人造铁磁性原子团,总自旋随尺度线性增加.根据拓扑挫折原理,可以在GNF中引入较大的净自旋和独特的自旋分布,如由三角形GNF单元构成的复杂分形结构,总自旋随分形级数呈指数上升.通过刻蚀技术制作具有一定拓扑结构的GNF可以实现可控自旋电子纳米材料和器件应用.     

Recent progress in perpendicularly magnetized Mn-based binary alloy films

In this article, we review the recent progress in growth, structural characterizations, magnetic properties, and related spintronic devices of tetragonal MnxGa and MnxA1 thin films with perpendicular magnetic anisotropy. First, we present a brief introduction to the demands for perpendicularly magnetized materials in spintronics, magnetic recording, and perma- nent magnets applications, and the most promising candidates of tetragonal MnxGa and MnxA1 with strong perpendicular magnetic anisotropy. Then, we focus on the recent progress of perpendicularly magnetized MnxGa and MnxA1 respec- tively, including their lattice structures, bulk synthesis, epitaxial growth, structural characterizations, magnetic and other spin-dependent properties, and spintronic devices like magnetic tunneling junctions, spin valves, and spin injectors into semiconductors. Finally, we give a summary and a perspective of these perpendicularly magnetized Mn-based binary alloy films for future applications.     

Magnetic two-dimensional van der Waals materials forspintronic devices

Magnetic two-dimensional (2D) van der Waals (vdWs) materials and their heterostructures attract increasing attention in the spintronics community due to their various degrees of freedom such as spin, charge, and energy valley, which may stimulate potential applications in the field of low-power and high-speed spintronic devices in the future. This review begins with introducing the long-range magnetic order in 2D vdWs materials and the recent progress of tunning their properties by electrostatic doping and stress. Next, the proximity-effect, current-induced magnetization switching, and the related spintronic devices (such as magnetic tunnel junctions and spin valves) based on magnetic 2D vdWs materials are presented. Finally, the development trend of magnetic 2D vdWs materials is discussed. This review provides comprehensive understandings for the development of novel spintronic applications based on magnetic 2D vdWs materials.     

Magnetism in transition-metal-doped silicon nanotubes

Using first-principles density functional calculations, we show that hexagonal metallic silicon nanotubes can be stabilized by doping with 3d transition metal atoms. Finite nanotubes doped with Fe and Mn have high local magnetic moments, whereas Co-doped nanotubes have low values and Ni-doped nanotubes are mostly nonmagnetic. The infinite Si24Fe4 nanotube is found to be ferromagnetic with nearly the same local magnetic moment on each Fe atom as in bulk iron. Mn-doped nanotubes are antiferromagnetic, but a ferrromagnetic state lies only 0.03 eV higher in energy with a gap in the majority spin bands near the Fermi energy. These materials are interesting for silicon-based spintronic devices and other nanoscale magnetic applications.     

MoSi2薄膜电子性质的第一性原理研究

采用第一性原理计算方法, 研究了四方MoSi₂薄膜的电子性质. 计算结果表明, 各种厚度的薄膜都是金属性的, 并且随着厚度的增加, 其态密度与能带结构都逐渐趋近于MoSi₂块体的特性. 通过对MoSi₂薄膜磁性的分析, 发现三个原子层厚的薄膜具有磁性, 其原胞净磁矩为0.33 μ_B; 而当薄膜的厚度大于三个原子层时, 薄膜不具有磁性. 此外, 进一步对单侧加氢饱和以及双侧加氢饱和结构下三原子层MoSi₂薄膜的电子性质进行了研究, 发现单侧加氢饱和的三原子层MoSi₂薄膜具有磁性, 其原胞净磁矩为0.26 μ_B, 而双侧加氢饱和三原子层MoSi₂薄膜是非磁性的. 双侧未饱和与单侧加氢饱和的三原子层MoSi₂薄膜的自旋极化率分别为30%和33%. 这些研究结果表明, 三原子层厚的MoSi₂ 超薄薄膜在悬空或者生长于基底之上时具有金属磁性, 预示着它在纳米电子学和自旋电子学器件等方面都有潜在的应用前景.     

纳米管中的自旋极化

结构缺陷、掺杂等可以导致纳米管的自旋极化，而自旋极化的纳米管可以利用载流子的自旋状态作为信息载体，实现一维的自旋电子传输。具有不同自旋极化结构的纳米管，根据其电子结构、自旋极化性质和输运性质的不同，可以用于实现不同用途的自旋电子器件。很多有关自旋极化的纳米管的理论和实验工作已经展开，然而其中仍有很多物理问题有待深入研究。     

微纳尺度多铁异质结中电驱动磁反转

近年来,多铁异质结中电控磁性研究引起了广泛关注,已成为多铁领域的热点.现代自旋电子学器件(如磁内存)通常利用电流产生的磁场或自旋转移扭矩效应驱动磁反转来实现数据擦写,但这带来高额能耗和热量,成为亟待解决的关键难题.而利用多铁异质结实施电场驱动磁反转则有望大幅降低能耗,从而实现高速、低能耗、高稳定性新型高密度磁存储、逻辑及其他自旋电子学器件.在当前器件发展的微型化趋势下,探索可集成化的微纳尺度电场驱动磁反转方案显得越发重要.本文针对发展新型磁电器件所面临的微型化关键问题,回顾了微纳尺度电场驱动磁反转研究的新进展,主要关注小尺度多铁异质结中电控磁的新特点、新方法及相关物理机理的实验和理论成果,讨论了进入纳米尺度将面临的挑战,并对未来研究工作提出一些展望.     

锰氧化物相竞争的理论研究

锰氧化物属于典型的强关联电子材料,具有包括庞磁电阻、电荷/轨道有序、电子相分离、多铁性等奇特的物理特性。这些现象涉及一系列凝聚态物理学基本问题,是近年来研究者一直关注的热点和难点。并且这些奇异的电磁性质也为开发量子调控器件提供了基本素材。虽然近20年来对锰氧化物的研究取得了丰硕成果,全世界的研究者仍在为理解并应用其特性作着孜孜不倦的努力。本综述将主要从理论角度,重点关注钙钛矿结构锰氧化物中多种相竞争和调制。由于有着多种竞争相互作用和多重量子自由度,锰氧化物有着丰富的相,这些相物理特性迥异,而自由能却可能相当接近。因此,自发或人为调制导致的相竞争是锰氧化物研究的一个核心问题,也是整个强关联物理领域中一个很有意义的课题。本综述将以电致电阻、多铁性和异质结界面处电子重组这三个具体实例,介绍如何采用蒙特卡罗模拟等方法研究其中的相竞争和调制。     

Half-metallic exchange bias ferromagnetic/antiferromagnetic interfaces in transition-metal chalcogenides

To investigate half-metallic exchange bias interfaces, magnetic structures at ferromagnetic (FM)/antiferromagnetic (AFM) interfaces in the zinc blende transition-metal chalcogenides, and with compensated and uncompensated AFM interfaces, were determined by the full-potential linearized augmented plane-wave method. With the uncompensated AFM interface, an antiparallel alignment of the Cr and Mn moments induces an excellent half-metallicity. More striking still, in the compensated AFM interface the Cr moments in the FM layer lie perpendicular to the Mn moments in the AFM layer but the Mn moments strongly cant to induce a net moment so as to retain the half-metallicity. These findings may offer a key ingredient for exchange biased spintronic devices with 100% spin polarization, having a unidirectional anisotropy to control and manipulate spins at the nanoscale.     

Recent developments in CVD growth and applications of 2D transition metal dichalcogenides

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with fascinating electronic energy band structures, rich valley physical properties and strong spin–orbit coupling have attracted tremendous interest, and show great potential in electronic, optoelectronic, spintronic and valleytronic fields. Stacking 2D TMDs have provided unprecedented opportunities for constructing artificial functional structures. Due to the low cost, high yield and industrial compatibility, chemical vapor deposition (CVD) is regarded as one of the most promising growth strategies to obtain high-quality and large-area 2D TMDs and heterostructures. Here, state-of-the-art strategies for preparing TMDs details of growth control and related heterostructures construction via CVD method are reviewed and discussed, including wafer-scale synthesis, phase transition, doping, alloy and stacking engineering. Meanwhile, recent progress on the application of multi-functional devices is highlighted based on 2D TMDs. Finally, challenges and prospects are proposed for the practical device applications of 2D TMDs.     

稀土掺杂锰氧化物庞磁电阻效应

过去十多年来,具有庞磁电阻效应的稀土掺杂锰氧化物成为了凝聚态物理研究的重要领域。锰氧化物的载流子自旋极化率高,且在居里温度附近表现出很大的磁电阻效应,因此在自旋电子学中有潜在的应用前景。另一方面,锰氧化物是典型的强关联电子体系,它对目前有关强关联体系的认识提出了很大挑战。本文综述了锰氧化物的各种性质及其物理原因。全文首先概述了锰氧化物的庞磁电阻效应及其晶格和电子结构,简单介绍了其他一些庞磁电阻材料;随后综述了锰氧化物的电荷/轨道有序相及其输运性质;在第四部分简单介绍了锰氧化物中庞磁电阻效应的机制;最后讨论了锰氧化物的一些可能的应用,如低场磁电阻效应、磁隧道结、磁p＿n结以及全钙钛矿的场效应管和自旋极化电子注入装置等。     

Modulation of the electronic states of perovskite SrCrO3 thin films through protonation via low-energy hydrogen plasma implantation approaches

Hydrogenation of transition metal oxides offers a powerful platform to tailor physical functionalities as well as for potential applications in modern electronic technologies.An ideal nondestructive and efficient hydrogen incorporation approach is important for the realistic technological applications.We demonstrate the proton injection on SrCro3 thin films via an efficient low-energy hydrogen plasma implantation experiments,without destroying the original lattice framework.Hydrogen ions accumu-late largely at the interfacial regions with amorphous character which extend about one-third of the total thickness.The Hx.SrCro3(HSCO)thin films appear like exfoliated layers which however retain the fully strained state with distorted perovskite structure.Proton doping induces the change of Cr oxidation state from Cr^4+to Cr^3+in HSCO thin films and a transition from metallic to insulat-ing phase.Our investigations suggest an attractive platform in manipulating the electronic phases in proton-based approaches and may offer a potential peeling off strategy for nanoscale devices through low-energy hydrogen plasma implantation approaches.     

稀土掺杂锰氧化物庞磁电阻效应

过去十多年来，具有庞磁电阻效应的稀土掺杂锰氧化物成为了凝聚态物理研究的重要领域。锰氧化物的载流子自旋极化率高，且在居里温度附近表现出很大的磁电阻效应，因此在自旋电子学中有潜在的应用前景。另一方面，锰氧化物是典型的强关联电子体系，它对目前有关强关联体系的认识提出了很大挑战。本文综述了锰氧化物的各种性质及其物理原因。全文首先概述了锰氧化物的庞磁电阻效应及其晶格和电子结构，简单介绍了其他一些庞磁电阻材料；随后综述了锰氧化物的电荷／轨道有序相及其输运性质；在第四部分简单介绍了锰氧化物中庞磁电阻效应的机制；最后讨论了锰氧化物的一些可能的应用，如低场磁电阻效应、磁隧道结、磁p-n结以及全钙钛矿的场效应管和自旋极化电子注入装置等。     

Coulomb interactions and nanoscale electronic inhomogeneities in manganites

We study electronic inhomogeneities in manganites using simulations on a microscopic model with Coulomb interactions amongst two electronic fluids-one localized (polaronic), the other extended-and dopant ions. The long range Coulomb interactions frustrate phase separation induced by the large on site repulsion between the fluids. A single phase ensues which is inhomogeneous at a nanoscale, but homogeneous on mesoscales, with many features that agree with experiments. This, we argue, is the origin of nanoscale inhomogeneities in manganites, rather than phase competition or disorder effects.