CrTe的半金属性和CrTe/ZnTe异质结的自旋二极管效应研究

基于密度泛函理论的第一性原理方法,对闪锌矿结构CrTe和CrTe/ZnTe(001)异质结的电子结构和自旋极化输运性质进行了计算研究。结果表明,CrTe是一种很好的半金属铁磁体,具有4.00μB/分子的磁矩和很大的半金属隙(0.84eV)。计算得到的电流-电压曲线显示CrTe/ZnTe(001)异质结具有优良的自旋二极管效应,因此,CrTe在自旋电子器件中应该有一定的应用。并从能带理论角度解释了CrTe/ZnTe(001)异质结中产生自旋二极管效应的机理。     

半导体自旋电子学的最新研究进展

自旋电子学起源于巨磁阻效应(GMR),目前已经成为凝聚态物理学领域的研究热点,其中半导体自旋电子学是自旋电子学中人们所关注的一个重要领域。从磁性半导体、自旋电子的注入、检测、输运等方面综述半导体自旋电子学的最新研究进展,并且指出目前半导体自旋电子学研究的重点及难点。     

自旋在有机半导体中的输运

当前的微电子器件主要是通过控制半导体中载流子的电荷来存储、处理和传输信息,电子的自旋自由度长期在这些应用中被忽略。自旋电子学主要是研究与载流子的自旋相关的各种现象和效应,为在微电子器件中集成这些自旋效应,产生各种更新更强的功能的自旋器件奠定基础。有机半导体材料由于自旋轨道作用和超精细作用很弱,自旋扩散长度被认为很长,因而是一种具有很强应用潜力的自旋电子材料。最近,我们研究组首次成功的在低温下,以有机材料Alq_3作为中间层,La_(2/3)Sr_(1/3)MnO_3(LSMO)和Co分别作为两个电极的三明治结构中,低温下获得了高达40%的巨磁电阻效应。磁电阻随有机材料厚度的增加指数衰减,根据修正后的Jullierre模型,自旋扩散长度估计为约45nm。另外,巨磁电阻效应随温度的升高而降低,在温度较高时,样品除了有巨磁电阻效应之外,还明显表现出一种物理机理完全不同的高场磁电阻效应,电阻随磁场的增加而持续降低。为了进一步研究这种高场磁电阻效应的物理机理,我们制备了仅有一个铁磁性电极的有机发光二极管LSMO/有机/Al器件,实验结果表明高场磁阻效应与有机材料和制备方法无关,同时,发光器件的电致发光效应随磁场的增大而...     

(Ga,Mn)As磁电输运性质的研究进展

综述了Ⅲ-Ⅴ族稀磁半导体(Ga,Mn)As磁电性质的研究进展,尤其是(Ga,Mn)As单层膜和多层膜结构的磁电输运性质的详细研究状况。关于(Ga,Mn)As的结构与物理性质的信息可由单层膜的反常霍尔效应、平面霍尔效应、电阻对温度的依赖关系与磁阻各向异性等磁电输运性质测量得到;而多层膜中观察到的自旋阀效应、自旋相关散射与层间交互耦合等现象,对加深稀磁半导体的基本物性认识、拓展稀磁半导体的实际应用空间非常重要。最后总结并展望了(Ga,Mn)As未来的发展趋势。     

界面自旋翻转对有限尺寸的铁磁体/非磁性半导体/铁磁体体系自旋注入的影响(英文)

本文考虑了界面自旋翻转效应后对有限尺寸的铁磁体/非磁性半导体/铁磁体异质结中的自旋注入问题进行了系统的理论探讨.由于自旋在两种介质界面上发生的翻转散射,自旋极化流的每一个分量在界面上都不可能连续.计算结果表明,当自旋注入效率从0增加到100%的过程中,铁磁体/非磁性半导体/铁磁体异质结的隧穿磁阻增大了两个数量级.这一事实证明界面的自旋翻转效应直接影响着铁磁体/非磁性半导体/铁磁体异质结的隧穿磁阻.     

自旋电子学的研究现状

自旋电子学主要研究电子自旋在固体物理中的作用,是一门结合磁学与微电子学的新兴交叉学科。本文简单介绍了自旋电子学的概念及其内容,综述了自旋电子学目前的研究,尤其是半导体自旋电子学。最后对自旋电子器件的应用进行了展望。     

应重视自旋电子学及其器件的产业化

法国的AlbertFert教授与德国的Peter Grtinberg因在纳米多层膜的磁性结构中发现巨磁电阻效应(GMR)而荣获2007年度的诺贝尔物理学奖,电子具有电荷与自旋2个自由度,在传统的电子学中,仅仅是电荷被电场调控,称之为电荷为基的电子学,而GMR效应的发现开拓了有效地控制自旋制备新颖电子器件的基础,自旋电子学可定义为以自旋为基的电子学,其中自旋在器件中起着核心的作用。目前,自旋电子学效应已呈现出丰富多彩的重要的技术上的应用,自旋电子学是十分重要的具有战略意义的研究领域,列入发达国家重点支持的计划中。从物理学的观点来看,过去的世纪属于电荷的世纪,那么未来的世纪可能属于自旋的世纪。     

炭纤维增强轻质矿粉混凝土的热电行为

炭纤维增强混凝土能用来感知温度,其因在于短炭纤维的P-型传导性引起的塞贝克(Seebeck)效应所致.通过测量添加炭纤维或矿质掺和物(飞灰、硅土粉)前后六种波特兰水泥基混凝土的热电功率,研究了炭纤维增强轻质混凝土热敏的能力及其矿质掺合物对Seebeck效应的影响.结果表明: 炭纤维增强轻质混凝土具有类似于炭纤维增强标准混凝土的Seebeck效应,只是Seebeck系数因掺合了矿粉而减低.掺有矿粉的炭纤维增强轻质混凝土可用作建筑物的热传感器.     

自旋电子学功能材料

巨磁电阻效应的发现开拓了磁电子学的新领域,20世纪90年代,磁电子学得到迅速的发展,并在应用上取得显著的经济效益与巨大的社会效应,本世纪初,研究的重点已转移到半导体自旋电子学的新方向,并已取得重要的进展.本文将结合我们科研组的研究工作,概述从磁电子学到半导体自旋电子学材料的发展,重点介绍稀磁半导体材料研究的进展.     

磁性材料进展概览

简要地介绍了磁性材料的进展,同时对磁性材料的分类提出了除按磁滞回线分类外还可以按交叉效应进行分类的观点。调控自旋将成为新世纪重要的研究领域。     

Rashba Effect in Functional Spintronic Devices

Exploiting spin transport increases the functionality of electronic devices and enables such devices to overcome physical limitations related to speed and power. Utilizing the Rashba effect at the interface of heterostructures provides promising opportunities toward the development of high-performance devices because it enables electrical control of the spin information. Herein, the focus is mainly on progress related to the two most compelling devices that exploit the Rashba effect: spin transistors and spin–orbit torque devices. For spin field-effect transistors, the gate-voltage manipulation of the Rashba effect and subsequent control of the spin precession are discussed, including for all-electric spin field-effect transistors. For spin–orbit torque devices, recent theories and experiments on interface-generated spin current are discussed. The future directions of manipulating the Rashba effect to realize fully integrated spin logic and memory devices are also discussed.     

Spin Currents and Intrinsic Spin-Hall Effect in Low Dimensional Systems

We consider the spin-Hall effect in two-dimensional electron systems (2DES) with Rashba and Dresselhaus spin-orbit couplings (SO). We find nonzero diagonal spin conductivity provided that Dresselhaus coupling is finite. In addition we consider the influence of disorder on spin conductivities in these systems. By comparing with the exact diagonalization method the finite quasiparticle lifetime (Born) approximation we argue that the latter one seems to be sufficient to describe the case when spin-orbit coupling is stronger or comparable with disorder strength. Furthermore, in the framework of Landauer–Buttiker formalism we show that the transverse and diagonal spin conductivities in Rashba plus Dresselhaus SO systems are robust against disorder for finite size systems.     

Spin current,spin accumulation and spin Hall effect

Abstract

Nonlocal spin transport in nanostructured devices with ferromagnetic injector (F1) and detector (F2) electrodes connected to a normal conductor (N) is studied. We reveal how the spin transport depends on interface resistance, electrode resistance, spin polarization and spin diffusion length, and obtain the conditions for efficient spin injection, spin accumulation and spin current in the device. It is demonstrated that the spin Hall effect is caused by spin–orbit scattering in nonmagnetic conductors and gives rise to the conversion between spin and charge currents in a nonlocal device. A method of evaluating spin–orbit coupling in nonmagnetic metals is proposed.     

Excitation and Amplification of Spin Waves by Spin–Orbit Torque

The emerging field of nanomagnonics utilizes high‐frequency waves of magnetization—spin waves—for the transmission and processing of information on the nanoscale. The advent of spin‐transfer torque has spurred significant advances in nanomagnonics, by enabling highly efficient local spin wave generation in magnonic nanodevices. Furthermore, the recent emergence of spin‐orbitronics, which utilizes spin–orbit interaction as the source of spin torque, has provided a unique ability to exert spin torque over spatially extended areas of magnonic structures, enabling enhanced spin wave transmission. Here, it is experimentally demonstrated that these advances can be efficiently combined. The same spin–orbit torque mechanism is utilized for the generation of propagating spin waves, and for the long‐range enhancement of their propagation, in a single integrated nanomagnonic device. The demonstrated system exhibits a controllable directional asymmetry of spin wave emission, which is highly beneficial for applications in nonreciprocal magnonic logic and neuromorphic computing.     

Quantum Hall effect in the field-induced spin density wave states

The Hall conductance is investigated in the field-induced spin density wave phases of the quasi-one-dimensional system. The role of the order parameters in the quantization of the Hall effect is shown in the framework of the topological number of the wave functions in the momentum space. A possible mechanism of the sign changes of the Hall conductance observed in the experiments is proposed in this framework.     

Spin Wave Excitation,Detection, and Utilization in the Organic-Based Magnet,V(TCNE)x (TCNE = Tetracyanoethylene)

Spin waves, quantized as magnons, have low energy loss and magnetic damping, which are critical for devices based on spin-wave propagation needed for information processing devices. The organic-based magnet [V(TCNE)_x; TCNE = tetracyanoethylene; x ≈ 2] has shown an extremely low magnetic damping comparable to, for example, yttrium iron garnet (YIG). The excitation, detection, and utilization of coherent and non-coherent spin waves on various modes in V(TCNE)_x is demonstrated and show that the angular momentum carried by microwave-excited coherent spin waves in a V(TCNE)_x film can be transferred into an adjacent Pt layer via spin pumping and detected using the inverse spin Hall effect. The spin pumping efficiency can be tuned by choosing different excited spin wave modes in the V(TCNE)_x film. In addition, it is shown that non-coherent spin waves in a V(TCNE)_x film, excited thermally via the spin Seebeck effect, can also be used as spin pumping source that generates an electrical signal in Pt with a sign change in accordance with the magnetization switching of the V(TCNE)_x. Combining coherent and non-coherent spin wave detection, the spin pumping efficiency can be thermally controlled, and new insight is gained for the spintronic applications of spin wave modes in organic-based magnets.     

(La,Pr)2/3Sr1/3MnO3薄膜激光诱导电阻效应

研究了钙钛矿锰氧化物La2/3Sr1/3MnO3和Pr2/3Sr1/3MnO3单晶薄膜的激光诱导电阻变化特性.低温铁磁金属相,激光诱导使薄膜的电阻增大,而在顺磁绝缘相则电阻减小,同时薄膜的绝缘体-金属相变(IMT)转变温度Tp向低温方向移动.对于Pr2/3Sr1/3MnO3薄膜,当激光功率为22mW时,光致电阻相对变化的最大值约为9.6%.光诱导效应致使薄膜的电阻发生变化,并使其IMT的转变温度点向低温方向移动,主要是由于光子能激发eg向下电子的跃迁,改变体系自旋极化方向.     

Many-Body Spin Correlations in Nonlinear Optical Spectroscopy

We study the role of spin correlations in nonlinear absorption due to optical transitions from a deep impurity level to states above a Fermi sea. We demonstrate that the Hubbard repulsion between two electrons occupying the impurity state leads to a logarithmic divergence of the third-order nonlinear optical susceptibility ⁽³⁾ at the absorption threshold. This divergence is a manifestation of the Kondo physics in the nonlinear optical response of Fermi sea systems. Remarkably, the light-induced Kondo temperature, which governs the shape of the Kondo-absorption spectrum, can be tuned by varying the intensity and frequency of the pump optical field. We also show that, for off-resonant pump excitation, the pump–probe spectrum exhibits a narrow peak below the linear absorption onset.     

Highly Efficient and Tunable Filtering of Electrons' Spin by Supramolecular Chirality of Nanofiber-Based Materials

Organic semiconductors and organic–inorganic hybrids are promising materials for spintronic-based memory devices. Recently, an alternative route to organic spintronic based on chiral-induced spin selectivity (CISS) is suggested. In the CISS effect, the chirality of the molecular system itself acts as a spin filter, thus avoiding the use of magnets for spin injection. Here, spin filtering in excess of 85% in helical π-conjugated materials based on supramolecular nanofibers at room temperature is reported. The high spin-filtering efficiency can even be observed in nanofibers assembled from mixtures of chiral and achiral molecules through chiral amplification effect. Furthermore and most excitingly, it is shown that both “up” and “down” orientations of filtered spins can be obtained in a single enantiopure system via the temperature-dependent helicity (P and M) inversion of supramolecular nanofibers. The findings showcase that materials based on helical noncovalently assembled systems are modular platforms with an emerging structure–property relationship for spintronic applications.