铁磁/半导体/铁磁结构的双量子环自旋输运的特性

研究了与铁磁/半导体/铁磁结构相关的双量子环自旋输运的规律,研究结果表明：总磁通为零条件下,铁磁电极磁化方向反平行时,双量子环与单量子环相比提高了自旋电子透射概率的平均值.铁磁电极磁化方向平行时,双量子环对提高自旋向下电子平均透射概率的效果更明显;双量子环受到Rashba自旋轨道耦合作用影响时,自旋电子的平均透射概率明显高于单量子环,即使再加上外加磁场的影响,透射概率较高这一特征依然存在;双量子环所含的δ势垒具有阻碍自旋电子输运的作用,随δ势垒强度Z的增大透射概率 关键词： 双量子环 Rashba自旋轨道耦合 透射概率 δ势垒')" href="#">δ势垒     

含δ势垒的铁磁/半导体/铁磁异质结中的自旋输运和渡越时间

研究了含δ势垒的铁磁/半导体/铁磁异质结中自旋相关的透射概率和渡越时间,讨论了量子尺寸效应和Rashba自旋轨道耦合效应对隧穿特性的影响.研究结果表明：δ势垒的存在降低了自旋电子的透射概率,改变了透射概率的位相.Rashba自旋轨道耦合强度的增加加大了透射概率的振荡频率.不同自旋取向的电子隧穿异质结时,渡越时间随着半导体长度、Rashba自旋轨道耦合强度以及两铁磁电极中的磁化方向的夹角的变化而变化. 关键词： δ势垒')" href="#">δ势垒 铁磁/半导体/铁磁异质结 Rashba自旋轨道耦合效应 渡越时间     

铁磁/半导体(绝缘体)/铁磁异质结中渡越时间与两铁磁层磁矩夹角变化的关系

在群速度概念的基础上, 研究了自旋极化电子隧穿通过铁磁体/半导体(绝缘体)/铁磁体异质结时, 渡越时间随两端铁磁层中磁矩夹角变化的关系. 研究结果表明: 当中间层为半导体层时, 由于半导体层中的Rashba自旋轨道耦合强度的影响, 自旋向上电子和自旋向下电子的渡越时间差会在两铁磁层相对磁矩夹角为π/2和3π/2附近出现一个极小值. 当中间层为绝缘体层时, 势垒高度的变化会导致不同取向的自旋极化电子渡越时间差的变化, 并当势垒高度超过一临界值时发生翻转. 关键词： 铁磁体/半导体(绝缘体)/铁磁体异质结 Rashba自旋轨道耦合强度 渡越时间 磁矩     

铁磁─反铁磁双层系统低温特性(英文)

采用自旋波的理论研究反铁磁层间耦合强度和不同自旋值对铁磁—反铁磁双层系统磁性质的影响，在层间反铁磁耦合情况下．得出了不同自旋值时每层子晶格交叉点的温度，在低温下表现出量子效应。     

铁磁/有机半导体/铁磁系统的电流自旋极化性质研究

根据有机半导体中的电流自旋极化注入和输运实验现象，理论上研究了铁磁/有机半导体/铁磁系统的电流自旋极化性质.考虑到有机半导体的具体特性，从自旋扩散理论和欧姆定律出发，得到了系统的电流自旋极化率.假设自旋极化子和不带自旋的双极化子为有机半导体中的载流子.通过计算发现，极化子为实现有机半导体中电流极化注入和输运的有效自旋载流子，即使它只占总载流子很少一部分.还进一步研究了自旋相关界面电阻和电导率匹配以及有机半导体长度等因素对系统电流自旋极化的影响. 关键词： 自旋电子学 自旋注入 有机半导体 极化子     

一维铁磁/有机共轭聚合物的自旋极化研究

针对最近关于自旋注入有机体的实验研究，理论上计算了有机分子与磁性原子接触时的自旋极化现象.通过调节磁性原子的自旋劈裂强度，发现有机分子链内的自旋极化弱于金属链，但强于半导体链.同时还研究了有机分子链内自旋极化随电子-声子耦合强度的变化关系以及界面耦合的自旋相关效应. 关键词： 界面耦合 自旋极化 自旋劈裂     

Cr2O3中反铁磁自旋波的低频拉曼光谱研究(英文)

反铁磁自旋波在高速和低能耗信息处理方面具有很大潜力。然而，在反铁磁体系中激发和检测太赫兹自旋波是具有挑战性的。在本工作中，我们验证了低频拉曼光谱可作为探测反铁磁体系中自旋波的有力工具。我们通过拉曼光谱系统研究了典型的单轴反铁磁体Cr₂O₃中的反铁磁自旋波，我们的测量范围低至2.3 cm^-1(69 GHz)。我们分析了自旋波的塞曼劈裂和自旋翻转相变。我们进一步通过偏振拉曼的方式确定了自旋波能支的角动量符号。我们还得到了Cr₂O₃的各向异性能，g因子和自旋翻转场随温度和磁场变化的函数关系。自旋波重整化理论解释了所有实验观测结果。     

一种等效于反铁磁海森伯混合自旋链的铁磁-反铁磁交替自旋链

利用严格对角化方法研究了一种自旋为1/2的铁磁-反铁磁交替自旋链的物理性质.计算了自旋关联函数、自旋z方向分量、自旋激发谱和磁化曲线等基本物理量,并将这些物理量和自旋为(1,1/2)的混合反铁磁自旋链对应的物理性质进行了比较.结果表明,当铁磁作用居于主导地位时,该模型的物理行为等效于混合自旋模型.因此,可以通过分析铁磁-反铁磁交替自旋链的物理性质研究混合自旋链的物理行为.     

热效应在电流驱动反铁磁/铁磁交换偏置场翻转中的显著作用

电流驱动的面内交换偏置场翻转具有无需外磁场辅助、抗磁场干扰以及强磁各向异性等优势,受到广泛关注.然而,在纳米级厚度薄膜系统中,反铁磁/铁磁异质结的阻塞温度较低,同时电流脉冲会产生大量的焦耳热,理论上电流热效应对于交换偏置场翻转有着显著作用,但是其作用机制缺乏相关研究和验证.我们制备了一系列反铁磁IrMn厚度不同的Pt/IrMn/Py异质结,系统性地研究了热效应在电流翻转交换偏置场中的作用机制.结果表明,在毫秒级电流脉冲下,焦耳热能够使得器件升温至阻塞温度以上,解除反铁磁/铁磁界面的交换耦合,同时电流产生的奥斯特场和自旋轨道矩能够翻转铁磁磁矩,在降温过程中完成交换偏置场的翻转.并且,在翻转过程中,反铁磁/铁磁异质结的各向异性磁阻曲线呈现与温度相关的两步磁化翻转现象,分析表明该现象起源于交换偏置耦合与铁磁直接交换作用之间的竞争关系.本文的研究结果厘清了热效应在电流驱动交换偏置场翻转过程中的重要作用,有助于推动基于电控交换偏置场的自旋电子器件发展.     

铁磁石墨烯体系的CT不变量子自旋霍尔效应

文章作者在垂直磁场作用下的铁磁石墨烯体系里预言了一种新类型的量子自旋霍尔效应.这量子自旋霍尔效应与自旋轨道耦合无关,体系也不具有时间反演不变性;但是有CT不变(C为电子-空穴变换、T为时间反演变换).由于量子自旋霍尔效应,体系的纵向电阻和自旋霍尔阻出现量子化平台.特别是,自旋霍尔阻的量子化平台有很强的抗杂质干扰能力.     

Effect of Rashba spin-orbit coupling on the spin-polarized transport in ferromagnet/semiconductor double tunnel junctions

Considering the Rashba spin-orbit interaction in the semiconductor, we study theoretically the spin-polarized transport in a two-dimensional ferromagnetic semiconductor double tunnel junctions by a quantum-mechanical approach. It is found that the transmission coefficient shows typical resonant transmission properties and the Rashba spin-orbit coupling has great different influences on the transmission coefficients of electrons with spin-up and down and tunnelling magnetoresistance (TMR). More importantly, the TMR is significantly enhanced by increasing the spin-orbit coupling, which is very useful for the designing of magnetic digital and memory sensor.     

Zero-field spin splitting in a two-dimensional electron gas with the spin-orbit interaction revisited

We consider a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction (SOI) in the presence of a perpendicular magnetic field. We derive analytical expressions of the density of states (DOS) of a 2DEG with the Rashba SOI in the presence of a magnetic field by using the Green's function technique. The DOS allows us to obtain the analytical expressions of the magnetoconductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and give rise to the beating patterns in the amplitude of the Shubnikov-de Haas (SdH) oscillations. We find a simple equation which determines the zero-field spin splitting energy if the magnetic field corresponding to any beat node is known from the experiment. Our analytical results reproduce well the experimentally observed non-periodic beating patterns, number of oscillations between two successive nodes and the measured zero-field spin splitting energy.     

Magnetotransport properties of a magnetically modulated two-dimensional electron gas with the spin-orbit interaction

We study the electrical transport properties of a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction in the presence of a constant perpendicular magnetic field (B(0)( ?z) which is weakly modulated by B1 = B1 cos(qx) ?z, where B(1) ? B(0) and q = 2π/a with a the modulation period. We obtain the analytical expressions of the diffusive conductivities for spin-up and spin-down electrons. The conductivities for spin-up and spin-down electrons oscillate with different frequencies and produce beating patterns in the amplitude of the Weiss and Shubnikov-de Haas oscillations. We show that the Rashba strength can be determined by analyzing the beating pattern in the Weiss oscillation. We find a simple equation which determines the Rashba spin-orbit interaction strength if the number of Weiss oscillations between any two successive nodes is known from the experiment. We compare our results with the electrically modulated 2DEG with the Rashba interaction. For completeness, we also study the beating pattern formation in the collisional and the Hall conductivities.     

Rashba spin-orbit effect on dwell time of electrons tunneling through semiconductor barrier

A study on characteristics of electrons tunneling through semiconductor barrier is evaluated, in which we take into account the effects of Rashba spin-orbit interaction. Our numerical results show that Rashba spin-orbit effect originating from the inversion asymmetry can give rise to the spin polarization. The spin polarization does not increase linearly but shows obvious resonant features as the strength of Rashba spin-orbit coupling increases, and the amplitudes of spin polarization can reach the highest around the first resonant energy level. Furthermore, it is found that electrons with different spin orientations will spend quite different time through the same heterostructures. The difference of the dwell time between spin-up and spin-down electrons arise from the Rashba spin-orbit coupling. And it is also found that the dwell time will reach its maximum at the first resonant energy level. It can be concluded that, in the time domain, the tunneling processes of the spin-up and spin-down electrons can be separated by modulating the strength of Rashba spin-orbit coupling. Study results indicate that Rashba spin-orbit effect can cause a nature spin filter mechanism in the time domain.     

Tunnel barrier and noncollinear magnetization effects on shot noise in ferromagnetic/semiconductor/ferromagnetic heterojunctions

Based on the scattering approach, we investigate transport properties of electrons in a one-dimensional waveguide that contains a ferromagnetic/semiconductor/ferromagnetic heterojunction and tunnel barriers in the presence of Rashba and Dresselhaus spin-orbit interactions. We simultaneously consider significant quantum size effects, quantum coherence, Rashba and Dresselhaus spin-orbit interactions and noncollinear magnetizations. It is found that the tunnel barrier plays a decisive role in the transmission coefficient and shot noise of the ballistic spin electron transport through the heterojunction. When the small tunnel barriers are considered, the transport properties of electrons are quite different from those without tunnel barriers.     

A pure spin-current injector of semiconductor quantum dots with Andreev reflection and Rashba spin-orbit coupling

We propose a four-terminal device consisting of two parallel quantum dots with Rashba spin-orbit interaction (RSOI), coupled to two side superconductor leads and two common ferromagnetic leads, respectively. The two ferromagnetic leads and two quantum dots form a ring threaded by Aharonov-Bohm (AB) flux. This device possesses normal quasiparticle transmission between the two ferromagnetic leads, and normal and crossed Andreev reflections providing conductive holes. For the appropriate spin polarization of the ferromagnetic leads, RSOI and AB flux, the pure spin-up (or spin-down) current without net charge current in the right lead, which is due to the equal numbers of electrons and holes with the same spin-polarization moving along the same direction, can be obtained by adjusting the gate voltage, which may be used in practice as a pure spin-current injector.     

Spin-dependent resonant tunneling in a periodic non-magnetic heterostructure with spin-orbit effects

We theoretically investigate the electron transport in a periodic non-magnetic heterostructure with both Dresselhaus and Rashba spin-orbit effects. We show that the transport properties obviously depend on the number of periods and the large spin polarization can be achieved in such a structure. We also show that for m>1, the resonance splitting occurs in the transmission curves of both spin-up and spin-down electrons when the transmission curves are plotted as a function of the electron energy or the well width.     

Spin-orbit torque from spin-flipping scattering at ferromagnetic metal/topological insulator interface

Recent experiments report large damping-like spin-orbit torque in a magnetic bilayer that consists of a topological insulator (TI) layer and a ferromagnetic metal (FM) layer. Here we examine the bilayer theoretically with particular attention to roles of conduction electrons in FM on the spin-orbit torque in this structure. We use electron scattering approach to address electron spin accumulation at the interface between TI/FM caused by the conduction electrons. While topological surface states are not well defined in this bilayer, we find that large damping-like spin-orbit torque can still arise through spin-flipping scattering of the conduction electrons at the TI-FM interface. The resulting damping-like spin-orbit torque is comparable in magnitude to that of the field-like spin-orbit torque. The ratio between the components of the spin-orbit torque relies on various details of the system. The result is compared with recent experimental results and other theoretical works.