Enhanced Spin Seebeck Effect in Monolayer Tungsten Diselenide Due to Strong Spin Current Injection at Interface

The spin current is significantly limited by the spin‐orbit interaction strength, material quality, and spin‐mixing conductance at material interfaces. Such limitations lead to spin current decay at the interfaces, which severely hinders potential applications in spin‐current‐generating thermoelectric devices. Thus, methodical studies on the enhancement of spin currents are indispensable. Herein, a novel approach for enhancing the spin current injected into a normal metal, Pt, using interface effects with a ferromagnetic insulator, yttrium iron garnet (YIG), is demonstrated. This is accomplished by inserting atomically thin monolayer (ML), tungsten diselenide (WSe₂) between Pt and YIG layers. A comparative study of longitudinal spin Seebeck effect (LSSE) measurements is conducted. Two types of ML WSe₂ (continuous and large‐area ML WSe₂ and isolated ML WSe₂ flakes) are used as intermediate layers on YIG film. Notably, the insertion of ML WSe₂ between the Pt and YIG layers significantly enhances the thermopower, V_LSSE/ΔT by a factor of approximately 5.6 compared with that of the Pt/YIG reference sample. This enhancement in the measured LSSE voltages in the Pt/ML WSe₂/YIG trilayer can be explained by the increased spin‐to‐charge conversion at the interface owing to the large spin‐orbit coupling and improved spin mixing conductance with the ML WSe₂ intermediate layer.     

Concepts of Spin Seebeck Effect in Ferromagnetic Metals

Spin Seebeck effect (SSE) and related spin caloritronics have attracted great interest recently. However, the definition of the SSE coefficient remains to be established, let alone a clean experiment to measure the SSE coefficient in ferromagnetic metals. The concept through a model based on the semi‐classical Botlzmann transport equation has been clarified. The model includes the vital spin‐flip process, which is frequent in metals, and points out that the length scale of SSE is much larger than the spin diffusion length. The model reveals how the spin‐flip process influences the transport equations and provides the simple relationship between the different spin‐flip relaxation times for spin‐up and ‐down electrons, which is very useful to understand the spin transport properties. This understanding allows to redefine the expression of the spin Seebeck coefficient.     

Dirac Cone Spin Polarization of Graphene by Magnetic Insulator Proximity Effect Probed with Outermost Surface Spin Spectroscopy

The effects of the proximity contact with magnetic insulator on the spin‐dependent electronic structure of graphene are explored for the heterostructure of single‐layer graphene (SLG) and yttrium iron garnet Y₃Fe₅O₁₂ (YIG) by means of outermost surface spin spectroscopy using a spin‐polarized metastable He atom beam. In the SLG/YIG heterostructure, the Dirac cone electrons of graphene are found to be negatively spin polarized in parallel to the minority spins of YIG with a large polarization degree, without giving rise to significant changes in the π band structure. Theoretical calculations reveal the electrostatic interfacial interactions providing a strong physical adhesion and the indirect exchange interaction causing the spin polarization of SLG at the interface with YIG. The Hall device of the SLG/YIG heterostructure exhibits a nonlinear Hall resistance attributable to the anomalous Hall effect, implying the extrinsic spin–orbit interactions as another manifestation of the proximity effect.     

自旋晶体管的最新研究进展

自旋晶体管是指利用电子自旋自由度构建的在结构上类似于传统半导体晶体管的三端自旋器件。对基于自旋劈裂的磁双极型自旋晶体管、基于热电子输运的自旋晶体管和基于Rashba效应的自旋晶体管的最新研究动态进行了评述,并对其发展前景做了展望。     

Plasmon‐Enhanced Photodetection in Ferromagnet/Nonmagnet Spin Thermoelectric Structures

The photothermoelectric (PTE) effect that originates from the temperature difference within thermoelectric materials induced by light absorption can be used as the mechanism for a light sensor in optoelectronic applications. In this work, a PTE‐based photodetector is reported using a spin thermoelectric structure consisting of CoFeB/Pt metallic bilayers and its signal enhancement achieved by incorporating a plasmonic structure consisting of Au nanorod arrays. The thermoelectric voltage of the bilayers markedly increases by 60 ± 10% when the plasmon resonance condition of the Au nanorods is matched to the wavelength of the incident laser. Full‐wave electromagnetic simulations reveal that the signal enhancement is due to the increase in light absorption and consequential local heating. Moreover, the alignment of the Au nanorods makes the thermoelectric voltages sensitive to the polarization state of the laser, thereby enabling the detection of light polarization. These results demonstrate the feasibility of a hybrid device utilizing plasmonic and spin‐thermoelectric effects as an efficient PTE‐based photodetector.     

Modulation of Spin Dynamics via Voltage Control of Spin‐Lattice Coupling in Multiferroics

Motivated by the most recent progresses in both magnonics (spin dynamics) and multiferroics fields, this work aims at magnonics manipulation by the magnetoelectric coupling effect. Here, voltage control of magnonics, particularly the surface spin waves, is achieved in La_0.7Sr_0.3MnO₃/0.7Pb(Mg_1/3Nb_2/3)O₃‐0.3PbTiO₃ multiferroic heterostructures. With the electron spin resonance method, a large 135 Oe shift of surface spin wave resonance (≈7 times greater than conventional voltage‐induced ferromagnetic resonance shift of 20 Oe) is determined. A model of the spin‐lattice coupling effect, i.e., varying exchange stiffness due to voltage‐induced anisotropic lattice changes, has been established to explain experiment results with good agreement. Additionally, an “on” and “off” spin wave state switch near the critical angle upon applying a voltage is created. The modulation of spin dynamics by spin‐lattice coupling effect provides a platform for realizing energy‐efficient, tunable magnonics devices.     

自旋电子学研究的最新进展

自旋极化电子的高效注入、自旋霍尔效应和自旋流的产生与探测都是目前自旋电子学中热门研究专题,世界一些著名学术刊物屡见报道。对这些重要内容的理论和实验的最新研究成果进行了介绍。通过自旋极化电子高效注入方法和材料的研究,人们期望研制出新一代自旋电子器件,进而实现应用电子自旋传输、记录和存储信息的目标。近期实验给出,自旋极化电子从铁磁金属注入半导体和金属都获得较高的极化率。各种注入方法中,自旋流直接注入法目前备受关注,因为自旋霍尔效应为自旋流的产生与探测提供了新的途径,即自旋霍尔效应可以产生自旋流,但因无霍尔电压故不容易测量;而逆自旋霍尔效应又将自旋流转化为电流,使得难以测量的自旋流又可以直接用电学方法测量。     

纳米尺寸自旋阀中电流驱动的自旋波发射

提出了在纳米赝自旋阀中的电流感应自旋传输矩的磁动力学描述,成功地解释了在磁纳米多层结构中的电流驱动微波发射和电流感应磁化翻转现象。自旋流极化由在电导匹配时的自旋流和化学势连续性边界条件决定。自旋矩的纵向和横向分量在自旋阀的电流驱动微波发射和电流感应磁化翻转现象中扮演了不同的角色:纵向自旋矩分量决定了电流感应磁化翻转(CIMS)效应,而横向自旋矩是自旋波发射(SWE)效应所不可缺少的。根据这一理论,由LLG方程自然得到自旋波发射的双模,分别为横向自旋矩引发的X和Y方向的振动,并引起磁多层电阻以频率2w或w(进动频率)随时间变化。磁场和自旋流共同决定了自旋波发射的频率和功率,这一理论预言了某种特殊的磁多层结构,如磁层相互垂直的结构,将具有大得多的微波发射效率,这一结论已经被实验所证实。     

半导体材料中自旋极化的光学注入与探测

综述了自旋电子学的一些新进展,重点介绍了自旋极化的光学注入、弛豫机制和光学探测等方面的内容,并涉及到与自旋有关的自旋霍尔效应(SHE)和纯自旋流等物理效应.     

InP单晶的磁光和热电效应

对同一原生非掺杂InP单晶进行了一系列物理测试分析,研究了材料的光电导率与温度的依从关系,在295~318 K内,温度系数为-3×10-4eV/K,测得的室温禁带宽度为1.339 2 eV。禁带宽度Eg的磁性系数为8.6×10-4eV/T,材料的磁光特性测量结果为1.8 T。由此数据可得,约化电子有效质量mr*为0.067m0。由热电功率测量结果可得室温塞贝克系数为565μV/K。由此值以及霍尔测量值,可计算出状态密度有效质量md*为0.075 7m0。由该值和上面提到的约化电子有效质量可得到InP样品的价带电子有效质量mv*为0.591m0。     

自旋场效应晶体管的电学特性研究(英文)

用非平衡格林函数方法研究一种自旋场效应晶体管的电子输运特性。结果表明,不考虑自旋散射的作用,当漏极电压比较小时该器件能达到很高的磁阻比率。对该器件在考虑自旋散射和不考虑自旋散射下的输出电流进行对比,发现在铁磁平行(反平行)的条件下,考虑自旋散射时的输出电流要比不考虑自旋散射时的输出电流小(大)。研究结果揭示了该器件的物理机制,为该器件的优化设计提供了理论指导。     

Large Area Artificial Spin Ice and Anti‐Spin Ice Ni80Fe20 Structures: Static and Dynamic Behavior

Artificial spin ice has been the subject of extensive investigation in the last few years due to advances in nanotechnology and characterization techniques. So far, most of the studies have been limited to local probe of small area magnetic elements due to limitations with lithographic techniques used. In this study, large area spin ice and anti‐spin ice Ni₈₀Fe₂₀ structures with three lattice configurations have been fabricated using deep ultraviolet lithography at 193 nm exposure wavelength. The static and dynamic properties are systematically characterized using vibrating sample magnetometer, magnetic force microscopy, and broadband ferromagnetic resonance spectroscopy. Intriguing static and dynamic behaviors are observed due to the geometrical arrangement of the nanomagnets in the lattice. When the nanomagnets are saturated at high field, multiple resonance peaks whose frequencies are strongly dependent on the orientation of the applied magnetic field are observed. The experimental results are in qualitative agreement with the micromagnetic simulations. These findings may find application in the design of magnetically controlled tunable microwave filters.     

基于超快电子自旋动力学的太赫兹辐射研究进展

回顾了近年来利用超快自旋动力学过程产生太赫兹(THz)辐射的研究进展。介绍了基于逆自旋霍尔效应和逆Rashba-Edelstein效应的瞬态自旋流-电荷流转换,指出铁磁/非磁性异质结构已被用于设计低成本、高效率的THz辐射源。通过优化膜厚、生长条件、衬底和结构,可进一步提高基于自旋电子学的THz发射器的效率和带宽。简述了THz发射光谱在研究超快自旋泽贝克效应形成动力学中的应用。     

Magnetically Enhanced Mechanical Stability and Super‐Size Effects in Self‐Assembled Superstructures of Nanocubes

Artificial materials from the self‐assembly of magnetic nanoparticles exhibit extraordinary collective properties; however, to date, the contribution of nanoscale magnetism to the mechanical properties of this class of materials is overlooked. Here, through a combination of Monte Carlo simulations and experimental magnetic measurements, this contribution is shown to be important in self‐assembled superstructures of magnetite nanocubes. By simulating the relaxation of interacting macrospins in the superstructure systems, the relationship between nanoscale magnetism, nanoparticle arrangement, superstructure size, and mechanical stability is established. For all considered systems, a significant enhancement in cohesive energy per nanocube (up to 45%), and thus in mechanical stability, is uncovered from the consideration of magnetism. Magnetic measurements fully support the simulations and confirm the strongly interacting character of the nanocube assembly. The studies also reveal a novel super‐size effect, whereby mechanically destabilization occurs through a decrease in cohesive energy per nanocube as the overall size (number of particles) of the system decreases. The discovery of this effect opens up new possibilities in size‐controlled tuning of superstructure properties, thus contributing to the design of next‐generation self‐assembled materials with simultaneous enhancement of magnetic and mechanical properties.     

Utilization of the Antiferromagnetic IrMn Electrode in Spin Thermoelectric Devices and Their Beneficial Hybrid for Thermopiles

The thermoelectric effect in various magnetic systems, in which electric voltage is generated by a spin current, has attracted much interest owing to its potential applications in energy harvesting, but its power generation capability has to be improved further for actual applications. In this study, the first instance of the formation of a spin thermopile via a simplified and straightforward method which utilizes two distinct characteristics of antiferromagnetic IrMn is reported: the inverse spin Hall effect and the exchange bias. The former allows the IrMn efficiently to convert the thermally induced spin current into a measurable voltage, and the latter can be used to control the spin direction of adjacent ferromagnetic materials. It is observed that a thermoelectric signal is successfully amplified in spin thermopiles with exchange‐biased IrMn/CoFeB structures, where an alternating magnetic alignment is formed using the IrMn thickness dependence of the exchange bias. The scalable signal on a number of thermopiles allowing a large‐area application paves the way toward the development of practical spin thermoelectric devices. A detailed model analysis is also provided for a quantitative understanding of the thermoelectric voltages, which consist of the spin Seebeck and anomalous Nernst contributions.     

Bismuth Doping–Induced Stable Seebeck Effect Based on MAPbI3 Polycrystalline Thin Films

In this article, the thermoelectric properties of a Bi‐doped CH₃NH₃PbI₃ (MAPbI₃) perovskite thin film are studied. Bi‐doped MAPbI₃ thin film samples are fabricated, and it is found that Bi doping could greatly enhance the stability and thermoelectric properties of MAPbI₃. The Bi dopant located at the grain boundaries to modify the carrier channel near grain boundaries, which is observed via scanning electron microscopy and atomic force microscopy, efficiently reduces ion migration and facilitates charge transport. In addition, the Bi dopant can also passivate the defects in bulk MAPbI₃, increasing the polarization effect of MAPbI₃ which is demonstrated by the capacitance‐frequency measurement, thus greatly enhancing the mobility of Bi‐doped MAPbI₃. In addition, Bi‐doped MAPbI₃ leads to grain size reduction; the small size effect not only effectively hinders the MAPbI₃'s crystal phase transition from the tetragonal phase to the cubic phase, but it could also make the structure of MAPbI₃ more stable. Especially, the Seebeck voltage variation of Bi‐doped perovskite was less than that of the undoped one, meaning Bi doping would lead to a much more stable state in MAPbI₃ thin films. The results show that Bi‐doped MAPbI₃ is a promising approach to develop high stable thermoelectric and photovoltaic properties in organic–inorganic hybrid perovskite materials.     

基于自旋阀结构的磁传感器的研究

自旋阀结构的发现为磁电子学以及磁传感器的研究揭开了新的一页。基于自旋阀结构的磁传感器由于具有灵敏度高、功耗小、高集成度等优点,因此在传感器工业中具有广泛的应用前景。本文介绍了基于自旋阀结构的磁传感器的研究方法。首先介绍了自旋阀结构及其特性,然后介绍了基于自旋阀结构的磁性薄膜的制备方法和结构优化,其次介绍了基于自旋阀薄膜的磁传感器芯片的制造工艺,最后介绍了基于惠斯通电桥结构的自旋阀磁传感器芯片。     

硅基自旋注入研究进展

自旋注入、自旋探测和自旋操控是构建半导体自旋电子器件的基础.在硅基材料上采用电的方式进行自旋注入,有利于自旋器件与微电子芯片的集成化,是当前该领域的研究热点课题之一.简要概述了硅基自旋注入的研究进展,首先介绍了半导体自旋注入的原理和方法,着重评述了以磁隧道结(MTJ)结构为核心的硅基自旋注入的研究进程,然后详细论述了硅基自旋注入的测试原理、器件结构扣实验方法,最后给出了硅基自旋注入的主要研究目标和发展方向,并展望了硅基自旋电子器件的前景.     

Fe/GaAs中自旋注入效率的研究

自旋电子学是近年来发展迅速的一个研究领域,利用了传导电子自旋这一自由度的自旋电子器件以其提高数据处理速度、降低能量消耗、容易增加集成密度等优点正引起人们的空前关注.文中阐述了自旋的漂移-扩散方程,并对以Fe/GaAs为代表的铁磁性金属/半导体结构(FM/SC)进行了简单分析.如果选取参数适当,可以在Fe/GaAs结中获得较大的自旋注入效率.