氮化硼纳米带功能化碳纳米管的热自旋输运性质

热自旋电子学器件结合了自旋电子学和热电子学各自的优点,对人类可持续发展具有重要作用.本文研究了锯齿形BN纳米带(ZBNRs)共价功能化碳纳米管(SWCNT)的电子结构,发现ZBNRs-B-(6,6)SWCNT为磁性半金属,nZBNRs-B-(6,6)SWCNT(n=2—8)为磁性金属;nZBNRs-N-(6,6)SWCNT(n=1—8)为双极化铁磁半导体;4ZBNRs-B-(4,4)SWCNT和4ZBNRs-N-(4,4)SWCNT为磁性半金属,4ZBNRs-B-(m,m)SWCNT(m=5—9)为磁性金属;4ZBNRs-N-(m,m)SWCNT(m=5—9)为双极化铁磁半导体.然后,基于锯齿形BN纳米带共价功能化碳纳米管设计了新型热自旋电子学器件,发现基于ZBNRs-N-(6,6)SWCNT的器件具有热自旋过滤效应;而8ZBNRs-N-(6,6)SWCNT和nZBNRs-B-(6,6)SWCNT(n=1,8)都存在自旋相关塞贝克效应.这些发现表明BN纳米带功能化碳纳米管在热自旋电子学器件方面具有潜在的应用.     

Heusler合金中近半金属性质的讨论:一种近半金属性质评估标准

如今在Heusler合金中发现了众多适用于自旋电子学领域的半金属材料及自旋无隙半导体,与此同时也伴随发现了一系列不能简单归类为半金属或金属的材料.为了促进这些化合物在自旋电子学领域的应用,本文提出了一种关于Heusler合金中近半金属性质的评估标准,即当一种材料的带隙在费米能级附近0.30 eV或0.2个电子态以内,具有一定的磁矩且没有高的电导时,可以判定其为近半金属材料.这项标准能够帮助Heusler合金在自旋电子学领域得到更全面地应用,并举一些示例加以说明.     

二维原子层谷电子学材料和器件

人为操控电子的内禀自由度是现代电子器件的核心和关键.如今电子的电荷和自旋自由度已经被广泛地应用于逻辑计算与信息存储.以二维过渡金属硫属化合物为代表的二维原子层材料由于其具有独特的谷自由度和优异的物理性质,成为了新型谷电子学器件研究的优选材料体系.本文介绍了能谷的基本概念、谷材料的基本物理性质、谷效应的调控和谷电子学器件的研究进展,并对谷电子学材料和器件的研究进行了总结与展望.     

过渡金属掺杂的扶手椅型氮化硼纳米带的磁电子学特性及力-磁耦合效应

基于密度泛函理论的第一性原理计算方法,研究了多种过渡金属(TM)掺杂扶手椅型氮化硼纳米带(ABNNR-TM)的结构特点、磁电子特性及力-磁耦合效应.计算的结合能及分子动力学模拟表明ABNNRTM的几何结构是较稳定的,同时发现对于不同的TM掺杂,ABNNRs能表现出丰富的磁电子学特性,可以是双极化磁性半导体、一般磁性半导体、无磁半导体或无磁金属.双极化磁性半导体是一种重要的稀磁半导体材料,它在巨磁阻器件和自旋整流器件上有重要的应用.此外,力-磁偶合效应研究表明:ABNNR-TM的磁电子学特性对应力作用十分敏感,能实现无磁金属、无磁半导体、磁金属、磁半导体、双极化磁性半导体、半金属等之间的相变.特别是呈现的宽带隙半金属对于发展自旋电子器件有重要意义.这些结果表明:可以通过力学方法来调控ABNNR-TM的磁电子学特性.     

ZnO一维纳米线及其异质结构的外延生长

一维纳米结构因其优异的光、电特性，在纳米电子学，光电子学器件等方面有重要的应用价值而倍受关注．在一维半导体纳米材料中，ZnO因激子束缚能大（60meV），可在室温获得高效的紫外发光而成为近年来继GaN材料后的又一研究热点．外延生长一维纳米结构ZnO及其量子阱材料除因量子尺寸效应更适宜做室温紫外发光、激光材料与器件外，还因界面和量子限制效应而具有许多新奇的光、电、和力学特性，可应用于纳米光电子学器件，传感器及存储器件，纳米尺度共振隧道结型器件和场效应晶体管的研制和开发．文章着重介绍了目前ZnO一维纳米结构制备，一维ZnO纳米异质结构和一维ZnO／Zn1-xMgxO多量子阱结构的外延生长和研究进展．     

半金属磁性材料研究进展

半金属材料是一种新型的功能自旋电子学材料，是一种具有特殊能带结构的物质，近年来13益受到人们的关注。半金属材料从微观上具有导体和绝缘体双重性质：对一种自旋取向的电子其能带结构呈现金属性，而另一自旋取向的电子其能带结构呈现绝缘体性．文章着重对Half—Heusler结构半金属材料、CrO2铁磁半金属、Fe3O4亚铁磁材料半金属、反铁磁材料半金属和钙钛矿及双钙钛矿半金属的结构特性进行分析和综述，并对半金属材料的应用原理和应用前景作了阐述。     

具有连续反量子点的石墨烯纳米带中纯自旋流的实现

热自旋电子学结合了热电子学和自旋电子学二者的优势,在构建高速、低能耗器件技术上具有广泛的应用前景.本文基于密度泛函理论和非平衡格林函数相结合的方法,研究了在铁磁态石墨烯纳米带中沿带宽方向引入连续反量子点(六元环缺陷)以获得纯自旋流的模型.计算发现,在纳米带的单边引入反量子点会破坏纳米带结构的完整性,导致器件的透射谱在费米能级附近呈现"X"形交叉.在温度场下,不同自旋的电子朝相反方向流动,形成了自旋流和电荷流,并且通过微调器件的化学势可以获得电荷流为0,自旋流不为0的纯自旋流.结果表明,对于具有W条链宽的锯齿型石墨烯纳米带,当沿纳米带带宽方向连续引入反量子点数满足(W/2-1)时,即可获得最大的纯自旋流,这一研究结果为设计基于石墨烯纳米带的纯自旋流器件提供了有力的理论依据.     

碳和氧掺杂紫磷烯作为双极磁性半导体材料的理论预测

紫磷烯是一种结构稳定且具有优异光电特性的新型二维材料,研究掺杂效应有助于理解其物理本质,对进一步开发纳米电子器件具有重要意义.本文采用基于密度泛函理论的第一性原理方法,研究了非金属元素B,C,N,O掺杂单层紫磷烯的电磁性质.计算结果表明,B和N掺杂之后没有产生磁性,体系依旧表现为非磁性半导体;而C和O掺杂导致体系发生自旋劈裂,紫磷烯由非磁性半导体转变成为双极磁性半导体,其自旋密度主要分布在磷原子和间隙区域内而非杂原子上.电场调控氧掺杂紫磷烯可使其载流子的自旋极化方向发生反转,当施加一定大小的正向或反向的静电场时,能带色散程度变强,氧掺杂紫磷烯转变成100%自旋极化向下或向上的单自旋半金属磁体.基于氧掺杂紫磷烯材料设计的场效应自旋滤通器可利用改变门电压方向的方法实现电流自旋极化方向的反转,表明氧掺杂紫磷烯有望成为二维自旋场效应晶体管、双极磁性自旋电子学器件、双通道场效应自旋滤通器以及场效应自旋阀的理想候选材料.     

磁性金属纳米结构的畴壁特性与磁逻辑电路构筑

自旋电子学由于其丰富的物理内涵和广泛的应用前景受到学术界和工业界的高度重视,成为近年来凝聚态物理和信息技术领域关注的焦点。本文介绍了利用磁性金属纳米结构实现作为自旋电子器件基础的自旋注入的方法,特别涉及利用铁磁金属纳米点接触结构钉扎磁畴的特点,研究自旋极化电流与磁畴壁的相互作用规律, 理解纳米结构中畴壁的动力学行为,并以此为基础构筑结构简单、性能优异的全金属磁逻辑电路,从而实现了由电信号驱动,通过电信号检测,并与CMOS技术兼容的目的。     

铁磁材料GdN的电子结构和磁学性质的理论研究

作为寻找新型自旋电子学功能材料的尝试，文章详细研究了稀土化合物GdN的电子结构和磁学性质，通过第一性原理的理论计算，作者发现该材料的导电性质随体积增加有很大变化：从半金属态到准金属态，最后成为半导体．同时，施加压力能改变其载流子浓度和位于多数自旋态的电子和空穴的迁移率．对其磁交换参数随品格常数变化的进一步研究和蒙特卡罗模拟表明，这个铁磁体系的居里温度可以通过加压或掺杂得到进一步提高，从而成为很有实用价值的自旋电子材料．     

与半导体相容的半金属铁磁体

文章在自旋电子学与新型计算机元件的背景下介绍了与半导体相容的半金属铁磁体，及其实验和理论研究进展情况．指出其中半稳能量低并且稳定性好的理论预测材料有可能不久通过外延方式在合适的基底上生长出来，并且得到实际应用．     

Search for new d0 half-metallic materials: theoretical investigation on KCaC1−xSix (x = 0; 0.25; 0.5; 0.75 and 1) compounds

In recent years, the investigations on d⁰ half-metallic materials have become the new trend in the search of novel materials for applications in spintronic devices. In this work, the structural, electronic and magnetic properties of KCaC${}_{1?x}$Si_x (x = 0; 0.25; 0.5; 0.75 and 1) compounds have been theoretically studied using the full-potential linearized augmented plane wave (FP-LAPW) method within framework of the density functional theory. The generalized gradient approximation scheme as proposed by Wu-Cohen (GGA-WC) and Tran-Blaha modified Becke-Johnson exchange potential with improved parameterization by Koller are adopted for the treatment of electron exchange-correlation. All considered materials show half-metallic characteristics with semiconducting majority spin channel and metallic minority one. The total spin magnetic moment is 1μ_B for ternary alloys and 4μ_B for quaternary compounds. Our obtained results suggest that these materials could be promising candidate for spintronic applications.     

岩盐结构SrC(111)表面和(111)界面的d~0半金属性

利用第一性原理方法,本文研究了岩盐结构的SrC块材、(111)表面和(111)界面的电子结构和磁性.块材的SrC被证实是一个良好的d~0半金属铁磁体.计算结果显示(111)方向的C表面和Sr表面都保持了块材的半金属性.对于(111)方向四个可能的界面,态密度的计算显示C-Pb界面呈现半金属特性.本文对岩盐结构SrC块材、(111)表面和(111)界面半金属性的研究结果,将为高性能自旋电子器件的实际应用提供一定的理论指导.     

Large magnetoresistance and perfect spin filter effect in Fe doped SnS2 half-metallic monolayers: A first principles study

In this work, the spin-resolved transport properties of the Fe doped SnS₂ monolayer devices have been investigated. The results show that the doping systems have the transport properties of negative differential resistance, large magnetoresistance effect and near 100% spin polarization effect when the magnetization directions of two electrodes are in parallel. Moreover, the mechanisms for the properties also have been discussed. The original reason of these results could be due to the half-metallic of the doping system. Our results imply that Fe doped SnS₂ monolayer is a promising candidate for the future spintronic devices.     

Half-metallic ferromagnetism and structural stability of zincblende phases of the transition-metal chalcogenides

An accurate density-functional method is used to study systematically half-metallic ferromagnetism and stability of zincblende phases of 3d-transition-metal chalcogenides. The zincblende CrTe, CrSe, and VTe phases are found to be excellent half-metallic ferromagnets with large half-metallic gaps (up to 0.88 eV). They are mechanically stable and approximately 0.31-0.53 eV per formula unit higher in total energy than the corresponding nickel-arsenide ground-state phases, and therefore would be grown epitaxially in the form of films and layers thick enough for spintronic applications.     

Prediction of Interesting Ferromagnetism in Janus Semiconducting Cr2AsP Monolayer

2D half-metallic materials that have sparked intense interest in advanced spintronic applications are essential to the developing next-generation nanospintronic devices. This study has adopted a first-principles calculation method to predict the magnetic properties of intrinsic, Se-doped, and biaxial strain tuning Cr₂AsP monolayer. The Janus Cr₂AsP monolayer is proven to be an intrinsic ferromagnetic (FM) semiconductor with an exchange splitting bandgap of 0.15 eV at the PBE+U level. Concentration-dependent Se doping, such as Cr₂As${}_{1-x}$Se_xP (x = 0.25, 0.50, 0.75), can regulate Cr₂AsP from FM semiconductor to FM half-metallicity. Specifically, the spin-up channel crosses the Fermi level, while the spin-down channel has a bandgap. More interestingly, the wide half-metallic bandgaps and spin bandgaps make them have important implications for the preparation of spintronic devices. At last, it also explore the effect of biaxial strain from -14% to 10% on the magnetism of the Cr₂AsP monolayer. There appears a transition from FM to antiferromagnetic (AFM) at a compressive strain of -10.7%, originating from the competition between the indirect FM superexchange interaction and the direct AFM interaction between the nearest neighboring Cr atoms. Additionally, when the compressive strain is -2% or the tensile strain is 6%, the semiconducting Cr₂AsP becomes a half-metallic material. These charming properties render the Janus Cr₂AsP monolayer with great potential for applications in spintronic devices.     

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.     

High efficiency giant magnetoresistive device based on two-dimensional MXene (Mn2NO2)

Due to the unique electronic structure of half-metals, characterized by the conductivity of majority-spin and the band gap of minority-spin, these materials have emerged as suitable alternatives for the design of efficient giant magnetoresistive (GMR) devices. Based on the first-principles calculations, an excellent GMR device has been designed by using two-dimensional (2D) half-metal Mn₂NO₂. The results show that Mn₂NO₂ has sandwiched between the Au/nMn₂NO₂ (n = 1, 2, 3)/Au heterojunction and maintains its half-metallic properties. Due to the half-metallic characteristics of Mn₂NO₂, the total current of the monolayer device can reach up to 1500 nA in the ferromagnetic state. At low voltage, the maximum GMR is observed to be 1.15 × 10³¹ %. Further, by increasing the number of layers, the ultra-high GMR at low voltage is still maintained. The developed device is a spintronic device exhibiting the highest magnetoresistive ratio reported theoretically so far. Simultaneously, a significant negative differential resistance (NDR) effect is also observed in the heterojunction. Owing to its excellent half-metallic properties and 2D structure, Mn₂NO₂ is an ideal energy-saving GMR material.     

First-principles study on the magnetism in ZnS-based diluted magnetic semiconductors

The electronic and magnetic properties of wurtzite ZnS semiconductor doped with transition metal (Cr, Mn, Fe, Co, and Ni) atoms are studied by using the first-principle’s method in this paper. The ZnS bulk materials doped with Cr, Fe, and Ni are determined to be half-metallic, while those doped with Mn and Co impurities are found to be semiconducting. These doped transition metal ions have long range interactions mediated through the induced magnetic moments in anions and cations of host semiconductors. These doped ZnS-based diluted magnetic semiconductors seem to be good candidates for the future spintronic applications.