自旋阀多层膜的电化学制备及其巨磁电阻效应

采用双槽控电位电沉积法在n-Si(111)基体上以NiFe 薄膜为缓冲层制备了[Ni80Fe20/Cu/Co/Cu]n自旋阀多层膜, 并确定了电沉积的工艺条件. 利用X射线衍射(XRD)表征了自旋阀多层膜的超晶格结构, 研究了NiFe缓冲层对自旋阀生长取向的影响. 采用四探针法研究了各子层厚度对自旋阀巨磁电阻效应的影响, 通过振动样品磁强计(VSM)测试了自旋阀的磁滞回线. 自旋阀的巨磁电阻(GMR)值最初随着铜层厚度的变化并发生周期性振荡, Cu 层厚度为3.6 nm时, GMR 达到最大值,随后逐渐减小. 随着Co层和NiFe 层厚度的增大, GMR 值的变化趋势均为先增大后减小. 当自旋阀的结构为NiFe(25 nm)/[Cu(3.6 nm)/Co(1.2 nm)/Cu(3.6 nm)/NiFe(2.8 nm)]30时, GMR 值可达5.4%, 对应的磁电阻灵敏度(SV)为0.2%·Oe-1, 饱和磁场仅为350 Oe.     

巨磁电阻材料及其研究进展

论述了最近几年巨磁电阻材料的研究进展，主要就钙钛矿，烧绿石和尖晶石等结构的磁电阻材料的机理，制备方法以及超磁电阻现象，室温低磁场问题进行了评述。     

La0.67Ba0.33MnO3中Bi掺杂产生的低场磁电阻增强效应

将Bi2O3掺杂到溶胶-凝胶法制备的La0.67Ba0.33MnO3(LBMO)微粉中, 结果发现随着Bi的掺杂, 材料的磁化强度和居里温度基本不变, 但电阻率发生明显变化, 在0～10% (摩尔分数)的掺杂范围内, 电阻率先急速上升后缓慢降低. 掺Bi可以使低温下的低场磁电阻得到显著增强, 但并不改变与双交换作用有关的本征磁电阻; 掺Bi也使室温下的磁电阻得到明显增强.     

有机自旋光电子学的基本过程

有机自旋光电子学的研究方向分为磁场效应和自旋注入两个方面.研究表明,外加低磁场能够显著改变非磁性有机半导体材料的光致发光、注入电流、电致发光和光电流.这称为有机半导体材料的磁场效应.近年来,非磁性有机半导体材料的磁场效应引起了广泛的关注和研究兴趣.首先,有机半导体材料的磁场效应是强有力的实验手段,用以研究有机电学、光学和光电器件中电荷传输和激发态中的有用和无用过程,为解决电荷传输和激发态过程中的瓶颈问题提供有效的实验手段,为实现磁-光-电多功能集成提供科学原理,尤其是磁场效应能够为提高能量转换效率、探测和传感光电子学器件的响应频谱范围和灵敏度提供新思路.同时利用磁电极,有机半导体材料和器件中自旋注入及其对电荷传输和激发态过程的调控可以用于发展新型功能化的自旋光电子学器件.本文综述并讨论了有机半导体材料和器件中的磁场效应和自旋注入的光电子学效应.     

择优掺杂的La-Ca-Na-Mn-O体系的庞磁电阻效应

利用溶胶-凝胶法制备出择优掺杂的名义组分为La_(1-x)(Ca_(1-y)Na_y)_xMnO_3(LCNM)的多晶样品.xRD测试表明样品均为钙钛矿结构.电输运测试表明所有样品均发生金属-绝缘体转变和顺磁一铁磁转变(转变温度分别用T_m和T_c表示),转变温度随Na含量的增加而增加,但是由于Ca,Na离子间价态的不同引起的磁不均匀性,同时含Ca和Na的样品电输运曲线在T_m温度以下出现肩型鼓包,同时表现出增宽的顺磁·铁磁转变过程,磁电阻测量发现所有样品均表现出庞磁电阻(CMR)效应,但是由于磁不均匀性,y约为0.25的样品表现出两个CMR峰.     

电沉积Co-Cu颗粒膜的巨磁电阻效应

从１９８８年Ｂａｉｂｉｃｈ首先在磁性Ｆｅ／Ｃｒ多层膜中发现巨磁电阻效应（ＧＭＲ）以来 ［１］,由于ＧＭＲ本身的科研价值和在磁记录、磁性传感器等方面的广泛应用前景 ,引起了人们的极大关注．继多层膜之后 ,人们在金属颗粒膜如Ｃｏ Ａｇ［２］,Ｃｏ Ｃｕ［３,４］等中也相继发现了巨磁电阻效应．颗粒膜是微颗粒镶嵌于薄膜中所构成的复合材料体系．原则上 ,颗粒的组成与薄膜的组成在制备条件上应互不固溶 ,因此颗粒膜区别于合金、化合物 ,属于非均匀相组成的材料．磁性颗粒膜是磁性粒子分布在非磁性金属材料薄膜中．在磁性颗粒与非…     

半导体Si上电沉积Cu-Co颗粒膜及其巨磁电阻效应

采用电化学沉积方法在半导体Si上制备Cu-Co金属颗粒膜. XRD测试结果表明制备态的薄膜形成了单相亚稳态面心合金结构, 薄膜经退火后, XRD谱图中出现了析出的纯金属Co的衍射峰, 这表明薄膜在退火过程中发生了相分离. TEM测试结果也进一步证实了磁性的Co颗粒从非磁性的铜基体中析出. 随着退火温度的增加, 颗粒膜巨磁电阻(GMR)效应不断增大, 当退火温度为450 ℃时, Co0.20Cu0.80薄膜的巨磁电阻效应达到最大, 磁阻率为8.21％. 之后, 磁阻率又随退火温度的升高而降低. 退火前后样品磁滞回线的变化表明薄膜中发生了从超顺磁性到铁磁性的转变, 矫顽力、剩余磁化强度和饱和磁化强度均随退火温度的增高而逐渐增大. 超顺磁性颗粒的作用导致了GMR－H与M－H曲线的不同.     

多核过渡金属配合物自旋阻挫的理论研究

区别于双核配合物，自旋阻挫是多核配合物重要的磁现象之一．在分子磁体系中，自旋阻挫引起体系基态的多变和简并以及可能的基态自旋中间值等特征．简要地介绍多核配合物磁耦合竞争自旋阻挫的理论研究进展．     

La-(Ca,Ba)-Mn-O材料磁电阻特性

用固相反应法制备了La2/3(CaxBa1-x)1/3MnO3(x=0.00, 0.40, 0.45, 0.55, 0.60, 1.00) 6种多晶CMR材料, 测量了材料在77～350 K范围内零磁场和0.4 T外磁场下的电阻率.在不同的温度区域呈现不同的电阻率以及磁电阻随温度的变化行为, 说明存在不同的磁电阻效应的机制.证实了高温下的电阻率峰为I-M转变.研究发现掺杂量x=0.55, 0.60两种材料在室温有较大的磁电阻, 表明掺杂量大小影响材料特性.     

(La1-xDyx)0.67Ca0.33MnO3的磁性和磁电阻特性

在La0.67Ca0.33MnO3中用Dy对La进行了部分替代.结果表明, 随替代量增加, 材料的居里温度和相变温度单调下降, 磁电阻比急剧增大.这些变化可以用稀土离子平均直径的减小和自旋团簇模型来解释.掺Dy使材料中形成大量无序自旋团簇, 外加磁场使自旋团簇取向一致, 从而增加了电子在团簇之间跳跃时的迁移率, 产生了磁场所致的庞磁电阻效应.     

2D Semiconducting Metal–Organic Framework Thin Films for Organic Spin Valves

2D conductive metal–organic frameworks (2D c‐MOFs) feature promising applications as chemiresistive sensors, electrode materials, electrocatalysts, and electronic devices. However, exploration of the spin‐polarized transport in this emerging materials and development of the relevant spintronics have not yet been implemented. In this work, layer‐by‐layer assembly was applied to fabricate highly crystalline and oriented thin films of a 2D c‐MOF, Cu₃(HHTP)₂, (HHTP: 2,3,6,7,10,11‐hexahydroxytriphenylene), with tunable thicknesses on the La_0.67Sr_0.33MnO₃ (LSMO) ferromagnetic electrode. The magnetoresistance (MR) of the LSMO/Cu₃(HHTP)₂/Co organic spin valves (OSVs) reaches up to 25 % at 10 K. The MR can be retained with good film thickness adaptability varied from 30 to 100 nm and also at high temperatures (up to 200 K). This work demonstrates the first potential applications of 2D c‐MOFs in spintronics.     

Magnetoresistance in Organic Spin Valves Based on Acid-Exfoliated 2D Covalent Organic Frameworks Thin Films

Covalent organic frameworks (COFs), as a burgeoning class of crystalline porous materials, have made significant progress in their application to optoelectronic devices such as field-effect transistors, memristors, and photodetectors. However, the insoluble features of microcrystalline two-dimensional (2D) COF powders limit development of their thin film devices. Additionally, the exploration of spin transport properties in this category of π-conjugated skeleton materials remains vacant thus far. Herein, an imine-linked 2D Py-Np COF nanocrystalline powder was synthesized by Schiff base condensation of 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl)tetraaniline and naphthalene-2,6-dicarbaldehyde. Then, we prepared a large-scale free-standing Py-Np COF film via a top-down strategy of chemically assisted acid exfoliation. Moreover, high-quality COF films acted as active layers were transferred onto ferromagnetic La_0.67Sr_0.33MnO₃ (LSMO) electrodes for the first attempt to fabricate organic spin valves (OSVs) based on 2D COF materials. This COF-based OSV device with a configuration of LSMO/Py-Np COF/Co/Au demonstrated a remarkable magnetoresistance (MR) value up to −26.5 % at 30 K. Meanwhile, the MR behavior of the COF-based OSVs exhibited a highly temperature dependence and operational stability. This work highlights the enormous application prospects of 2D COFs in organic spintronics and provides a promising approach for developing electronic and spintronic devices based on acid-exfoliated COF thin films.     

Magnetoresistance in La0.5Sr0.5MnO2.5

Resistance measurements indicate the presence of magnetoresistance in the La_0.5Sr_0.5MnO_2.5 brownmillerite related compound. An 80 % of magnetoresistance is found at 75 K. In spite of the partial break‐up occurring at the 3D network of octahedra sharing corners, characteristic of the full oxygen content perovskite phase, the oxygen deficient compound exhibits complex magnetic and electric properties. Such behavior can be explained on the basis of ferromagnetic and metallic clusters randomly distributed at the octahedral layers separated from each other by an insulating antiferromagnetic matrix. AC susceptibility measurements suggest spin glass behavior at low temperature as a consequence of the competition between different magnetic interactions.     

并五苯分子电荷注入导致自旋极化的密度泛函理论研究

用密度泛函理论研究了不带自旋的空穴注入并五苯后体系的自旋相关特性. 电荷注入后并五苯分子中存在自发自旋极化行为. 当注入电荷量达一定程度,分子磁矩随注入电荷量的增加呈线性增长,最大磁矩可达1μB. 注入电荷和并五苯分子的相互作用导致分子体系结构发生变化,同时电荷密度分布及自旋密度分布也发生了变化. 注入电荷先填充自旋劈裂的碳原子pz轨道.     

Spin–Spin Coupling Between Two meta-Benzyne Moieties In a Quinolinium Tetraradical Cation Increases Their Reactivities

The reactivity of a carbon-centered σ,σ,σ,σ-type singlet-ground-state tetraradical containing two meta-benzyne moieties was examined in the gas phase. Surprisingly, the tetraradical showed higher reactivity than its individual meta-benzyne counterparts. The reactivity of meta-benzynes is controlled by their (calculated) distortion energy ΔE_2.3, singlet–triplet spitting ΔE_S–T, and electron affinity (EA_2.3) of the meta-benzyne moiety at the transition state geometry for hydrogen-atom abstraction reactions. The addition of a second meta-benzyne moiety to a meta-benzyne does not significantly change EA_2.3. However, ΔE_2.3 is substantially decreased for both meta-benzyne moieties in the tetraradical, and this explains their higher reactivities. The decrease in ΔE_2.3 for each meta-benzyne moiety in the tetraradical is rationalized by stabilizing spin–spin coupling between one radical site in each meta-benzyne moiety. Therefore, spin–spin coupling between the meta-benzyne moieties in this tetraradical increases its reactivity, whereas spin–spin coupling within each meta-benzyne moiety decreases its reactivity.     

有机电路及其基本元器件

半导体电路及其元器件是实现现代信息传递的重要组成部分,随着无机电路特别是硅基电路的研究发展进入瓶颈,有机电路及其基本元器件的研究对于电路及系统的未来发展意义更加重大。近十年来,有机电路及其基本元器件取得了飞速的发展,多种基本元件器性能已经达到可应用程度,特别是在显示领域,基于有机半导体制备的OLED显示电路已经成为新一代显示器的选择。同时,有机电路也因其所具有的低成本、可弯折、高透光等特性而具有了更多的发展空间。本综述从构成有机电路的各基本部件出发,以各部分器件在电路系统中的应用为线索,从系统信息采集、信息处理、信息存储和信息输出4个方面简述了各部分基础元件的发展情况,并以基于有机场效应晶体管的器件为基础,对器件的结构、电性能的优化以及所面临的问题进行了讨论。     

Huge Tunneling Magnetoresistance in Magnetic Tunnel Junction with Heusler Alloy Co2MnSi Electrodes

Magnetic tunnel junction with a large tunneling magnetoresistance has attracted great attention due to its importance in the spintronics applications. By performing extensive density functional theory calculations combined with the nonequilibrium Green's function method, we explore the spin-dependent transport properties of a magnetic tunnel junction, in which a non-polar SrTiO$_{3}$ barrier layer is sandwiched between two Heusler alloy Co$_{2}$MnSi electrodes. Theoretical results clearly reveal that the near perfect spin-filtering effect appears in the parallel magnetization configuration. The transmission coefficient in the parallel magnetization configuration at the Fermi level is several orders of magnitude larger than that in the antiparallel magnetization configuration, resulting in a huge tunneling magnetoresistance (i.e. $>10^6$), which originates from the coherent spin-polarized tunneling, due to the half-metallic nature of Co$_{2}$MnSi electrodes and the significant spin-polarization of the interfacial Ti 3d orbital.