Spin-Polarized Tunneling in Fully Epitaxial Semiconductor-Based Magnetic Tunnel Junctions

Tunneling magneto-resistance (TMR) in magnetic heterostructures is a very important phenomenon for future spin-electronic devices. This paper presents our TMR studies on two epitaxial magnetic tunnel junctions (MTJs): GaMnAs/AlAs/GaMnAs ferromagnetic/ nonmagnetic semiconductor MTJs, and MnAs/AlAs/MnAs ferromagnetic-metal/ semiconductor MTJs, which are both compatible with semiconductor device technology.     

大尺度结构对气动光学效应影响的实验研究

为了深入研究细光束穿越可压缩混合层后光束畸变的机理,本文提出将双曝光CCD相机成像技术与纹影技术相结合进行流场与光束畸变的同步测量.利用纹影技术获得可压缩混合层密度梯度场特征,进而获得大尺度结构的密度梯度场分布;利用CCD相机成像技术获取通过混合层后光束畸变特性;双曝光技术的引入可以得到大尺度结构的移动对细光束畸变的影...     

Tunneling of Holes in Spin Polaron Theory

The single-particle tunneling current is calculated for normal metal–superconductor and superconductor–superconductor junctions using the spin polaron theory.     

平面型共振隧穿二极管的制作

采用离子注入方法制作了一种新型平面共振隧穿二极管（RTD）,通过离子注入将器件之间进行隔离,避免了传统台面型RTD中采用的台面刻蚀所带来的一些缺点,并且表现出良好的I-V特性,峰谷电流比为3．4．通过该方法制作的RTD将更有利于RTD的平面集成．     

Multidataset Refinement Resonant Diffraction,and Magnetic Structures

The scope of Rietveld and other powder diffraction refinements continues to expand, driven by improvements in instrumentation, methodology and software. This will be illustrated by examples from our research in recent years. Multidataset refinement is now commonplace; the datasets may be from different detectors, e.g., in a time-of-flight experiment, or from separate experiments, such as at several x-ray energies giving resonant information. The complementary use of x rays and neutrons is exemplified by a recent combined refinement of the monoclinic superstructure of magnetite, Fe₃O₄, below the 122 K Verwey transition, which reveals evidence for Fe²⁺/Fe³⁺ charge ordering. Powder neutron diffraction data continue to be used for the solution and Rietveld refinement of magnetic structures. Time-of-flight instruments on cold neutron sources can produce data that have a high intensity and good resolution at high d-spacings. Such profiles have been used to study incommensurate magnetic structures such as FeAsO₄ and β–CrPO₄. A multiphase, multidataset refinement of the phase-separated perovskite (Pr_0.35Y_0.07Th_0.04Ca_0.04Sr_0.5)MnO₃ has been used to fit three components with different crystal and magnetic structures at low temperatures.     

Resonant Magnetization Tunneling in the Molecular Magnet Mn12 Acetate

I review the evidence for thermally assisted resonant tunneling between spin states in the molecular magnet known as Mn₁₂acetate. The hysteresis loops for a sample show steps at regular intervals of magnetic field, every 4.6 kOe. At these same fields, the magnetic relaxation rate increases markedly. This system can be modeled as a double-well potential with energy levels corresponding to projections of the spin along the anisotropy axis. A magnetic field tilts this potential and regularly brings levels in opposite wells into resonance, allowing tunneling between the wells. The field interval between steps quantitatively agrees with the independently measured value of the anisotropy parameter. The data imply that the tunneling is driven in part by an internal transverse magnetic field, perhaps of hyperfine origin. However, the resonances have a Lorentzian line shape with no hint of the inhomogeneous broadening expected from a random internal field.     

Non-Exponential Relaxation in a Resonant Quantum Tunneling System of Magnetic Molecules

We have studied the low temperature relaxation behavior of the octanulcear iron molecular magnet, Fe8. For temperatures below 400mK we observed a crossover to a quantum tunneling regime. In this regime the relaxation is non-exponential and we argue that it results from evolving intermolecular dipole fields. At the very beginning of the relaxation, the magnetization follows a square-root time dependence. A simple model is presented for a longer time range that is in good agreement with the data over 4 decades in time. Numerical calculations of the local field distribution indicate unusual correlation effects.     

Fracture Resistance of Residually-Stressed Ceramic Laminated Structures

We have studied the effect of residual stresses on fracture resistance and crack arrest behavior of asymmetric ceramic laminated Si ₃ N ₄/Si ₃ N ₄–TiN structures. Using the compliance method, we assessed the technique of R-curve construction for laminar composites. For laminar structures with layers varying by their elastic characteristics we developed an analytical method for calculation of fracture resistance – crack length dependence. The method applicability is verified by calculation of stress intensity factors for laminar specimens with an edge crack. The calculated results are compared to the experimental data.     

Resonant anomalous X-ray reflectivity as a probe of ion adsorption at solid-liquid interfaces

We discuss new opportunities to understand processes at the solid-liquid interface using resonant anomalous X-ray reflectivity (RAXR). This approach is illustrated by determination of element-specific density profiles at mica surfaces in aqueous electrolyte solutions containing Rb⁺ and Sr²⁺. The total interfacial electron density profile is determined by specular reflectivity (i.e., reflected intensity vs. momentum transfer, q, at an energy, E, far from any characteristic absorption edge). RAXR spectra (i.e., intensity vs. E at fixed q) reveal element-specific ion distributions. Key differences in the interaction of Rb⁺ and Sr²⁺ with mica are observed using resonant anomalous X-ray reflectivity: Rb⁺ adsorbs in a partially hydrated state, but Sr²⁺ adsorbs in both fully and partially hydrated states.     

采用Zeeman效应与饱和吸收法的激光器稳频

由于塞曼效应中性原子的超精细能级在磁场中会产生塞曼分裂,且对于左旋和右旋圆偏振光原子能级的偏移不同,因此利用Zeeman效应的这种特性与饱和吸收相结合的方法对光栅外腔反馈的半导体激光器系统进行稳频。这种方法能够将激光频率稳定地锁在原子吸收谱线的峰值处,锁频后激光器不易失锁,用于激光冷却铷原子实验。     

Effect of stress on interface transformation in thin semiconducting layers

The effect of high pressure (1.2 GPa)–high temperature (up to 1400 K) treatment (HP-HT) on the structural properties of GaMnAs/GaAs, AlGaAs/GaAs and Si/SiO₂/Si (SOI) structures was studied by high resolution X-ray diffractometry. GaMnAs layers remain strained after the HP-HT treatment, while it results in anisotropic strain relaxation of AlGaAs. The change in lattice parameters of A(III)B(V) layers is explained as an effect of relaxation of the misfit strain via creation of misfit dislocations and of other extended defects, as well as by diffusion of Mn or Al to dislocations. The treatment of SOI structures resulted in increased (as compared to the effect of annealing at 10⁵ Pa) strain between the Si top layer and the Si bulk.     

Observation of Combined Ferromagnetic/Paramagnetic Phase in Ga1?xMnxAs by Magnetic Circular Dichroism

Magnetic properties of a series of Ga_1–xMn_xAs layers with different Mn and hole concentrations has been studied by measuring magneto-absorption and magnetic circular dichroism (MCD). We first focus on comparing the MCD spectra of samples with unambiguous ferromagnetic or paramagnetic magnetization. We then investigate MCD in a sample with parameters between these two extremes, and interpret the observed behavior in terms of the coexistence of ferromagnetic domains and paramagnetic regions that may result, for example, from inhomogeneities in the sample caused, e.g., by compositional or doping fluctuations.     

Creation of Nonlocal Spin-Entangled Electrons via Andreev Tunneling, Coulomb Blockade, and Resonant Transport

We discuss several scenarios for the creation of nonlocal spin-entangled electrons which provide a source of electronic Einstein–Podolsky–Rosen (EPR) pairs. Such EPR pairs can be used to test nonlocality of electrons in solid state systems, and they form the basic resources for quantum information processing. The central idea is to exploit the spin correlations naturally present in superconductors in form of Cooper pairs possessing spin-singlet wavefunctions. We show that nonlocal spin-entanglement in form of an effective Heisenberg spin interaction is induced between electron spins residing on two quantum dots with no direct coupling between them, but each of them being tunnel-coupled to the same superconductor. We then discuss a nonequilibrium setup with an applied bias where mobile and nonlocal spin-entanglement can be created by coherent injection of two electrons, in a pair (Andreev) tunneling process, into two spatially separated quantum dots and subsequently into two Fermi liquid leads. The current for injecting two spin-entangled electrons into different leads shows a resonance and allows the injection of electrons at the same orbital energy, which is a crucial requirement for the detection of spin-entanglement via the current noise. On the other hand, tunneling via the same dot into the same lead is suppressed by the Coulomb blockade effect of the quantum dots. We discuss Aharonov–Bohm oscillations in the current and show that they contain h/e and h/2e periods, which provides an experimental means to test the nonlocality of the entangled pair. Finally, we discuss a structure consisting of a superconductor weakly coupled to two separate one-dimensional leads with Luttinger liquid properties. We show that strong correlations again suppress the coherent subsequent tunneling of two electrons into the same lead, thus generating again nonlocal spin-entangled electrons in the Luttinger liquid leads.     

聚能效应在深水井壁钢管上射孔的应用

利用聚装药理论，采用普通爆破器材，成功地在深水井井壁钢管上射孔而达到注浆堵水的目的。文中论述了聚能装药各参数的选择普通爆破器材的防水处理及可靠起爆等问题。     

Monochromatization of resonance radiation in Zeeman atomic absorption spectrometry

Two methods of background correction in atomic absorption spectrometry with nonselective atomic effects are investigated: first, with a source possessing a continuous spectrum and, second, that of correction based on the Zeeman effect. The parameters of the monochromator, which was developed expressly for Zeeman atomic absorption spectrometry, are considered. __________ Translated from Izmeritel’naya Tekhnika, No. 9, pp. 20–24, September, 2007.     

Experimental Detection of Resonant Tunneling in the Doped Structure with a Single Quantum Well by the Admittance Spectroscopy Method

Technical Physics Letters - The admittance measurements of heterostructures with quantum wells (QW) InxGa1 – xAs/GaAs (0.19 ≤ x ≤ 0.3) precisely grown by the MOCVD method were...     

层层叠加制备三维静电纺纳米纤维结构

以通孔金属片为静电纺丝的负极制备了通孔阵列纳米纤维薄膜,将多层纳米纤维薄膜在溶剂中叠加构建了三维纳米纤维结构。扫描电子显微镜结果表明,对于聚苯乙烯、聚乙烯吡咯烷酮和聚己内酯3种不同的高分子材料,均可形成带有规则有序通孔结构的纳米纤维薄膜,孔的大小可以通过模板的选择进行调节。在水中将聚苯乙烯纤维薄膜层层叠加形成了三维纳米纤维结构。在叠加四层聚苯乙烯纤维薄膜的三维结构上培养NIH3T3细胞,细胞可以在三维空间内生长,三维纤维结构表现出良好的生物相容性。     

氧化镁磁隧道结磁电阻效应的研究进展

概述了近年来关于氧化镁磁隧道结磁电阻效应的最新研究进展,介绍了势垒层厚度、偏压、温度以及微结构等因素对磁电阻效应的影响.氧化镁磁隧道结的磁电阻效应与铁磁电极层和势垒层间的界面化学态与磁状态密切相关,势垒层厚度、偏压和温度等对磁电阻效应的影响关系表现出与传统氧化铝磁隧道结不同的变化特点.根据氧化镁磁隧道结磁电阻效应的研究状况,对其将来的发展进行了展望.     

Observation of Vortex Clustering in Nano-Size Superconducting Pb Island Structures by Low-Temperature Scanning Tunneling Microscopy/Spectroscopy

Using low-temperature scanning tunneling microscopy/spectroscopy, we have studied superconductivity and vortex formation on Pb nano-size superconducting island structures by measuring the tunneling conductance at the bottom of the superconducting gap and making its spatial mapping. Peculiar clustering of vortices, which is not observed in large-scale superconductors, is observed in the nanosize superconductors.     

Giant Magneto-Optical Properties in Hybrid Nanostructures of Diluted Magnetic Semiconductors With Ferromagnetic Co Wires

Giant Zeeman effects of excitons were studied in hybrid nanostructures of diluted magnetic semiconductor (DMS) quantum wells (QWs) with ferromagnetic Co, where the DMS-QW wires with the width of 200 nm were sandwiched in the Co wires with the width of 400 nm. When the direction of the Co magnetization is normal to the wire plane, a magnetic field B ^⊥ _Co‐flux perpendicular to the well plane can be applied from the Co wires to all of the DMS-QW wire. In addition, the use of a Co/Pt multilayered film with the perpendicular magnetization at zero external field was examined instead of the pure Co film. The excitonic photoluminescence spectrum from the DMS-QW shows significant broadening in the hybrid structures, indicating the giant Zeeman shift of excitons induced by B ^⊥ _Co‐flux.