硬盘驱动器巨磁电阻(GMR)磁头:从微米到纳米

近年来电脑硬盘存储密度的飞速增长(年增长100％)已超出摩尔定律的预言．这种惊人的高速增长中，最关键的因素是自旋阀纳米多层膜结构，即巨磁电阻(GMR)读传感器磁头的应用．事实上，巨磁电阻磁头读传感器(reader sensor)已经实现由微电子器件向纳米电子器件转化，并且形成大规模产业．这一过程包含了自旋电子学、材料科学、微电子工程学、化学、微机械力学和工程学等诸学科和相关微加工技术综合性挑战极限，进入纳米科技领域实质性进步．     

复合结构丝中的电流密度分布和巨磁阻抗效应

提出了由中间为高电导率的非铁磁性金属丝外面包裹一层铁磁材料组成的复合结构丝的电流 密度分布和巨磁阻抗(GMI)效应模型，并对Cu/FeCoNi复合丝进行了数值模拟. 结果表明：在 相同的磁性材料几何尺寸和磁特性时，Cu/FeCoNi复合丝铁磁层内的电流随频率的升高比匀 质FeCoNi铁磁丝内的电流更趋于表面分布，而且开始出现趋肤效应时对应的频率明显降低. 当在比较低的频率下就可以观察到明显的MI变化时，复合结构丝中的电阻和电抗变化主要是 由趋肤效应引起，趋肤效应仍然是引起复合结构材料(包括多层薄膜结构) 关键词： 电流密度 巨磁阻抗效应 趋肤效应     

A DNA‐Programmed Liposome Fusion Cascade

Chemically engineered and functionalized nanoscale compartments are used in bottom‐up synthetic biology to construct compartmentalized chemical processes. Progressively more complex designs demand spatial and temporal control over entrapped species. Here, we address this demand with a DNA‐encoded design for the successive fusion of multiple liposome populations. Three individual stages of fusion are induced by orthogonally hybridizing sets of membrane‐anchored oligonucleotides. Each fusion event leads to efficient content mixing and transfer of the recognition unit for the subsequent stage. In contrast to fusion‐protein‐dependent eukaryotic vesicle processing, this artificial fusion cascade exploits the versatile encoding potential of DNA hybridization and is generally applicable to small and giant unilamellar vesicles. This platform could thus enable numerous applications in artificial cellular systems and liposome‐based synthetic pathways.     

Aggregate Conformation and Rheological Properties of Didodecyldimethylammonium Bromide in Aqueous Solution

Aggregation behavior of didodecyldimethylammonium bromide (DDAB) in aqueous solution was investigated using negative-staining and freeze-fracture transmission electron microscopy (TEM) methods. With the concentration increase, the vesicle size enlarged from the range of 100–200 nm to 500–3000 nm and the structure transform from unilamella to multilamella. Rheological and viscosity measurement results indicated that the system exhibited a gel-like material characteristic and shearing thinning in property, as shown that the apparent viscosity decreased gradually during the shear rate ascended from 1 × 10^?4–1 × 10⁴ s^?1. Furthermore, the relationship between aggregate conformation and solution rheological properties was discussed.     

熊猫型保偏光纤光栅温度和压力传感特性的实验研究

对熊猫型保偏光纤光栅的传感特性进行了深入的实验研究,采用温箱和压力罐分别进行了温度和压力传感特性的实验研究.实验结果表明:在0～2.5 MPa的压强范围内,熊猫型保偏光纤光栅两个偏振方向上的压力敏感系数分别为0.004 88 nm/MPa和0.003 52 nm/MPa;在15～50 ℃的温度范围内,两个偏振方向上的温度敏感系数为0.01018 nm/℃和0.008 8 nm/℃.该光纤光栅两偏振态对温度和压力的不同敏感特性可用于解决光纤光栅的交叉敏感问题.     

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.     

Point‐to‐Plane Nonhomogeneous Electric‐Field‐Induced Simultaneous Formation of Giant Unilamellar Vesicles (GUVs) and Lipid Tubes

It is well‐known that homogeneous electric fields can be used to generate giant unilamellar vesicles (GUVs). Herein we report an interesting phenomenon of formation of GUVs and lipid tubes simultaneously using a nonhomogeneous electric field generated by point‐to‐plane electrodes. The underlying mechanism was analyzed using finite element analysis. The two forces play main roles, that is, the pulling force (F) to drag GUVs into lipid tubes induced by fluid flow, and the critical force (Fc) to prevent GUVs from deforming into lipid tubes induced by electric fields. In the center area underneath the needle electrode, the GUVs were found because F is less than Fc in that region, whereas in the edge area the lipid tubes were obtained because F is larger than Fc. The diffusion coefficient of lipid in the tubes was found to be 4.45 μm² s^?1 using a fluorescence recovery after photobleaching (FRAP) technique. The method demonstrated here is superior to conventional GUV or lipid tube fabrication methods, and has great potential in cell mimic or hollow material fabrication using GUVs and tubes as templates.     

Genetic differentiation and subspecies development of the giant panda as revealed by DNA fingerprinting

Over the last 100 years giant pandas (Ailuropoda melanoleuca) have been separated into six completely isolated mountain ranges. DNA fingerprinting revealed different differentiation patterns in giant pandas, including early-stage, late-stage, recent divergence and recent genetic depression. A separation around 10 000 years ago resulted in highly significant differences in DNA fingerprints and morphological characteristics between Qinling and Sichuan populations. Supported by morphological differences, the genetic data were used to classify the Qinling population as a new subspecies, A. m. qinlingensis, while the Sichuan populations were classified into the original subspecies, A. m. melanoleuca. Thus, the Qinling population deserves management as a separate unit. In the Sichuan populations, two management units were defined, including Qionglai-Minshan and Daxiangling-Xiaoxiangling-Liangshan. Our data suggest urgent measures are needed to establish green corridors between subpopulations in each mountain range to increase gene flow and genetic variation to ensure long-term survival.     

Optical Properties of Amorphous Co‐Containing Alloys in the IR Region of the Spectrum and Their Magnetoresistive Characteristics

The optical properties of amorphous and nanocrystalline tapes of CoFeNiSiB alloys and the ac magnetoresistive effect in them have been investigated. It is shown that the magnetoresistive effect in these alloys increases by about a factor of two after lowtemperature treatment and subsequent laser annealing of these tapes in an external magnetic field. Correlation between the anomalous behavior of the dielectric function of these alloys in the IR region of the spectrum and their magnetoresistive characteristics after thermal annealings has been established. The interrelation between the density of localized electronic states near the Fermi level and the value of the magnetoresistive effect has been revealed. The influence of the induced magnetic anisotropy on the transverse permeability in amorphous and nanocrystalline CoFeNiSiB alloys and, consequently, also on the magnetoresistive effect has been analyzed.