界面自旋翻转对有限尺寸的铁磁体/非磁性半导体/铁磁体体系自旋注入的影响(英文)

本文考虑了界面自旋翻转效应后对有限尺寸的铁磁体/非磁性半导体/铁磁体异质结中的自旋注入问题进行了系统的理论探讨.由于自旋在两种介质界面上发生的翻转散射,自旋极化流的每一个分量在界面上都不可能连续.计算结果表明,当自旋注入效率从0增加到100%的过程中,铁磁体/非磁性半导体/铁磁体异质结的隧穿磁阻增大了两个数量级.这一事实证明界面的自旋翻转效应直接影响着铁磁体/非磁性半导体/铁磁体异质结的隧穿磁阻.     

锗基半导体器件的界面磁阻效应和体磁阻效应

本工作对Ag/p-Ge:Ga/Ag器件的界面磁阻和体磁阻效应进行了研究,结果表明该器件的体磁阻效应远大于界面磁阻效应.对界面磁阻而言,界面局部等离子体的形成与淬灭受外加磁场的影响较小,致使界面磁阻很小;而对体磁阻而言,磁场导致载流子复合速率加快,使载流子浓度急剧下降,从而导致体磁阻数值较大.进一步研究发现,采用低载流子浓度Ge制备的器件可以获得更为优异的体磁阻效应.本工作也研究了不同磁场施加方向对体磁阻效应的影响,发现低温时体磁阻具有明显的各向异性.当温度低于200 K时,垂直方向的体磁阻明显大于平行方向的体磁阻,其中当温度为10 K时,垂直方向体磁阻最大值约为123％@1 T,远大于平行方向的体磁阻数值(仅约为41％@1 T).机理分析认为,体磁阻效应的各向异性源于不同磁场构型下几何效应的差异,而低温下载流子迁移率的增加导致这种几何效应的影响更为明显.     

半导体自旋电子学的最新研究进展

自旋电子学起源于巨磁阻效应(GMR),目前已经成为凝聚态物理学领域的研究热点,其中半导体自旋电子学是自旋电子学中人们所关注的一个重要领域。从磁性半导体、自旋电子的注入、检测、输运等方面综述半导体自旋电子学的最新研究进展,并且指出目前半导体自旋电子学研究的重点及难点。     

P型半导体金刚石膜的磁阻

研究了p-型异质外延和同质金刚石膜的在不同温度和磁场下的磁阻,磁阻器件的结构为条形和圆盘形,实验结果表明磁阻强烈依赖于磁场、温度和样品的几何形状,圆盘结构的磁阻大于条形结构,条形结构的磁阻还取决于不同的长-宽比。利用F-S薄膜理论,计算磁场为5T时条形和圆盘结构的磁阻分别为0.38和0.74,讨论了霍耳效应对磁阻的影响。给出了形状效应的可能机制。     

双极性巨磁阻传感器性能测试与应用前景分析

介绍巨磁阻效应的发现、发展与目前的应用情况,在自制的实验平台上,对国内某公司生产的自旋阀型巨磁阻传感器的线性区间、静态灵敏度、分辨率、磁滞等方面进行测试。在测试结果的基础上,对巨磁阻传感器的应用进行探讨,并为以后其在涡流传感器的应用奠定基础。     

NiFeNb薄膜的磁特性及磁阻效应研究

研究了射频磁控溅射膜（Ｎｉ８１Ｆｅ１９）１００－Ｎｂｘ的各向异性磁阻效应ＡＭＲ、矫顽力Ｈｃ、饱和磁化强度４ｘｍｓ和饱和磁化场Ｈ。研究其作为磁阻磁头材料和低磁场高灵敏度材料的可能性。我们发现Ｎｂ的含量对（Ｎｉ８１Ｆｅ１９）１００－ｘＮｂｘ的各向异性磁阻效应ＡＭＲ＝２％、矫顽力Ｈｃ＝１１９Ａ／ｍ和饱和磁化场Ｈｘ＝４４５Ａ／ｍ，适宜于低磁场高灵敏度检测材料。     

胶料输送电瓶车用开关磁阻电机控制策略研究

本文以12/10结构开关磁阻电机在胶料输送电瓶车驱动系统中的应用为研究背景,重点研究了开关磁阻电机在起动、助力、发电状态的运行控制。根据系统的性能要求,分别提出了开关磁阻电机在起动、助力、发电三种工作模式下的控制方法。在此基础上,构建了开关磁阻电机的驱动系统实验平台,设计了开关磁阻电机的控制软件。实验证明,研究的胶料输送电瓶车开关磁阻电机驱动系统运行控制方法性能良好,具有很好的应用前景。     

金刚石膜的磁阻效应和压阻效应

介绍了p型异质外延金刚石膜磁阻效应和压阻效应的特性及应用展望，阐述了目前理论和实验的研究状况，提出了今后有待进一步研究的问题。     

在短脉冲激光作用下薄膜的损伤机制

计算了不同材料的能带带隙、初始电子密度、激光波长和激光脉宽等参效对薄膜的抗激光损伤闭值的影响,研究了在不同脉冲宽度激光作用下多光子离化和雪崩离化两种损伤机制的竞争．结果表明,在以平均电子能量不变为特征的雪崩电离的建立期间,光电离速度影响初始电子的浓度,从而影响雪崩电离和光电离之间的竞争．激光脉冲的宽度越大,雪崩电离对电子发展的贡献越大,而多光子离化的贡献越小．     

雪崩晶体管在半导体激光器电源中的应用

介绍一种可用于半导体激光器的纳秒脉冲驱动电路。利用晶体管的雪崩效应,通过两级雪崩晶体管阵列,得到8ns,5A的大电流窄脉冲。大电流窄脉宽驱动电源是半导体激光器获得高峰值功率输出的重要保证。     

A comparison of avalanche breakdown probabilities in semiconductor materials

Abstract

Using a hard dead space impact ionization model, the dependence of breakdown probabilities on overbias ratio in single photon avalanche diodes is investigated theoretically in a variety of semiconductor materials for the simple case of constant electric field, that is, in a p⁺-i-n⁺ diode structure. By using avalanche widths of 2 μm, the effects of dead space are minimized so that the breakdown probability results are determined primarily by the enabled ionization coefficients of the materials. The results illustrate how the slope of breakdown probability with overbias ratio is affected by the enabled ionization coefficients ratio and by the field dependences of ionization coefficients, which should be taken into account when choosing semiconductor materials for single photon avalanche diodes.     

Lattice Effects and Irreversible Magnetoresistance in Gd Doped La—Ca—Mn—O

The Gd substituting effects for La in La0.67Ca0.33MnO3 has been studied .With increasing the substituting amount of Gd,the phase transition temperature of metal-isolator for the samples decreases,the corresponding peak resistivity increases,the Curie temperature decreases monotonically.The substitution of La-Ca-Mn-O with 11% Gd for La improved the magnetoresistance ratio by an order of magnitude.The effects of substituting Gd can be explained in terms of the lattice effects.An irreversible MR behaviour was observed in Gd-substituting compounds.This effect became marked when the substituting amount of Gd was greater than 7%.A maximum irreversible increment of MR ratio as large as 91% was obtained when Gd substituting amount was 11%.     

A fiber-optically triggered avalanche transistor

A silicon bipolar transistor operating in the avalanche region was optically triggered into secondary breakdown. This transistor has been given the name fiber-optically triggered avalanche transistor (FOTAT). The FOTAT acts as an optical power discriminator. That is, secondary breakdown occurs when the triggering optical power exceeds the triggering threshold of the FOTAT. This secondary breakdown is seen as a negative resistance between the collector and emitter. High voltage (>100 V) nanosecond transition duration pulses are generated using this negative resistance     

Discrimination capability of avalanche counters detecting different ionizing particles

The discrimination capability of avalanche counters to detect different ionizing particles has been studied using a ²⁵²Cf source. Pulse height, pulse-height resolution and timing properties have been measured as a function of the reduced applied voltage for parallel-plate and parallel-grid avalanche counters. At the highest applied voltages, space charge effects shift the pulse-height signal of the avalanche counter away from being linearly proportional to the stopping power of the detected particles and cause the pulse-height resolution to deteriorate. To optimize the avalanche counter capability, without loss of time resolution, it appears better to operate the detector at voltages well below the breakdown threshold. Measurements with ³²S ions are also reported.     

磁电阻材料及其应用的研究进展

本文综述了磁电阻 (MR)材料的研究进展 ,并对目前研究热点的四类巨磁电阻 (GMR)材料进行了概括评述 ,侧重论述MR材料在信息存储等领域的应用 ,明确指出开发和应用MR材料的关键问题是提高各类GMR材料的室温MR值和降低其工作磁场     

Microchannel avalanche photodetector based on a Si-SiO2 structure

A new avalanche photodetector is developed and realized on the basis of a Si-SiO₂ microchannel structure. The new device is analogous to the well-known vacuum microchannel plates but possesses better technological characteristics. A considerable increase in the photocurrent amplification coefficient is achieved due to decreased fluctuations of the semiconductor breakdown voltage and suppressed local avalanche processes in inhomogeneities of the semiconductor responsible for the microplasma breakdown.     

基础油对羰基铁磁流变液摩擦性能的影响

采用四球摩擦磨损试验机,在有外加磁场和无外加磁场条件下,考察了基础油对羰基铁磁流变液的摩擦系数的影响,记录了试验时间内摩擦系数随时间的变化曲线.结果表明,在较低载荷下,基础油的运动黏度值与磁流变液的流变性能有直接关系;基础油的摩擦性能决定了磁流变液的摩擦性能.     

Topographic curvature effects in applied avalanche modeling

This paper describes the implementation of topographic curvature effects within the RApid Mass MovementS (RAMMS) snow avalanche simulation toolbox. RAMMS is based on a model similar to shallow water equations with a Coulomb friction relation and the velocity dependent Voellmy drag. It is used for snow avalanche risk assessment in Switzerland. The snow avalanche simulation relies on back calculation of observed avalanches. The calibration of the friction parameters depends on characteristics of the avalanche track. The topographic curvature terms are not yet included in the above mentioned classical model. Here, we fundamentally improve this model by mathematically and physically including the topographic curvature effects. By decomposing the velocity dependent friction into a topography dependent term that accounts for a curvature enhancement in the Coulomb friction, and a topography independent contribution similar to the classical Voellmy drag, we construct a general curvature dependent frictional resistance, and thus propose new extended model equations. With three site-specific examples, we compare the apparent frictional resistance of the new approach, which includes topographic curvature effects, to the classical one. Our simulation results demonstrate substantial effects of the curvature on the flow dynamics e.g., the dynamic pressure distribution along the slope. The comparison of resistance coefficients between the two models demonstrates that the physically based extension presents an improvement to the classical approach. Furthermore a practical example highlights its influence on the pressure outline in the run out zone of the avalanche. Snow avalanche dynamics modeling natural terrain curvature centrifugal force friction coefficients.     

La_(0.60)Sr_(0.40-x)K_xMnO_3系列材料的磁电阻效应

利用溶胶-凝胶法(sol-gel)制备了多晶类钙钛矿型稀土锰氧化物La0.60Sr0.40-xKxMnO3(x=0.00,0.15,0.20,0.30)。发现K+取代部分Sr2+后,可使样品的居里温度降至室温附近,并且使样品的室温磁电阻比替代前明显增大。在1.8T的磁场下,x=0.30的样品磁电阻峰值为21%,相应的峰值温度为304K。而母体La0.60Sr0.40MnO3的磁电阻峰值仅为6.4%,峰值温度为373K。可见K+离子替代使室温附近样品的庞磁电阻效应有了明显的改善。     

Dielectric breakdown processes in anodic Ta2O5 and related oxides

The dielectric breakdown properties during the anodic oxidation of valve metals (Ta, Nb, Al, etc.) are reviewed. First, the theories developed for insulating films flanked by metal electrodes are analysed. The major emphasis is placed on the avalanche models since they give the best account of the experimental facts observed with electrolytic contacts, i.e. during the anodization. Some hints to increase the breakdown potential are finally given.