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881.
882.
Yongsheng Liu Jincang Zhang Shixun Cao Xiaoyong Zhang Xi Li Kang Deng 《Solid State Communications》2006,138(2):104-109
In the compound MnBi, a first-order transition from the paramagnetic to the ferromagnetic state can be triggered by an applied magnetic field and the Curie temperature increases nearly linearly with an increase in magnetic field by ∼2 K/T. Under a field of 10 T, TC increases by 20 and 22 K during heating and cooling, respectively. Under certain conditions a reversible magnetic field or temperature induced transition between the paramagnetic and ferromagnetic states can occur. A magnetic and crystallographic H-T phase diagram for MnBi is given. Magnetic properties of MnBi compound aligned in a Bi matrix have been investigated. In the low temperature phase MnBi, a spin-reorientation takes place during which the magnetic moments rotate from being parallel to the c-axis towards the basal plane at ∼90 K. A measuring Dc magnetic field applied parallel to the c-axis of MnBi suppresses partly the spin-reorientation transition. Interestingly, the fabricated magnetic field increases the temperature of spin-reorientation transition Ts and the change in magnetization for MnBi. For the sample solidified under 0.5 T, the change in magnetization is ∼70% and Ts is ∼91 K. 相似文献
883.
884.
采用飞秒时间分辨瞬态简并四波混频技术,在室温下测量了GaAs体材料及其量子阱材料GaAs/Al0.3Ga0.7As的光学极化超快退相时间,当激光中心波长为785nm,受激载流子浓度为1011cm-2时,它们的退相时间分别为28fs和46fs.量子阱材料的退相时间比体材料的长,这是由于量子阱中的载流子在垂直于GaAs/AlGaAs界面的运动受到限制,运动呈现二维特性,大大减小了载流子的散射概率.实验中观察到瞬态简并四波混
关键词:
时间分辨简并四波混频
飞秒激光脉冲
退相
密度矩阵 相似文献
885.
886.
采用短焦距透镜设计水平场景无畸变折反射全景成像系统,会使系统更加小型化,然而短焦距透镜的畸变会对系统成像产生影响。为此建立了具有径向畸变的相机模型;根据这一相机模型,研究了采用短焦距摄像头的水平场景无畸变折反射全景成像系统中,透镜畸变对系统成像的影响,结果表明短焦距透镜的畸变会对系统成像产生严重影响;为了消除透镜畸变的影响,对反射镜的设计进行了改进,在反射镜面形微分方程中包含了透镜畸变消除的参量;按新的方法,设计了一套由短焦距摄像头组成的水平场景无畸变折反射全景成像系统。 相似文献
887.
888.
Zhao Qian Feng Songlin Ning Dong Zhu Haijun Wang Zhiming Deng Yuanming 《Journal of Crystal Growth》1999,200(3-4)
In situ ultra high vacuum scanning probe microscopy (SPM) and low-temperature photoluminescence (PL) studies have been performed on Si-doped self-organized InAs/GaAs quantum dots samples to investigate the Si doping effects. Remarkably, when Si is doped in the sample, according to the SPM images, more small dots are formed when compared with images from undoped samples. On the PL spectra, high-energy band tail which correspond to the small dots appear, with increasing doping concentration, the integral intensity of the high-energy band tail account for the whole peak increase too. We relate this phenomenon to a model that takes the Si atom as the nucleation center for QDs formation. 相似文献
889.
Rebuilding of metal components with laser cladding forming 总被引:4,自引:0,他引:4
Laser cladding forming (LCF) is a novel powerful tool for the repairing of metal components. Rebuilding of V-grooves on medium carbon steel substrates has been carried out with laser cladding forming technique using stainless steel powder as the cladding material. Microstructure of the deposited layers has been characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDAX), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Mechanical properties of the rebuilt V-groove samples have been evaluated by tensile and impacting tests and microhardness measurement. Experimental results show that good fusion bonding between the rebuilt layers and the substrate has been formed, and the microstructure of the cladding layers is mainly composed of fine, dense and defect-free epitaxial columnar dendrites. Due to the effect of grain size refinement, the tensile strength, impacting toughness, elongation and microhardness of the rebuilt samples have been greatly enhanced compared to those of the substrate. Microhardness is also very uniform throughout the rebuilt regions. With the growth of the deposited layers, the microhardness increases gradually. The good ductility of the deposited regions is verified by the SEM fracture analysis. 相似文献
890.