共查询到20条相似文献,搜索用时 62 毫秒
1.
用电弧熔炼的方法制备了Gd2(Fe1-xCox)15Ga2(0≤x≤10)和Gd2(Fe08Co02)17-yGay(0≤y≤8)化合物,通过X射线衍射和磁性测量手段研究了它们的结构和磁性.实验结果表明它们都是2∶17型结构的单相化合物.Gd2(Fe1-xCox)15Ga2的单胞体积V随Co含量的增加单调下降,而居里温度TC单调上升,15K下的饱和磁化强度Ms随Co含量的增加开始时略有增大,在x=02时出现极大值,然后单调下降;对Gd2(Fe08Co02)17-yGay的样品,随Ga含量的增加单胞体积增加,居里温度和饱和磁化强度单调下降.用Co替代Fe,或用Ga替代Fe和Co都能导致Fe或Co次晶格出现室温单轴各向异性,这可能与Ga原子的择优占位有关. 相似文献
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用SQRID直流磁强研究了La1.85Cr0.15Cu1-xFexO4-y(x=0.0,0.002,0.004和0.006)多晶样品在不同磁场下(H=0.01,0.03,0.05T)正常态的直流磁化率与温度关系和超导转变温的关系呈宽峰行为。随着Fe掺杂的增多,直流磁化率与温度的关系由宽峰行为迅速转变为Curie-Wiss行为。与此同时,超导转变温度也由不掺Fe的31.0K增加到33.6K(x=0. 相似文献
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用SQUID直流磁强计研究了La(1.85)Sr(0.15)Cu(1-x)FexO(4-y)(x=0.002,0.004和0.006)多晶样品在不同磁场下(H=0.01,0.03,0.05T)正常态的直流磁化率与温度关系和超导转变温度与Fe掺杂含量的关系.实验结果表明,不掺Fe的样品其直流磁化率与温度的关系里宽峰行为,随着Fe掺杂的增多,直流磁化率与温度的关系由宽峰行为迅速转变为Curie-Weiss行为.与此同时,超导转变温度也由不掺Fe的31.0K增加到33.6K(x=0.002),然后再单调降低.这清楚地表明,载流子浓度才是影响超导的最重要的因素。对于掺Fe的样品,其正常态直流磁化率X与温度T的关系可以用X=a+bT+c/(T一T0)很好地表示.我们认为,式中a+bT项是由于Cud带泡利硕磁的贡献.增加磁场时,对于同一个接Fe样品,居里常数C增大而常数项a减小.这是由于掺Fe的样品在Fermi面存在不满的窄带(dx2上Hubbrd带),它是产生居里硕磁的原因.增加磁场时,它往高能量方向移动,窄带的电子空得更多,这些电子移向较宽的Cu杂化带.这样一来,增加磁场时,每个Cu离子的磁矩增大.而Cud带的Fe 相似文献
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研究了La2-xSrxCu1-yFeyO4(x=0.13,0.15,0.17和y=0.0,0.002,0.004,0.006)多晶样品在不同磁场下(H=1,3和5T)正常态直流磁化率与温度的关系和超导转变温度与Fe掺杂含量的关系.结果表明,不掺杂样品的正常态直流磁化率呈宽峰行为.随着Fe掺杂量的增多,直流磁化率与温度的关系由宽峰行为变为Curie-Weiss行为.与此同时,超导转变温度随Fe掺杂含量的变化而变化.这表明载流子浓度是影响超导的重要因素.对Fe掺杂样品,其正常态直流磁化率与温度的关系可以用X=a+bT+c/(T-T0)很好的表示.我们认为,其中a+bT项是带Pauli顺磁的贡献.对同一掺Fe样品,增加外磁场时,居里常数c增大而常数项a减小.这是由于在Fermi面存在不满的窄带(dx2上Hubbard带),它是导致居里顺磁的原因.增加磁场时它往高能方向移动,窄带的电子空得更多,这些电子移向较宽的杂化带,导致每个Cu离子的磁矩增大,而带的Fermi面电子态度减小.我们的实验结果也表明,超导电性与能带结构密切相关. 相似文献
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铁酸盐的水热氧化晶化法制备及其生成条件研究 总被引:1,自引:0,他引:1
研究了空气氧化M^2+(M=Mn、Fe、Co、Ni)和Fe^2+的碱性悬浮液制备铁酸盐MFe2O4的条件,考察了原料配比、pH值、氧化温度、氧化时间对生成MFe2O4的影响。利用XRD及SEM检测氧化过程中沉淀物的形态和结构表明,在343 ̄358K和R=2OH^-/(M^2+Fe^2+)=1.0、M^2/Fe^2+=0.5(摩尔比)下用300mL/h的空气氧化Mx/3Fe1-x/3(OH)2悬浮液 相似文献
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利用X-光衍射,电阻率和电势等实验手段,系统地研究了La1.85-xSr0.15+xCu1-xMxO4(M=Cr,Mn,Fe,Co,Ga and Al)体系的结构和输运性质。结果表明;所有的三阶离子掺杂都能在较低的掺杂浓度下抑制超导电性,并且引起金属到绝缘体的转变。磁性离子和非磁性离子掺杂引起显著不同的热电势变化,并用d-p杂化态的变化和局域自旋散射来进行分析讨论。 相似文献
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研究了稀土五磷酸盐GdxY1-x)P5O14:Ce0.01,Tb0.02体系中以Gd^3+子晶格为中介的Ce^3+→Gd^3+→Tb^3+的能量传递现象。当x>0.7,在室温下激发Ce^3+离子可以产生有效的Tb^3+的发光。对x=1和0时,激发Ce^3+产生Tb^3+的发光,前者的强度约为后者的10倍。 相似文献
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报道了x=0.214组份、低补偿度(K《1)n-Hg_(1-x)Cd_xTe晶体在0.3─30K温度范围,0─7T强磁场下的横向磁阻、电子霍耳迁移率、霍耳系数测量结果,观测到了磁致金属-绝缘体相变和相变后的温度激活输运行为。分析实验数据,提出:低补偿度、组份:x=0.2附近的n-Hg_(1-x)Cd_xTe,磁致金属-绝缘体相变(MIT)发生的机理是载流子在浅施主杂质态上的磁冻结;发生磁冻结的前提是热冻出(thermalfreeze-out),即首先必须在很低的温度下将导带电子冻出到施主态上。相变后的温度激活输运行为可以表示成R_H(T)=R_(H0)exp[a/kT],它实际上反映了磁冻结在施主上的电子,随温度的升高,逐步热激发到导带的过程,从磁致MIT后的激活能初步推知,导带下存在两个浅施主能级。 相似文献
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Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide 总被引:1,自引:0,他引:1
Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs. 相似文献
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S. G. Nedel’ko M. A. Krysyuk A. L. Apanasenko L. N. Lymarenko Z. T. Moroz 《Journal of Applied Spectroscopy》1997,64(1):55-61
Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped
with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly
described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation
(5.5·104 Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum
cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics
of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure
crystals is analyzed (preliminarily).
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997. 相似文献
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A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output. 相似文献
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The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper. 相似文献
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We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed. 相似文献
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Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell. 相似文献
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A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques. 相似文献
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Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing. 相似文献
20.
Yepeng Guan 《中国光学快报(英文版)》2008,6(6)
Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate. 相似文献