Magnetic and electronic properties of NiAs-type chromium chalcogenides

We have computed spin-dependent energy bands, spin moments and density of states of NiAs-type CrX (X=S, Se and Te) chalcogenides using linear combination of atomic orbitals method within density functional theory as well as full potential augmented plane wave method. In addition, magnetic properties have also been computed using spin polarized relativistic Korringa-Kohn-Rostoker method. We have also obtained the first ever theoretical electron momentum densities of CrX compounds considering linear combination of atomic orbitals and compared the results with the isotropic Compton profiles measured using 20 Ci ¹³⁷Cs Compton spectrometer. The Fermi surface topology and magnetic properties are discussed in terms of majority and minority energy bands and density of states. In addition, to highlight the role of Cr (3d) electrons in such type of chalcogenides, we have also reported the magnetic Compton profile of CrTe using the Korringa-Kohn-Rostoker method.     

Probing mechanical properties of thin film and ceramic materials in micro- and nano-scale using indentation techniques

In this study, we report on the mechanical properties, failure and fracture modes in two cases of engineering materials; that is transparent silicon oxide thin films onto poly(ethylene terephthalate) (PET) membranes and glass-ceramic materials. The first system was studied by the quazi-static indentation technique at the nano-scale and the second by the static indentation technique at the micro-scale. Nanocomposite laminates of silicon oxide thin films onto PET were found to sustain higher scratch induced stresses and were effective as protective coating material for PET membranes. Glass-ceramic materials with separated crystallites of different morphologies sustained a mixed crack propagation pattern in brittle fracture mode.     

热压制备(AgSbTe2)100-x-(GeTe)x合金的热电性能

以Pb粉、Te粉、Ag粉、Ge粉为原材料,在真空气氛下合成(AgSbTe₂)_100-x-(GeTe)_x (x=80---90) (TAGS)合金热电材料, X射线衍射(XRD)分析表明,热压烧结后合金具有低温菱形结构. 通过热压烧结法将TAGS粉末制备成块体材料,运用XRD和扫描电子显微镜对材料的物相成分、 晶体结构和形貌进行了表征.采用直流四探针法测定样品的电导率,当样品两端的温差为1---4℃ 的情况下测量Seebeck系数.通过材料热电性能测试,研究了30---500℃温度范围内不同组分 样品性能参数的变化.结果表明,所制备的TAGS热电材料具有纳米结构, 其性能随着组分的变化而变化, TAGS-80具有较好的热电性能,在530℃时具有最高热电优值(ZT=1.80).     

Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese-zinc ferrite composites

This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability (μ^?) dispersion region in polymer composites of manganese-zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn-PU) and polyaniline (MnZn-PANI) are measured in the frequency range from 1 MHz to 3 GHz in a longitudinal magnetization field of up to 700 Ое and in the temperature interval from −20 °С to +150 °С. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the μ^?. It is established that, at high frequencies, the μ^? of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the “single domain” state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the “single domain” state in ferrite is not reached. The frequency and temperature dependence of μ^? in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn-PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization.     

GaN非线性光学效应研究进展

本文简述了对非线性光学材料的一般要求，详细介绍了GaN材料的极化效应，以及因此而具有的良好非线性光学效应。以波长转换为例说明了它在未来全光网络中的应用前景。     

铁电压控谐振器的研究

研究了单端加载铁电叉指电容的微带半波长谐振器的压控特性.铁电材料为LaAlO3衬底上脉冲激光淀积的SrTiO3,叉指电容电极为金.测量了谐振器77K下的压控谐振性能.谐振频率在6GHz左右,70V偏压下的压控频率范围大于180MHz.在10～40V内,谐振频率与偏置电压之间呈良好的线性关系,谐振器的有载Q值为60～90.     

980 nm脉冲激发下Er3+掺杂材料中4Ⅰ13/2→4Ⅰ15/2跃迁的瞬态行为

在过去的几十年人们对Er3+掺杂的玻璃材料进行了广泛的研究,因为Er3+的4Ⅰ13/2→4Ⅰ15/2跃迁能够给出适合红外光通讯窗口的1.5 μm的发射.据我们所知,目前关于脉冲激光激发下Er3+掺杂材料1.5 μm发射的动力学行为研究报道仍很少.我们引入了转移函数理论,研究了980nm脉冲激发下Er3+的4Ⅰ13/2能级荧光的动力学行为.发现在980nm脉冲激发后,其荧光衰减遵循双指数规律,4Ⅰ13/2能级布居分为指数上升和指数下降两个过程.     

大冷量新型蓄冷材料G-M制冷机的研究进展及应用

随着大型低温真空泵、高低温超导器件、核磁共振成像仪、红外探测器、低温光电子学器件的迅速发展,以及作为传统蓄冷材料的铅(Pb)等有害物质的限制使用,对大冷量新型蓄冷材料G-M制冷机的发展提出了迫切的需要。文中主要介绍国内外大冷量G-M制冷机及新型磁性蓄冷材料的最新研究进展和应用情况,并提出了下一步的研究方向。     

微接触印刷法制造聚合物多层次准三维立体微结构

直接用聚合物稀溶液作为“印墨”进行微接触印刷,制作了诸如聚苯乙烯和聚甲基丙烯酸甲酯等聚合物的微细结构,通过重复交叉盖印得到多层次准三维立体微结构,并用可聚合的双(甲苯磺酸)-2,4-己二炔-1,6-二醇脂的丙酮稀溶液作微接触印刷,观察了微条纹上的聚合.对聚合物溶液的微接触印刷的过程中溶剂挥发等因素的影响进行了观察分析,结果表明,溶剂挥发时间对微图形的准确复制是十分重要的,过长或过短的溶剂挥发时间都不利于得到清晰精确的微结构.     

Fluctuations in apparent mass at the bottom of granular columns due to different arrangements

We report the fluctuations in apparent mass at the bottom of granular columns due to various configurations. It is found that the fluctuations decrease with the increase in the ratio of diameters of silo to grain. For the arrangement of different grain layers in a column, the higher fluctuations appear when the larger grains are stacked at the bottom layer while reversing the order of grain-layers leads to smaller fluctuations. We attribute this behavior to the randomness in the direction of frictional forces between the grains and the confining wall. Moreover, due to polydisperse media, the development of inhomogeneous force transmission in grains may cause this to happen.