Evolution of domain structure in Fe_3GeTe_2

Two-dimensional(2D)magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices.The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism.Here,we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe₃GeTe₂(FGT)with a thickness range of 11.2-112 nm.Three types of domain structures and their corresponding hysteresis loops can be obtained.The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness,which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields.These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness.Our finding not only enriches the fundamental magnetism,but also paves a way towards spintronics based on 2D magnet.     

对称正定问题多搜索方向共轭梯度法的收敛性理论

In this paper, we give the convergence and consistence theory of multiple search direction conjugate gradient method (see [10]) and give some upper bound estimations of iterative value and error of our method.     

热结构稳态响应的耦合灵敏度分析方法

研究结构稳态热变形和热应力的灵敏度分析方法,给出了直接法和伴随法两种算法。考虑了温度场的耦合作用,在直接法中需要计算温度场对设计变量的导数,在伴随法中需要计算热载荷对温度场的导数。对尺寸和形状两类设计变量的灵敏度分析算例,验证了本文方法的精度。伴随法在应用程序中的实现,为大型结构优化提供了高效率的灵敏度计算方法。     

Preparation and characterization of superfine ammonium perchlorate (AP) crystals through ceramic membrane anti-solvent crystallization

In this paper, a novel ceramic membrane anti-solvent crystallization (CMASC) method was proposed for the safe and rapid preparation ammonium perchlorate (AP) crystals, in which the acetone and ethyl acetate were chosen as solvent and anti-solvent, respectively. Comparing with the conventional liquid anti-solvent crystallization (LASC), CMASC which successfully introduces ceramic membrane with regular pore structure to the LASC as feeding medium, is favorable to control the rate of feeding rate and, therefore, to obtain size and morphology controllable AP. Several kinds of micro-sized AP particles with different morphology were obtained including polyhedral-like, quadrate-like to rod-like. The effect of processing parameters on the crystal size and shape of AP crystals such as volume ratio of anti-solvent to solvent, feeding pressure and crystallization temperature were investigated. It is found that higher volume ratio of anti-solvent to solvent, higher feeding pressure and higher temperature result in smaller particle size. Scaning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the resulting AP crystals. The nucleation and growth kinetic of the resulting AP crystals were also discussed.     

Controlled chemical co-precipitation and solid phase synthesis,microstructure and photoluminescence of La3PO7:Eu3+ phosphors

Eu³⁺-doped oxy-phosphate (La₃PO₇:Eu³⁺) with monoclinic phase has been synthesized via solid phase and co-precipitation methods. The products present various regular morphologies after high temperature thermal treatment, such as bulk with holes, leaf-like flake, nano-rod and so on. All the phosphors exhibit the characteristic fluorescence of Eu ion, the electric dipole transition ⁵D₀→⁷F₂ of Eu³⁺ ions is dominant indicating that the sites of Eu³⁺ ions in La₃PO₇ have no the inversion center. Furthermore, the intensity of ⁵D₀→⁷F₂ increases due to the introducing of surfactant and increasing of the calcination temperature.     

Interfacial structure of oxidized inner pores in precursor-derived Si–C–N ceramics

Inner pore channels were commonly found in precursor-derived Si–C–N ceramics. After annealing in air at 1420 °C, their oxidation structures were investigated by analytical TEM. A carbon-rich ring was frequently observed under the silica layer inside the pore channels, which consisted of graphite-like clusters in size of 20–30 nm. Origin of such interfacial structure is due to the excessive free-carbon in the amorphous Si–C–N matrix that had survived the oxidation process. This graphitic interface could further improve the oxidation resistance of the SiO₂ over-layer. This novel interfacial structure was also found by annealing in N₂, reaffirming the effect of composition of Si–C–N matrix.     

Spinnablity and structure characterization of mullite fibers via sol–gel-ceramic route

Viscosity and rheology behaviors of the mullite sols prepared from aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate has been investigated. Rheological measurement suggested that mullite sols exhibited good spinniabilty when the evaporation of the solvent is allowed during sol–gel process. Spinnable sols showed shear-thinning flow behavior with high viscosity to the time of gelation. By adjusting temperature, the gelation degree and viscosity of the sol could be stabilized at a certain value and the sol–gel transition could be transferred to the spinning line of a laboratory dry-spinning apparatus. Continuous mullite fibers were obtained from such sols using sol gel dry-spinning method. The final ceramic fibers had smooth surfaces with an average diameter of 50 μm. Structure evolution of mullite ceramic fibers were characterized by MAS NMR and specific surface area analyses.     

Novel Designs for Centrifugal Countercurrent chromatography: V. Comparative Studies on Performance of Various Column Configurations

The conventional toroidal coil in centrifugal countercurrent chromatography has a low level of stationary phase retention, since a half of each helical turn is entirely occupied by the mobile phase. In order to cope with this problem, several new column designs including zigzag, saw-tooth and figure-8 patterns have been introduced and their performance was compared in terms of retention of the stationary phase (Sf), peak resolution (Rs), theoretical plate number (N) and column pressures. Overall results of experiments indicate that the figure-8 column yields the highest Rs when the lower phase is used as the mobile phase. Since the column pressure of all these new columns are much lower than that in the traditional toroidal coil column, the separation efficiency can be improved using a long separation column without a risk of column damage by high back pressure.