Low field induced giant anisotropic magnetocaloric effect in DyFeO_3 single crystal

We have investigated the anisotropic magnetocaloric effect and the rotating field magnetic entropy in Dy FeO3 single crystal. A giant rotating field entropy change of -ΔS R M= 16.62 J/kg·K was achieved from b axis to c axis in bc plane at 5 K for a low field change of 20 k Oe. The large anisotropic magnetic entropy change is mainly accounted for the 4 f electron of rare-earth Dy3+ ion. The large value of rotating field entropy change, together with large refrigeration capacity and negligible hysteresis, suggests that the multiferroic ferrite Dy FeO3 singlecrystal could be a potential material for anisotropic magnetic refrigeration at low field, which can be realized in the practical application around liquid helium temperature region.     

Magnetism induced by Mn atom doping in SnO monolayer

The structural, magnetic properties, and mechanism of magnetization of SnO monolayer doped with 3 d transition metal Mn atom were studied using first-principles calculations. The calculated results show that the substitution doping is easier to realize under the condition of oxygen enrichment. Numerical results reveal that the spin-splitting defect state of the Mn doped system is produced in the band gap and the magnetic moment of 5.0 μB is formed. The induced magnetic moment by Mnsubis mostly derived from the 3 d orbital of the doped Mn atom. The magnetic coupling between magnetic moments caused by two Mn atoms in SnO monolayer is a long-range ferromagnetic, which is due to the hole-mediated p–p and p–d interactions. The calculated results suggest that room-temperature ferromagnetism in a SnO monolayer can be induced after substitutional doping of a Mn atom.     

Multi-bubble motion behavior of uniform magnetic field based on phase field model

Aiming at the interaction and coalescence of bubbles in gas–liquid two-phase flow, a multi-field coupling model was established to simulate deformation and dynamics of multi-bubble in gas–liquid two-phase flow by coupling magnetic field, phase field, continuity equation, and momentum equation. Using the phase field method to capture the interface of two phases, the geometric deformation and dynamics of a pair of coaxial vertical rising bubbles under the applied uniform magnetic field in the vertical direction were investigated. The correctness of results is verified by mass conservation method and the comparison of the existing results. The results show that the applied uniform magnetic field can effectively shorten the distance between the leading bubble and the trailing bubble, the time of bubbles coalescence, and increase the velocity of bubbles coalescence. Within a certain range, as the intensity of the applied uniform magnetic field increases, the velocity of bubbles coalescence is proportional to the intensity of the magnetic field, and the time of bubbles coalescence is inversely proportional to the intensity of the magnetic field.     

FORMATION AND MAGNETIC PROPERTIES OF NEW COMPOUNDS R3Fe29-xCrx(R=Y,Ce,Nd,Sm,Gd,Tb,and Dy)

A systematic investigation of structure and magnetic properties of the new R₃Fe_29-xCr_x compounds(R=Y,Ce,Nd,Sm,Gd, Tb,and Dy)has been performed. The Curie temperature of R₃Fe_29-xCr_x increased with increasing atomic number fromR=Ce to Gd and de creased from Gd to Dy. The saturation magnetization of R₃Fe_29-xCr_x at 4.2 K decreased gradually with increasing atomic number from R=Y to Dy,except for Ce. The spin reorientations of the easy magnetization d irection were observed at around 230 K for Nd₃Fe_24.5Cr_4.5 and 180 K for Tb₃Fe_28.0Cr_1.0,and the magnetohistory effects were obser ved for Nd₃Fe_24.5Cr_4.5 and Sm₃Fe_24.0Cr_5.0 in a low field of about 0.04 T. First order magnetization process occurs in magnetic field of around 2.3 T at room temperature for Tb₃Fe_28.0Cr_1.0. The saturation magnetization of Y₃Fe_27.2Cr_1.8 at 4.2 K is 52.2μ_B/f.u., which corresponds to an average magnetic moment of 1.92μ_B per each Fe atom.     

A method based on magnetic moment measurement to identify the structural transition of quenched Fe1-xGax（x=0.15-0.30） alloys

A method based on the measurement of Fe average atomic magnetic moment to identify the structural transition caused by the increase of Ga content in quenched Fe 1-x Ga x alloys (0.15 ≤ x ≤ 0.30) is proposed.The quenched Fe 1-x Ga x alloys show a change of the Fe average atomic magnetic moment from 2.25μ B to 1.78μ B and then to 1.58μ B,which corresponds to the structural transition from A2 to D0 3 and then to B2.The relationship between the structure and the magnetostriction is clarified,and the maximum magnetostriction appears in the A2 phase.The variation tendency of the magnetostriction is well characterized,which also reflects the structural transition.     

Martensitic transformation and giant magnetic entropy change in Ni_(42.8)Mn_(40.3)Co_(5.7)Sn_(11.2) alloy

The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg.K is obtained at 215 K under a magnetic field of 30 kOe （1 Oe = 79.5775 A.m-1）. The effective refrigerant capacity of Ni42.8Mn40.3Co5.7Sn11.2 alloy reaches 72.1 J/kg under an applied field changing from 0 to 30 kOe. The external magnetic field shifts the martensitic transition temperature about 3-4 K/10 kOe towards low temperature, indicating that magnetic field can retard the phase transition to a certain extent. The origin of large magnetic entropy change is discussed in the paper.     

Room-temperature ferromagnetism with high magnetic moment in Cu-doped AlN single crystal whiskers

Ferromagnetism is investigated in high-quality Cu-doped A1 N single crystal whiskers.The whiskers exhibit roomtemperature ferromagnetism with a magnetic moment close to the results from first-principles calculations.High crystallinity and low Cu concentrations are found to be indispensable for high magnetic moments.The difference between the experimental and theoretical moment values is explored in terms of the influence of nitrogen vacancies.The calculated results demonstrate that nitrogen vacancies can reduce the magnetic moments of Cu atom.     

Structural deformation of nitro group of nitromethane molecule in liquid phase in an intense femtosecond laser field

The structural deformation of NO_2 group induced by an intense femtosecond laser field of liquid nitromethane(NM)molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy(CARS) technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO_2 torsional mode couples with the CN symmetric stretching mode and that the NO_2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO_2 torsional mode in liquid NM(50.8±0.3 cm~(-1)) at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.     

The influence of surface effects on Frederiks transition in nematic liquid crystal doped with ferroelectric nanoparticles

Motivated by our recent work,in this work,we present the numerical study of the anchoring effect on the Frederiks threshold field in a nematic liquid crystal doped with ferroelectric colloidal nanoparticles.Assuming weak anchoring conditions,we employ the relaxation method and Maxwell construction to numerically solve the Euler–Lagrangian differential equation for the total free energy together the Rapini–Papoular surface energy to take into account anchoring of nematic liquid crystal molecules at the substrates.In this study,we focus our attention on obtaining the phase diagrams of Frederiks transition for different values of anchoring strength which have been not computed in our previous work.In this way,the effect of nanoparticle radius,nanoparticle volume fraction,nanoparticle polarization,and cell thickness on the Frederiks transition for different values of anchoring conditions are summarized in the phase diagrams.The numerical results show that by increasing the nanoparticles size and nanoparticle volume fraction in the ferronematic system,the Frederiks threshold field is strongly reduced.     

Improved dielectric and electro-optical parameters of nematic liquid crystal doped with magnetic nanoparticles

This study investigates the effect of magnetic nanoparticles(NPs) on the weakly polar nematic liquid crystal(NLC).Different parameters of dielectric data were measured for both the homeotropic and planar aligned samples as a function of frequency and temperature and the substantial changes have been noticed for the doped systems. Dielectric permittivity has been increased after the dispersion of magnetic NPs in the pure NLC. Dielectric anisotropy has also been influenced by incorporating the magnetic NPs with the NLC molecules. These results were attributed to the dipole–dipole interaction between the magnetic nanoparticles and nematic liquid crystal molecules. Electro-optical study indicated the faster rise time and fall time of the doped systems as compare to pure NLC. Threshold voltage has been calculated and found to be decreased for the doped systems. Moreover, we have also calculated the rotational viscosity and the splay elastic constant for pure and the doped systems. Both the rotational viscosity and splay elastic constant of the doped systems are found to be considerably lower than those of pure NLC. Change in these properties has been explained on the basis of molecular disturbances created by the interaction between the magnetic nanoparticle and LC director. This study reveals that the inclusion of magnetic NPs in weakly polar NLC can be useful to enhance the basic properties of the weakly polar NLC and make it a promising material for many display applications.     

Determining the sum of flexoelectric coefficients in nematic liquid crystals by the capacitance method

A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic （PAN） and hybrid aligned nematic （HAN） cells, the dependences of the capacitance on the sum of flexoelectric coefficients and the applied voltage are obtained by numerical simulations, and the distributions of the director and the electric potential for different applied voltages and flexoelectric coefficients are also given. Based on this theoretical analysis, we propose an experimental design for measuring the capacitance of a liquid crystal cell using the improved precision LCR meter E4980A （Agilent）. Through comparing the experimental data with the simulated results, the sum of flexoeletric coefficients can be determined.     

Two-Dimensional Spatial Solitons in Nematic Liquid Crystals

We study the propagation of spatial solitons in nematic liquid crystals, using the self-similar method. Analytical solutions in the form of self-similar solitons are obtained exactly. We confirm the stability of these solutions by direct numerical simulation, and find that the stable spatial solitons can exist in various forms, such as Oaussian solitons, radially symmetric solitons, multipole solitons, and soliton vortices.     

Measurement of neutron cross sections and resonance parameters of ^169Tm below 100 eV

The neutron total cross-sections of thulium （^169Tm） were measured in the neutron energy region from 0.01 eV to 100 eV by using the time-of-flight method at the Pohang Neutron Facility, which consists of an electron linac, a water-cooled tantalum target with a water moderator, and a 12 m time of flight path, Two thulium plates with different thicknesses were used for the neutron transmission measurement. The background level was determined by using a notch-filter of Co, In, and Cd sheets. The present measurement was compared with the previous ones, and a new set of resonance parameters of ^169Tm isotope was obtained from the transmission rate by using the SAMMY code, with a comparison with the recommended parameters by Mughabghab.     

Energy calibration of a BC501A liquid scintillator using a γ-γ coincidence technique

An accurate energy calibration of a BC501A liquid scintillator by means of Compton scattering of γ-rays is described.The energy resolution and the position of the Compton edge have been precisely determined using a γ-γ coincidence technique and fitting the coincidence spectrum with a Gaussian function superimposed on a quadratic polynomial for the background.The position of the Compton edge relative to the position of the maximum and the half height of the distribution in dependence on the relevant energy resolution is discussed in detail.The results indicate that the maximum energy of the recoil Compton electron does not occur at the half height distribution but at 0.90±0.05 of the maximum height in the energy range considered.The energy resolution varies from 15.6% to 8.02% for electrons in the energy region from 0.5 MeV to 3 MeV.     

染料掺杂聚合物分散胆甾相液晶薄膜激光特性研究

采用激光染料DCM、向列相液晶TEB30A、手性剂S-811、聚乙烯醇(PVA), 通过微胶囊法制备了聚合物分散胆甾相液晶薄膜, 测量激光辐射谱, 研究了其激光辐射机理和温度调谐特性. 利用正交偏光显微镜观察器件织构, 看到液晶微滴分散均匀, 尺寸较大, 约为80 μm, 并且微滴中液晶分子呈现平面态排列织构. 以532 nm的Nd:YAG固体激光器作为抽运源, 测得在634.5 nm和680.2 nm波长处出现了尖锐的激光辐射峰, 线宽分别约为0.25 nm, 0.29 nm. 并与染料掺杂胆甾相液晶激光器件进行比较. 升高器件温度, 其输出激光波长蓝移, 获得666.7 nm至643.9 nm共22.8 nm的调谐范围. 由实验结果分析得出, 激光辐射机理为光子禁带末端激光, 出射波长分别对应光子禁带的两个边沿.     

Electro-optical properties cholesteric liquid of polymer stabilized crystal film＊

Liquid crystals （LCs） and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopant and monomer concentrations on the electro-optical properties, such as contrast ratio, driving voltage, hysteresis width and response time, are investigated. The reasons of electro-optical properties influenced by the concentrations of the materials are discussed. Through the proper material recipe, the electro-optical properties of polymer stabilized cholesteric LC film can be optimized.     

α-decay half-lives of superheavy nuclei and general predictions

The generalized liquid drop model （GLDM） and the cluster model have been employed to calculate the α-decay half-lives of superheavy nuclei （SHN） using the experimental α-decay Q values. The results of the cluster model are slightly poorer than those from the GLDM if experimental Q values are used. The prediction powers of these two models with theoretical Q values from Audi et al. （QAudi） and Muntian et al. （QM） have been tested to find that the cluster model with QAudi and QM could provide reliable results for Z 〉 112 but the GLDM with QAudi for Z 112. The half-lives of some still unknown nuclei are predicted by these two models and these results may be useful for future experimental assignment and identification.     

Critical size of iron nanoparticles on liquid substrates

We study the iron atomic aggregates deposited on silicone oil surfaces by using atomic force microscopy.The aggregates are composed of disk-shaped nanoparticles with the mean diameterΦc≈31.7 nm and height Hc≈4.5 nm,which are nearly independent of the nominal film thickness.The experiment shows that a material condensation process must occur in the nanoparticles during the growth period.The anomalous phenomenon is explained.     

Study on gamma response function of E J301 organic liquid scintillator with GEANT4 and FLUKA

The gamma response function is required for energy calibration of EJ301 （5 cm in diameter and 20 cm in height） organic liquid scintillator detector by means of gamma sources. The GEANT4 and FLUKA Monte Carlo simulation packages were used to simulate the response function of the detector for standard 22Na, 60Co, 137Cs gamma sources. The simulated results showed a good agreement with experimental data by incorporating the energy resolution function to simulation codes. The energy resolution and the position of the maximum Compton electron energy were obtained by comparing measured light output distribution with simulated one. The energy resolution of the detector varied from 21.2% to 12.4% for electrons in the energy region from 0.341 MeV to 1.12 MeV. The accurate position of the maximum Compton electron energy was determined at the position 81% of maximum height of Compton edges distribution. In addition, the relation of the electron energy calibration and the effective neutron detection thresholds were described in detail. The present results indicated that both packages were suited for studying the gamma response function of EJ301 detector.     

Oxygen quenching in a LAB based liquid scintillator and the nitrogen bubbling model

The oxygen quenching effect in a Linear Alkl Benzene （LAB） based liquid scintillator （LAB as the solvent, 3 g/L 2, 5 diphe-nyloxazole （PPO） as the fluor and 15 mg/L p-bis-（o-methylstyryl）-benzene （bis-MSB） as the h-shifter） is studied by measuring the light yield as a function of the nitrogen bubbling time. It is shown that the light yield of the fully purged liquid scintillator is increased by 11% at room temperature and the room atmospheric pressure. A simple nitrogen bubbling model is proposed to describe the relationship between the relative light yield （oxygen quenching factor） and the bubbling time.