Microstructure characteristics and effect of grain orientation on magnetic properties of Fe_(63)Co_(32)Gd_5 alloy ribbons

By using the melt spinning techniques, the Fe63Co32Gd5 alloy ribbons with 15-50 m in thickness and 3-7 mm in width were prepared at the wheel speeds of 15, 20, 25 and 35 m/s. The rapid solidification microstructures were characterized by three layers, the middle layer of which reaches 80% thickness and forms the column grain of(Fe,Co) solid with Gd solution. Grain refinement takes place with the increase of the wheel speed. And after 0.5 h heat treatment at 823 K, the ribbon thickness becomes larger and the middle layer of column grain is very orderly perpendicular to the ribbon plane. The coercivity of quenched and annealed Fe63Co32Gd5 ribbons both have the inflection point at the wheel speed of 20 m/s, and the tendency is declining. The heat treatment processing makes the coercivity become lower by improving the order of(Fe,Co)17Gd2 compound. The saturation magnetization of quenched ribbons increases with the enhancement of wheel speed, whereas that of annealed ones decreases firstly and then increases. The minimum coercivity is 5.30×103 A/m and the maximum saturation magnetization is 163.62 A·m2/kg, which is obtained in the conditions of the wheel speed of 35 m/s and 0.5 h heat treatment at the temperature of 823 K.

Structures and physical properties of R_2TX_3 compounds

Rare-earth compounds have been an attractive subject based on the unique electronic structures of the rare-earth elements. Novel ternary intermetallic compounds R2TX3 （R = rare-earth element or U, T = transition-metal element, X = Si, Ge, Ga, In） are a significant branch of this research field due to their complex and intriguing physical properties, such as magnetic order at low temperature, spin-glass behavior, Kondo effect, heavy fermion behavior, and so on. The unique physical properties of R2TX3 compounds are related to distinctive electronic structures, crystal structures, micro- interaction, and external environment. Most R2TX3 compounds crystallize in A1B2-type or derived A1B2-type structures and exhibit many similar properties. This paper gives a concise review of the structures and physical properties of these compounds. Spin glass, magnetic susceptibility, resistivity, and specific heat of R2 TX3 compounds are discussed.

Preparation and Microwave Absorbing Characteristics of Multi-Walled Carbon Nanotube/Chiral-Polyaniline Composites

The multi-walled carbon nanotubes (MWCNTs)/chiral-polyaniline composite was synthesized by in-situ chemical polymerization. Morphology, structure as well as thermal stability of the hybrid composites were characterized by using various techniques. Moreover, the complex permeability, permittivity, and microwave absorbing characteristics of the MWCNTs/chiral-polyaniline composites have been studied. Compared with those of the polyaniline (PANI) and MWCNTs, the real part () and imaginary part () of the complex permittivity as well as dielectric dissipation factor of the MWCNTs/chiral-PANI composites were much greater, while the real part () and imaginary part () of the complex permeability and the magnetic dissipation factor were smaller. The results indicate that the microwave absorption of MWCNTs/chiral-PANI composites was mainly attributed to the dielectric loss rather than magnetic loss.

Numerical study on the dependence of ZnO thin-film transistor characteristics on grain boundary position

The dependence of transistor characteristics on grain boundary （GB） position in short-channel ZnO thin film transistors （TFTs） has been investigated using two-dimensional numerical simulations. To simulate the device accurately, both tail states and deep-level states are taken into consideration. It is shown that both the transfer and output characteristics of ZnO TFTs change dramatically with varying GB position, which is different from polycrystalline Si （poly-Si） TFTs. By analysing the mechanism of the carrier transportation in the device, it is revealed that the dependence is derived from the degrees of carrier concentration descent and mobility variation with CB position.

Phonon relaxation and heat conduction in one-dimensional Fermi Pasta Ulam β lattices by molecular dynamics simulations

The phonon relaxation and heat conduction in one-dimensional Fermi Pasta-Ulam （FPU） β lattices are studied by using molecular dynamics simulations. The phonon relaxation rate, which dominates the length dependence of the FPU β lattice, is first calculated from the energy autoeorrelation function for different modes at various temperatures through equilibrium molecular dynamics simulations. We find that the relaxation rate as a function of wave number k is proportional to k^1.688, which leads to a N^0.41 divergence of the thermal conductivity in the framework of Green-Kubo relation. This is also in good agreement with the data obtained by non-equilibrium molecular dynamics simulations which estimate the length dependence exponent of the thermal conductivity as 0.415. Our results confirm the N^2/5 divergence in one-dimensional FPU β lattices. The effects of the heat flux on the thermal conductivity are also studied by imposing different temperature differences on the two ends of the lattices. We find that the thermal conductivity is insensitive to the heat flux under our simulation conditions. It implies that the linear response theory is applicable towards the heat conduction in one-dimensional FPU β lattices.

Surface pressure anisotropy and complex relaxation of silica nanoparticle monolayer at the air-water interface

We report the anisotropy effect and the relaxation dynamics of surface pressure of silica nanoparticle monolayer at the air-water interface. The anisotropy of surface pressure occurs when the water surface is fully covered by particles and becomes more prominent with the increase of surface concentration. Hence, the conception of surface tensor was proposed to characterize the monolayer properties. The dynamics of pressure relaxation involves three timescales which are related to the damping of surface fluctuation, rearrangement of particle rafts and particle motion inside each raft. The anisotropy decays when the layer is kept static and the process is accelerated remarkably by barrier oscillation. The underlying physics mechanism is also discussed in detail for the origin of pressure anisotropy and its decay dynamics.

Enhanced ferroelectricity and ferromagnetism in Bi_(0.9)Ba_(0.1)FeO_3/La_(2/3)Sr_(1/3)MnO_3 heterostructure grown by pulsed laser deposition

Bi0.9Ba0.lFeO3 （BBFO）/La2/3Srl/3MnO3 （LSMO） heterostructures are fabricated on LaA103 （100） substrates by pulsed laser deposition. Giant remnant polarization value （~ 85 μC/cm2） and large saturated magnetization value （~ 12.4 emu/cm3） for BBFO/LSMO heterostructures are demonstrated at room temperature. Mixed ferroelectric domain structures and low leakage current are observed and in favor of enhanced ferroelectrie properties in the BBFO/LSMO het- erostructures. The magnetic field-dependent magnetization measurements reveal the enhancement in the magnetic moment and improved magnetic hysteresis loop originating from the BBFO/LSMO interface. The heterostructure is proved to be effective in enhancing the ferroelectric and ferromagnetic performances in multiferroic BFO films at room temperature.

Application of yolk-shell Fe3O4@N-doped carbon nanochains as highly effective microwave-absorption material

Yolk-shell Fe3O4@N-doped carbon nanochains, intended for application as a novel microwave-absorption material, have been constructed by a three-step method. Magnetic-field-induced distillation-precipitation polymerization was used to synthesize nanochains with a one-dimensional （1D） structure. Then, a polypyrrole shell was uniformly applied to the surface of the nanochains through oxidant-directed vapor-phase polymerization, and finally the pyrolysis process was completed. The obtained products were characterized by X-ray diffraction （XRD）, X-ray photoelectron spectra （XPS）, and thermogravimetric analyses （TGA） to confirm the compositions. The morphology and microstructure were observed using an optical microscope, scanning electron microscope （SEM）, and transmission electron microscope （TEM）. The N2 absorption-desorption isotherms indicate a Brunauer-Emmett-Teller （BET） specific surface area of 74 m^2/g and a pore width of 5-30 nm. Investigations of the microwave absorption performance indicate that paraffin-based composites loaded with 20wt.% yolk-shell Fe3O4@N-doped carbon nanochains possess a minimum reflection loss of -63.09 dB （11.91 GHz） and an effective absorption bandwidth of 5.34 GHz at a matching layer thickness of 3.1 mm. In addition, by tailoring the layer thicknesses, the effective absorption frequency bands can be made to cover most of the C, X, and Ku bands. By offering the advantages of stronger absorption, broad absorption bandwidth, low loading, thin layers, and intrinsic light weight, yolk-shell Fe3O4@N-doped carbon nanochains will be excellent candidates for practical application to microwave absorption. An analysis of the microwave absorption mechanism reveals that the excellent microwave absorption performance can be explained by the quarter-wavelength cancellation theory, good impedance matching, intense conductive loss, multiple reflections and scatterings, dielectric loss, magnetic loss, and microwave plasma loss.