Synthesis and Properties of Magnetic Composites of Carbon Nanotubes/Fe Nanoparticle

Magnetic composites of carbon nanotubes （CNTs） are synthesized by the in situ catalytic decomposition of benzene at temperatures as low as 400℃ over Fe nanoparticles （mean grain size = 26 nm） produced by sol-gel fabrication and hydrogen reduction. The yield of CNT composite is up to about 3025% in a run of 6 h. FE- SEM and HRTEM investigations reveal that one-dimensional carbon species are produced in a large quantity. A relatively high value of magnetization is observed for the composite due to the encapsulation of ferromagnetic Fe3 C and/or α-Fe. The method is suitable for the mass-production of CNT composites that contain magnetic nanoparticles.     

Microstructure of Epitaxial Er2O3 Thin Film on Oxidized Si （111） Substrate

Er2O3 thin films are grown on oxidized Si （111） substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction （GIXRD）, atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er2O3 thin film is a mosaic of single-crystal domains. The interplanar spacing d in-plane residual strain tensor ell and the strain relaxation degree ε are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulk Er2O3. In-plane strains in three sets of planes, i.e. （440）, （404）, and （044）, are isotropic.     

Study on superstructure in ion co-doped BiFeO3 by using transmission electron microscopy

La3+and V5+co-doped Bi Fe O3 ceramics are synthesized by rapid liquid sintering technique. The modulated structure in Bi0.85La0.15Fe0.97V0.03O3 is investigated by using transmission electron microscopy(TEM). Two kinds of superstructures are observed in the samples. One is the component modulated superstructure and twin-domain, which is generated by La3+ordered substitution for Bi3+and frequently appears. The chemical composition of the superstructure is explored by x-ray energy dispersive spectroscopy(EDS). The model of the ordered structure is proposed. Simulation based on the model is conducted. The second is the fluorite-type δ-Bi2O3 related superstructure. The relation between the ferroelectric property and the microstructure of the sample is also discussed.     

Study of nanocrystalline Fe－Al－N soft magnetic thin films

Fe－Al－N films were fabricated by reactive sputtering using a radio-frequency magnetron sputtering system. The effects of Al and N content and annealing temperature on microstructure and magnetic properties were investigated. The Fe－Al－N films, which have good soft magnetic properties, consist of nanocrystalline α-Fe grains and a small amount of other phases in the boundaries of α-Fe grains. The average α-Fe grain size is about 10－15nm. A slight amount of Fe－N and Al－N compounds precipitate in the boundaries of α-Fe grains and suppress their growth. Annealing improves the soft magnetic properties slightly by releasing the residual stress and reducing defects.     

Enhancement of microwave absorption of nanocomposite BaFe_(12)O_(19)/α-Fe microfibers

Nanocomposite BaFe12O19/α-Fe microfibers with diameters of about 1-5 μm are prepared by the organic gelthermal selective reduction process. The binary phase of BaFe12O19 and α-Fe is formed after reduction of the precursor BaFe12O19/α-Fe2O3 microfibers at 350℃ for 1 h. These nanocomposite microfibers are fabricated from α-Fe (16-22 nm in diameter) and BaFe12O19 particles (36-42 nm in diameter) and basically exhibit a single-phase-like magnetization behavior, with a high saturation magnetization and coercive force arising from the exchange-coupling interactions of soft α-Fe and hard BaFe12O19 . The microwave absorption characteristics in a 2-18 GHz frequency range of the nanocomposite BaFe12O19/α-Fe microfibers are mainly influenced by their mass ratio of α-Fe/BaFe12O19 and specimen thickness. It is found that the nanocomposite BaFe12O19/α-Fe microfibers with a mass ratio of 1:6 and specimen thickness of 2.5 mm show an optimal reflection loss (RL) of 29.7 dB at 13.5 GHz and the bandwidth with RL exceeding 10 dB covers the whole Ku-band (12.4-18.0 GHz). This enhancement of microwave absorption can be attributed to the heterostructure of soft, nano, conducting α-Fe particles embedded in hard, nano, semiconducting barium ferrite, which improves the dipolar polarization, interfacial polarization, exchange-coupling interaction, and anisotropic energy in the nanocomposite BaFe12O19/α-Fe microfibers.     

Excellent ethanol sensing properties based on Er_2O_3-Fe_2O_3 nanotubes

In this work, pure α-Fe2O3 and Er2O3-Fe2O3 nanotubes were synthesized by a simple single-capillary electrospinning technology followed by calcination treatment. The morphologies and crystal structures of the as-prepared samples were characterized by scanning electron microscopy and x-ray diffraction, respectively. The gas-sensing properties of the as-prepared samples have been researched, and the result shows that the Er2O3-Fe2O3 nanotubes exhibit much better sensitivity to ethanol. The response value of Er2O3-Fe2O3 nanotubes to 10 ppm ethanol is 21 at the operating temperature240?, which is 14 times larger than that of pure α-Fe2O3 nanotubes(response value is 1.5). The ethanol sensing properties of α-Fe2O3 nanotubes are remarkably enhanced by doping Er, and the lowest detection limit of Er2O3-Fe2O3 nanotubes is300 ppb, to which the response value is about 2. The response and recovery times are about 4 s and 70 s to 10 ppm ethanol,respectively. In addition, the Er2O3-Fe2O3 nanotubes possess good selectivity and long-term stability.     

The first principles investigation of ferrite magnetic response with mismatch stress

The quasi-ferrite model is proposed and an appropriate PBE exchange functional with the spin density functional theory(SDFT) is selected for the calculation of the relation between magnetic moment and residual stress in ferrite using a quantum mechanics code. The relationship between ferrite magnetism and the carbon content is determined,and then a ferrite interstitial solid solution(ISS) model in a low carbon concentration state is replaced with an α- Fe model in the case of majority magnetic calculation. The band structure of the loaded-Fe is compared with that of the unloaded α-Fe. The comparison shows that the energy of Fe atomic 3d orbital changes a little,while the energy of electron orbital of iron core below 3d almost keeps unchanged. The relationship between the magnetic moment and the stress appears intermittent due to the Bragg total reflection. The change in the magnetic moment due to lattice mismatch is much larger than that caused by mechanical loading.     

Raman Scattering Detection of Stacking Faults in Free-Standing Cubic-SiC Epilayer

We report on stacking fault （SF） detection in free-standing cubic-SiC epilayer by the Raman measurements. The epilayer with enhanced SFs is heteroepitaxially grown by low pressure chemical vapour deposition on a Si（100） substrate and is released in KOH solution by micromechanical manufacture, on which the Raman measurements are performed in a back scattering geometry. The TO line of the Raman spectra is considerably broadened and distorted. We discuss the influence of SFs on the intensity profiles of TO mode by comparing our experimental data with the simulated results based on the Raman bond polarizability （BP） model in the framework of linearchain concept. Cood agreement with respect to the linewidth and disorder-induced peak shift is found by assuming the mean distance of the SFs to be 11 A in the BP model.     

Step Structure in Cold-Rolled Deformed Nanocrystalline Nickel

The microstructure characteristic of the cold-rolled deformed nanocrystalline nickel metal is studied by transmission electron microscopy. The results show that there are step structures nearby the grain boundary （CB）, and the contrast of stress field in front of the step corresponds to the step in the shape. It is indicated that the interaction between twins and dislocations is not a necessary condition to realizing the deformation. In the later stage of the deformation when the grain size becomes about lOOnm, the deformation can depend upon the moving of the boundary of the stack faults （SFs） which result from the partial dislocations emitted from CBs. However, when the size of SFs grows up, the local internal stress which is in front of the step gradually becomes higher. When this stress reaches a critical value which stops the gliding of the partial dislocations, the SFs will stop to grow up and leave a step structure behind.     

High-Pressure and High-Temperature Behaviour of Gallium Oxide

High-temperature and high-pressure behaviours of β-Ga2O3 powder are studied by energy-dispersive x-ray diffrac- tion in a diamond anvil cell （DAC）. It is found that the phase transition from the monoclinic β-Ga2O3 to the trigonal α-Ga2O3 occurs at around 19.2 GPa under cold compression. By heating the powder to 2000 K at 30 GPa, we confirm that α-Ga2O3 is the most stable structure at the high pressure. Furthermore, the structural transition from β-Ga2O3 to α-Ga2O3 is irreversible. After laser heating, the recrystallized Ga2O3 has a preferable （012） orientation. This interesting behaviour is also discussed.     

Fabrication and Characterization of Mn0.5Zn0.5Fe2O4 Magnetic Nanofibers

Mn0.5Zn0.5Fe2O4 Magnetic nanofibers were fabricated by calcining electrospun polymer/inorganic composite nanofibers and characterized by thermogravimetric and differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and a vibrating sample magnetometer. The experimental results show that the pure spinel structure is basically formed when the composite nanofibers are calcined at 450°C for 2h. With the increasing calcination temperature, both the saturation magnetization and coercivity of nanofiber samples increase initially along with the growth of Mn0.5Zn0.5Fe2O4 nanocrystals contained in the nanofibers. However, when the calcination temperature reaches 550°C, the saturation magnetization of nanofibers starts to dramatically decrease owing to the formation of the α-Fe2O3 phase at this temperature. The prepared Mn0.5Zn0.5Fe2O4 nanofibers calcined at 500°C for 2h have diameters ranging from 100 to 200nm. Their saturation magnetization and coercivity are 12.37emu/g and 4.81kA/m at room temperature, respectively.     

Synthesis, structure and antiferromagnetic behaviour of brannerite MnV2O6

Brannerite MnV 2 O 6 with plate-like shape is successfully synthesized by hydrothermal method.Its crystal structure and morphology are investigated by x-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscope (TEM),high resolution transmission electron microscopy (HRTEM) and select area electronic diffraction (SAED).The results show that the brannerite MnV 2 O 6 with monoclinic structure has a uniform plate-like shape with a diameter of about 5-8 μm and a thickness of about 500 nm.SAED patterns further confirm the structure of the brannerite MnV 2 O 6 and the single crystalline character of the plate crystal.Magnetic properties are measured by superconducting quantum interference device (SQUID) in a temperature range of 2-300 K under a magnetic field of 1 T.The magnetic measurement results indicate that the material undergoes an antiferromagnetic transition with a N’eel temperature of 17 K.Above 50 K,the inverse susceptibility is fitted well to the Curie-Weiss law with a calculated moment of 5.98 μ B.Finally,the origin of antiferromagnetic behaviour in the brannerite MnV 2 O 6 is explained by means of Anderson model.     

Synthesis and Photoluminescence Properties of GaAs Nanowires Grown on Fused Quartz Substrates

GaAs nanowires are synthesized on fused quartz substrates by using molecular beam epitaxy via a vapor-liquidsolid mechanism with gold as the catalyst. High resolution-transmission electron microscopy is used to probe crystal quality and growth direction. Miero-photolumineseenee measurements are carried out to examine the optical properties of GaAs NWs. The low-temperature photoluminescenee （PL） emission of nanowires （NWs） has a peak at 1.513eV, 2meV lower than the zinc blende GaAs free exciton energy. The temperature-dependent band gap of NWs is seen to be somewhat different from that observed in bulk OaAs, and the PL rapidly quenches above 150K, with an activation energy of 6.3meV reflecting the presence of the longitudinal twins＇ structure.     

Synthesis and room-temperature NO_2 gas sensing properties of a WO_3 nanowires/porous silicon hybrid structure

We report on the fabrication and performance of a room-temperature NO2 gas sensor based on a WO3 nanowires/porous silicon hybrid structure. The W18O49 nanowires are synthesized directly from a sputtered tungsten film on a porous silicon （PS） layer under heating in an argon atmosphere. After a carefully controlled annealing treatment, WO3 nanowires are obtained on the PS layer without losing the morphology. The morphology, phase structure, and crystallinity of the nanowires are investigated by using field emission scanning electron microscopy （FESEM）, X-ray diffractometer （XRD）, and high-resolution transmission electron microscopy （HRTEM）. Comparative gas sensing results indicate that the sensor based on the WO3 nanowires exhibits a much higher sensitivity than that based on the PS and pure WO3 nanowires in detecting NO2 gas at room temperature. The mechanism of the WO3 nanowires/PS hybrid structure in the NO2 sensing is explained in detail.     

Thermal Expansion Anomaly and Spontaneous Magnetostriction of Y2Fe14Al3 Compound

The structure and magnetic properties of Y2Fe14Al3 compound are investigated by means of x-ray diffraction and magnetization measurements. The Y2Fe14Al3 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion is found in Y2Fe14Al3 compound in the temperature range from 403 to 491K by x-ray dilatometry. The coefficient of the average thermal expansion is α^- = -2.54Х 10^-5 K^-1. The spontaneous magnetostrictive deformations from 283 to 470 K are caJculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 5.74 × 10^-3 to nearly zero with temperature increasing from 283 to 470K, the spontaneous linear magnetostrictive deformation λc along the c-axis is larger than the spontaneous linear magnetostrictive deformation λa in basal-plane in the same temperature below 350 K.     

Phase-Transition and Magnetic Moment of the Gd3+ Ion in the Gd2Fe17 Compound

The structure and magnetic phase transitions of the Gd2Fe17 compound are investigated by using a differential thermal/thermogravimetric analyzer, x-ray diffraction, and magnetization measurements. The result shows that there are two phase structures for the Gd2Fe17 compound： the hexagonal Th2Nilr-type structure at high temperatures （above 1243℃）, and the rhombohedral Th2Zn17-type structure, respectively. A method to measure the magnetic moments of the Gd-sublattice and the Fe-sublattice in the Gd2Fe17 compound is presented. The moments of the Gd-sublattice and the Fe-sublattice in the Gd2Fe17 compound from 77 to 500 K are measured in this way with a vibrating sample magnetometer. A detailed discussion is presented.     

Aligned Structures of Fe304 Nanoparticles in a Curable Polymer Carrier Induced by a Magnetic Field

To understand the interaction in dipolar systems, it is necessary to investigate the structures formed by the interacting particles. We introduce a polymer acrylic resin carrier to fix the structures in the magnetic fluid （Fe3O4）. An aligned structure is investigated, which is formed under a magnetic field, and fixed in the cured acrylic resin film by evaporating the solvent at room temperature. The aligned structure is confirmed with the help of optical microscopy and optical diffraction for the cured film. Furthermore, we find substructures by using a scanning electronic microscope. Based on the curable and observable structures, a platform can be developed for investigating the aligned structures and configurations dominant by dipolar interaction. This is also helpful for the development of magnetic devices with orderly aligned structures.     

Electronic and magnetic properties of BiFeO_3 with intrinsic defects:First-principles prediction

The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies （denoted as VFe, VBi, and Vo, respectively） are investigated using the first-principles density functional theory plus U calculations. It is revealed that the structural distortions associated with those vacancies impose significant influences on the total density of state and magnetic behaviors. The existence of VBi favors the excitation of the O2p state into the band gap at 0.4 eV, while the O2p and Fe3d orbitals are co-excited into the band gap around 0.45 eV in VFe- Consequently, a giant net magnetic moment of 1.96 P-B is generated in VFe, and a relatively small moment of 0.13 P-B is induced in VBi, whereas Vo seems magnetically inactive. The giant magnetic moment generated in VFe originates from the suppression of the spatially modulated antiferromagnetic spin structure. Furthermore, VFe and VBi have strong influences on dielectric function, and induce some strong peaks to occur in the lower energy level. In contrast, VO has a small effect.     

Room-Temperature Anisotropic Ferromagnetism in Fe-Doped In2O3 Heteroepitaxial Films

Fe-doped In2O3 films are grown epitaxially on YSZ （100） substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the （100） direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2,5 kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.     

Thermodynamical Phase Equilibrium of Iron Nitrides at Low Temperatures

The presence of α-Fe(N),γ‘-Fe4N and ε-Fe2N1-x phases and the phase equilibrium between αFe(N) and γ′-Fe4N,and γ′-Fe4N and ε-Fe2N1-x have been studied at low temperatures below 350℃ ,according to the binary Fe-N phase diagram calculated using the sublattice-compound energy model,The α-Fe(N),γ′-Fe4N and ε-Fe2N1-x phases would be thermodynamically stable at the low temperatures.Thermodynamic phase equilibrium of the iron nitrides is supproted by the experimental results,explaining the phase formation and its stability in the Fe-N system at low temperatures.