Iron-containing coatings obtained by microplasma method on aluminum with usage of homogeneous electrolytes

The microplasma synthesis method of multicomponent oxide coatings including iron oxide on an aluminum alloy surface has been studied. The homogeneous electrolytes containing iron complexes with Edta⁴⁻ under pH 9-10 have been used. The dynamics reducing the pH of the electrolyte during formation process have been studied. The content of iron in the coatings has been measured spectrophotometricaly. Morphlogy and phase composition of the coatings have been studied by the scanning electron microscopy and X-ray powder diffraction.     

Microstructural and magnetic properties of CoPt nanowires

In this work, the magnetic and microstructural properties of CoPt nanowires are presented as a function of the electrolyte pH and current density during electrodeposition into anodized alumina templates. CoPt nanowires of high aspect ratio have been prepared using electrolyte pH values in the range from 2 to 6. The as-made samples exhibit a face centered cubic (fcc) structure with soft magnetic properties which transform into the face centered tetragonal (fct) L10 phase after thermal treatment. Different pH values of the electrolyte during electrodeposition lead to significantly different microstructures and, therefore, different magnetic properties. The CoPt nanowires prepared at high pH value are composed of fcc nanorods of about 25 nm in length. Thermal annealing of these samples leads to a preferred (0 0 1) orientation (along the direction perpendicular to the direction of nanowires) which increases with annealing time. On the other hand, the CoPt nanowires prepared at lower pH value are composed of uniform fcc nanograins with the size ∼2−3 nm. Magnetization curves for the later sample are virtually identical in both directions indicating an isotropic behavior.     

非晶Fe89.7P10.3合金纳米线阵列的磁性研究

利用电化学沉积方法在阳极氧化铝模板中制备了Fe_89.7P_10.3非晶 合金纳 米线阵列.利用x射线衍射仪、透射电子显微镜、振动样品磁强计和穆斯堡尔谱仪研究了样品的结构和磁性,发现纳米线阵列是非晶结构，且拥有垂直磁各向异性和高的矫顽力，H_c =304×10⁴A/m.纳米线内部的平均超精细场和平均同质异能移分别为2 15×10⁶ A/m和007 mm/s；而纳米线末端的平均超精细场（233×10⁶ A/m ）大于内 部的值，平均同质异能移（004 mm/s）小于内部的值.另外，纳米线内部Fe原子磁矩与线轴的夹角约为16°，而在纳米线末端Fe原子磁矩与线轴的夹角约为28°.这些结果表明，由于形状各 向异性，在纳米线中实现了无序非晶合金磁矩的有序排列. 关键词： 非晶合金 纳米线阵列 垂直磁各向异性 穆斯堡尔谱     

AuPd纳米粒子作为催化剂制备硼纳米线及其场发射性质

利用化学气相沉积法,采用不同组分的金属合金纳米粒子AuPd作为催化剂,在Si(111)基底上成功制备大面积、高密度的硼纳米线薄膜.纳米线的平均长度约为10μm,直径在50—130 nm之间.结构分析表明,纳米线为单晶结构,硼纳米线的直径随着元素Pd在合金催化剂中比例的增加而减少.场发射特性测试结果表明,通过调整催化剂组分可以实现对硼纳米线的尺寸和密度的调控.     

Magnetoelectric and magnetoelastic interactions in NdFe3(BO3)4 multiferroics

Complex experimental and theoretical investigations of the magnetic, magnetoelectric, and magnetoelastic properties of neodymium iron borate NdFe₃(BO₃)₄ along various crystallographic directions have been carried out in strong pulsed magnetic fields up to 230 kOe in a temperature range of 4.2–50 K. It has been found that neodymium iron borate, as well as gadolinium iron borate, is a multiferroic. It has a much larger (above 300 μC/m²) electric polarization controlled by the magnetic field and giant quadratic magnetoelectric effect. The exchange field between the rare-earth and iron subsystems (～50 kOe) has been determined for the first time from experimental data. The theoretical analysis based on the magnetic symmetry and quantum properties of the Nd ion in the crystal provides an explanation of the unusual behavior of the magnetoelectric and magnetoelastic properties of neodymium iron borate in strong magnetic fields and correlation observed between them.     

Preparation and chemical stability of iron-nitride-coated iron microparticles

Iron-nitride-coated iron microparticles were prepared by nitridation of the surface of iron microparticles with ammonia gas at a temperature of 510 °C. The phases, composition, morphology, magnetic properties, and chemical stability of the particles were studied. The phases were α-Fe, ε-Fe₃N, and γ-Fe₄N. The composition varied from the core to the surface, with 99.8 wt% Fe in the core, and 93.8 wt% Fe and 6 wt% N in the iron-nitride coating. The thickness of the iron-nitride coating was about 0.28 μm. The chemical stability of the microparticles was greatly improved, especially the corrosion resistance in corrosive aqueous media. The saturation magnetization and the coercive force were 17.1×10³ and 68 kA/m, respectively. It can be concluded that iron-nitride-coated iron microparticles will be very useful in many fields, such as water-based magnetorheological fluids and polishing fluids.     

InN纳米线的低压化学气相沉积及其场发射特性研究

利用低压化学气相沉积方法在以Au作催化剂的Si衬底上生长了InN纳米线. 扫描电子显微镜分析表明，这些纳米线的直径在60—100 nm的范围内, 而其长度大于1 μm.高分辨透射电子显微镜图像表明，合成的纳米线中含有六方相和立方相的InN晶体.这些InN纳米线具有良好的场发射特性和稳定的场发射电流，其开启场为10.02 V/μm(电流密度为10 μA/cm²)，在24 V/μm 的电场下，其电流密度达到5.5 mA/cm².此外，对InN纳米线的场发射机理也进行了讨论. 关键词： InN纳米线 场电子发射 非线性Fower-Nordheim曲线     

热压铁氧体的制备条件和磁性

本文从实验上研究了起始粉料的制备方法和热压条件对磁头用的Mn-Zn及Ni-Zn热压铁氧体的密度、显微结构和磁性的影响。实验结果表明,化学共沉淀法制备的铁氧体粉料比氧化物法及硫酸盐法制备的要好。适当选择热压条件,可以获得晶粒分布均匀、晶粒大小不同(10μm—300μm)的高密度铁氧体;可以获得μ₀=7420以及B_m=4950Gs的高密度Mn-Zn铁氧体和μ₀等于100—2500的高密度Ni-Zn铁氧体。     

Properties of transparent,conducting ZnO films deposited by reactive bias sputtering

Transparent ZnO thin films of resistivity 2×10^?3 Ωcm have been prepared by a reactive bias sputtering technique. Carrier concentration and mobility were determined by Hall probe measurements. Microstructure and grain size were studied using a scanning electron microscope and an X-ray diffractometer. Optical constants were measured for the wavelength range 0.35 to 2.50 μm and infrared reflectivity for the range 2.5 to 20 μm. These optical properties were modelled by the Drude theory of free electrons utilizing measured electrical transport parameters.     

Study of catalytic properties of sol-gel-derived CoO x -SiO2 film systems by the example of the growth of carbon nanomaterials

Film catalytic samples in the Si-Co-O system in the composition range from 15 to 90 mol % Co have been prepared using the sol-gel technology. Carbon nanomaterials have been fabricated by pyrolytic synthesis using these films as catalysts. Raman spectroscopy of materials has shown that multiwalled carbon nanotubes are formed by pyrolysis on catalytic films containing Co₃O₄. The dependence of the carbon material length on the synthesis time has been considered. It has been shown that the average growth rate of tubes and fibers is ～3 μm/min.     

Study on the coercivity of granular solid iron

The iron granular solid, in which ultrafine iron particles are dispersed, has been prepared with both SiO₂ and Cu matrices using the sol-gel method. The structure and morphology of these granular solid samples are investigated by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The magnetic properties are measured using a vibrating sample magnetometer with 20 kOe maximum applied field. It is found that the coereivity decreases very slightly with temperature from 80 to 300 K for these Fe–SiO₂ and Fe–Cu granular solid samples with different average size of iron particles from 50 to 300 Å. The magnetic anisotropy has been obtained from the measured magnetization curves for these granular solid samples using the law of approach to saturation, and the obtained values of the effective magnetic anisotropy are all more than 10⁶ erg/cm³, which are larger than the value of the magnetocrystalline anisotropy for bulk iron. The coercivity vs temperature for these granular solid samples has been calculated using the Kneller and Luborsky theory, in which the magnetic anisotropy values obtained from the law of approach to saturation are used. The trends of the calculated coercivity as a function of temperature are in reasonable agreement with the observations.     

Growth,structure, and cathodoluminescence of Dy-doped ZnO nanowires

Dy-doped ZnO nanowires have been prepared using high-temperature and high-pressure pulsed-laser deposition. The morphology, structure, and composition of the as-prepared nanostructures are characterized by field emission scanning electron microscopy, X-ray diffraction, Raman scattering spectrometry, X-ray photoelectron spectrometry, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The alloying droplets are located at the top of the as-prepared Dy-doped ZnO nanowires, which means that the growth of the Dy-doped ZnO nanowires is a typical vapor-liquid-solid process. The luminescence properties of Dy-doped ZnO nanowires are characterized by cathodoluminescence spectra and photoluminescence spectra at low temperature (8 K). Two peaks at 481 and 583 nm, respectively, are identified to be from the doped Dy³⁺ ions in the CL spectra of Dy-doped ZnO nanowires.     

Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

MBE growth of ZnSe nanowires on oxidized silicon substrate

We report the growth of single crystalline ZnSe nanowires on oxidized Si(100) substrates by molecular-beam epitaxy using Au nano-particles as the catalysts. It was found that average length decreased while the average diameter increased as we increased the temperature from 230 to 320 ^°C. It was also found that crystal quality of the ZnSe nanowires prepared at 320 ^°C was poorer than the ZnSe nanowires prepared at 230 ^°C and 280 ^°C.     

Dimorphic magnetorheological fluid with improved rheological properties

A type of dimorphic magnetorheological (MR) fluid was prepared by adding wire-like iron nanostructures into the conventional carbonyl iron based MR fluid. The Fe nanowires were synthesized through reducing Fe²⁺ ion with excessive sodium borohydride in aqueous solution. The rheological behaviors of the dimorphic MR fluids were measured with a rotational rheometer and the sedimentation properties were also studied in this work. It was found that the Fe wires additives can greatly enhance the stress strength of the dimorphic MR fluids comparing with the conventional MR fluids. The sedimentation of the dimorphic MR fluids was also mitigated greatly.     

Controlled synthesis and magnetic properties of hard magnetic CoxC (x=2, 3) nanocrystals

We report our recent results in synthesis and characterization of cobalt carbide (Co₃C and Co₂C) nanoparticles and nanowires. The synthesis methods were based on a simple one-pot tetraethylene glycol reduction process. By changing the synthesis parameters, the nanocrystal morphology can be adjusted from nanoparticles with different size to nanowires. The magnetic properties of the nanostructure and their correlation to the crystalline structures and the nanoscale morphology have been investigated theoretically and experimentally. It is revealed that the properties are related to both the crystal structures and the morphology.     

Synthesis and magnetic properties of spinel CoFe2O4 nanowire arrays

Spinel CoFe₂O₄ nanowire arrays were synthesized in nanopores of anodic aluminum oxide (AAO) template using aqueous solution of cobalt and iron nitrates as precursor. The precursor was filled into the nanopores by vacuum impregnation. After heat treatment, it transformed to spinel CoFe₂O₄ nanowires. The structure, morphology and magnetic properties of the sample were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicate that the nanowire arrays are compact. And the individual nanowires have a high aspect ratio, which are about 80 nm in diameter and 10 μm in length. The nanowires are polycrystalline spinel phase. Magnetic measurements indicate that the nanowire arrays are nearly magnetic isotropic. The reason is briefly discussed. Moreover, the temperature dependence of the coercive force of the nanowire arrays was studied.     

Controlled Cu content of electrodeposited CoCu nanowires through pulse features and investigations of microstructures and magnetic properties

CoCu alloy nanowire arrays embedded in anodic alumina template were fabricated by ac pulse electrodeposition. Different off-times between pulses in an electrolyte with constant concentration of Co⁺² and Cu⁺² and acidity of 4 were employed. The effect of deposition parameters on the alloy contents, microstructures and magnetic properties of Co_xCu_1−x nanowires were studied. It is shown that Co content decreased by increasing the off-time between pulses in a wide range (x = 0.53-0.07). These results are in consistence with saturation magnetization, which was reduced with increase in the off-time between pulses. It was also found that by optimizing the off-times, it is possible to fabricate CoCu nanowires with mixed phase of hcp Co, fcc Cu and fcc CoCu crystal phase.     

Synthesis,structure, and magnetic properties of iron and nickel nanoparticles encapsulated into carbon

Nanocomposites based on iron and nickel particles encapsulated into carbon (Fe@C and Ni@C), with an average size of the metal core in the range from 5 to 20 nm and a carbon shell thickness of approximately 2 nm, have been prepared by the gas-phase synthesis method in a mixture of argon and butane. It has been found using X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy that iron nanocomposites prepared in butane, apart from the carbon shell, contain the following phases: iron carbide (cementite), α-Fe, and γ-Fe. The phase composition of the Fe@C nanocomposite correlates with the magnetization of approximately 100 emu/g at room temperature. The replacement of butane by methane as a carbon source leads to another state of nanoparticles: no carbon coating is formed, and upon subsequent contact with air, the Fe₃O₄ oxide shell is formed on the surface of nanoparticles. Nickel-based nanocomposites prepared in butane, apart from pure nickel in the metal core, contain the supersaturated metastable solid solution Ni(C) and carbon coating. The Ni(C) solid solution can decompose both during the synthesis and upon the subsequent annealing. The completeness and degree of decomposition depend on the synthesis regime and the size of nickel nanoparticles: the smaller is the size of nanoparticles, the higher is the degree of decomposition into pure nickel and carbon. The magnetization of the Ni@C nanocomposites is determined by several contributions, for example, the contribution of the magnetic solid solution Ni(C) and the contribution of the nonmagnetic carbon coating; moreover, some contribution to the magnetization can be caused by the superparamagnetic behavior of nanoparticles.     

Magnetic properties of 2 nm α-Fe particles

Ultrafine metallic iron particles with a mean diameter of 2 nm have been prepared on a carbon support and were studied by in situ Mössbauer spectroscopy. It is found that even in these extremely small particles, containing on the average about 350 atoms, most of the atoms are in environments which are quite similar to those of iron atoms in bulk -Fe. The surface hyperfine field is larger than the bulk value at 5 K, but decreases rapidly with increasing temperature. The magnetic energy constant was found to beK (3.0±1.0)×10⁵ J m^–3.