Electrical and magnetic properties of [(CoFeZr)x(Al2O3)1 ? x/(α-SiH)]n multilayer structures

The concentration dependences of the electrical resistivity and complex permeability of [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n multilayer structures and (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites have been studied. It has been established that introduction of a semiconductor interlayer into the (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites substantially decreases the electrical resistivity of [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n multilayer structures. The concentration dependences of the real and imaginary parts of the complex permeability of the [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n nanomultilayer structures substantially differ from those of the (Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} composites. The real part of the complex permeability of the [“(Co₄₅Fe₄₅Zr₁₀) _x (Al₂O₃)_{100 − x} ”/“α-Si: H”] _n nanomultilayer structures follows the curve with a minimum near the percolation threshold of the composite, and the imaginary part smoothly decreases as the ferromagnetic phase concentration increases. The results obtained are explained by the increase in the bifurcation temperature due to the conduction electrons of the semiconductor interlayer, which favor magnetic ordering of ferromagnetic grains.     

Ferromagnetic resonance, magnetic properties, and resistivity of (CoFeZr)x(Al2O3)1 ? x/Si multilayer nanostructures

Comparative investigations of static magnetic properties, magnetoresistance, and ferromagnetic resonance data of multilayer nanostructures consisting of CoFeZr-Al₂O₃ composite magnetic layers and amorphous silicon semiconductor spacers were performed in a layer thickness range below 5 nm. The influence of layer dimension parameters and chemical peculiarities of silicon on the inner structure and type of magnetic interactions in nanostructures with 35 and 46 at % magnetic phase composite layers is discussed.     

Tuning X/(TiO2)x–(SiO2)100 – x (0 < x < 40) xerogel photocatalysts

Microporous (TiO₂) _x –(SiO₂)_{100 − x} (0 < x < 40) xerogels have been produced by sol–gel methods either by partial pre-hydrolysis or reflux of tetraethoxysilane and titanium isopropoxide. These have been characterised by ²⁹Si nuclear magnetic resonance, X-ray diffraction, EXAFS at the Ti–K edge, X-ray photoelectron spectroscopy, temperature-programmed reduction, FT infrared, N₂ adsorption at 78 K (BET), transmission electron microscopy and dynamic light scattering (DLS). These were dip coated onto fused silica and characterised by atomic force microscopy and UV–visible absorption. Their photoactivity in removal of alkylphenol ethoxylate TX100 from water was less than for less porous titania. The advantages of including thermally removable PEG or PPG templates in terms of increasing surface, meso-porosity and photon absorbance at visible wavelengths to give nanoengineered photocatalytic films are described.     

Ferromagnetic resonance and magnetic microstructure in nanocomposite films of Cox(SiO2)1 ? x and (CoFeB)x(SiO2)1 ? x

This paper reports on the results of the investigation of the relation between the magnetic microstructure and ferromagnetic resonance (FMR) in ferromagnetic metal-insulator composites by using granular alloys (Co₄₁Fe₃₉B₂₀) _x (SiO₂)_{1 − x} and Co _x (SiO₂)_{1 − x} as an example. A comparative analysis of the properties of FMR spectra and parameters of random magnetic anisotropy leads to correlations between these quantities. It has been found that the main mechanism that determines the FMR line width in the films under investigation is the exchange narrowing mechanism.     

Profile of the refractive index distribution over the depth of (HfO2)x(Al2O3)1 ? x films

Capabilities of the method of laser null ellipsometry for the study of optical parameters of thin films of multicomponent alloys are demonstrated. Films of alloys (HfO₂) _x (Al₂O₃)_{1 − x} on single-crystal silicon are obtained by the chemical vapor deposition with the use of the following volatile compounds: hafnium dipivaloylmethanate (IV) and aluminum acetylacetonate (III). The selection of initial sets for their optical parameters is justified. The selected model is shown to correspond to experimental data. In films deposited from the mixture of precursors, the refractive index increases from a substrate to a film surface. Due to the separation of sources, films described by a single-layer model were deposited. This fact is indicative of the homogeneous distribution of components over the film thickness.     

Magnetic and band parameters of (3HgS)1–x(Al2S3)x (x = 0.5) crystals doped with manganese

Investigations of magnetic susceptibility (χ) of (3HgS)_1–x (Al₂S₃) _x (x = 0.5) crystals doped with manganese investigated by the Faraday method in the range of Т = 77–300 K and Н = 0.25–4 kOe demonstrate that peculiar magnetic properties can be due to the presence of clusters of the Mn–S–Mn–S type in these crystals. Based on the investigation of kinetic coefficients of the crystals performed for Т = 77–300 K and Н = 0.5–5 kOe, it is established that the crystals demonstrate conductivity of the n-type, and their electric conduction only very slightly depends on the temperature and shows a maximum, the Hall coefficient is independent of the temperature, while the temperature dependences of mobility exhibit a maximum. Using the concentration dependence of the effective electron mass at the Fermi level, the width of the forbidden band, the matrix element of interatomic interaction, and the effective mass on the conduction-band bottom are obtained. Based on investigations by optical methods, the presence of direct optical interband transitions in the crystals is established and the value of the optical forbidden band (at Т = 300 K) is determined.     

Optical properties of (In2Se3)1–x·(CuIn5Se8)x solid solutions

Single crystals of In₂Se₃ and CuIn₅Se₈ compounds and (In₂Se₃)_1–x·(CuIn₅Se₈)_x solid solutions have been grown from the melt using the Bridgman method and their composition and structure determined. It is shown that the crystals have n-type conductivity. Their transmission spectra were studied in the self-absorption edge region at 80 and 295 K. Based on the spectral measurements, the band gap width (E_g) was determined and the band gap concentration dependences were plotted. It is found that E_g varies with the x composition nonlinearly. Using the dielectric model of Van Vechten–Bergstresser and the Hill–Richardson pseudo potential model, E_g(x) was calculated theoretically.     

Structural and electrical investigation of (Ag3AsS3)x(As2S3)1?x superionic glasses

Structural studies of (Ag₃AsS₃) _x (As₂S₃)_1−x chalcogenide superionic glasses in the compositional range x = 0.3–0.9 were performed by scanning electron microscopy. Temperature and compositional dependences of transmission coefficient, electrical conductivity, and activation energy were investigated     

Electronic properties of LiMn2?xTixO4

Ti-substituted LiMn₂O₄ (LiMn_2−x Ti _x O₄, x=0, 0.15, 0.30, 0.45, 0.60, and 0.75) has been synthesized using solid-state reactions. Their crystal and electronic structures were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). XRD data suggested that the lattice parameters of LiMn_2−x Ti _x O₄ increase due to the replacement of Mn by Ti ions. XPS results indicated that the substituted Ti ions were in +4 oxidation state; consequently, the normal oxidation state of Mn ions has been detected by measuring the binding energy splitting of Mn 3s states, which decreases with the content of substituted Ti. The valence band spectra suggested that the intensity of e _g level of Mn 3d orbitals increased due to the increase of the Mn³⁺/Mn⁴⁺ ratio.     

XANES and USXES studies of interatomic interactions in (Co41Fe39B20)x(SiO2)1 ? x nanocomposites

The electronic structure and phase composition of (Co₄₁Fe₃₉B₂₀) _x (SiO₂)_{1 − x} nanocomposites are studied by x-ray absorption near-edge spectroscopy, which is extremely sensitive to the chemical environment of elements in multicomponent compounds. An analysis of the recorded Fe L _{2, 3}, Co L _{2, 3}, B K, Si L _{2, 3}, and O K absorption spectra demonstrates interatomic interactions between the elements of the metallic and dielectric components of the nanocomposites. As a result of these interatomic interactions, a complex multiphase system, whose electronic structure should determine the transport and magnetic properties of the nanocomposites, forms. In particular, the transformation of the fine structure of the iron L _{2, 3} spectra reflects a change in the ratio of divalent to trivalent iron in its oxides and/or silicates. CoO and complex boron oxides are found to exist in the nanocomposites. The electrical conductivity of a FeO · F₂O₃ · CoO grain embedded in the silicate-oxide medium of the nanocomposites is controlled by electron exchange between Co²⁺, Fe²⁺, and Fe³⁺ ions. The dielectric component consists of a mixture of silicon oxide and the silicates/borosilicates of transition metals. Original Russian Text ? é.P. Domashevskaya, S.A. Storozhilov, S.Yu. Turishchev, V.M. Kashkarov, V.A. Terekhov, O.V. Stogneĭ, Yu.E. Kalinin, A.V. Sitnikov, S.L. Molodtsov, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 1, pp. 135–141.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

Magnetic anisotropy and magnetoelectric properties of Tb1 ? xErxFe3(BO3)4 ferroborates

Magnetic and magnetoelectric properties of ferroborate single crystals with complex composition (Tb_{1 − x} Er _x Fe₃(BO₃)₄, x = 0, 0.75) and with competing exchange Tb-Fe and Er-Fe interactions are investigated. Jumps in electric polarization, magnetostriction, and magnetization are observed as a result of spin-flop transitions, as well as a considerable decrease in the critical field upon an increase in the Er concentration, in a field H _c parallel to the c axis. The observed behavior of phase-transition fields is analyzed and explained using a simple model taking into account anisotropy in g factors and exchange splitting of funda-mental doublets of the easy-axis Tb³⁺ ion and easy-plane Er³⁺ ion. It is established that magnetoelectric and magnetostriction anomalies under spin-flop transitions are mainly controlled by the Tb subsystem. The Tb subsystem makes a nonmonotonic contribution ΔP _a (H _a , T) to polarization along the a axis: the value of ΔP _a reverses its sign and increases with temperature due to the contribution from the excited states of the Tb³⁺ ion. Original Russian Text ? A.K. Zvezdin, A.M. Kadomtseva, Yu.F. Popov, G.P. Vorob’ev, A.P. Pyatakov, V.Yu. Ivanov, A.M. Kuz’menko, A.A. Mukhin, L.N. Bezmaternykh, I.A. Gudim, 2009, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2009, Vol. 136, No. 1, pp. 80–86.     

Low-field magnetization of ludwigites Co3O2BO3 and Co3 ? xFexO2BO3 (x ≈ 0.14)

Ludwigite single crystals of compositions Co₃O₂BO₃ and Co_{3 − x} Fe _x O₂BO₃ (x ≈ 0.14) have been synthesized. The crystal structure is investigated at room temperature, and the magnetization is studied in the temperature range T = 4.2–100 K in magnetic fields of up to 600 Oe. The orthorhombic symmetry is revealed, and the unit cell parameters are determined. A number of features are established for the temperature dependence of the magnetization. In unsubstituted Co₃O₂BO₃, two magnetic transitions are found at T _C1 = 43 K and T _C2 = 15 K. At temperatures below 40 K, spin-glass state is revealed. Substitution of iron ions for cobalt ions leads to a noticeable shift in the magnetic transitions toward the high-temperature range: T _C1 = 83 K and T _C2 = 74 K. A ferromagnetic ordering of the P type is found in the Co_{3 − x} Fe _x O₂BO₃ (x ≈ 0.14) compound. Original Russian Text ? N.V. Kazak, N.B. Ivanova, V.V. Rudenko, A.D. Vasil’ev, D.A. Velikanov, S.G. Ovchinnikov, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 5, pp. 916–919.     

Dynamics and distribution of doped holes in the CuO2 plane of slightly doped antiferromagnetic YBa2(Cu1 ? zLiz)3O6 + x (x < 0.1) studied by Cu(1) NQR

Incidence of doped holes in the CuO₂ plane on the AF state was studied by Cu(1) nuclear quadrupole resonance (NQR) in slightly doped YBa₂(Cu_{1 − z} Li _z )₃O_{6 + x} compounds. Inhomogeneous distribution of doped holes in the plane was detected in the low temperature measurements of transverse (1/T ₂) and longitudinal (1/T ₁) relaxation rates. We establish that at lower T the holes motion slows down and we estimate that the holes localize finally in restricted regions (∼3 lattice constants) in the Coulomb potential of the Li+ ions. Also we compared the hole behavior in slightly doped YBa₂(Cu_{1 − z} Li _z )₃O_{6 + x} samples with that in slightly doped Y_{1 − y} Ca _y Ba₂Cu₃O₆. A stronger trapping potential of the in-plane Li⁺ impurities was concluded as compared to slightly doped Y_{1 − y} Ca _y Ba₂Cu₃O₆ compound with out-of-plane Ca²⁺ impurities.     

(Sb2Te3)0.75(1－x)(Bi2Te3)0.25(1－x)(Sb2Se3)x机械合金化粉体的制备及其冷压烧结样品的热电性能研究

采用机械合金化法制备了p型赝三元(Sb₂Te₃-Bi₂Te₃-Sb₂Se₃)合金粉体，对其进行XRD分析表明Te，Bi，Sb，Se单质粉末，经100h球磨后实现了合金化；SEM分析表明所得机械合金化粉体材料颗粒均匀、细小，颗粒尺寸在10nm到100nm量级.使用这种粉体制备了冷压烧结块体样品，在室温下测量了温差电动势率(α)和电导率(σ)，研究了烧结温度对材料热电性能的影响，结果表明在低于300℃的烧结温区，样品室温下的热电性能随烧结温度的升高不断提高，功率因子(α²σ)由未烧结样品的0.59μW cm^-1K^-2升高到在300℃下烧结样品的15.9μW cm^-1K^-2，这一结果对确定材料的最佳烧结温度具有重要意义. 关键词： 赝三元热电材料 机械合金化 冷压 烧结     

Novel synthesis of NixZn1?xFe2O4 (0?≤?x?≤?1) nanoparticles and their dielectric properties

Nanocrystalline Ni _x Zn_1−x Fe₂O₄ (0 ≤ x ≤ 1) ferrite powders with average particle size 15–20 nm have been successfully prepared at a very low temperature (180 °C) by a novel auto combustion process using citric acid and ethylenediamine as a coordinating agent and bridging ligand, respectively. Phase purity of the solid solutions has been confirmed by X-ray diffraction. Morphological characterizations of the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. Extensive Fourier transformed infrared spectroscopic characterization has been carried out to identify the plausible mechanism of the synthesis process. Composition-dependent electrical properties (resistivity and dielectric constant) of the synthesized solid solution have been investigated. Interestingly, a non-linear variation of dielectric permittivity with respect to composition has been observed. The room temperature electrical resistivity as well as the dielectric permittivity of Ni_0.5Zn_0.5Fe₂O₄ was found to decrease with the decrease of particle size.     

Ti1－x(Hf0.919Zr0.081)xNiSn的制备及热电性能

采用固相反应法合成了单相的Ti_1-x(Hf_0.919Zr_0.081) _xNiSn (x＝0.00—0.15)，并用放电等离子烧结方法制备出密实块体材料. 研究 了Hf和Zr同时在Ti位上的等电子合金化对Ti基半Heusler化合物热电性能的影响规律. 结果 表明：少量的Hf和微量的Zr在Ti位上的等电子合金化，显著地降低了体系的热导率κ，同时 显著地提高了体系的Seebeck系数α. 组成为Ti_{0.85关键词： 半Heusler 固相反应 热电性能}     

Structure, ferroelectric and piezoelectric properties of?(Bi0.98?xLa0.02Na1?x)0.5BaxTiO3 lead-free ceramics

Lead-free (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La²⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi_0.5Na_0.5TiO₃ ceramics, the (Bi_0.98−x La_0.02Na_1−x )_0.5Ba _x TiO₃ ceramics possess much smaller coercive field E _c and larger remanent polarization P _r. Because of the low E _c (3.38 kV/mm), large P _r (46.2 μC/cm²) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d ₃₃=181 pC/N and k _p=36.3%. The depolarization temperature T _d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T _d.