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.     

Modification of the optical spectra of mixed K2CoxNi1–x(SO4)2?6H2O crystals

We propose a new method for obtaining K₂Co _x Ni_1–x (SO₄)₂⋅6H₂O (x = 0, 0.4, 0.8, 1) crystals, involving the use of the chlorides (CoCl₂⋅6H₂O and NiCl₂⋅6H₂O) in an aqueous solution instead of the widely used sulfates. We have studied the transmission spectra of the grown single crystals in the range λ = 200–900 nm and the IR reflectance spectra in the 2.5–20 μm region. We have observed a change in the position and intensity of the absorption bands as a function of the composition of the crystals. Based on the Tanabe–Sugano diagrams, we determined the crystal field splitting (D_q) and its dependence on the nickel concentration. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 126–130, January–February, 2009.     

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.     

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.     

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.     

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     

Structure and magnetism of semiconductor crystals of the (Ga1 ? xMnx)2Se3 (x = 0?0.04) compounds

Neutron diffraction and magnetic measurements have been used to study the effect of doping with Mn³⁺ ions on the fine crystal structure of the Ga₂Se₃ monoclinic compound. It has been established that the structural state of the crystals is changed even at a relatively low doping level (x = 0.04). Arguments in favor of the fact that local Jahn-Teller distortions are responsible for the formation of the fine structure and magnetism in compounds of this class are presented.     

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.     

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.     

Elektronen-Spin-Resonanz an (La1??xGdyCex)Al2

In the EPR of (La_1––x Gd _y Ce _x )Al₂ a bottleneck in the relaxation of the conduction electrons to the lattice is present at sufficiently high Gd-concentrations. The bottleneck can be broken by decreasing the Gd-concentration or by adding Cerium as a spin-flip-scatterer.g-factor and line broadening are measured for (La_1–y Gd _y )Al₂ and (La_1––x Gd _y Ce _x )Al₂ as a function of temperature and Gd- and Ce-concentrations. The Cerium induced relaxationsrate _eL (Ce) increases linearly with Ce-concentration up tox0.025. This corresponds to the fact, well known by measurements of the Kondo anomalies, that Cerium impurities show no significant interaction up to rather high concentrations.     

Band alignment and interfacial properties of atomic layer deposited (TiO2)x(Al2O3)1?x gate dielectrics on Ge

(TiO₂) _x (Al₂O₃)_1−x (x=0.7,0.8,0.9) gate dielectrics were deposited on Ge by atomic layer deposition using trimethylaluminium and Ti isopropoxide. The interfacial properties and band alignment were investigated by means of transmission electron microscopy (TEM) and X-ray photoemission spectroscopy. High-resolution TEM results show that the (TiO₂)_0.8(Al₂O₃)_0.2 film annealed at 500°C is amorphous with sharp interface between (TiO₂)_0.8(Al₂O₃)_0.2 and Ge. The conduction-band offsets are enhanced from 1.04 to 1.40 eV with increasing Al content. Capacitance equivalent thickness of 15.8 ? for (TiO₂)_0.9(Al₂O₃)_0.1 gate dielectrics is achieved with a gate leakage current of 2.70×10⁻⁵ A/cm² at V _g=+1 V.     

Transport studies at the Mott transition of the two-dimensional organic metal κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x

The two-dimensional organic conductor κ-(BEDT-TTF)₂Cu[N(CN)₂]Br _x Cl_{1- x} undergoes a transition from an insulator to a superconductor upon substituting Cl by Br. We have performed in- and out-of-plane electric-transport measurements on the alloyed series with x = 20%, 40%, 70%, 80%, 85%, and 90% as a function of temperature in order to explore the bandwidth-controlled phase transition between the Mott insulator and the Fermi-liquid. All crystals exhibit a similar semiconducting behavior of ρ(T) from room temperature down to 100 K. Below approximately 50 K, a metal-to-insulator transition is found for compounds with x < 70%. Out of this Mott insulating state, magnetic order develops below T _N ≈ 25 K. The Br-rich samples cross a bad-metal regime before they become coherent metals and eventually superconducting at T _c ≈ 12 K. For these systems the resistivity at T _c ≤ T ≤ T ₀ reveals a ρ(T) ∝ T ² dependence associated with a strongly correlated Fermi-liquid, limited by some characteristic temperature T ₀. The conclusions are corroborated by data from microwave, magnetic and optical experiments.     

Anomalous effect of magnetic field on the low-temperature thermal expansion of the Bi2Sr2?xLaxCuO6+δ and Nd2?xCexCuO4?δ HTSC systems in the non-superconducting phase

The thermal expansion of single crystals of the Bi₂Sr_2−x La _x CuO_6+δ high-temperature superconducting (HTSC) system in the insulating phase with compositions having no superconducting transition to a temperature of 1.8 K (x ≥ 0.8) is measured in an arbitrary direction in the (ab) plane in the temperature range of 7–50 K. Temperature regions of material compression upon heating are found. The study of anomalies in magnetic fields of 3 and 6 T, parallel and perpendicular to the c-axis revealed an anisotropic and nonmonotonic effect of the field on thermal expansion. Such anomalies for the n-type Nd_2−x Ce _x CuO_4−δ HTSC sample also having no superconducting transition are detected for the first time. The results show that the anomaly nature is caused by anisotropic electronic ordering, probably, by the charge density wave in the CuO₂ plane and superconductivity fluctuations in the insulating phase.     

Anomalous enhancement of the thermoelectric power in gallium-doped p-(Bi1 ? xSbx)2Te3 single crystals

The effect of gallium on the temperature dependences (5 K ≤ T ≤ 300 K) of Seebeck coefficient α, electrical conductivity σ, thermal conductivity k, and thermoelectric efficiency Z of mixed p-(Bi_0.5Sb_0.5)₂Te₃ semiconductor single crystals is studied. The hole concentration decreases upon gallium doping; that is, gallium causes a donor effect. The Seebeck coefficient increases anomalously, i.e., much higher than it should be at the detected decrease in the hole concentration. This leads to an enhancement of the thermoelectric power. The observed changes in the Seebeck coefficient indicate a noticeable gallium-induced change in the density of states in the valence band.     

(Bi1-x Agx)2(Te1-ySey)3粉体的机械合金化制备及其放电等离子烧结体的热电输运特性

采用机械合金化制备了n型(Bi_1-xAg_x)₂(Te_1-ySe_y)₃合金粉体,对其进行XRD分析表明Bi,Te,Ag,Se单质粉末,经2h球磨后实现了合金化;SEM分析表明随着机械合金化时间延长粉体颗粒变得均匀、细小,颗粒尺寸在微米至亚微米数量级.采用放电等离子烧结制备了块体样品,研究了合金成分和球磨时间对热电性能的影响.结果表明材料的热电性能与掺杂元素有密切关系,Ag有利于提高功率因子和降低晶格热导率,球磨10h的(Bi_0.99Ag_0.01)₂(Te_0.96Se_0.04)₃合金粉末的烧结块体具有最大的功率因子和最低的晶格热导率,并在323K取得最高ZT值0.52. 关键词： 1-xAg_x)₂(Te_1-ySe_y)₃合金')" href="#">(Bi_1-xAg_x)₂(Te_1-ySe_y)₃合金 机械合金化 放电等离子烧结 热电性能     

Co(S1-xSex)2系统中的铁磁量子相变

针对Co(S_1-xSe_x)₂系统在x=0.11附近发生的铁磁金属到顺磁金属相变,制备了一系列不同Se替代浓度的多晶样品.通过对其结构和电阻率-温度ρ(T)关系的系统观测,结果发现,样品铁磁相变温度T_C随着Se替代浓度x值的增加,以(1-x)^1/2关系单调下降,其二级铁磁相变转变为一级相变 关键词： 量子相变 自旋量子涨落 1-xSe_x)₂')" href="#">Co(S_1-xSe_x)₂     

(La0.7Sr0.3MnO3 )m(BiFeO3)n 超晶格结构的导电机理

利用射频磁控溅射的方法在SrTiO₃(001) 基片上制备了(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构.对所制备的超晶格结构进行了50—150℃温度范围内的电流-电压测试分析.结果表明,随着BiFeO₃薄膜的厚度减小,温度的升高,(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构的电流变大.进一步根据介质导电模型对(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构的导电特性做了分析.在温度较低或者电场较弱时,所制备的(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构表现为欧姆导电,而在高温,高电场的情况下,其导电行为由空间电荷限制电流机理主导. 关键词： 超晶格薄膜 多铁 空间电荷限制电流     

Ue(1)-covariant Rξ gauge for the two-Higgs doublet model

A U _e (1)-covariant R _ξ gauge for the two-Higgs doublet model based on BRST (Becchi-Rouet-Stora-Tyutin) symmetry is introduced. This gauge allows one to remove a significant number of nonphysical vertices appearing in conventional linear gauges, which greatly simplifies the loop calculations, since the resultant theory satisfies QED-like Ward identities. The presence of four ghost interactions in these types of gauges and their connection with the BRST symmetry are stressed. The Feynman rules for those new vertices that arise in this gauge, as well as for those couplings already present in the linear R _ξ gauge but that are modified by this gauge-fixing procedure, are presented.     

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.