The effect of adding aluminum and iron to Tb–Dy–Ho–Co multicomponent alloys on their structure and magnetic and magnetocaloric properties

A comprehensive analysis of the structure, phase composition, surface topology features, and magnetic and magnetocaloric properties of Tb_0.3Dy_0.35Ho_0.35Co_1.75 T _0.25 (T = Al, Fe) multicomponent alloys has been performed. The specifics of variations in the structure and functional properties induced by the partial substitution of cobalt atoms in the 3d sublattice of RCo₂ with aluminum or iron atoms have been determined.     

Effect of cooling speed on structure and properties of rapidly solidified Pb–25wt.% Sn alloy

The effect of cooling speed on structure, hardness, mechanical and electrical transport properties of rapidly solidified Pb–25wt.% Sn alloy have been investigated. A single roller melt spinning technique with linear speeds 15.7 and 31.7 m/s, was used for the preparation of specimens. The results showed that a lower cooling speed increased the precipitation of Sn in a Pb-matrix phase as compared with the higher cooling speed. This decomposition behavior decreased the electrical resistivity and increased the internal friction, thermal diffusivity and Vickers microhardness of the lower cooling speed as compared with those of the higher cooling speed.     

Effect of fuel on the formation structure,transport and magnetic properties of LaMnO3+ δ nanopowders

Single-step low-temperature solution combustion (LCS) synthesis was adopted for the preparation of LaMnO_{3+ δ} (LM) nanopowders. The powders were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), surface area and Fourier transform infrared spectroscopy (FTIR). The PXRD of as-formed LM showed a cubic phase but, upon calcination (900°C, 6 h), it transformed into a rhombohedral phase. The effect of fuel on the formation of LM was examined, and its structure and magnetoresistance properties were investigated. Magnetoresistance (MR) measurements on LM were carried out at 0, 1, 4 and 7 T between 300 and 10 K. LM (fuel-to-oxidizer ratio; ψ = 1) showed an MR of 17% at 1 T, whereas, for 4 and 7 T, it exhibited an MR of 45 and 55%, respectively, near the T _M-I. Metallic resistivity data below T _M-I showed that the double exchange interaction played a major role in this compound. It was interesting to observe that the sample calcined at 1200°C for 3 h exhibited insulator behavior.     

Correlation of dielectric properties,Raman spectra and calorimetric measurements of β-cyclodextrin-polyiodide complexes (β-cyclodextrin)2 ·BaI7 ·11H2O and (β-cyclodextrin)2 ·CdI7·15H2O

The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)₂·BaI₇·11H₂O and (β-CD)₂·CdI₇·15H₂O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba²⁺ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm^?1, 170?cm^?1 and 165–166?cm^?1 are due to the charge transfer interactions in the polyiodide chains.     

Electronic structure and optical properties of LiXH3 and XLiH3 （X= Be,B or C）

The equilibrium lattice constant, the cohesive energy and the electronic properties of light metal hydrides LiXH3 and XLiH3 （X = Be, B or C） with perovskite lattice structures have been investigated by using the pseudopotential plane-wave method. Large energy gap of LiBeH3 indicates that it is insulating, but other investigated hydrides are metallic. The pressure-induced metallization of LiBeH3 is found at about 120 GPa, which is attributed to the increase of Be-p electrons with pressure. The electronegativity of the p electrons of X atom is responsible for the metallicity of the investigated LiXH3 hydrides, but the electronegativity of the s electrons of X atom plays an important role in the metallicity of the investigated XLiH3 hydrides. In order to deeply understand the investigated hydrides, their optical properties have also been investigated. The optical absorption of either LiBeH3 or BeLiH3 has a strong peak at about 5 eV, showing that their optical responses are qualitatively similar. It is also found that the optical responses of other investigated hydrides are stronger than those of LiBeH3 and BeLiH3 in lower energy ranges, especially in the case of CLiH3.     

Determination of Chemical Effect on the Kβ1/Kα, Kβ2/Kα, Kβ2/Kβ1 and Kβ/Kα X-Ray Intensity Ratios of 4d Transition Metals

It is clear that detailed studies performed under identical experimental conditions are desirable to determine the effect of the chemical environment on the value of intensity ratios. To better understand this effect, we conducted measurements on Kβ₁/Kα, Kβ₂/Kα, Kβ₂/Kβ₁ and Kβ/Kα x-ray intensity ratios. The Kα and Kβ_1,2 emission spectra for compounds of 4d transition metals Y, Zr, Nb, and Mo were measured using a Si(Li) solid-state detector. The samples were excited by 22.69 keV x-rays emitted from a ¹⁰⁹Cd radioisotopes source. The experimental results for pure elements are compared with the other experimental and theoretical values.     

Effect of hyperstoichiometric manganese on the structure and transport, magnetic, and magnetoresistance properties of manganite-lanthanum (La0.7Ca0.3)1 ? x Mn1 + x O3 perovskites

Ceramic (La_0.7Ca_0.3)_{1 ? x} Mn_{1 + x} O₃ samples are studied by X-ray diffraction, resistive, magnetic, ⁵⁵Mn NMR, and magnetoresistance methods. The concentration changes of lattice parameter a of the cubic perovskite structure and its average ionic radius are in good agreement if the concentrations of anion and cation vacancies and nanostructured clusters with Mn²⁺ in the A positions increase with x. Phase transition temperatures T _ms and T _c weakly depend on x, and the electrical resistivity and the activation energy decrease substantially with increasing x due to a change in the imperfection of the perovskite structure. An analysis of the broad asymmetric ⁵⁵Mn NMR spectra of the samples indicate a high-frequency Mn³⁺? Mn⁴⁺ electron superexchange and nonuniform magnetic and valence states of these ions because of a nonuniform distribution of ions and defects, which decrease the amplitude resonance frequency with increasing x. The magnetoresistive (MR) effect near phase-transition temperatures T _ms and T _c increases substantially with x and is caused by the effect of a magnetic field on the scattering of charge carriers by intracrystallite nanostructured heterogeneities of an imperfect perovskite structure. The second MR effect is located in the low-temperature range, is related to tunneling through mesostructural crystallite boundaries, and decreases weakly with increasing x. A correlation is found between the hyperstoichiometric manganese content, the imperfection of the perovskite structure, and the magnitude of the MR effect.     

Effect of chemical modification on the structure and dielectric and magnetic properties of multiferroic (1 – x)BiFeO3-xDyFeO3 solid solution

The solid solution of (1-x)BiFeO₃-xDyFeO₃ was prepared by solid state reactions in the form of ceramics. The effects of chemical modification by means of aliovalent ionic substitution of Ti⁴⁺ for Fe³⁺ on the structure and dielectric properties were investigated. A morphotropic phase boundary bridging the perovskite rhombohedral phase and the orthoferrite orthorhombic phase was identified at x around 0.1. The chemical modification was found to stabilize the perovsite phase. The dielectric performance of the solid solution was improved by the substitution of Ti⁴⁺ for Fe³⁺, which decreased the electric conductivity by reducing oxygen vacancies, as evidenced by the decrease in loss tangent values. Magnetic hysteresis and large saturated magnetization (0.5 μ_B/f.u.) were realized in 0.92BiFeO₃-0.08DyFeO₃ with 2% substitution of Ti⁴⁺ for Fe³⁺, which is believed to arise from the disruption of the spiral spin modulation after structural modification, and the interaction between the spins of the Dy³⁺ and Fe³⁺ at low temperatures which decouples the antiferromagnetic order between the Fe³⁺ ions.     

Effect of Sc substitution on the structure,electrical, and magnetic properties of multiferroic BiFeO3 thin films grown by a sol–gel process

Multiferroic BiFeO₃ (BFO), Bi_1−xSc_xFeO₃ (BSF), and BiFe_1−xSc_xO₃ (BFS) (x=0.3 mol%) thin films are prepared on Pt/Ti/SiO₂/Si substrates using a sol–gel technique. The effect of Sc substitution along with the annealing ambient (N₂ and O₂) on the structure, electrical, and magnetic properties of the films are reported. X-ray diffraction (XRD) analysis reveals that the films can be prepared with the single-phase perovskite structure by annealing at 700 °C for 10 min either in O₂ or N₂ ambient. The unit cell volume increases on the substitution of Sc, which are 61.39, 62.50, and 62.57 (Å)³ for BFO, BSF, and BFS, respectively. X-ray photoelectron spectroscopy (XPS) study reveals that the chemical environments of Bi and Fe are different in BFO, BSF, BFS films. Similarly, XPS spectra for Sc2p lines in BSF and BFS also have different peak positions; this indicates Sc doping has certain chemical impact on BSF and BFS films. Systematic studies of Sc substitution along with the effect of annealing ambient on the dielectric constant (ε) and dielectric loss (tan δ), leakage current, remnant polarization (P_r), coercive field (E_c), and magnetic properties of the films are carried out. The room temperature values of ε and tan δ at 1 kHz for BFO and BFS films annealed in N₂ ambient are (∼208; 0.035) and (∼235; 0.023), respectively. The comparative value of leakage current for the BFO and BFS films at an applied field strength of 50 kV/cm are 2.997×10⁻⁴ and 1.87×10⁻⁵ A/cm², respectively. Room temperature value of coercive magnetization for BFS films has one order small compared to that of the BFO films; this indicates BFS films are magnetically soft and more suitable for potential device applications. Finally, among the studied compositions, the BFS films annealed in N₂ ambient show the best property.     

Effect of Sr content on structure and electrical properties of La1−x Sr x MnO3 from ITSOFC cathode view point

The samples belonging to La_1−x Sr _x MnO₃ series, prepared by combustion route without using fuel, exhibit crystal structural phase transition with the change in Sr content. Less than 40 mol% Sr is partially substituted in the crystal structure of LaMnO₃. The structural phase transition from rhombohedral to cubic, cubic to tetragonal, and tetragonal to orthorhombic takes place on 40, 60, and 80 mol% addition of Sr. The highest electrical conductivity in La_0.4Sr_0.6MnO₃ is understood to be due to the maximum concentration of polaron. The polarons are formed due to the conversion of Mn³⁺ to Mn⁴⁺ so as to achieve electroneutrality after substitution of Sr²⁺ for La³⁺.     

Influence of Chemical Effect on the Kβ/Kα Intensity Ratios and KβEnergy Shift of Co, Ni, Cu, and Zn Complexes

报导了钴、镍、铜、锌络合物中的化学效应对Kβ/Kα强度比和Kβ能量位移的影响. 实验样品用241Am环状放射源发出的能量为59.5 keV的γ射线激发. 对样品发射的K段X射线进行检测的检测器在5.9 keV处的分辨率为150 eV. 观察了不同配体对钴、镍、铜、锌络合物的Kβ/Kα强度比和Kβ能量转移的影响,并试图解释这些配体的性质对中心原子产生的化学效应. 对实验得到的Kβ/Kα强度比数据,理论计算获得的Kβ/Kα强度比数据及其它实验得到的纯钴、镍、铜、锌的Kβ/Kα强度比数据进行了比较.     

Effect of CoSi2 buffer layer on structure and magnetic properties of Co films grown on Si（001） substrate

Buffer layer provides an opportunity to enhance the quality of ultrathin magnetic films.In this paper,Co films with different thickness of Co Si2buffer layers were grown on Si(001)substrates.In order to investigate morphology,structure,and magnetic properties of films,scanning tunneling microscope(STM),low energy electron diffraction(LEED),high resolution transmission electron microscopy(HRTEM),and surface magneto-optical Kerr effect(SMOKE)were used.The results show that the crystal quality and magnetic anisotropies of the Co films are strongly affected by the thickness of Co Si2buffer layers.Few Co Si2monolayers can prevent the interdiffusion of Si substrate and Co film and enhance the Co film quality.Furthermore,the in-plane magnetic anisotropy of Co film with optimal buffer layer shows four-fold symmetry and exhibits the two-jumps of magnetization reversal process,which is the typical phenomenon in cubic(001)films.     

Effect of external uniaxial stress on the electronic properties and symmetry of p-GaAs/AlxGa1−xAs quantum wells

Abstract

The results of experimental and theoretical investigations of the energy spectrum and electronic properties of symmetric p-[001] Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As heterostruc-tures under uniaxial [110] compression are presented. The stress-induced piezoelectric field breaks the confining potential symmetry in the quantum well and lifts the degeneracy of the hole subbands. A redistribution of holes in the spin subbands of the ground state takes place, which is revealed in the different shifts of the Shubnikov-de Haas oscillation maxima corresponding to the different spin subbands. The [110] uniaxial compression significantly modifies the band structure, which leads to a strong aniso-tropy of the Fermi surface. The electrical resistance becomes strongly anisotropic under applied compression, decreasing in the direction parallel to the compression and increasing in the perpendicular direction.     

Electronic structure,mechanical and optical properties of ternary semiconductors Si1-xGexC (X = 0, 0.25, 0.50, 0.75, 1)

The electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si_1-xGe_xC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243?eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si _0.75 Ge _0.25 C, Si _0.50 Ge _0.50 C, Si _0.25 Ge _0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657?eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si_1-x Ge_xC (X?=?0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results.     

Crystal structure and electrical properties of GdxMn1 ? xS and TixMn1 ? xSe solid solutions

Regions of the existence of sulfide Gd _x Mn_{1 − x} S and selenide Ti _x Mn_{1 − x} Se solid solutions have been identified. Their electrical and thermoelectric properties have been studied in the temperature range 80–900 K. It has been established that the substitution of Gd²⁺ and Ti²⁺ ions for Mn²⁺ cations initiates reversal of the type of charge carrier with respect to the starting compounds MnS and MnSe. The cation substitution in solid solutions brings about a change from the hole conduction (α > 0) characteristic of the manganese monosulfide and monoselenide to the electronic conduction (α < 0).     

Dielectric, magnetoelectric, structure, and dissipative properties and the Mössbauer effect in PbFe1/2Nb1/2O3 ceramics in wide frequency and temperature ranges

High-quality fine-grained ceramic samples of classical multiferroics PbFe_1/2Nb_1/2O₃ (PFN) were synthesized. Their dielectric, magnetoelectric, and magnetic characteristics, including the Mössbauer effect, were measured over wide ranges of temperatures (10–1000 K) and field frequencies (from 25 Hz to 1 MHz). The temperature dependence of the dielectric loss exhibits a maximum between 150 and 170 K, likely due to magnetic ordering. The dependence of ? on the magnetic field displays an anomalous increase near the Curie temperature (370 K) that rises to 40% upon heating.     

Effect of oxygen deficiency on the magnetic, electrical, magnetoelectric, and magnetoelastic properties of La1 ? x Sr x MnO3 ? δ manganites

This paper reports on a study of the effect of oxygen deficiency on the magnetic and electrical properties of the La_{1 − x} Sr _x MnO_{3 − δ} manganites (x = 0, 0.2, 0.4; δ = 0, 0.13, 0.2). In compositions with x = 0 and δ = 0.13 and 0.2, the temperature dependence of the magnetization M (T) can be approximated by the Langevin function with the moment of superparamagnetic clusters μ = 77μ_B (δ = 0.13) and 86μ_B (δ = 0.2) at temperatures of 25 K ≤ T ≤ 250 K, with the exception of a small temperature range near 132 K in which a maximum characteristic of the LaMnO₃ antiferromagnet is seen. These compositions, as well as Sr-doped compositions with δ ≠ 0, reveal a difference between the magnetizations of the sample cooled in a weak magnetic field and in zero field. At T = 6 K in a magnetic field of 16 kOe, the compositions with x = 0.2 and 0.4, δ = 0.13 possess a magnetic moment per formula unit lower than that with δ = 0, as well as reveal an anomalous relation between the Curie temperature T _C and the Curie paramagnetic point gJ, namely, T _C > gJ. The magnetization of compositions with x = 0.2 and 0.4, δ = 0.2 follows the Langevin function with μ = 40μ_B and 130μ_B, respectively. The electrical resistivity of samples with x = 0.4 and δ = 0.13 and 0.2 is one to two orders of magnitude larger than that of the composition with x = 0.4, δ = 0, which evidences partial or complete compensation of acceptor defects (Sr²⁺ ions) by donor defects (doubly charged O²⁻ vacancies). The above properties of oxygen-deficient compositions suggest that they contain an insulating ferro-antiferromagnetic magnetically double-phase state. The magnetoresistance and volume magnetostriction in samples with x = 0.4 and δ = 0, 0.13, and 0.2 are small; indeed, in a magnetic field of 8 kOe, they do not exceed 1.4% and 6 × 10⁻⁶, respectively. On this basis, it is concluded that the unbalanced doubly charged donors (O vacancies) are in the state with antiparallel spins and, thus, do not initiate the formation of ferron-type ferromagnetic clusters. The significance of both compensated and unbalanced doubly charged donors consists in that they give rise to the formation of fractured Mn-O-Mn bonds, which bring about lowering of the magnetic moment per formula unit in compositions with x = 0.2 and 0.4 and δ = 0.13 and the transition to superparamagnetism in compositions with x = 0.2 and 0.4, δ = 0.2. Original Russian Text ? L.I. Koroleva, D.M. Zashchirinskiĭ, T.M. Khapaeva, L.I. Gurskiĭ, N.A. Kalanda, V.M. Trukhan, R. Szymczak, B. Krzumanska, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2201–2205.     

First-principles study on the structure,electronic and magnetic properties of HoSin （n=1-12, 20） clusters

The structure, electronic and magnetic properties of HoSin（n= 1 - 12, 20） clusters have been widely investigated by first-principles calculation method based on density flmctional theory （DFT）. From our calculation results, we find that for HoSin（n=1- 12） clusters except n = 7.10, the most stable structures are a replacement of Si atom in the corresponding pure Sin＋1 clusters by Ho atom. The doping of Ho atom makes the stability of Si clusters enhance remarkably, and HoSin（n = 2, 5, 8, 11） clusters are more stable than their neighboring clusters. The magnetic moment of Ho atom in HoSin （n = 1 - 12, 20） clusters mainly comes from of electron of tto, and never quenches.     

Electronic structure,elastic and thermodynamic properties of α-phase Na3N under pressure from first principles

The structural, electronic, elastic and thermodynamic properties of α-phase Na₃N under pressure are investigated by performing first principles calculations within generalized gradient approximation. The elastic constants, bulk modulus, shear modulus, Young's modulus, and Poisson's ratio dependencies on pressure are also calculated. The thermodynamic properties of the α-phase Na₃N are calculated using the quasi-harmonic Debye model. The dependencies of the heat capacity and the thermal expansion coefficient, as well as the Grüneisen parameter on pressure and temperature are investigated systematically in the ranges of 0–1 GPa and 0–100 K.     

Effect of Mg doping and substrate temperature on the properties of pulsed laser deposited epitaxial Zn1?xMgxO thin films

In this paper, we report on the pulsed laser deposition of epitaxial (0002) oriented Zn_1−x Mg _x O thin films onto (0001) sapphire substrate in O₂ ambient at different deposition temperatures. Pulsed laser deposited Zn_1−x Mg _x O films showed (0002) oriented hexagonal wurtzite structure up to 34% of Mg concentration. The bandgap of Zn_1−x Mg _x O thin films is successfully tuned from 3.3 to 4.2 eV by adjusting the Mg concentration x=0.0 to x=0.34. Pulsed laser deposited Zn_1−x Mg _x O thin films were characterized by XRD, AFM, SEM, PL and UV–VIS spectrometer. We have also studied the effect of deposition temperature on to the structure, surface morphology and optical properties of Zn_1−x Mg _x O thin films.