Crystallization behaviour of amorphous Sc100−x Fe x alloys near x=25 composition

A detailed study of the process of crystallization in amorphous Fe₂₅Sc₇₅, Fe₂₈ Sc₇₂ and Fe₂₅Sc₄₅Zr₃₀ alloys has been carried out using differential scanning calorimetry, X-ray diffraction and Mössbauer spectroscopic techniques. The complex multi-stage transformation process in Fe₂₅Sc₇₅ and Fe₂₈Sc₇₂ is understood in terms of polymorphous formation of an intermediate metastable crystalline phase of orthorhombic structure (a = 0.521 nm, b = 0.648 nm and c = 1.212 nm) and of likely Sc₃Fe stoichiometry, before final eutectic crystallization to stable Fe₂Sc and -Sc.     

Magnetic, Electrical and Thermodynamic Properties of UCuT x Al11−x Alloys Where T = Mn, Fe and x=4 and 5

The structure, magnetic, electrical, and thermodynamic properties of UCuT _x Al_11?x alloys, where T = Mn or Fe and x=4 or 5 are presented. The behavior of the Fe alloys is ferromagnetic-like with the Curie points amounting to 180 and 230 K, and the saturation magnetic moments under magnetic field of 5 T equal to 4.75 and 6.02 μ_B/f.u., respectively, whereas under a magnetic field of about 34 T the magnetic moments amount to 6.9 and 9.0 μ_B/f.u. for the alloys with x=4 and 5, respectively. The Curie points are reflected in the temperature dependence of the specific heat in which the anomalies are found at 180–200 and 230 K for alloys with x=4 and 5, respectively, however, it shows no reflection in the temperature dependence of the electrical resistivity. The field dependence of the magnetization at T=1.9 K for both compounds exhibits considerable hysteresis. There is a pronounced difference between ZFC and FC magnetization in its temperature dependence below the Curie point for materials with x=4 and 5. The Mn alloys exhibit ferrimagnetic-like character for which, supposedly, the interplay of the uranium and manganize sublattices is responsible. Magnetic transitions are determined at T _N =300 (x=4) and 380 K (x=5). However, those anomalies do not find confirmation in the temperature dependence of the specific heat and the electrical resistivity. Magnetic moments determined at T=1.9 K and in a magnetic field of 5 T are very low and in both cases amount to about 0.35 μ_B/f.u. and these values are slightly higher in a magnetic field of 34 T reaching a value of about 1.5 μ_B/f.u. Also for the Mn alloys the clear difference between ZFC and FC magnetization in its temperature dependence below the Curie point is observed.     

Microscopic Scenario for x = 1/8 Anomaly in La2 − x Sr x CuO4

We adopt a t ₁-t ₂-t ₃-J-G model for explanation of x = 1/8 anomaly in La_{2 ? x} Sr _x CuO₄ family compound. The calculated charge susceptibility shows a maximum near Q = (π, π) at intermediate temperatures and near (π, π/2) as temperature approaches zero, in agreement with neutron scattering experiments. Coulomb repulsion G between the first neighbors turns out to be the source of Charge Density Waves (CDW) in narrow band t ^eff ₁, t ^eff ₂, t ^eff ₃ < G. For physically realistic hopping values we obtain the CDW amplitude e _Q = x. The in-phase domain structure as a candidate for “stripe” picture is proposed.     

Structural and Magnetic Studies of Ca2?x Sm x MnO Compounds (x=0–0.4)

The Ca_2?x Sm _x MnO₄ (x=0?C0.4) compounds were synthesized by a solid?Csolid method and characterized by XRD at room temperature. The XRD profiles were indexed with a tetragonal structure (I/4mmm space group) for x??0.3 and orthorhombic one (Pnma space group) for x=0.4. The magnetic measurements were studied as a function of temperature (T=2?C300?K) and applied field (?? ₀ H=0?C10?T). When the temperature decreases, each compound has shown first a ferromagnetic?Cparamagnetic (FM?CPM) transition and then an antiferromagnetic?Cferromagnetic (AFM?CFM) one. The transition temperatures are found to be Sm-doping dependent. For all compounds, a spin-glass phenomenon is evidenced by FC/ZFC magnetization curves.     

Electrical properties of n-Cd1 ? x Co x GeAs2 (x = 0.05–0.15) at high pressures

The resistivity (??) and Hall coefficient (R _H) of n-Cd_{1 ? x} Co _x GeAs₂ with x = 0.05?C0.15 were measured as functions of temperature (at atmospheric pressure) and pressure (up to p = 7 GPa). The temperature-dependent ?? data were used to determine the ionization energy of a cobalt-related impurity center. In the ??(p) and R _H(p) curves, we identified structural semiconductor-semiconductor phase transitions under both increasing and decreasing pressure. Using a mixed-phase structure-effective medium model, we assessed the dynamics of the variation of phase composition with pressure.     

Cu-NQR Study on Single Crystals Sr14−x Ca x Cu24O41 with x = 0–11.5

Cu-nuclear quadrupole resonance (NQR) measurements have been performed on single crystals Sr_14–x Ca _x Cu₂₄O₄₁ (Ca _x ) with x = 0–11.5, in order to clarify the relation between the magnetic order around x = 11.5 and local environments at the Cu sites upon x. Cu-NQR frequency _Q for the ladders at 4.2 K increases linearly with increasing x, whereas _Q for the nonmagnetic Zhang–Rice (ZR) sites in the chains does not. Detailed site assignment of the spectra, which are different from those in the previous paper, is presented.     

Effective Electron Correlation and Spin Density Fluctuation in Iron-Based Fluorides SrFe1?x Co x AsF (x=0,0.125)

Using first-principles calculation, we study effective electron correlation and spin density fluctuation in iron-based fluorides SrFe_1?x Co _x AsF (x=0, 0.125). We obtain the observed magnetic moment of Fe atom with a strongly attractive electron correction. Whereas, different from the parent compound, the density of state of superconducting SrFe_1?x Co _x AsF (x=0.125) near to the Fermi energy is reduced for both signs of effective electron correlation, and suggests strong instability there. In addition, spin density fluctuation resulted from the effective correlation exists in Co-doped compound, may propagate in the form of collective excitation and manifest as spin fluctuation with specific q-vector in momentum space.     

非线性方程x=Ax+λBx的可解性

X是实Banach空间,FX是楔形,(0,1)X是闭单位球,Ω,DX是两个有界开集,D;用和分别表示D_F≡D∩F关于F的闭包和边界,A:→F是半紧1—集压缩,B:(—Ω)_F→F全连续,当F∩(0,1)非紧或F是锥以及A和B满足某些补充假设时,本文证明了固有向量集∑={x∈(-Ω)_F|x∈Ax+λBx,对采个λ∈[0,m/β]}中有一连通分支C使得C∩F(A)≠φ,C∩≠φ,这里F(A)={x∈(-Ω)_F|x=Ax}。     

Mg-xAl-Zn(x=3,6,9)合金腐蚀行为比较研究

对不同Al含量的AZ系列镁合金(AZ31、AZ61和AZ91)在3.5%NaCl溶液中的腐蚀性能进行了比较研究,以便找到合适的耐腐蚀材料。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对其显微结构进行了表征。在3.5%NaCl溶液中,采用极化曲线、电化学阻抗谱(EIS)和浸泡实验对其耐腐蚀性进行了测试。结果表明,AZ系列镁合金的腐蚀行为先是点蚀,后扩展为面蚀。AZ61的极化电阻(R_P)高达288.88Ω·cm²,腐蚀电流密度低为0.0026 mA/cm²,平均腐蚀速率为2.86×10^-4 g/(h·cm²),AZ61具有更优的耐蚀性能。随着Al含量提高,镁合金的耐蚀性能先升高再降低,耐蚀性能的升高归因于β-Mg₁₇Al₁₂相的粗化和连续性。     

蒙太奇手法在影视音乐中的1＋1=x现象

本文应用蒙太奇手法去探讨该手法在影视音乐中的特殊现象,着重论述蒙太奇手法的剪辑作用;蒙太奇在时间和空间上的对比手段,对影视艺术的剪辑起到了不可估量的作用。     

Antiferromagnetism and the Effect of Exchange Bias in LaCr1−x Fe x O3 (x=0.40 to 0.60)

LaCr_1?x Fe _x O₃ (x=0, 0.4, 0.45, 0.6 and 1.0) have been prepared in single phase form with Pbnm space group. The x=0 sample exhibits antiferromagnetic (AFM) transition at Néel temperature T _N =290 K and it is found to reduce with increase in doping concentration up to x=0.45. Magnetization reversal below a compensation temperature of 100 K was observed in the x=0.45 sample and it is explained in terms of competition between two AFM interactions and associated magnetic anisotropy. Exchange bias was observed in the x=0.45 sample and the temperature dependence of exchange bias field and vertical magnetization shift were analyzed.     

AC Potential-Dependent Concentration Variation and Domain Wall Pinning in Co1−x Zn x (x=0.4−0.5) Nanorods

The Co_1?x Zn _x (x=0.4?0.5) nanorods were synthesized via an AC electrochemical deposition method into anodized aluminum oxide (AAO) templates at different voltages ranging from 10 to 18 V, and nanorods of varying concentrations of Co and Zn were obtained. The characterization tools were used to examine different aspects of nanorods, e.g., shape, size, morphology, chemical composition, and magnetic behavior. Scanning electron microscope (SEM) images show that CoZn nanorods have length L=1μm and diameter d=50 nm. The grain size was calculated to be 25.4 nm using an X-ray diffraction (XRD) technique. The XRD also shows some other phases of ZnCoO. The M?H loops measured by a vibrating sample magnetometer (VSM) at room temperature show pure ferromagnetic behavior at all AC potentials. The nanorods show magnetic isotropic behavior due to strong magnetic interactions and presence of random nanorods. The potential-dependent coercivity H _c and saturation magnetization M _s show a non-linear curve which is explained on the basis of magnetic islands and domain wall pinning. This study is useful to tune the magnetic properties of nanorods by a simple and low-cost technique.     

方程dx/dt=Φ(y)-F(x),dx/dt=-g(x)极限环的唯一性问题

本文研究方程其中的极限环的唯一性,本文把文[1]的定理6.11在条件减弱的情况下推广到方程(1),并举出应用这一定理的一个例子。     

Thermal Properties of La1−x A x CoO3 (A = Ca and Ba)

The thermal properties of La_1?x A _x CoO₃ (A = Ca, Ba and 0.0≤x≤0.3) for temperature (1 K≤T≤300 K) have been investigated using the Modified Rigid ion model (MRIM) with pair wise interionic interaction potential. The temperature dependent (1 K≤T≤300 K) variation of specific heat and thermal expansion for La_1?x A _x CoO₃ (A = Ca, Ba and 0.0≤x≤0.3) has presented proper interpretation of the experimental data. Also the effect of lattice distortions on the thermal properties of these perovskite cobaltates has been studied by an atomistic approach. In addition, the results on the cohesive energy (?), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θ _D ) and Gruneisen parameter (γ) are also discussed.     

Magnetic Properties of Ru-rich Ru2?x Fe x CrZ (Z=Si, Ge)

The properties of Heusler compounds Ru_2?x Fe _x CrGe are investigated and compared with those of Ru_1.9Fe_0.1CrSi. Ru₂CrGe is confirmed to exhibit an antiferromagnetic transition with Ne??l temperature 13?K by magnetic susceptibility and specific heat measurements. When Fe is substituted for Ru, a peak in the magnetic susceptibility is observed, and in the lower temperature region irreversibility between temperature dependences of magnetization for zero-field-cooling and field-cooling conditions is found. Nevertheless, in specific heat of Ru_1.9Fe_0.1CrGe, there is no anomaly to indicate phase transition. The specific heat is almost identical to that for Ru_1.9Fe_0.1CrSi. The above results demonstrate that the magnetic states in the low temperature region of Fe-substituted samples are spin-glass-like states. Slight substitution of Fe for Ru destroys the long-range-order and lead to peculiar spin-glass-like states.     

Two phase co-existence in YBa2(Cu1−x Co x )3O7−δ superconductor with x=0.03

Co-doped impurity-free YBa₂(Cu_1–x Co _x )₃O_7–(123Co_x) with x=0.03 superconducting samples have been synthesized using conventional solid state reaction techniques. A Rietveld analysis of X-ray diffraction data for these specimens reveals that two structures (one tetragonal represented by T-YBCO, and the other orthorhombic represented by O-YBCO) co-exist at this composition of the cuprate. The use of a single tetragonal or single orthorhombic structure as the model for the refinements does not produce acceptable fits to the X-ray diffraction pattern. The refinements show that the T-YBCO phase at 298 K has tetragonal symmetry (P4/mmm) with a=0.387879(4) nm, c=1.17314(1) nm, and that the O-YBCO phase has at 298 K an orthorhombic symmetry (Pmmm) with a=0.387555(4) nm, b=0.389400(4) nm, c=1.17363(1) nm, respectively.     

Electrical properties of (Ni1−x )Li x )O (x=0.1 and 0.2) under various relative humidities

Rocksalt-type (Ni_1–x Li _x )O (x=0.1 and 0.2) was synthesized at 1350° C in air and its electrical resistivity (R) was measured under various relative humidities (H). R increases with increasing H in the range 0H79%, reaches a maximum value, then decreases in the range 79%<H100%. The increase in R is explained by an electron boundary layer model. On the other hand, the decrease in R is explained by ionic conductivity.