Critical behavior of single crystal CuCr2Se4−x Br x (x=0.25)

The doping of bromine has prominent effect on the transport properties of CuCr₂Se₄, where the conductivity of CuCr₂Se_4?x Br _x changes from metallic behavior with x=0 to semiconductor with x=1. In this work, the critical behavior of single crystal CuCr₂Se_4?x Br _x with x=0.25, which lies at the boundary between the metallic and insulating state, is investigated through the magnetization under high magnetic field. The critical exponents β=0.39±0.03 and γ=1.25±0.05 are obtained by the Kouvel–Fisher method, and δ=4.79±0.01 is generated by the critical iso-thermal analysis. The obtained exponent β is close to the prediction of the three-dimensional (3D) Heisenberg model, while γ approaches that of the 3D-Ising model. Although the bromine doping has prominent effect on the transport behavior, the critical exponents are hardly changed. The obtained results indicate that the ferromagnetism is established through one-dimensional Cr–Se–Cr bonds. However, the nearest-neighbor magnetic interaction belonging to the 3D-Heisenberg model also contributes to the ferromagnetic exchange.     

Electron work function in YNi3 − x T x (T = Cu,Fe, Mn; x = 0, 0.5) intermetallics

The electron work function in cast samples and cylindrical compacts of YNi_{3 ? x} T _x (T = Cu, Fe, Mn; x = 0, 0.5) intermetallics is determined using the contact potential difference method. A correlation is found between the electron work function and the electronegativity of elements substituting Ni in the YNi₃ structure.     

Magnetism influenced by structural disorder in melt-spun DyMn6 − x Ge6 − x Fe x Al x (x = 2.5, 3)

Different chemical and/or geometrical orders were found in melt-spun DyMn_6???x Ge_6???x Fe _x Al _x with x = 2.5 and 3 having fully amorphous and mixed (crystalline and amorphous) structure, respectively. Thermal variations in magnetization M from liquid helium up to room temperature for both samples are similar. Magnetization value at zero field cooled curve reaches about 0.1 μ_B per formula unit at 2 K and then increases. Two maxima are visible, the first at 50 K (a sharp effect) and the second very broad ranging from 150 to 200 K. ⁵⁷Fe Mössbauer spectrometry investigation revealed a remaining magnetic component in addition to a prevailing quadrupolar feature. Application of a weak external magnetic field causes an increase in the mean hyperfine magnetic field B _hyp and the volume fraction of magnetic component. This observation was confirmed by results of M(T), M(H) and AC magnetic susceptibility measurements. In short-range ordered crystallographic zones characteristic of melt-spun DyMn_6???x Ge_6???x Fe _x Al _x (x = 2.5, 3) alloys, the related magnetic ordering, called the mictomagnetism or the cluster spin glass appears.     

Electro-optic effect in SrTiO3 and Sr1–x Ca x TiO3 (x = 0.014)

The results of the investigation of the quadratic electro-optic effect in Sr_1–x Ca _x TiO₃ with x = 0.014 (SCT) and in nominally pure SrTiO₃ (STO) at room temperature in applied direct-current (dc) and alternating-current (ac) electric fields have been presented. It has been shown that the quadratic (in polarization) electro-optic coefficients of STO and SCT crystals coincide within the accuracy of the determination (±5%). It has been found that, in nominally pure STO measured in a dc electric field, there is a relaxation of the electro-optic effect with a relaxation time τ ≈ 30 s due to the formation of a space charge in the sample. No similar effect in SCT has been observed. A possible mechanism for the formation of a space charge in STO and SCT has been discussed.     

Mössbauer Study of La1−x Ca x Mn1−y 57Fe y O3 with x=0,0.25; y=0.01

Temperature dependent Mössbauer measurements are done on the samples of La_1–x Ca _x Mn_1–y ⁵⁷Fe _y O₃ with x=0 and 0.25, and y=0.01. With decreasing temperature, the specimen with x=0.25 shows a paramagnetic to ferromagnetic transition around 175 K. In the specimen x=0.0, the temperature dependence of both the center shift () and the recoilless fraction (f) can be fitted very well with the Debye theory with a _D=320±50 K. But for the specimens with x=0.25, f and show distinct deviations from the Debye behavior in the temperature range in which the resistivity shows a sharp decrease. Dips observed in both the f and around the transition temperature suggest that the Jahn–Teller distortion observed in these systems is dynamic in nature.     

Structural deformations of the cubic lattice of the Zn1 ? x Fe x Se (x = 0.001) crystal

The structural state of a Zn_{1 ? x} Fe _x Se (x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.     

Co_(2~-)基Heusler合金Co_2FeAl_(1–x)Si_x(x=0.25,x=0.5,x=0.75)的结构、电子结构及热电特性的第一性原理研究

运用基于密度泛函理论的第一性原理方法,对Co_2FeAl_(1–x)Si_x(x=0.25, 0.5, 0.75)系列Heusler合金的电子结构、四方畸变、弹性常数,声子谱以及热电特性进行了计算研究.结果显示, Co_2FeAl_(1–x)Si_x系列合金的电子结构均为半金属特性,向下自旋态(半导体性)均呈现良好的热电特性,并且随着硅原子浓度的增加功率因子随之增加.计算的声子谱不存在虚频,均满足动力学稳定性条件,弹性常数均满足玻恩稳定性条件,机械稳定性均良好.随着晶格常数c/a的比值变化,体系的能量最低点均出现在c/a=1处,即结构稳定性不随畸变度c/a的变化而变化,说明不存在马氏体相变.此系列合金薄膜的电子结构呈现较高的自旋极化率,在替代浓度x=0.75时自旋极化率达到100%,且当x=0.75时薄膜在畸变度c/a=1.2时存在马氏体相变.随着晶格畸变度的改变,总磁矩也发生变化,且主要由Fe和Co两种过渡金属原子的磁矩变化所决定.     

Structure and dielectric properties of Bi6 − x Sr x Ti2 − x Nb2 + x O18 (x = 0–2) solid solutions

The structural and electrophysical characteristics of a series of solid solutions of layered perovs-kite-like oxides Bi_{6 ? x} Sr _x Ti_{2 ? x} Nb_{2 + x} O₁₈ (x = 0, 0.25, 0.5, 1.0, 1.5, 2.0) have been studied. The temperature dependences of the relative permittivity ?/?₀(T) and dielectric loss tangent tanδ have been measured. The dependences of the maximum of the permittivity ?/?₀, Curie temperature T _C, lattice parameters, and the unit cell volume on x have been obtained. The structural parameter a, which corresponds to the polar direction, and the value of the orthorhombic distortion of the unit cell have been found to demonstrate noticeable negative deviations from the Vegard’s law. It has been established that the variations of the orthorhombic distortion correlate with the variations of the permittivity maximum; however, they do not markedly influence the Curie temperature that varies linearly over entire range of changes in x.     

Superionic conductivity of the heterovalent solid solutions R 1−x M x F 3−x (R=REE, M=Ca, Ba) with tysonite-type structure

The fluorine-ion conductivity of anion-deficient solid solutions R _1−x Ca_xF_3−x and R _1−x Ba_xF_3−x having the tysonite (LaF₃) structure was investigated by the impedance spectroscopy method. R _1−x Ca_xF_3−x (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho) and R _1−x Ba_xF_3−x (R=La, Pr, Nd) single crystals were grown from the melt by the Bridgman-Stockbarger method. The electrophysical measurements were performed in the frequency range 5−5×10⁵ and temperature range 300–700 K. The temperature dependences of the electrical conductivity for the crystals studied is determined by the migration of fluorine anions along various structural positions. It is shown that, from the standpoint of increasing the conductivity of tysonite matrices RF₃ (R=La, Pr, Nd), doping by CaF₂ and BaF₂ is less promising than SrF₂. Fiz. Tverd. Tela (St. Petersburg) 41, 638–640 (April 1999)     

Hyperfine interactions in R x Gd1− x Fe3 intermetallics R = Tb,Y

The structural and magnetic properties of rare earth iron intermetallic compounds Tb _x Gd_1?x Fe₃ and Y _x Gd_1?x Fe₃ (x = 0. 0, 0. 1, 0. 2, 0. 4, 0. 5, 0. 6, 0. 8, 1. 0) was studied by X-ray diffraction, the ⁵⁷Fe Mössbauer effect and SQUID measurements. All investigated compounds crystallize in the rhombohedral PuNi3-type of crystal structure. The investigation of magnetic properties of R _x Gd_1?x Fe₃ proved their ferrimagnetic behavior. The Curie temperature of the investigated compounds decreases with the increase of R concentration from 721K (GdFe₃) to 655K (TbFe₃) and 533K (YFe₃). The saturation magnetic moment MS in the R _x Gd _1?x Fe₃ system increase with x parameter. The Mössbauer spectra are analyzed using four sextets, corresponding to three crystallographically (b, c, h) and four magnetically (b, c, h₁, h₂) inequivalent sites for iron. The mean hyperfine magnetic field increases with increase of the Gd concentration     

Microstructure of annealed Ti48.5Ni(51.5– x )Cu x (x = 6.2–33.5) thin films

(Ni, Cu)-rich Ti–Ni–Cu amorphous films with a Cu content of 6.2–33.5 at. % formed by sputtering were annealed at 773, 873 and 973 K for 1 h and their microstructures investigated. Two types of precipitate were observed in the annealed films: a Ti(NiCu)₂ phase for the Ti_48.5Ni₄₀Cu_11.5, Ti_48.6Ni_35.9Cu_15.5, Ti_48.3Ni_28.4Cu_23.3 and Ti_48.3Ni_23.9Cu_27.8 films, plus a TiCu phase for the Ti_48.5Ni₁₈Cu_33.5 films. These precipitates were found to have coherency with the B2 matrix in the films annealed at 773 K and were densely distributed within the grains. However, in the films annealed at 873 K, their size increased 10-fold and their density decreased. Annealing at 973 K promoted grain-boundary precipitation and, accordingly, the density of the precipitates in the grain interiors decreased. On the other hand, the annealed Ti_48.9Ni_44.9Cu_6.2 films showed no precipitates in their grain interiors, but the number of grain-boundary precipitates increased with increasing annealing temperature. It was also found that grain size decreased with increasing Cu content and was significantly decreased for the Ti_48.5Ni₁₈Cu_33.5 films.     

Heat capacity and dielectric properties of multiferroics Bi1 − x Gd x FeO3 (x = 0–0.20)

The heat capacity and the permittivity of multiferroics Bi_{1 ? x} Gd _x FeO₃ (x = 0, 0.05, 0.10, 0.15, 0.20) have been studied in the temperature range 130–800 K. It has been found that insignificant substitution of gadolinium for bismuth markedly shifts the temperature of antiferromagnetic phase transition and increases the heat capacity over a wide temperature range. It has been shown that the temperature dependence of the excess heat capacity is due to the manifestation of three-level states. Additional anomalies characteristic of the phase transitions have been revealed in the temperature dependences of the heat capacity for the compositions with x = 0.1 and 0.15 at T ≈ 680 K and T ≈ 430 K, respectively. The results of studies of the heat capacity have been discussed simultaneously with the data of structural studies.     

Optical spectroscopy and electronic structure of compounds HoNi5 − x Al x (x = 0, 1, 2)

The optical properties of the compounds HoNi_{5 ? x} Al _x (x = 0, 1, 2) have been investigated using the ellipsometric method in the wavelength range from 0.22 to 16 μm. The electronic structure of these intermetallic compounds has been calculated in the local electron-spin density approximation with the correction for strong electronic interactions in the 4f shell of the holmium ions. The experimental dispersion dependences of optical conductivity in the region of interband light absorption have been interpreted based on the results of the calculation of the electron density of states. The plasma and relaxation frequencies of electrons have been determined.     

方程x＋y=xyz的正整数解及其应用

本文探讨了非线性方程x＋y=xyz的正整数解，月个正整数的最大公因数和最小公倍数的关系。将结果应用在方程gcd（α1，α2，…，αn）＋1cm（α1，α2，…，αn）=α1，α2，…，αn的求解问题上。     

Synthesis and physicochemical properties of Li2 Me x Zr1 − x O3 − δ (Me = Nb,Ti; x = 0.05, 0.1) solid solutions

Complex lithium metallates Li₂ Me _x Zr_{1 ? x} O_{3 ? δ} (Me = Nb, Ti, x = 0.05, 0.1) with iso-and heterovalent substitutions for Zr⁴⁺ ions in lithium zirconate are synthesized for the first time using a citrate technique. The inclusion of Ti⁴⁺ and Nb⁵⁺ ions in the crystal structure of Li₂ZrO₃ is confirmed by means of X-ray diffraction and NMR. It is shown that in the temperature range of 750–820 K, Li₂Ti_0.1Zr_0.9O₃ solid solution has higher conductivity than phases of undoped lithium zirconate.     

Magnetic and optical properties of Zn1– x Fe x O ( x = 0.05 and 0.10) diluted magnetic semiconducting nanoparticles

We have investigated the magnetic and optical properties of chemically low temperature-synthesized Zn_{1– x} Fe _x O (x = 0.05 and 0.10) diluted magnetic semiconducting nanoparticles (～7 nm). Observed magnetic behaviour of x = 0.05 samples showed that the net magnetic interaction was antiferromagnetic-like, a feature established by Curie–Weiss fit, concave Arrott–Belov–Kouvel (ABK) plots with the absence of spontaneous magnetization even at 5 K and stretched exponential-type time-dependent magnetization behaviour. Optimization of the Fe(x) dopant concentration in Zn_{1– x} Fe _x O gave the most favourable room-temperature ferromagnetism for x = 0.10, as supported by finite coercive field (～94.4 Oe) and remanent magnetization (0.011 µ_B/Fe ion) from strong hysteretic magnetization vs. magnetic-field curves at room temperature. The Curie temperature of the x = 0.10 sample was estimated at ～388 K. The existence of a room-temperature ferromagnetic phase was further established by the convex nature of the ABK plots with finite spontaneous magnetization. The observed magnetic behaviour for different x values is best explained by a magnetic polaron model.     

ф(x)=(1/x)integral from n=0 to x((ydy)/(e~y-1))数值表

纯金属多晶体中原子的热振动对X射线衍射强度的影响,通常由所谓Debye-Waller因子e~(-2M)来表达,其中h=普朗克常数=(6.6252±0.005)×10~(-27)尔格一秒;k=玻耳兹曼常数=(1.3804±0.0001)×10~(-16)尔格/度;m=原子质量;该金属在特定状态下的德拜示征温度。 因此中φ(x)函数对于强度计算、示征温度的计算都很有用,目前我们所能找到的φ(x)值表失之太简,x的间距太大。为了解决研究工作的需要,我们另作了计算,方法如下:     

Spatial spin-modulated structure and hyperfine interactions of 57Fe nuclei in multiferroics BiFe1–x T x O3 (T = Sc,Mn; x = 0, 0.05)

The results of the Mössbauer studies on ⁵⁷Fe nuclei in multiferroics BiFe_1–x T _x O₃ (T = Sc, Mn; x = 0, 0.05) in the temperature range of 5.2–300 K have been presented. The Mössbauer spectra have been analyzed in terms of the model of an incommensurate spatial spin-modulated structure of cycloid type. Information has been obtained about the effect of the substitution of Sc and Mn atoms for Fe atoms on the hyperfine parameters of the spectrum: the shift and the quadrupole shift of the Mössbauer line, the isotropic and anisotropic contributions to the hyperfine magnetic field, and also the parameter of anharmonicity of the spatial spin-modulated structure.     

Pressure Dependence on the Magnetic Structures of TbNi 1−x Cu x ( x =0.3 & 0.4) Using Neutron Techniques

In the TbNi 1 m x Cu x series, the Cu substitution has two main effects: the increase of the cell volume (～4.3% from TbNi to TbCu), and the increasing importance of antiferromagnetic interactions. In this sense, the magnetic structures of these compounds evolve from a non-collinear ferromagnetic (FM) arrangement to an incommensurate antiferromagnetic (AFM) one for Cu concentration larger than 35%. In this paper, we present the effects of pressure on the magnetic structures of the compounds which are closer to this critical concentration: TbNi 0.7 Cu 0.3 (FM) and TbNi 0.6 Cu 0.4 (AFM). It appears that a global antiferromagnetic behaviour is favoured by pressure.     

Properties of La1 ? x Sr x Mn0.925Zn0.075O3 (x = 0.075, 0.095, 0.115) ceramics

The EPR spectra and conductivity of La_{1 ? x} Sr _x Mn_0.925Zn_0.075O₃ (x = 0.075, 0.095, 0.115) ceramics with a crystal structure examined by X-ray diffraction have been studied. At x = 0.095, a pronounced magnetic-field dependence of the electrical resistivity has been revealed in the temperature range from 190 to 228 K. For samples with x = 0.075 and 0.115, no similar behavior has been observed. The EPR linewidth linearly increases with increasing temperature in the range from 180 to 380 K for all the samples; the slope decreases as the strontium concentration increases.