Higher <Emphasis Type="Italic">η</Emphasis><Subscript>c</Subscript>(<Emphasis Type="Italic">nS</Emphasis>) and <Emphasis Type="Italic">η</Emphasis><Subscript>b</Subscript>(<Emphasis Type="Italic">nS</Emphasis>) mesons

The hyperfine splittings in heavy quarkonia are studied in a model-independent way using experimental data on dielectron widths. Relativistic correlations are taken into account together with the smearing of spin-spin interaction. The radius of smearing is fixed by known G/ψ−η _c(1S), ψ(2S)−η _c′(2S) splittings, which appears to be small, r _ss ≅ 0.06 fm. Nevertheless, even with such a small radius, substantial suppression of hyperfine splittings (∼50%) is observed in bottomonium. For nS b states (n = 1, 2, ..., 6), our predicted splittings (in MeV) are 28, 12, 10, 5, 6, 3. For the 3S and 4S charmonium states, the splittings 16(2) and 12(4) MeV are obtained. The text was submitted by the authors in English.     

High-temperature study of SrFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−<Emphasis Type="Italic">z</Emphasis></Subscript> perovskites

The structure of high-temperature SrFe_{1 − x} Mo _x O_{3 − z} (0 ≤ x ≤ 0.5) phases was studied. Such studies are necessary to understand the mechanism of oxygen transport in membrane materials used for high-temperature oxygen separation.     

Magnetostriction of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S (<Emphasis Type="Italic">x</Emphasis> = 0.27) crystals

The magnetostriction of Fe _x Mn_{1 − x} S (x = 0.27) single crystals in strong magnetic fields up to 120 kOe has been investigated. It has been found that the magnetostriction reaches colossal values (±3 × 10⁻⁴) atypical of compounds of 3d elements. It has been found that the magnetostriction changes sign when varying temperature and magnetic field; this behavior indicates an important role of the spin-phonon interactions in the formation of the magnetic order in solid solutions of iron-manganese sulfides.     

Physical properties of Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Dy<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Si crystals

The results of experimental investigation of magnetic and electric properties of Fe_1?x Dy _x Si crystals are reported. It is shown that the magnitude and position of the anomaly observed in the temperature dependences of magnetization are controlled to a considerable extent by the external magnetic field. It is found that the introduction of Dy ions leads to a weak magnetoresistive effect.     

Metal-insulator transition in Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S crystals

Results of an experimental study of MnS, FeS, and Fe _x Mn_1?x S single crystals are presented. The phase composition, the lattice parameters, and the state of paramagnetic ions in Fe _x Mn_1?x S have been determined by x-ray diffraction analysis and Mössbauer spectroscopy. A sequence of transitions have been found in iron manganese sulfide with x = 0.29 at temperatures T ₁ ≈ 25–50 K, T ₂ ≈ 125 K, and T ₃ ≈ 190 K with a change in kinetic properties and the formation of a metallic state at low temperatures T ≈ 2 K. The possibility of a Mott-Hubbard transition in Fe _x Mn_1?x S sulfides with variation of the composition and the temperature is discussed.     

Spectral-luminescent properties of AgLa<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> solid solutions

The luminescent properties of AgLa_{1 − x} Eu _x (MoO₄)₂ (x = 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) under laser excitation (λ = 337.1 nm) are studied. It is shown that, upon substitution of Eu³⁺ for La³⁺, the symmetry of luminescence centers does not vary. According to the X-ray diffraction data, all samples have scheelite-like structure; the pattern of variation in volumes of their unit cells counts in favor of the presence of a continuous series of solid solutions. It is found that an increase in the europium concentration in AgLa_{1 − x} Eu _x (MoO₄)₂ leads to an increase in the luminescence intensity with a maximum at x = 0.9.     

Seebeck coefficient of Ln<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> perovskites in paramagnetic state

The Seebeck coefficient is a function of carrier concentration and configurational entropy. In this report, we semi-theoretically investigate the Seebeck coefficient of Ln _x Ca_1−x MnO₃ (Ln=Rare-earth) perovskites based on the electronic structure of the 3d orbitals of Mn ions, using the developed Heikes model, Boltzmann transport model, and diffusion model. The results show that the Seebeck coefficient of such a strongly correlated electron system in paramagnetic state is remarkably affected by site degeneracy. As temperature decreases, the evolution of the spin and orbital degrees of freedom together with the change in phonon scattering mode describes the Seebeck coefficient behavior satisfactorily. The phonon drag effect at low temperature is also discussed.     

Dual structures and transition regions in <Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript>-(1−<Emphasis Type="Italic">x</Emphasis>)Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> crystals

Model concepts of dual structures are developed as applied to crystals of xPbTiO₃-(1?x)Pb(Zn_1/3Nb_2/3)O₃ solid solutions in the range 0 ≤ x ≤ 0.08. The conditions of the formation of dual structures upon partial and complete relaxation of internal mechanical stresses are considered. A new model of transition regions is proposed for analyzing several variants of changing the unit cell parameters that satisfy the condition of complete stress relaxation inside the transition regions in crystals at concentrations x = 0.045 and 0.08. The influence of the intermediate phase P4mm and stability of its 90° domain structure on the formation of dual structures at x ≥ 0.045 is discussed.     

Magnetism and superconductivity in Eu(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)As<Subscript>2</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0, 0.04)

We report Eu-local-spin magnetism and Ni-doping-induced superconductivity (SC) in a 112-type ferroarsenide system Eu(Fe_1?xNi_x)As₂. The non-doped EuFeAs₂ exhibits two primary magnetic transitions at ~100 and ~40 K, probably associated with a spin-density-wave (SDW) transition and an antiferromagnetic ordering in the Fe and Eu sublattices, respectively. Two additional successive transitions possibly related to Eu-spin modulations appear at 15.5 and 6.5 K. For the Ni-doped sample with x = 0.04, the SDW transition disappears, and SC emerges at T_c = 17.5 K. The Eu-spin ordering remains at around 40 K, followed by the possible reentrant magnetic modulations with enhanced spin canting. Consequently, SC coexists with a weak spontaneous magnetization below 6.2 K in Eu(Fe_0.96Ni_0.04)As₂, which provides a complementary playground for the study of the interplay between SC and magnetism.     

Electronic structure and ground state parameters of Ru<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript><Emphasis Type="Italic">Me</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al refractory alloys

The electronic structure and ground state parameters of B2 RuAl-based refractory alloys have been investigated in the framework of the density functional theory using the exact muffin-tin orbital method in combination with the coherent potential approximation. It has been demonstrated that the number of states at the Fermi level for the Ru_{1 − x} Me _x Al alloys as a function of the alloying metal content has a minimum, which indicates a change in the Fermi surface topology and the presence of specific features in the behavior of elastic constants. It has been concluded that the electronic structure of the alloys can be described in terms of the rigid band model. The nonlinear variations of the lattice parameters of the alloys has been explained.     

Magnetocaloric properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>K<Emphasis Type="Italic">x</Emphasis>MnO<Subscript>3</Subscript> manganites

A technology for obtaining single-phase ceramic samples of La_{1 − x} K _x MnO₃ manganites, as well as the dependence of their structure parameters on the potassium content, is described. The magnetocaloric effect in the samples has been measured by two direct methods, the classical method and the magnetic field modulation method, and has been calculated from the specific heat data. The values of the magnetocaloric effect obtained by these methods are significantly different. The observed discrepancies have been explained. Correlation between the doping level and the value of the effect has been found. It has been shown that the magnetic-field dependence of variation of the magnetic entropy near T _C in weak fields corresponds to theoretical calculations and that the value of the magnetocaloric effect in high magnetic fields can be predicted using this dependence.     

Polarization characteristics of graded thick Ba<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> films

The barium strontium titanate ceramics Ba_{1 − x} Sr _x TiO₃ with a spatially variable composition has been prepared according to the thick film technology (tape casting). The strontium content over the film thickness is varied from 0 to 30 mol %. The structure and polarization characteristics of the samples prepared have been investigated. It has been found that the polarization characteristics of multilayer structures are determined by the ratio between the thicknesses of layers with different compositions and by their properties. No shift of the hysteresis loops in the graded thick Ba_{1 − x} Sr _x TiO₃ ( _x = 0–0.3) films has been revealed. The results obtained have been analyzed in the framework of modern theoretical approaches.     

Thermal and magnetic properties of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript>

The thermodynamic and magnetic properties of the La_{1 − x} Pb _x MnO₃ (0.24 ≤ x ≤ 0.40) solid solution system were investigated in the temperature range of 4.2–340 K. All objects were ferromagnetics with Curie temperature T _C ≈ 320–340 K, which slowly increased with x. The M(T) behavior in the magnetic ordering region indicated a nonuniform ground state, due possibly to the competition of ferromagnetic and antiferromagnetic interactions. The increase in the saturation magnetic moment with x can be described by a simple model of the binary bonds in La_{1 − x} Pb _x MnO₃.     

Theory of the giant magnetoresistance in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>A<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript>

To clarify the origin of the giant magnetoresistance (GMR) observed in La_1?x A _x MnO₃ (A²⁺=Sr²⁺, Pb²⁺, Ba²⁺ and Ca²⁺), we have investigated theoretically the electrical resistivity ρ of carriers in the background of Mn spins which interact with each other through the double exchange interaction. It has been found that extraordinarily large pin fluctuations caused by the instability of the ferromagnetic state are responsible for the transport anomalies including the GMR.     

Crystal structure and magnetic susceptibility of (CuInSe<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(2MnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The crystal structure of samples in the (CuInSe₂)_{1 ? x} (2MnSe) _x system at room temperature and their magnetic susceptibility in the temperature range 77–1000 K are investigated. It is established that compositions with concentrations 0≤ x ≤ 0.2 form solid solutions with a tetragonal structure, space group I \(\bar 4\)2d (122). The specific magnetic susceptibility χ of samples with 0.1 ≤ x ≤ 0.4 at 77 K lies in the range 9 × 10^?4?1.6 × 10^t-3cm³/g. The temperature dependence of the inverse magnetic susceptibility of the sample with x = 0.4 suggests the presence of a component with antiferromagnetic ordering and a reliably measured Néel temperature that is characteristic of MnSe. The dependences χ = f(T) of the compositions with x = 0.1, 0.2, 0.3, and 0.4 indicate the occurrence of magnetic phase transitions with a change in the spin state.     

Hall effect in the Ce(Al<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript> heavy-fermion system

The influence of substitution on the binding energy of many-body states and the formation of the magnetically ordered state in a heavy-fermion compound (CeAl₂) have been studied by measuring the transport characteristics (Hall effect, resistivity) in intermetallic compounds of the Ce(Al_1?x M _x )₂ system (M = Ni, Co; x ≤ 0.08). It is established that the Hall coefficient R _H in Ce(Al_1?x Co _x )₂ intermetallides with x = 0.05 and 0.08 grows by more than an order of magnitude as the temperature decreases from 1.8 to 300 K. The experimental data are used to estimate the effective mass of charge carriers, the relaxation time, and the localization radius of many-body states.     

Spectral-luminescent properties of LiRbLa<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript> solid solutions

The luminescent properties of LiRbLa_{2 − x} Eu _x (MoO₄)₄ (x = 0.002, 0.02, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0) solid solutions are investigated under laser excitation {λ_ex = 337.1 nm). It is established that the composition containing 50 at % Eu³⁺ is the brightest of the considered set of phosphors and has the highest quantum yield.     

Metallic-like conductivity of asymmetric <Emphasis Type="Italic">p</Emphasis>-In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As quantum wells

The temperature dependence of the conductivity of the two-dimensional hole gas in an asymmetric GaAs/In _x Ga_{1 ? x} As/GaAs quantum well has been investigated. It is shown that fast spin relaxation leads to metallic-like behavior of the temperature dependence of the conductivity.