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.     

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.     

Charge density of Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sb

Charge density calculations and electronic band structures for Ga _x Al_{1 − x} Sb with x = 1.0, 0.5 and 0.0 are presented in this work. The calculations are performed using the empirical pseudopotential method. The charge density is computed for a number of planes, i.e. z = 0.0, 0.125 and 0.25 A ₀ by generating the potential through a number of potential parameters available in the literature. The virtual crystal approximation was applied for the semiconducting alloy. The characteristics of the band structure and charge density are observed to be affected by the potential parameters. Calculated band gaps and the nature of gaps are in good agreement with the experimental data reported. The ionicity is also reasonably in good agreement with other scales proposed in the literature; however the formulation needs to be improved. The present work also demands indirect experimental band gap for the alloy.      

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.     

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.     

Features of properties of microinhomogeneous PdMn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>1− <Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Complex investigation of the properties of PdMn _x Fe_{1? x} ternary alloys with interacting magnetic and structural order parameters has been performed. It is shown that the complex structural and magnetic state near the transition from the atomically ordered PdFe ferromagnet to the intermetallic antiferromagnetic PdMn compound leads to unusual features not only in magnetic and lattice characteristics but also in electronic properties.     

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.     

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.     

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.     

Magnetic properties of single crystals of the Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S solid solutions (0 ≤ <Emphasis Type="Italic">x</Emphasis> < 0.3)

The Cr _x Mn_{1 − x} S single crystals have been synthesized based on manganese monosulfide as a result of cation substitution, and their magnetic properties have been studied. It has been established that the Cr _x Mn_{1 − x} S solid solutions with a face-centered cubic NaCl structure are formed in the concentration region 0 ≤ x < 0.3. The unit cell parameter of the solid solution decreases as the degree of substitution increases due to the variation in the ionic radius of cations. These substances are antiferromagnets. An increase in the degree of cation substitution in the Cr _x Mn_{1 − x} S solid solutions is accompanied by a decrease in the number of 3d electrons in the d shell of manganese monosulfide and causes a decrease in the magnetic transition temperature from 149 K (x = 0) to 96 K (x = 0.29), which differs from previously known results.     

Energy spectrum of charge carriers in Bi<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Analysis of the quantum oscillations of magnetoresistance (the Shubnikov-de Haas effect) in Bi_{1 ? x} Sb _x alloys with an antimony content in the range 0.255 < x < 0.260 has revealed a Lifshitz electronic-topological transition, which quite possibly can be explained in terms of the existence of a saddle point in the energy spectrum of these compositions. Such a peculiarity comes into existence when the direct band gap at the L point of the Brillouin zone in the semiconductor region of the compounds with x > 0.04 becomes negative. This compel one to revise essentially all earlier calculations based on the previously obtained values of the band parameters. In order to check the agreement between the new values of the band parameters and the data on the density of states obtained from measurements of the thermopower in the classical limit of strong magnetic fields, theoretical calculations of the charge carrier concentration n and the density of states at the Fermi level ρ(E _F) have been performed for the case of negative values of the direct band gap at the L point E _gL. The calculations of the parameters n and ρ(E _F) have demonstrated that the change in E _gL and the corresponding correction of the band parameters ensure good agreement with the experimental data. According to these calculations, one electronic-topological transition occurs at an antimony content x ～ 0.165, when a saddle point appears in the energy spectrum. The second transition is associated with the transformation of the six ellipsoids of the Fermi surface into three dumbbell-like figures at antimony concentrations in the range 0.255 < x < 0.260.     

Spectroscopy of charge transfer states in Mg<Subscript>1 – <Emphasis Type="Italic">x</Emphasis> </Subscript>Ni<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>O

Photoluminescence and photoluminescence excitation spectra of solid solution Mg_1–xNi_xO (x = 0.008) have been analyzed. The contributions of charge transfer electronic states and nonradiative Auger relaxation to the formation of the photoluminescence spectrum are discussed.     

Ordered phases of lithium nickelite Li<Subscript>1−<Emphasis Type="Italic">x</Emphasis>−<Emphasis Type="Italic">z</Emphasis></Subscript>Ni<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

A symmetry analysis of ordering in lithium nickelite Li_1?x?zNi_1+xO₂ (Li_1?x?z□_yNi_1+xO₂) was performed with regard to the substitution of Li and Ni atoms and the occurrence of structural vacancies □ in the metal sublattice. For all the ordered phases, the k ₉ ⁽³⁾ ray of the Lifshitz {k₉} star is present in the order-disorder transition channel. This ray determines the consecutive alternation of atomic planes filled with only Ni atoms or only Li atoms and vacancies in the \([1\bar 11]_{B1} \) direction. It was shown that the rhombohedral ordered LiNiO₂ phase is formed in the defect-free lithium nickelite, whereas a family of three monoclinic Li₃□Ni₄O₈ (C2/m space group) and Li₂□Ni₃O₆ (C2/m and C2 space groups) superstructures arises as the concentration of structural vacancies increases. For all the superstructures, the order-disorder phase-transition channels were determined and the distribution functions of Li and Ni atoms have been calculated. The long-range order parameters describing each superstructure were found as functions of the Li_{1?x? z}Ni_1+xO₂ composition.     

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.     

Elasticity moduli of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Te solid solutions

Results of investigations into the temperature dependences (4.2–300 K) of the low-frequency ultrasound velocity in Cd _x Hg_1–x Te single crystals are presented. The elastic moduli and the Debye temperatures are calculated for different solid solution compositions. Based on the data obtained, possible stresses are estimated on the heteroboundary of the materials with a number of substrates.     

Fabrication and magnetic characterization of Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> nanowire arrays

Co _x Pt_1−x (x≥0.7) alloy nanowires are grown into self-synthesized anodic alumina templates by electrodeposition. Magnetic and magnetization properties of Co _x Pt_1−x alloy nanowires are measured as functions of wire length, temperature, and field orientation. X-ray diffraction shows that as-prepared CoPt nanowires are of fcc polycrystalline structure. A crossover of easy axis of magnetization is observed from parallel to perpendicular of the nanowire axis as a function of length. The coercivity (H _c) and remanent squareness (SQ) of Co _x Pt_1−x nanowire arrays are derived from hysteresis loops measured at various angles (θ) between the field and wire axis. H _c(θ) and SQ(θ) curves show bell-shaped or otherwise bell-shaped behavior corresponding to the easy axis of their magnetization.     

Magnetic state of a Zn<Subscript>1 −<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se bulk crystal

The spin system of a Zn_{1 ?x} Cr _x Se bulk crystal (x = 0.045) was studied using thermal-neutron diffraction and magnetic measurements. Previously, it was reported in the literature that thin films (～200 nm thick) of this type of semiconductors exhibit a ferromagnetic order. In this study, the ferromagnetic order is found to be absent in the bulk crystal.     

The magnetic properties of nanosized La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.8)

Magnetic properties of La_1−x Ca _x MnO₃ (0.5 ≤ x ≤ 0.8) samples with an equivalent average particle size ~50 nm prepared by a sol–gel method were investigated. The charge ordering (CO) transition that is observed in the bulks disappears and the ferromagnetic (FM) transition occurs in all the prepared samples. For all the samples, the spontaneous magnetization (M _S) value is much lower than the corresponding theoretic value, which shows that the majority of the sample is antiferromagnetic (AFM). However, the M _S value is much larger than the corresponding value reported by some other groups. The invisible of CO transition and the large M _S value can be attributed to the good connection among the adjacent particles. Moreover, the exchange bias (EB) phenomenon is observed except the x = 0.5 sample. With x increasing, the M _S value decreases and the EB field increases, which can be understood by considering the coexistence of FM phase with Mn³⁺–Mn⁴⁺ spin clusters in the shell and the AFM phase in the core of the nanoparticles.     

Rubidium-cation conductivity of Rb<Subscript>3–2<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> solid solutions

New Rb₃PO₄-based ceramic materials with high rubidium-cation conductivity in the Rb_3–2x Pb _x PO₄ system have been synthesized and studied. Introduction of Pb²⁺ cations leads to a sharp increase in the conductivity of rubidium orthophosphate due to formation of cation vacancies and, at temperatures 350–550°C, also due to the stabilization of high-temperature cubic modification Rb₃PO₄. At high temperatures, the electrolytes prepared have very high ion conductivity higher than 10^–1 S cm^–1 at 700°C, which is higher than the values previously obtained in similar systems with additions of tin and cadmium ions. The factors influencing the transport properties of the materials under study are discussed.