Specific features of the behavior of the optical properties of TbNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The optical properties of the TbNi_{5 ? x} Cu _x intermetallic compounds have been investigated in the spectral range 0.08–5.64 eV by the ellipsometric method. It is shown that substitution of nickel for copper atoms leads to a significant change in the frequency dependence of the optical conductivity; this change is related to modification of the electronic spectrum. The formation of a new interband absorption band has been revealed, whose intensity increases with an increase in the copper content. The concentration dependences of the plasma and relaxation frequencies of conduction electrons in the compounds under study are determined. Self-consistent calculation of the electronic structure of the TbNi₅ binary compound has been performed in the approximation of local electron spin density. The electron density of states for two spin projections and the optical conductivity of this compound have been calculated.     

Magnetic structure of Ce<Subscript>2</Subscript>Fe<Subscript>17 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

The magnetic structure of intermetallic compounds Ce₂Fe_{17 − x} Mn _x (0 ≤ x ≤ 3) was studied using neutron diffraction. The neutron diffraction patterns measured at 4.2 K contain satellites indicating a modulated structure with the wave vector k = [0, 0, τ]. As the concentration x increases, the value of τ increases, while the average magnetic moment of Fe/Mn atoms decreases. A change in the magnitudes of the average magnetic moment and wave vector k is explained by competition between exchange interactions at distances of nearest neighbor transition element atoms.     

Optical properties and ferromagnetism of ternary Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te nanocrystals

Cd_1−x Mn _x Te (x = 0, 0.1, 0.2) nanocrystals have been synthesized by mechanical alloying (MA) Cd, Mn, and Se elemental powders. XRD patterns and HRTEM images confirmed the formation of cubic Cd_1−x Mn _x Te nanocrystals. All the diffraction peaks from elemental Cd, Mn, and Te powders disappeared completely in those XRD patterns of as-milled Cd_1−x Mn _x Te nanocrystals for more than 20 h. When the MA process was carried out for 40 h, typical zinc blende structure diffraction mode was exhibited in the XRD pattern. Subsequently, capping the surface of as-milled Cd_1−x Mn _x Te nanocrystals with long chain trioctylphosphine/trioctylphosphine oxide/nitric acid (TOP/TOPO/NA) molecules has achieved colorful dispersion solution, which shows similar optical properties to those CdTe nanocrystals prepared by wet chemical process. The grain size is within the range of 2–8 nm for the capped Cd_1−x Mn _x Te nanocrystals being ball milled for 40 h. The PL excitation peak red shifts to longer wavelength side with increasing Mn concentration. Pure CdTe nanocrystals show ferromagnetism behavior at room temperature, the saturation magnetization value and magnetic hysteresis loop increase with the content of substituting Mn ions within the Cd_1−x Mn _x Te nanocrystals.     

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.     

Optical and electrical properties of β-Tl<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>InS<Subscript>2</Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.015) single crystals

The peculiarities of fundamental optical absorption, thermally stimulated conductivity, and depolarization currents in β-Tl_{1 ? x} Cu_xInS₂ (0 ≤ x ≤ 0.015) single crystals have been investigated in the temperature range 4.2–300 K. It is found that the temperature coefficient of the band gap E _g changes near the temperature of the structural phase transition.     

Magnetothermal properties of Gd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>2</Subscript> compounds

The heat capacity of pseudobinary intermetallic compounds Gd_1−x Y _x Ni₂ (0≤x≤1) has been studied. The magnetic contribution to the total heat capacity is isolated with the use of the data obtained for the paramagnetic analogs Lu_1−y Y _y Ni₂ possessing the same molar masses as the gadolinium compounds. It has been found that the difference between the entropies of the Gd_1−x Y _x Ni₂ (x<0.8) compounds and the corresponding paramagnetic Lu_1−y Y _y Ni₂ analogs reaches larger values than those expected from the calculations performed under the assumption that only Gd ions contribute to the magnetic part of the total entropy. The existence of an additional contribution of magnetic nature to the entropy of the Gd_1−x Y _x Ni₂ compounds, as well as the large values of the γ coefficient in the linear-in-temperature term of the heat capacity, is assigned to the spin fluctuations induced by the f—d exchange in the subsystem of Ni 3d electrons.     

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.     

Transport properties and ferromagnetism of Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S sulfides

We have studied the resistivity and thermoelectromotive force (thermo emf) in a temperature range of T = 80–1000 K, the magnetic susceptibility and magnetization in a temperature range of T = 4.2–300 K at an external magnetic field of up to 70 kOe, and the structural characteristics of Co _x Mn_1?x S sulfides (0 ≤ x ≤ 0.4). Anomalies in the transport properties of these compounds have been found in the temperature intervals ΔT ₁ = 200–270 K and ΔT ₂ = 530–670 K and at T ₃ ～ T _N. The temperature dependences of the magnetic susceptibility, magnetization, and resistivity, as well as the current-voltage characteristics, exhibit hysteresis. In the domain of magnetic ordering at temperatures below the Néel temperature (T _N), the antiferromagnetic Co _x Mn_1?x S sulfides possess a spontaneous magnetic moment that is explained using a model of the orbital ordering of electrons in the t _2g bands. The influence of the cobalt-ion-induced charge ordering on the transport and magnetic properties of sulfides has been studied. The calculated values of the temperatures corresponding to the maxima of charge susceptibility, which are related to a competition between the on-site Coulomb interaction of holes in various subbands and their weak hybridization, agree well with the experimental data.     

Evolution of the optical properties of DyNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> compounds in dependence of aluminum concentration

The refractive (n) and absorption (k) indices of intermetallic DyNi_{5 ? x} Al _x compounds (x = 0, 0.5, 1, 1.5, 2) have been measured by ellipsometry at room temperature in the spectral range of 0.22–15 μm. It is established that the replacement of nickel by aluminum atoms leads to significant changes in the dispersion relations of the optical conductivity σ(E) in the interband absorption range. With an increase in Al content, the spectrum σ(E) (containing three maxima for DyNi₅) is gradually transformed into a single-peak structure. The results obtained are discussed on the basis of the data on the electronic spectrum of these compounds. Concentration dependences of the plasma and relaxation frequencies of conduction electrons are determined.     

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.     

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.     

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.     

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.     

Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloy nanoparticles embedded SiO<Subscript>2</Subscript> films: synthesis and structure

Cu–Ni fcc alloy nanoparticles (NPs) of tunable atomic ratios were generated in SiO₂ films. The films were prepared using the Cu(NO₃)₂ and Ni(NO₃)₂ co-doped inorganic–organic hybrid silica sols by single dipping. Transparent, crack-free, glassy SiO₂ films of 310 ± 10 nm in thickness embedded with high mol percent of Cu–Ni alloy NPs were yielded after annealing at 750 °C in 10% H₂-90% Ar atmosphere. Nominal compositions of the films were 20 mol% (Cu–Ni)-80 mol% SiO₂. Optical spectral study of the heat-treated films showed disappearance of Cu plasmon bands due to Cu–Ni alloy formation. Grazing incidence X-ray diffraction (GIXRD) studies revealed the formation of Cu–Ni alloy (2:1, 1:1 and 1:2) NPs inside the SiO₂ film. GIXRD showed a systematic shifting of the diffraction peaks with respect to the fcc Cu–Ni alloy composition, maintaining the nominal ratios. Transmission electron microscopy (TEM) studies of the representative Cu_0.5Ni_0.5-doped film showed existence of homogeneously dispersed Cu–Ni alloy NPs of average size 6.35 nm inside the SiO₂ matrix. The energy dispersive X-ray scattering (EDX) analysis of the individual NPs using the nano-probe (scanning TEM mode) confirmed the presence of both the Cu and Ni with the desired atomic ratio.     

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.     

X-ray spectra and electronic band structure of nitrogen in Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N solid solid solutions

The electronic energy structure of the valence band and the x-ray absorption near edge structure (XANES) region of nitrogen in Al _x Ga_1?x N solid solutions and binary crystals of gallium nitride GaN and aluminum nitride AlN are calculated using the local coherent potential method and the cluster version of the muffin-tin approximation within the framework of the multiple scattering theory. It is demonstrated that the calculated electron densities of states correlate with the nitrogen K x-ray emission and nitrogen K x-ray absorption spectra. The electronic energy structure of the top of the valence band and the XANES region in Al _x Ga_1?x N solid solutions are compared with those in the binary crystals of the GaN and AlN nitrides, and an interpretation of their specific features is proposed. An analogy is drawn between the evolution of the electronic energy structure of the valence band and the XANES region in the alloys under investigation and the evolution of the electronic band structure in the Al _x B_1?x N and B _x Ga_1?x N alloys. General trends in the transformation of the structure and variations in properties of these alloys are discussed.     

Optical absorption and exciton-phonon interaction in solid solutions Cu<Subscript>6</Subscript>PS<Subscript>5</Subscript>I<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

We have studied the optical absorption edge of solid solutions Cu₆PS₅I_{1 − x} Cl _x at high absorption levels in the temperature range of 77–320 K. In a superionic state, we have revealed the Urbach behavior of the absorption edge, determined its parameters, and studied their temperature and concentration variations. We consider exciton-phonon interaction as a mechanism by which the Urbach bundle is formed and show that this bundle can be described in terms of the Dow-Redfield model.     

Low temperature features of the local structure of Sm<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S

The particular features of the local electronic and local crystal structures of the mixed-valence compound Sm_{1 ? x} Y _x S are studied by the XAFS spectroscopy methods in the temperature range 20–300 K for the yttrium concentration x = 0.17, 0.25, 0.33, and 0.45. The temperature behavior of the valence of Sm, as well as of the lengths and the Debye-Waller factors of the bonds Sm-S, Sm-Sm(Y), Y-S, and Y-Sm(Y), has been determined. The violation of the Vegard law has been observed. A model for the estimation of the energy width of the 4f level and of its position with respect to the Fermi level is proposed.     

Magnetic and magnetoresistive properties of Gd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Se selenides

Gd _x Mn_1–x Se (0 ≤ х ≤ 0.15) solid solutions are synthesized on the basis of manganese monoselenide. Their magnetic and electrical properties are studied in the temperature range of 80–900 K in magnetic fields up to 10 kOe. An FCC lattice with the Fm3m space group and antiferromagnetic ordering of the magnetic moments of manganese ions is found. A monotonic reduction in the Néel temperature and an increase in the effective magnetic moment along with the gadolinium concentration are observed. Anomalies in the temperature dependence of electrical resistivity and a shift in the temperatures of anomalies in a magnetic field are found.     

Magnetic and dielectric properties of orthorhombic and hexagonal multiferroics Tb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript>

The transition from a stable orthorhombic structure to a hexagonal structure has been revealed in Tb_1−x Y _x MnO₃ multiferroics at x = 0.2–0.4. It has been shown that almost single-phase crystals with an orthorhombic or hexagonal structure can be obtained by choosing the growth conditions. It has been found that the magnetic and dielectric properties of orthorhombic single crystals with x = 0.2–0.3 are similar to the properties of pure TbMnO₃ and are characterized by a strong anisotropy of the magnetic susceptibility at low temperatures and by the presence of a number of magnetic phase transitions, including those to the ferroelectric state. New spontaneous (T ≤ 15 K) and magnetic-field induced (H | C ₆) phase transitions accompanied by the appearance of an uncompensated rare-earth magnetic moment ∼1 μ_B/mole have been observed in hexagonal single crystals with x = 0.3–0.5.