Magnetic circular dichroism (MCD) spectroscopy was used to study the features of the electronic structure of an epitaxial La0.7Ca0.3MnO3 film in the range of 1.2 - 4 eV. The study of the temperature behavior of the MCD spectra made it possible to establish a correlation between the magnetooptical and transport properties of the sample. The data obtained were analyzed in comparison with MCD data for polycrystalline manganite films of various RE1-xAxMnO3 compositions. The MCD spectra of the films were compared with the spectra of the off-diagonal component of the permittivity tensor calculated from the data of the magneto-optical Kerr effect for films of the same composition. A unified set of ground and excited electronic states characteristic of RE1-xAxMnO3 manganites in the visible and near infrared ranges has been identified. These results are important for a qualitative theoretical description of the electronic structure of strongly correlated magnetic oxides.

Magnesium doped polycrystalline ceramic samples of cooper chromite (I) with 0.6-4.0 at % Mg content have been synthesized. Phase composition of ceramics has been investigated by X-ray diffraction. Temperature dependencies of electrical resistivity and Seebeck coefficient have been measured by four probe method and analyzed in frame of variable range hopping conductivity. The density of localized electronic states and characteristic energy of its variation near Fermi energy have been estimated. It was obtained that the density of localized states at Fermi energy increases with an increase of Mg content, while characteristic energy of variation of localized state density near Fermi energy decreases. Obtained results show that relatively large values of Seebeck coefficient in Mg doped copper chromite (I) can be understood within variable range hopping transport of holes with rapidly increasing density toward valence band maximum.

Magnesium-doped polycrystalline ceramic samples of cooper chromite (I) have been prepared by solid phase synthesis. Phase composition and crystal structure of synthesis have been investigated by X-ray diffraction. Microstructure of samples has been investigated by scanning electron microscopy. Thermal conductivity and electrical conductivity have been measured in the temperature range 78<T<320 K. Significant reduction of thermal conductivity with an increase of synthesis duration have been observed. This effect was explained by formation of small amount of MgCr2O4 and Cr2O3 and CuO crystallites operating as effective phonon scatters. Formation of the MgCr2O4 phase is observed in X-ray diffraction patterns and SEM images of the samples with Mg content higher than 3 at. %. Formation of a small amount of Cr2O3 or CuO phase could be due to deviation of precursor's content from stoichiometry. Obtained results open a perspective of thermoelectric figure of merit enhancement for copper chromite-based material.

Electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements are used to study samples of ceramic solid solutions CuCr1 – xMgxO2 (x = 0–0.013). An analysis of the temperature dependences of the EPR linewidth, static magnetic susceptibility, and the effect of illumination on the EPR spectra indicates two mechanisms for the effect of magnesium doping on the magnetic properties of copper chromite. The substitution of chromium by magnesium in the crystal lattice suppresses antiferromagnetic fluctuations and leads to a decrease in the EPR linewidth and an increase in magnetic susceptibility at a temperature close to the temperature of the antiferromagnetic transition. An increase in the concentration of mobile holes leads to a decrease in the spin relaxation time of chromium ions. The data obtained are of interest both for fundamental physics and for practical applications in the field of solar energy.

We investigated thermoelectric and magnetic properties of polycrystalline CuCr1-xMgxO2 (x = 0; 0.002; 0.008; 0.015; 0.030) ceramic samples, synthesized by a special chemical homogenization method (nitrate synthesis). Temperature dependencies of magnetization were measured in magnetic field H = 1000 G. Transition temperature do not noticeably shift with variation of Mg content. Seebeck coefficient S increases with temperature for all investigated samples. At room temperature S decreases from nearly 700 mV/K in pristine material to about 250 mV/K for the copper chromite with 3at.% Mg. Heat conductivity k of all investigated samples is close to the heat conductivity of undoped CuCrO2 crystals. Resistivity of investigated samples decreases several orders of magnitude with increase of Mg content up to 3%. Temperature dependence of resistivity and Seebeck coefficient was interpreted by hopping conductivity in the presence of the Coulomb (parabolic) gap in the density of states. ? 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 17th European Thermoelectric Conference.

CoFe2O4 (111) epitaxial films on a single crystalline (100) ZrO2(Y2O3) substrates and non-oriented CoFe2O4 films on a metal tape were grown by the metalloorganic chemical vapour deposition (MOCVD) method. The CoFe2O4/ZrO2(Y2O3) films contain the coherent high-angle boundaries between variant domains due to the complex epitaxial distortions compared to polycrystalline state of the CoFe2O4/(metal tape) film. The structural peculiarities of films with variant structure lead to the strong anisotropy of its magnetooptical properties. Moreover a significant magnetorefractive effect, up to 1 % at 6 kOe, is revealed in both the polycrystalline and epitaxial films with variant structure in the near infrared spectral range.

The results of a study of copper chromite ceramic samples doped with magnesium are presented. The samples were synthesized according to the solid-phase method using a special procedure for preparing the initial mixture, which ensures a uniform distribution of magnesium with its content from 0.2 to 6%. The substitution of chromium for magnesium in the crystal lattice is confirmed by Raman scattering of light and EPR spectra. As the magnesium content increases from 0 to 6 at.%, the resistivity of the synthesized samples decreases by more than 3 orders of magnitude at room temperature. High thermopower values were obtained, and it was shown that the main charge carriers are holes, and the predominant mechanism of hole transport in doped samples is hopping transfer over localized states, whose density decreases with an increase in energy near the Fermi energy. It is shown that the localization radius increases with an increase in magnesium content.

The mixed ligand complexes [K2(acac)2(H2O)]∞ (I), [K2(acac)2(phen)(H2O)]∞ (II), [Na(acac)(H2O)]∞ (III), [Na3(acac)3(iPrOH)]∞ (IV), [Na3(acac)3(Py)]∞ (V) and [Na2(acac)2(phen)]∞ (VI) (Hacac=pentane-2,4-dione; phen=1,10-phenanthroline; iPrOH=iso-propanol; Py=pyridine) were synthesized by the reaction of the alkaline metal tert-butyloxide in dried solvent (iPrOH, benzene or Py) with Hacac and phen. The products were characterized by elemental analysis, 1H NMR and FTIR spectroscopy, and thermal analysis. The single-crystal structures were determined for the novel compounds II, IV and VI, and refined for I. The structures of I–VI consist of one-dimensional polymeric chains or ribbons which are described as a combination of formal binuclear structural blocks, [M2(acac)2], of four types. Quantum chemical calculations on the four isomers of [M2(acac)2] allowed us to explain different stabilities of the formal building blocks with M=Na and K.

Thin epitaxial La1−хKхMnO3 films were grown using two-stage procedure. Influence of substitution of La3+ ions with K+ ions on the optical and electrical properties of La1−xKxMnO3 films (х=0.05, 0.10, 0.15 и 0.18) has been studied in detail. A noticeable magnetorefractive effect in the films under study was detected in the infrared range. Magnetorefractive effect as well as transverse magneto-optical Kerr effect and magnetoresistance have the maximum in optimally doped sample with x=0.18 corresponding to the highest Curie temperature. The experimental data for compositions close to optimally doped films are in good agreement with the data calculated in the framework of a theory developed for manganites. The resonance-like contribution to magnetoreflection spectra of manganite films has been observed in the vicinity of the phonon bands. It is shown that magnetic and charge inhomogeneities strongly influence on the magneto-optical effects in films. Thin films of La1−xKxMnO3 with the large values of Kerr and magnetorefractive effect are promising magneto-optical material in the infrared range.

The magnetotransmission, magnetoreflection, and magnetoresistance of the La0.7Ca0.3MnO3 and La0.9Ag0.1MnO3 epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.

Results of investigation of resistivity and magnetoresistance of manganites La 1 − x K x MnO 3 ( x = 0.050–0.175) are presented. Behavior of resistivity ρ( T ) in the paramagnetic and ferromagnetic phases has been described. To describe ρ( T ) near the phase-transition temperature, notions of the percolation theory have been used. Two maxima have been found in the dependence ρ( T ); their appearance has been attributed to the ceramic nature of the studied samples. The observed increase in magnetoresistance with a decrease in temperature is caused by intergranular spin-polarized tunneling of charge carriers.

A method for the synthesis of potassium pivalates (trimethylacetates) from potassium tert -butoxide and pivalic acid was proposed. The complexes of the formulas [K(H 2 O)(Piv)] ∞ ( I ) and [K 2 (Phen)(H 2 O) 2 (Piv) 2 ] ∞ ( II ) (Piv denotes the pivalate anion and Phen denotes 1,10-phenanthroline) were obtained and characterized by elemental analysis and IR and 1 H NMR spectroscopy. The crystal structures of complexes I and II were determined using X-ray diffraction. Crystal structure I has a layered motif with two nonequivalent K atoms (C.N.s 5 + 2 and 6). The coordination of phenanthroline in II gives rise to a ribbon motif, the structure containing three nonequivalent K atoms (C.N.s 6, 6 + 1, and 8).

Complex experimental investigations of the structural, optical, and magneto-optical properties (magnetotransmission, magnetoreflection, and transversal Kerr effect, as well as the magnetoresistance, of La0.7Ca0.3MnO3 epitaxial films indicate that magnetoreflection and magnetotransmission in manganite films can reach giant values and depend strongly on the magnetic and charge homogeneity of the films, their thickness, and spectral range under investigation. It has been shown that the optical enhancement of the magnetorefractive effect occurs in thin films as compared to manganite crystals. In the region of the minimum of the reflectance near the first phonon band, the resonance-like magnetorefractive effect has been observed, which is accompanied by change of the sign of the magnetoreflection. A model based on the theory of the magnetorefractive effect has been proposed to qualitatively explain this behavior.

The heat capacity of the manganite La 0.87 K 0.13 MnO 3 has been measured in the temperature range 80–350 K. The nature of the ferromagnetic phase transition and the critical properties of heat capacity near the Curie temperature have been studied. The regularities of variations in the universal critical parameters near the phase transition point have been established. The calculated critical exponent and amplitudes of the heat capacity with allowance for corrections on the scaling (α = −0.13 and A + / A − = 1.178) correspond to the critical behavior of the 3 D Heizenberg model.

A technology of obtaining the single-phase ceramic samples of La1-xKxMnO3 manganites and the dependence of their structural parameters on the content of potassium has been described. Magnetocaloric effect (MCE) in the obtained samples has been measured by two independent methods: by classical direct methodic and by a method of magnetic field modulation. The values of MCE obtained by both methods have been substantially differed. The explanation of the observed divergences is given. The correlation between the level of doping and MCE value has been defined. The value of TC determined by the MCE maximum has been conformed to the literature data received by other methods.