The spin states of Co atoms in PrBaCo 2 O 5 + δ with regard to the paramagnetic contribution of Pr 3+ ions have been determined from magnetic property studies for δ = 0.52 and 0.74. Results obtained without considering the paramagnetic contribution of Pr 3+ ions are inconsistent with available experimental data. With a decrease in temperature, the metal–insulator transition in PrBaCo 2 O 5.52 becomes sharper according to a sharp change in spin states (from HS/LS to LS/IS) of Co 3+ ions. In this case, Co 3+ ions occupying octahedra pass from the high-spin state (HS, S = 2) to the low-spin one (LS, S = 0) and those occupying pyramids pass from the LS-state to the intermediate spin state (IS, S = 1), as follows from the available structural data. In PrBaCo 2 O 5.74 , the metal–semiconductor transition occurs smoothly from HS/LS to the HS/IS state upon the smooth transition of the Co 3+ ion state from (LS, S = 0) to the (IS, S = 1) state in pyramides without change in the spin state of ions Co 3+ (HS, S = 2) and Co 4+ (LS, S = 1/2) in octahedrons.

The synthesis and the structural and magnetic characteristics of ternary nonstoichiometric Fe 65 – x Al 35 – y M x , y (M y = Ga, B, Sn; M x = V, Mn; x = 3, 5, 10 at %) compounds are experimentally and theoretically studied. Quantum-mechanical calculations of the energy of formation and an electronic structure explain the characteristic features of the phase transformations that occur during the synthesis and describe the experimentally observed changes in the magnetic parameters for various impurity elements.

Efficient stereoselective methods for the synthesis of 5α-androst-1-ene-3β,17β-diol, which is used as a reference compound for identification of anabolic steroids and their metabolites, were elaborated. The key factor of the synthesis is the use of the sodium borohydride—cerium(III) chloride system as a reducing agent.

Temperature dependences of electrical resistivity of Co2MnZ (Z = Al, Si, Ga, Ge, Sn) Heusler alloys were measured in a temperature range of 78–300 K; their magnetization was measured at 5 and 300 K in fields up to 30 kOe. It was found that, for the Co2MnAl and Co2MnGa alloys, the Mooij rule [Mooij J.H. Phys. Stat. Sol. (a). 1973. V. 17. P. 521] does not hold. A correlation between electronic and magnetic characteristics of the Co2MnZ alloys and atomic number of element Z is found.

The reaction of perfluorobiphenyl with tert-butylamine in an autoclave affords the aminodefluorination product, N-tert-butyl-2,2′,3,3′,4′,5,5′,6,6′-nonafluorobiphenyl-4-amine, and the oxidation of the latter with meta-chloroperbenzoic acid gives the new stable nitroxide radical, N-tert-butyl-N-(2,2′,3,3′,4′,5,5′,6,6′-nonafluorobiphenyl)amine N-oxide, in quantitative yield. According to the X-ray diffraction analysis, the crystallization from heptane results in the spontaneous precipitation of the solid paramagnet as one of the two polymorphs, either triclinic $$\left( {P\bar 1} \right)$$ or monoclinic (P21/n). The electrochemical oxidation and reduction of nitroxide occur irreversibly. The heating of a toluene solution of the paramagnet leads to the oxidation of the solvent and the generation of the corresponding hydroxylamine and the benzyl radical, which enters into the recombination reaction with the initial radical to form alkoxyamine.

During the electroreduction of 4-phenyl-1,2,4-triazoline-3,5-dione under aprotic conditions, a chain reaction of its transformation to triazolo[1,2-a]triazole-1,3,5,7-tetraone is initiated, with the mechanism including the transformation of the initially formed radical anion of the starting compound into the radical anion of the product, the difference in the formation potentials of which is 2.39 V, that corresponds to an electron upconversion value of over 50 kcal mol−1. For complete conversion of 4-phenyl-1,2,4-triazoline-3,5-dione in both MeCN and THF, it was enough to pass 0.1 F mol−1 of electricity at the reduction potential of the starting compound. Cyclic voltammetry was used to study in detail the reaction mechanism, which includes a rapid reversible dimerization to π-dimer of the initially formed radical anions, relatively slowly undergoing conversion into the key intermediate of the entire process, a σ-dimeric dianion. Further, the σ-dimeric dianion acts as an electron donor for the molecule of the starting compound, turning itself into a separated dimeric radical anion, which eliminates nitrogen with the formation of the radical anion of the product, that also reduces the molecule of the starting substrate, thus closing the catalytic cycle.

The field dependence of magnetization at T = 4.2 K and in magnetic fields of up to 70 kOe, temperature dependences of magnetization (2 K < T < 300 K), heat capacity (2 K < T < 30 K) and magnetic susceptibility (2 K < T < 1000 K) for Mn1.99Co0.96Al1.05 and Mn1.79Co1.25Al0.96 alloys, closed in composition to the Mn2CoAl spin gapless semiconductor, were studied. Alloys studied were demonstrated to be the band ferromagnets. Their high-field (H > 11 kOe) magnetization is described in the Stoner models with the Rhodes-Wohlfarth parameter pRW = 1.3 for Mn1.99Co0.96Al1.05 and pRW = 2.3 for Mn1.79Co1.25Al0.96. When the composition deviates from the stoichiometric Mn2CoAl, the spontaneous moment decreases slightly, the effective moment, on the contrary, increases. In this case, a negative sign of the temperature-independent component of the paramagnetic susceptibility is observed. The density of states n(EF) at Fermi level and the Debye temperature ΘD of studied alloys have the usual values for 3d-metal alloys.

The field dependences of the signal of induction transducer U~(H), proportional to the magnetic incremental permeability, were obtained on plastically deformed samples of low-carbon steel subjected to compression in the range of elastic deformation. It was found that the greater the relative elongation of the samples, the greater the magnetic fields in which maxima in the U~(H) curves are observed. The additional elastic compression results in the presence of three maxima in the U~(H) curves instead of two. These maxima are associated with the displacement of 90° and 180° domain walls. Most likely, for small values of compressive stresses in the samples, the third maximum in the U~(H) curves was not visible because of its close position to the maximum in the negative field. Fittings by pseudo-Voigt functions were carried out to determine the fields corresponding to three maxima. A new approach was proposed for the evaluation of internal stresses via determination of the fields of two maxima in the U~(H) curve associated mainly with the displacement of 90° domain walls.

A subnanometric resolution method for studying the local atomic structure of interface and surface of low contrast multilayered nanoheterostructure thin films is applied to the Fe/Cr multilayer sample with GMR (Giant Magnetoresistance) effect. We consider combination of the X-ray reflectivity (XRR) and the Extended X-ray absorption Fine Structure (EXAFS) spectroscopy with angular resolution. The XRR experiment has been carried out according to standard procedure using a specialized X-ray diffractometer "Empyrean" at the Institute of Metal Physics (Ekaterinburg). We have applied a measurement method proposed earlier by V. P. Romanov et al. This approach allowed us to separate the diffuse and pure specular contributions. To determine the concentration depth-profile of element from XRR data, we have implemented the Levenberg-Marquardt (L-M) algorithm for nonlinear inverse problem. Thus, the phase problem for X-ray specular reflectivity has been solving. The EXAFS measurements has been performed using synchrotron facilities (National Research Centre "Kurchatov Institute"). {The Fe and Cr K absorption spectra} were recorded in fluorescence mode with angular resolution. The experimental results for depth-resolved local atomic structure of Fe/Cr multilayer with GMR effect has been obtained. A depth resolution of 2-3 angstrom was reached. Atomic structure of Fe and Cr atoms located at seven depth points including interface for the Al2O3/Cr(100 angstrom)/[Fe(8 angstrom)/Cr(10,5 angstrom)](2)/Cr(20 angstrom) multilayered sample was obtained. It was shown what chromium oxides were present on the surface of the sample.

We report on the results of analysis of optical absorption, EPR signals under optical excitation and magnetic susceptibility of hydrothermal Zn 1 – x Mn x O single crystals. In the absorption spectra of polarized light at temperatures of 4.2 and 77.3 K, narrow intense a , b , c , and d lines are observed in the energy range 1.877–1.936 eV of light quanta. The spectrum of these lines differs significantly from the spectra of donor and acceptor excitons for ZnO:Co and ZnO:Ni. The intensity of allowed and forbidden EPR signals of the Mn 2+ ( d 5 ) ions does not change under the action of light in the impurity absorption band, while the EPR signals of uncontrollable Fe 3+ ( d 5 ) ions under illumination practically disappear. New experimental results for Zn 1 – x Mn x O lead to the conclusion that the d 5 / d 4 donor level of the Mn 2+ ion falls into the valence band, while the bandgap of Zn 1 – x Mn x O contains several dangling bond hybrid (DBH) states due to hybridization of 3 d orbitals of the Mn 2+ ion with the p -bonds of the nearest O 2– oxygen ions. Electron transitions from the DBH states to the conduction band form a broad impurity absorption band of Zn 1 – x Mn x O, below the edge of which the a , b , c , and d lines referred to as donor excitons [( h loc + d 5 ) e ] and emerging as a result of Coulomb interaction of a free s -electron and a hole localized on DBH states ( p + d 5 ) are observed. The detection of donor excitons [( h loc + d 5 ) e ] makes it possible to study in detail the DBH states in the bandgap, which is important for photocatalysis in the visible light range.

In this paper the results of the study of optical absorption, photo-EPR signals and magnetic measurements of hydrothermal single crystals of zinc oxide doped with manganese were presented. Several lines were detected in optical absorption spectra at the temperature of 4.2 K and 77.3 K for σ- and π- polarizations of light in a 1.72–2.3 eV spectral range. These lines are attributed to a donor exciton [(d5 + h)e] that emerges as a result of the Coulomb binding of a free s electron and a hole, which is localized on p–d hybridized states. Properties of these lines are significantly different from the properties of lines of donor and acceptor excitons in II-VI:3d compounds. In EPR-spectra of Zn1-xMnxO crystals the intensity of allowed and forbidden EPR-signals of Mn2+ (d5)-ions does not change under the illumination while the intensity of EPR-signals of unintentional Fe3+ (d5)-ions decreases by 70 %. The value of the magnetic susceptibility of Zn1-xMnxO (x = 0.0009) is in linear dependence with temperature, which agrees with the Curie equation. Temperature dependence of the inverse value of the Mn2+ magnetic susceptibility indicates that the exchange interaction in ZnO:Mn crystals is absent. New experimental results allow us to assume that investigated Zn1-xMnxO (x = 0.0009) samples are semiconductors in the forbidden gap of which the donor level of d5/d4 does not exist. The hybridization of d5 states of Mn2+ and p states of the nearest four oxygen ions O2- leads to pushing out the antibonding DBH-states (d5 + p) into the forbidden gap. The transitions of electrons from DBH-states to the conduction band provide a broad band of the impurity absorption in ZnO:Mn. Below this band we observed a, b, c and d lines, which are called dbh-donor excitons [(d5+h)e].

The nanocomposite artificial crystals with embedded magnetic nanoparticles are obtained from opal matrices composed of the submicron SiO2 spheres. The introduced particles are sized from 5 to 60 nm. These artificial crystals contain particles of several rare earth titanates with pyrochlore structure. Low temperature magnetic properties of these nanocomposite materials have been investigated. The frequency and magnetic field dependences of AC magnetic susceptibility of nanocomposites with Gd2Ti2O7, Dy2Ti2O7, Sm2Ti2O7, Nd2Ti2O7 and Er2Ti2O7 particles have been measured in temperature range from 2 to 10 K at frequencies from 1 Hz to 10 kHz. It has been established that magnetic field dependences of these rare earth nanocomposite titanates obey Cole-Cole-like formula written for magnetic field dependency of AC magnetic susceptibility.

The existence of the critical grain size Dc for reconstructive martensitic transformations implies that at austenite grain diameters D smaller than Dc the transformation is suppressed during cooling down to absolute zero temperature. In the case of athermal macrokinetics, martensite crystals divide connected (free from boundaries) volumes of austenite, which allows the use of fractal type models for the processing of results. This study shows that the symmetric model of orthogonal coupling of martensite crystals, developed to estimate the amount of formed martensite in single-crystal samples, can also be applied for an initial polycrystalline sample with a known austenite grain size distribution. A step-by-step algorithm for the theoretical estimation of Dc is proposed under the assumption that the formation of each succeeding generation of martensite crystals begins in the largest continuous volumes of retained austenite. If the estimated cumulative fraction of martensite coincides with the observed resultant value, the count is stopped, and the size of the largest of untransformed continuous volumes of retained austenite is taken as Dc. A detailed analysis of results was carried out for a sample of the alloy Fe - 29.96%Ni - 1.83% Cr in which the volume fraction of the largest grains (with the size D = 310–315 µm) was approximately 58% and four autocatalytic bursts were detected during cooling; the bursts corresponded mainly to the generations of martensite crystals associated with the austenite regions related to the transformation of the initial coarse grains. The amount of martensite crystals was determined by the increase in magnetization and by X-ray diffraction. With the cumulative fraction of martensite ≈70%, Dc was estimated to be ≈ 25.44 µm.

This work is a brief review of investigations of the magnetic properties of binary and pseudobinary intermetallics containing non-Kramers praseodymium ions. Special attention is paid to the PrNi 5 , PrCu 5 , PrNi 2 , and PrAl 2 compounds and substitutional solid solutions based on them.

The magnetic properties of an EuBaCo 1.9 O 5.36 single crystal are studied in the temperature range T = 2–300 K and the magnetic field range H ≤ 90 kOe. This binary layered cobaltite single crystal has vacancies in the cobalt and oxygen sublattices, in contrast to the stoichiometric EuBaCo 2 O 5.5 composition. All cobalt ions in EuBaCo1.9O5.36 are in a trivalent state. The single crystal has an orthorhombic structure with space group Pmmm , and its unit cell parameters are a = 3.883 Å, b = 7.833 Å, and c = 7.551 Å. The field and temperature dependences of the magnetization of the single crystal demonstrate that it is ferrimagnet below T C = 242 K. At T < 300 K, all three spin states of the Co 3+ ions are present. The nearest-neighbor interactions give antiferromagnetic (AFM) and ferromagnetic (FM) contributions to the exchange energy. The ratio of the AFM to the FM contributions changes when temperature decreases because of a change in the spin state of the Co 3+ ions. The single crystal exhibits signs of mictomagnetism at low temperatures in high magnetic fields. At T = 2 K and H = 90 kOe, the zero-field and nonzero-field magnetizations are strongly different because of a uniaxial magnetic anisotropy, which tends to set magnetization along the magnetic field applied in cooling throughout the crystal volume. As a result, a complex ferrimagnetic structure with a noncollinear direction of Co 3+ spins appears. The following phenomena characteristic of mictomagnets are also observed in the EuBaCo 1.9 O 5.36 single crystal: a shift in a magnetization hysteresis loop when temperature decreases, retained hysteretic phenomena and no magnetization saturation in high magnetic fields, and an orientation transition. The mictomagnetic state in EuBaCo 1.9 O 5.36 is shown to be caused by the structural distortions induced by vacancies in the cobalt and oxygen sublattices and by the frustration of AFM and FM exchange interactions.

Studies of structural and phase transformations in the cast and melt-quenched ferromagnetic four-component alloy Ni54Mn20Fe1Ga25 were performed using transmission and scanning electron microscopy and X-ray diffraction, The obtained data have been compared with the results of studies of physical characteristics (electrical resistance, thermopower, magnetic susceptibility, magnetization, and temperature coefficients of linear expansion and relative elongation ΔL/L measured by the method of dilatometry) in the temperature range of 2–870 K. This work has established the effects of quenching on the microstructure, magnetic state, critical temperatures, and specific features of thermoelastic martensitic transformations in the alloy.

Results of structural, magnetic, and Mössbauer studies of quasi ordered alloys Fe 65 Al 35 − x M x ( M x = Ga, B; x = 0, 5 at %) are presented. The magnetic state of examined structurally–single-phase alloys at low temperatures is interpreted from the viewpoint of magnetic phase separation. An explanation is proposed for the observed behavior of magnetic characteristics of Fe 65 Al 35 and Fe 65 Al 30 Ga 5 in the framework of the model of two magnetic phases, a ferromagnetic-type one and a spin density wave. The boron-doped alloy Fe 65 Al 30 B 5 is shown to demonstrate behavior that is typical of materials with the ferromagnetic type of ordering.

Comprehensive experimental and theoretical study of atomic and magnetic structure of the 18-nuclei complex [Ni-6(Pymeid)(6)Ni-12(OH)(6)(mu 3OH)(16)Cl-2 (H2O)(2)] 38H(2)O (H(2)pymeid - N-(2-pyridyl)methyliminodipropionic acid) with rare polycubane planar architecture is reported. Magnetic moments of Ni-II ions (S = 1) in the sectional metal-oxygen Ni-18 core are coupled ferro- and antiferromagnetically, so that the complex is a single-molecule magnet (SMM) with the total spin in the ground state S = 10, and the blocking temperature T-b = 14.3 K. The ac - susceptibility, chi '', obeys the Arrhenius law with the effective barrier U-eff = 18.9 cm(-1) (27.2 K). QTM regime is observed at T <= 8 K. Magnetic anisotropy is characterized by remanent magnetization M-0 = 0.7 mu(B) and coercive field H-c = 340 Oe. Electronic structure and values of the local moments and the exchange constants are calculated in the LDA + U DFT approach. Two complementary 3-nuclei cubane fragments are linked antiferromagnetically to the main 12-nuclei ferromagnetic core. The ligands moderate the exchange couplings in the adjacent cubanes by shifting respective 3d DOS peaks of peripheral Ni ions towards lower energies.

The magnetic properties of metamaterials based on an opal matrix with transition-metal (iron, nickel, cobalt) particles have been studied. Magnetization curves and magnetic hysteresis loops have been measured and the dependences of real and imaginary parts of magnetization have been determined using the dynamic ac susceptibility measuring procedure. Structural studies of metamaterials have been performed. The saturation magnetization and coercive force of the studied metamaterials have been found to depend weakly on the temperature. The temperature dependence of magnetic susceptibility at a temperature above 30 K can be described adequately by Curie–Weiss law and, at lower temperature, deviates from the law.