New Publications

Quasi-bound States in the Continuum in a Finite Chain of Dielectric Scatterers: Theory and Experiment

Balyzin, M.; Sadrieva, Z.; Belyakov, M.; Kapitanova, P.; Sadreev, A.; Bogdanov, A. A. Edited by: Chew WC; He S Source: 2018 PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM (PIERS-TOYAMA), 2516-2519; 2018 Book Series: Progress in Electromagnetics Research Symposium

Electron Paramagnetic Resonance of Cr3+ Ions in ABO(3) (A = Sc, In, Ga) Diamagnetic Crystals

Vorotynov, A. M.; Rudenko, V. V.; Ovchinnikov, S. G.; Molokeev, M. S. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 127 (6):1067-1073; 10.1134/S1063776118120245 DEC 2018

A magnetic resonance method is applied to the investigation of a number of isostructural diamagnetic compounds ABO3 (A = Sc, In, and Ga) with small additions of Cr3+ ions (S = 3/2) sufficient to observe single-ion and pair spectra. It is shown that the resonance spectra for isolated Cr3+ ions can be described to a good accuracy by the ordinary axial spin Hamiltonian for 3d ions in octahedral oxygen environment. The parameters of the spin Hamiltonian are determined for single Cr3+ ion and Cr3+–Cr3+ pair. Lattice distorsions of the parent ABO3 crystals caused by the Cr3+ impurities is discussed.

Composition, Structure and Reduction Reactivity of Composite Materials of the alpha-Fe2O3-CaFe2O4 System by Hydrogen

Yumashev, Vladimir V.; Kirik, Nadezhda P.; Shishkina, Nina N.; Knyazev, Yuriy, V; Zhizhaev, Anatoly M.; Solovyov, Leonid A. Source: JOURNAL OF SIBERIAN FEDERAL UNIVERSITY-CHEMISTRY, 12 (1):54-72; 10.17516/1998-2836-0108 2019

In this paper, α-Fe2O3–CaFe2O4 composite materials obtained by high-temperature solid-phase synthesis from Ca and Fe (III) oxides with varying molar ratio CaO/Fe2O3 in the range 0.15-1.00 were investigated. The materials are characterized by Х-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS) and simultaneous thermal analysis (STA) in the hydrogen temperature-programmed reduction mode (H2-TPR). SEM-EDS studies of the specimens were revealed a formation of the “core-shell” type complex microstructure of material with the hematite phase as the “core”. H2-TPR of the specimens allowed to establish a decrease of the contribution of low-temperature forms of lattice oxygen in areas of 350-510 °С (up to 2.6 times) and 510-650 °С (up to 1.7 times), and the growth of the contribution of the high-temperature oxygen form in the range of 650-900 °С (up to 2 times) with an increase in the content of the phase CaFe2O4 from 33.4 to 97.5 wt. %. Relying on the assessment of lattice oxygen mobility, it was suggested, that the samples with content of CaFe2O4 phase more than 55.4 wt. % are promising for use as oxygen carriers in chemical looping processes of syngas production

Spin-dependent electrical hole extraction from low doped p-Si via the interface states in a Fe3Si/p-Si structure

Tarasov, A. S.; Lukyanenko, A., V; Rautskii, M., V; Bondarev, I. A.; Smolyakov, D. A.; Tarasov, I. A.; Yakovlev, I. A.; Varnakov, S. N.; Ovchinnikov, S. G.; Baron, F. A.; Volkov, N. V. Source: SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 34 (3):10.1088/1361-6641/ab0327 MAR 2019

Spin accumulation effect in Fe3Si/p-Si structure with low boron doped silicon substrate was found. Calculated spin lifetimes are comparable with results reported earlier but for structures with highly doped semiconductors (SC) with or without a tunnel barrier introduced between the SC and ferromagnet (FM). Electrical characterization of a prepared Fe3Si/p-Si diode allowed the determination of possible reasons for the pronounced spin signal. Analysis of the forward bias I-V curve revealed a Schottky barrier at the Fe3Si/p-Si interface with a height of ${\phi }_{Bp}=0.57\,{\rm{eV}}.$ Then, using impedance spectroscopy, we observed interface states localized in the band gap of silicon with energy of E LS  = 40 meV. Such states most probably cause the observed spin signal. We believe that in our experiment, spin-dependent hole extraction was performed via the interface states resulting in the minority spin accumulation in the silicon valence band. The observed effect paves the way to the development of different spintronic devices based on FM/SC structures without dielectric tunneling barriers.

Tamm plasmon in a structure with the nanocomposite containing spheroidal core-shell particles

Pankin, P. S.; Vetrov, S. Y.; Timofeev, I., V Source: JOURNAL OF OPTICS, 21 (3):10.1088/2040-8986/ab04d8 MAR 2019

Spectral peculiarities of the structure consisting of a photonic crystal coated with a nanocomposite (NC) have been investigated. The NC used contains spheroidal nanoparticles with a dielectric core and a metallic shell, which are uniformly dispersed in a transparent matrix. The spectral manifestation of the observed Tamm plasmon polariton (TPP) and Fabry–Perot mode has been examined. A significant polarization sensitivity of the spectra upon variation in the nanoparticle shape has been demonstrated. The dispersion curves presented for the TPP and Fabry–Perot mode are shown to be in good agreement with the spectra obtained by the transfer matrix method.

Correlation between magneto-optical and transport properties of Sr doped manganite films

Samoshkina, Yu E.; Edelman, I. S.; Rautskii, M., V; Molokeev, M. S. Source: JOURNAL OF ALLOYS AND COMPOUNDS, 782 334-342; 10.1016/j.jallcom.2018.12.158 APR 25 2019

The features of electronic structure of La0.7Sr0.3MnO3, Pr0.8Sr0.2MnO3, and Pr0.6Sr0.4MnO3 polycrystalline films of different thickness have been investigated using magnetic circular dichroism (MCD) in the range of 1.1–4.2 eV. The temperature behavior of the samples electrical resistance were also has been studied. It was found that films with high Sr content (0.3 and 0.4) act as high-temperature semiconductors, while the maximum in the temperature dependences of resistivity these films indicates the transition of the samples to the metallic state at some temperature TM-S, which is different for different sample thickness. The films with the lower Sr content (0.2) act as insulators in the used temperature range. The MCD spectra have been decomposed to the Gaussian-shaped lines, and the temperature dependence of intensity of each line has been analyzed in comparison with temperature dependence of the films magnetization and with their electric conductivity type. Different temperature behavior of the intensity of four specified Gaussian-lines was revealed for semiconductor films. In the case of insulating Pr0.8Sr0.2MnO3 samples, the intensity of three specified Gaussian lines changes with the temperature in the same way as the magnetization changed. It was established that the lanthanide (La, Pr) type does not affect the MCD spectra shape for the films with the same electrical conductivity type. Besides, the correlation between the MCD data of the films and their conductivity type was revealed. Due to the detailed analysis of the specified Gaussian lines with taking into account the well-known in the literature absorption bands, lying outside the studied spectral region, the MCD bands for the studied manganite films have been identified with electronic transitions of a different nature

Core-shell Nanosize Particles Mg@Ni: Synthesis and Properties

Churilov, Grigory N.; Nikolaev, Nikita S.; Osipova, Irina, V; Cherepakhin, Alexander, V; Nemtsev, Ivan, V; Velikanov, Dmitriy A.; Andyuseva, Valentina G. Source: JOURNAL OF SIBERIAN FEDERAL UNIVERSITY-MATHEMATICS & PHYSICS, 12 (1):28-35; 10.17516/1997-1397-2019-12-1-28-35 2019

Magnetic Properties of Fe1-xCoxSi Single Crystals at Low Co Impurity Concentrations

Yurkin, Gleb Yu; Patrin, Gennady S.; Yarikov, Stanislav A. Source: JOURNAL OF SIBERIAN FEDERAL UNIVERSITY-MATHEMATICS & PHYSICS, 12 (1):94-99; 10.17516/1997-1397-2019-12-1-94-99 2019

Li substituent tuning of LED phosphors with enhanced efficiency, tunable photoluminescence, and improved thermal stability

Zhao, Ming; Xia, Zhiguo; Huang, Xiaoxiao; Ning, Lixin; Gautier, Romain; Molokeev, Maxim S.; Zhou, Yayun; Chuang, Yu-Chun; Zhang, Qinyuan; Liu, Quanlin; Poeppelmeier, Kenneth R. Source: SCIENCE ADVANCES, 5 (1):10.1126/sciadv.aav0363 JAN 2019

Solid-state phosphor-converted white light-emitting diodes (pc-WLEDs) are currently revolutionizing the lighting industry. To advance the technology, phosphors with high efficiency, tunable photoluminescence, and high thermal stability are required. Here, we demonstrate that a simple lithium incorporation in NaAlSiO4:Eu system enables the simultaneous fulfillment of the three criteria. The Li substitution at Al sites beside Na sites in NaAlSiO4:Eu leads to an enhanced emission intensity/efficiency owing to an effective Eu3+ to Eu2+ reduction, an emission color tuning from yellow to green by tuning the occupation of different Eu sites, and an improvement of luminescence thermal stability as a result of the interplay with Li-related defects. A pc-WLED using the Li-codoped NaAlSiO4:Eu as a green component exhibits improved performance. The phosphors with multiple activator sites can facilitate the positive synergistic effect on luminescence properties.

Numerical calculation of high frequency magnetic susceptibility in thin nanocrystalline magnetic films

Izotov, A., V; Belyaev, B. A.; Solovev, P. N.; Boev, N. M. Source: PHYSICA B-CONDENSED MATTER, 556 42-47; 10.1016/j.physb.2018.12.006 MAR 1 2019

Two numerical micromagnetic methods most suitable for calculation of the high frequency magnetic susceptibility of nanocrystalline thin films were considered in detail. The methods are based on the Landau–Lifshitz equation, linearized around the equilibrium state leading to an eigenvalue problem or solved using an undetermined coefficients technique. An analysis and estimation of an efficiency of the methods were carried out. Several conclusions about their advantages and shortcomings, as well as specifics of their practical application were drawn.

Effect of Oxygen Nonstoichiometry on Electrical Conductivity and Thermopower of Gd0.2Sr0.8FeO3-delta Ferrite Samples

Dudnikov, Vyacheslav; Orlov, Yury; Fedorov, Aleksandr; Solovyov, Leonid; Vereshchagin, Sergey; Burkov, Alexander; Novikov, Sergey; Ovchinnikov, Sergey Source: MATERIALS, 12 (1):10.3390/ma12010074 JAN 1 2019

The behavior of the resistivity and thermopower of the Gd0.2Sr0.8FeO3−δ ferrite samples with a perovskite structure and the sample stability in an inert gas atmosphere in the temperature range of 300–800 K have been examined. It has been established that, in the investigated temperature range, the thermoelectric properties in the heating‒cooling mode are stabilized at δ ≥ 0.21. It is shown that the temperature dependencies of the resistivity obtained at different δ values obey the activation law up to the temperatures corresponding to the intense oxygen removal from a sample. The semiconductor‒semiconductor electronic transitions accompanied by a decrease in the activation energy have been observed with increasing temperature. It is demonstrated that the maximum thermoelectric power factor of 0.1 µW/(cm·K2) corresponds to a temperature of T = 800 K.

Engineering mode hybridization in regular arrays of plasmonic nanoparticles embedded in 1D photonic crystal

Gerasimov, V. S.; Ershov, A. E.; Bikbaev, R. G.; Rasskazov, I. L.; Timofeev, I. V.; Polyutov, S. P.; Karpov, S. V. Source: JOURNAL OF QUANTITATIVE SPECTROSCOPY & RADIATIVE TRANSFER, 224 303-308; 10.1016/j.jqsrt.2018.11.028 FEB 2019

We analytically and numerically study coupling mechanisms between 1D photonic crystal (PhC) and 2D array of plasmonic nanoparticles (NPs) embedded in its defect layer. We introduce general formalism to explain and predict the emergence of PhC-mediated Wood–Rayleigh anomalies, which spectral positions agree well with the results of exact simulations with Finite-Difference Time-Domain (FDTD) method. Electromagnetic coupling between localized surface plasmon resonance (LSPR) and PhC-mediated Wood–Rayleigh anomalies makes it possible to efficiently tailor PhC modes. The understanding of coupling mechanisms in such hybrid system paves a way for optimal design of sensors, light absorbers, modulators and other types of modern photonic devices with controllable optical properties.

Renormalization of triplet populations of a spin dimer in zero magnetic field with quantum transport

Val'kov, V. V.; Aksenov, S. V. Source: LOW TEMPERATURE PHYSICS, 45 (2):165-175; 10.1063/1.5086406 FEB 2019

Based on the nonequilibrium Keldysh technique in the atomic representation, the effect of inducing a varied population of magnetic states of a spin dimer interacting with electrons transported through a system in a zero magnetic field was studied. In order to find the filling numbers of the quantum states of the system under the strong nonequilibrium condition, a system of kinetic equations was derived and solved by the method of nonequilibrium diagram technique for Hubbard operators. Numerical analysis of these equations made it possible to reveal nonequilibrium renormalizations when accounting for strong spin-fermion correlations.

Magnetic field induced local structural transformations in the optically excited states F-5(2) and F-5(3) of HoFe3(BO3)(4) single crystal

Malakhovskii, A., V; Gnatchenko, S. L.; Kachur, I. S.; Piryatinskaya, V. G.; Gudim, I. A. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 476 177-182; 10.1016/j.jmmm.2018.12.078 APR 15 2019

We measured absorption spectra of transitions 5I8 → 5F2, 5F3 in Ho3+ ion in the HoFe3(BO3)4 single crystal at temperature 2 K as a function of magnetic field 0–65 kOe directed along a and c axes. The spectra were decomposed to the Lorentz shape components and magnetic field dependences of their parameters: position, intensity and line width, were obtained. Substantial difference between dependences of the energy and intensity of the transitions on magnetic field was revealed. So, the abrupt changes of the electron transition energies were mainly observed at the reorientation magnetic phase transitions in the crystal. A number of singularities in the magnetic field dependences of the electron transition intensities were revealed both at the reorientation transitions and outside of them. The singularities in the average intensities of transitions into multiplets at the reorientation magnetic transitions are due to the changes of the odd part of the crystal field, responsible for the allowance of f-f transitions, and also are due to the changes of the magnetic state. The singularities in behavior of intensity of each separate transition are due to the local even distortions in the excited states, which mix the electron states.

Tunable magnetic properties of Ni-doped CoFe2O4 nanoparticles prepared by the sol-gel citrate self-combustion method

Omelyanchik, Alexander; Singh, Gurvinder; Volochaev, Mikhail; Sokolov, Alexey; Rodionova, Valeria; Peddis, Davide Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 476 387-391; 10.1016/j.jmmm.2018.12.064 APR 15 2019

The nanostructured spinel ferrites with complex stoichiometry are an important family of the materials in a number of applications, especially in electronics through their good electrical and magnetic properties. In the framework of this study, a set of mixed cobalt and nickel ferrites was prepared with the sol–gel self-combustion route. The structural and morphological features of particles were studied with X-ray diffraction (XRD), Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray analysis (EDX) techniques. The prepared particles show a crystalline nature with a monotonic distribution of the elements and particles size distribution in the range of 17–29 nm. The obtained particles demonstrate good magnetic properties with tunable saturation magnetization and magnetic anisotropy, i.e., coercivity depending on chemical composition.

Dissipation in granular high-temperature superconductors: New approach to describing the magnetoresistance hysteresis and the resistive transition in external magnetic fields

Semenov, S. V.; Balaev, A. D.; Balaev, D. A. Source: JOURNAL OF APPLIED PHYSICS, 125 (3):10.1063/1.5066602 JAN 21 2019

An approach to describing the R(H) magnetoresistance hysteresis in granular high-temperature superconductors and behavior of the R(T) resistive transition in these objects in an external magnetic field is proposed. The dissipation is attributed to the subsystem of intergrain boundaries, which form a Josephson junction network. The approach is based on accounting for the effect of magnetic moments of superconducting grains on the resulting (effective) field in the intergrain medium. The described procedure includes (i) establishing of the degree of magnetic flux crowding in the intergrain medium by comparing the experimental data on the R(H) magnetoresistance hysteresis and magnetization M(H), (ii) determining the effective field Beff in the intergrain medium as a function of external field H and temperature T with regard to the thermomagnetic prehistory, and (iii) fitting the experimental R(H) and R(T) dependences using the Arrhenius expression R ∼ exp(–EJ/ kB T), where EJ is the parameter corresponding to the Josephson coupling energy. The fundamental novelty of the proposed approach is the extraction of the functional dependences of EJ on the effective field Beff in the intergrain medium rather than on the external field H, as was made in many previous works. It is shown that the proposed approach makes it possible to adequately describe both the R(H) hysteretic dependences and R(T) dependences of the Y-Ba-Cu-O high-temperature superconductor samples with different morphologies and critical current densities.

Magnetic properties of the warwickite MnMgBO4

Eremina, R. M.; Moshkina, E. M.; Muftakhutdinov, A. R.; Gilmutdinov, I. F.; Lyadov, N. M. Source: SOLID STATE COMMUNICATIONS, 290 64-66; 10.1016/j.ssc.2018.12.019 MAR 2019

Magnetic properties of a new single crystal MnMgBO4 have been studied. It was determined that below 16 K antiferromagnet spin order was observed with the axis of easy magnetization along the c axis crystal. The short antiferromagnetic range order was observed below 100 K. The Curie–Weiss temperature has been determined in single crystal MnMgBO4 as θCW = −98 K and the frustration parameter has been estimated as 6.125.

Magnetodielectric effect in a metamaterial consisting of xerogel with embedded epsilon-Fe2O3 iron oxide nanoparticles

Dubrovskiy, A. A.; Balaev, D. A.; Krasikov, A. A.; Yakushhkin, S. S.; Kirillov, V. L.; Martyanov, O. N. Source: SOLID STATE COMMUNICATIONS, 289 27-29; 10.1016/j.ssc.2018.11.020 FEB 2019

The ε-Fe2O3 iron oxide is a fairly rare polymorphic modification, which only exists in the form of nanoparticles embedded, as a rule, into a silica gel matrix. This magnetically ordered iron oxide, which exhibits a significant room-temperature coercivity, is a ferroelectric; therefore, the magnetoelectric and magnetodielectric properties of this material evoke keen interest. In this work, we investigate the magnetodielectric (MD) effect in a metamaterial consisting of xerogel SiO2 with embedded ε-Fe2O3 nanoparticles 9 nm in size on average in a concentration of 20 mass.%. This bulk material exhibits the MD effect in a wide temperature range. The temperature behavior of the permittivity is related to the magnetic state of the ε-Fe2O3 oxide, which undergoes the magnetic transition from the magnetically hard to magnetically soft phase in the temperature range of 80–150 K, indicating the interplay of the ε-Fe2O3 magnetic and charge subsystems.

L1(0) ordered phase formation at solid state reactions in Cu/Au and Fe/Pd thin films

Zharkov, Sergey M.; Moiseenko, Evgeny T.; Altunin, Roman R. Source: JOURNAL OF SOLID STATE CHEMISTRY, 269 36-42; 10.1016/j.jssc.2018.09.009 JAN 2019

To understand the mechanism of mass transfer during solid state reactions and order-disorder transitions the formation processes of CuAuI and L10-FePd ordered structures at solid state reactions in Cu/Au и Fe/Pd bilayer thin films have been carried out using the method of in situ electron diffraction (ED). The value of the long-range order (LRO) parameter has been estimated for the L10 type ordered structures being formed; the order-disorder transition temperatures have been determined. The formation mechanism of the L10 type ordered structures formed at the initial stages of the solid state reaction in the Cu/Au and Fe/Pd thin films has been suggested. In the case of Cu/Au it has been shown that the interdiffusion of copper and gold at the initial stage of the solid state reaction results in the reduced size of the grains of the initial materials, as a result, nanocrystalites of the Cu-Au solid solution are formed, and further, grains of the CuAuI ordered solid solution appear and their growth begins.

Photoluminescence tuning in a novel Bi3+/ Mn4+co- doped La2ATiO6:( A = Mg, Zn) double perovskite structure: phase transition and energy transfer

Xing, Gongcheng; Feng, Yuxin; Pan, Min; Wei, Yi; Li, Guogang; Dang, Peipei; Liang, Sisi; Molokeev, Maxim S.; Cheng, Ziyong; Lin, Jun Source: JOURNAL OF MATERIALS CHEMISTRY C, 6 (48):13136-13147; 10.1039/c8tc05171b DEC 28 2018

Red-emitting phosphors are indispensable compounds which are used to achieve a warm white light in phosphor-converted white light emitting diodes (pc-WLEDs). However, the luminous efficiency and stability of red phosphors are still big challenges. In this work, we developed red-emitting double perovskite phosphors La2ATiO6:Bi3+,Mn4+ (A = Mg, Zn) (LAT:Bi3+,Mn4+) and discuss the relationship between the double perovskite phosphor structure and the luminescence performance in detail. According to the Rietveld refinement results for the La2Mg(1−w)ZnwTiO6:Bi3+,Mn4+ (0 ≤ w ≤ 1) (LM(1−w)ZwT:Bi3+,Mn4+) solid solution, the proposed mechanism of the spectral adjustment is ascribed to the appearance of the phase transition, which results in a lower local structural symmetry of the [LaO12] polyhedron and the variation of the crystal field environment for Mn4+. Notably, this is the first time that the influence of the local structure variation on the luminescence tuning in double perovskite structure phosphors has been revealed, and this could offer guidance for the development of new phosphor system. By designing Mg2+/Zn2+ cation substitution, the internal quantum efficiency (IQE) is remarkably enhanced beyond 20%. In addition, we succeeded in achieving a Bi3+/Mn4+ co-doped energy transfer in the double perovskite structure phosphors. Owing to the Bi3+ → Mn4+ energy transfer in LAT, the red emission of the Mn4+ ions could be dramatically enhanced. The energy transfer efficiency of LAT:Bi3+,Mn4+ eventually exceeded 90%. The IQE and the thermal stability were all enhanced by around 30% compared to the non-co-doped samples, respectively. These results indicate that the Bi3+ → Mn4+ energy transfer strategy could play a pivotal role in the development of highly efficient red-emitting phosphors. The performance of the fabricated pc-WLEDs devices indicates that LAT:Bi3+,Mn4+ could be a promising red phosphor for near ultraviolet (n-UV) based warm pc-WLEDs.

Influence of different organic fuels on the phase composition, structure parameters and magnetic properties of hexaferrites BaFe12O19 synthesized by the sol-gel combustion

Zhuravlev, V. A.; Itin, V. I.; Minin, R. V.; Lopushnyak, Yu. M.; Svetlichnyi, V. A.; Lapin, I. N.; Velikanov, D. A.; Lilenko, I. Yu Source: JOURNAL OF ALLOYS AND COMPOUNDS, 771 686-698; 10.1016/j.jallcom.2018.08.294 JAN 15 2019

Phase composition, structure parameters, morphology and basic magnetic characteristics – the specific saturation magnetization values and the magnetic anisotropy fields of the nanostructured BaFe12O19 powders prepared by the sol-gel combustion with the following annealing at 850°С for six hours are investigated. As organic fuels the following materials are used: carbamide (CON2H4), sucrose (C12H22O11), glycine (C2H5NO2) and citric acid (C6H8O7). The influences of the type of the organic fuels on the properties of synthesized materials are analysed. It is shown that in the powders obtained the distribution of particles on the size, the values of saturation magnetizations and the anisotropy fields depend on the fuel type. The sample synthesized using carbamide has the smallest content of the target phase BaFe12O19, the widest particle size distribution and the lowest value of the saturation magnetization in comparison with the other samples. The narrowest distribution of the particles on the size and the highest value of the specific saturation magnetization are observed in the material synthesized with the use of citric acid as an organic fuel. A comparison of the experimental hysteresis loops with the calculated magnetization curves is made. It is shown that the paraprocess plays a significant role in the magnetization processes of the synthesized materials (χpara. ≈ 0.125*10−3 cm3/g). A technique for determining the values of the anisotropy fields and the magnetomechanical ratios from experiments on FMR is also described. Calculations of the magnetization curve and the ferromagnetic resonance line of hexaferrites powders with uniaxial anisotropy were carried out in the independent grains approach.

Polymorphism in MnSe1-xTex thin-films

Romanova, O. B.; Aplesnin, S. S.; Sitnikov, M. N.; Kharkov, A. M.; Masyugin, A. N.; Yanushkevich, K. I. Source: SOLID STATE COMMUNICATIONS, 287 72-76; 10.1016/j.ssc.2018.10.009 JAN 2019

To establish the polymorphic transition in polycrystalline MnSe1–ХTeХ (0.1 ≤ X ≤ 0.2) films, their structural, magnetic, kinetic, and optical properties have been investigated in the temperature range of 77–800 K and magnetic fields of up to 12 kOe. Using X-ray diffraction analysis, the coexistence of two crystalline phases in the films has been found. The magnetic moment of the films has been shown to increase with the increasing substitute concentration and decreasing temperature. The impedance maxima and thermopower sign change in the region of the polymorphic and magnetic transitions have been observed. The variation in the structural characteristics has been established using the infrared spectroscopy and thermal expansion coefficient data. The experimental results are explained within a model of domains and domain walls.

Ferromagnet-antiferromagnet transition in layered perovskites of Sr3YCo4O10.5 type

Troyanchuk, I. O.; Bushinsky, M., V; Tereshko, N., V; Lanovsky, R. A.; Sikolenko, V. V.; Ritter, C.; Orlov, Yu S.; Ovchinnikov, S. G. Source: MATERIALS RESEARCH EXPRESS, 6 (2):10.1088/2053-1591/aaef21 FEB 2019

Sr1−xYxCoO2.65 (x = 0.2) with layered perovskite structure was studied by neutron diffraction, synchrotron x-ray and magnetometry methods. It is shown that in the 90–375 K temperature range the crystal structure can be described by the monoclinic space group A2/m with the superstructure 42a p × 22a p × 4a p (with a p corresponding to the unit cell parameter of the primitive cell) while basic diffraction peaks are well indexed in the space group I4/mmm (2a p × 2a p × 4a p ) shows an almost standard magnetization. The basic magnetic structure is G-type antiferromagnetic with average magnetic moments of 2.7 μ B/Co and 1.7 μ B/Co in anion-deficient CoO4+γ and stoichiometric CoO6 layers, respectively. A ferromagnetic component of about 0.27 μ B/Co is determined from the magnetization measurements at 8 K. Sr0.8Y0.2CoO2.65 shows an almost standard magnetization versus temperature dependence whereas Sr0.75Y0.25CoO2.65 exhibits an antiferromagnet-ferromagnet transition accompanied by a structural transformation. There is practically no spontaneous magnetization in x = 0.3. The type of the magnetic structure and the high value of TN suggest that the Co3+ ions are in both structural layers predominantly in the low-spin (LS)/high-spin (HS) state mixture. It is proposed that the ferromagnetic component is due to the orbital ordering occurring at TN in the CoO5 pyramids and the concomitant appearance of ferromagnetic coupling between the Co3+(HS) ions located in these CoO5 pyramids in the anion-deficient CoO4+γ layer.

The magnetic dipole-dipole interaction effect on the magnetic hysteresis at zero temperature in nanoparticles randomly dispersed within a plane

Kornogortsev, S., V; Fel'k, V. A.; Li, O. A. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 473 410-415; 10.1016/j.jmmm.2018.10.091 MAR 1 2019

The dipole-dipole interaction effect on the magnetic hysteresis of nanoparticles randomly dispersed within a plane is studied by micromagnetic simulation. The dependence of the coercive field with the concentration of nanoparticles varies from nonlinear and monotonic to non-monotonic dependence with a maximum at a certain concentration. It happens when the ratio of the magnetic anisotropy constant to the maximal dipole energy changes from value much larger than 1 to the value much less than unity.

Peculiarities of a magnetic transition in a quasi-one-dimensional ferromagnet PbMnBO4

Pankrats, A.; Kolkov, M.; Martynov, S.; Popkov, S.; Krasikov, A.; Balaev, A.; Gorev, M. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 471 416-422; 10.1016/j.jmmm.2018.09.098 FEB 1 2019

Near the Curie temperature TC = 30.3 K, the temperature dependences of the magnetization and heat capacity of a single-crystal ferromagnet PbMnBO4 in the magnetic fields of 1, 3, 10 and 30 kOe are studied. In the strong magnetic fields, both the magnetic contribution to the specific heat and the nonlinearity of the field dependences of the magnetization are maintained up to the temperatures exceeding TC more than twice. It is assumed that in PbMnBO4 the difference between TC, the paramagnetic Curie temperature θ = 49 K and the broad temperature region above TC where the magnetic contribution to the specific heat is significant is due to the quasi-one-dimensional character of the magnetic structure of this ferromagnet. Using both the estimation of TC from the Ginzburg-Landau field theory and the θ value, the total exchange interaction parameters 2J ≈ 40.4 K (intrachain) and zJ′ ≈ 8.8 K (interchain) are determined, with z′ = 4 being the number of neighboring chains. The estimation shows that the Ginzburg-Landau field theory describing the quasi-one-dimensional behavior of PbMnBO4 is well applicable in the temperature range from to T = S2J ≈ 80 K. Above this temperature, the mean field approximation with the exchange parameter λθ based on the paramagnetic Curie temperature θ describes well the experimental temperature dependences of the magnetization in the strong magnetic field and the specific heat is determined by the lattice contribution.

Crystallographic, thermal and spectroscopic characterization of the anhydrous thiourea- barbituric acid and thiourea-2-thiobarbituric acid co-crystals

Golovnev, Nicolay N.; Molokeev, Maxim S.; Sterkhova, Irina V.; Lesnikov, Maxim K. Source: JOURNAL OF MOLECULAR STRUCTURE, 1176 865-870; 10.1016/j.molstruc.2018.09.035 JAN 2019

Thiourea (Tu) crystallizes with barbituric acid (H2ba) and 2-thiobarbituric (H2tba) in the aqueous solution to yield co-crystals H2ba∙Tu (1) and H2tba∙Tu (2). Powder of 1 was also obtained from individual compounds via kneading with H2O. The structure of compounds was solved by the X-ray single crystal diffraction technique. In 12, NH⋯O, NH⋯S, CH⋯S and CH⋯O hydrogen bonds form the different 3D nets. In structure 1, centrosymmetric dimers of H2ba and Tu molecules are formed by two NH⋯O and NH⋯S hydrogen bonds, respectively. These dimers alternate in one-dimensional tapes. In compound 2, the same molecules are not bound by hydrogen bonds. Here, infinite chains are formed consisting of alternating molecules of H2tba and Tu. In these chains, each of the molecules is connected to the other by two NH⋯S hydrogen bonds. The compounds have been characterized by powder XRD, TG-DSC, and FT-IR.

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