Публикации 2017

Propagating Bloch bound states with orbital angular momentum above the light line in the array of dielectric spheres

Bulgakov, Evgeny N.; Sadreev, Almas F. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION, 34 (6):949-952; Doi: 10.1364/JOSAA.34.000949 JUN 1 2017

We present propagating Bloch bound states in the radiation continuum with orbital angular momentum in an infinite linear periodical array of dielectric spheres. The bound states in the continuum demonstrate a giant Poynting vector spiraling around the array. They can be excited by a plane wave with incident linear polarization with a small tilt relative to the axis of the array.

Anisotropy of the Magnetoresistive Properties of Granular High-Temperature Superconductors Resulting from Magnetic Flux Compression in the Intergrain Medium

Semenov, S. V.; Balaev, D. A.; Pochekutov, M. A.; Velikanov, D. A. PHYSICS OF THE SOLID STATE, 59 (7):1291-1297; Doi; 10.1134/S1063783417070241 JUL 2017

To elucidate the origin of the well-known anisotropy of the magnetoresistive properties of granular high-temperature superconductors (HTSs), which is related to the mutual orientation of magnetic field H and transport current j, we investigate the hysteretic dependences of magnetoresistance R(H) of the yttrium HTS sample at the perpendicular (Hj) and parallel (H || j) configurations. The hysteretic R(H) dependences are analyzed using the concept of the effective field in the intergrain boundaries through which superconducting current carriers tunnel. The effective degree of magnetic flux compression in the intergrain medium at the perpendicular configuration was found to be twice as much as at the parallel one. This approach explains well the anisotropy of the magnetoresistive properties of granular HTSs, which was previously reported by many authors, and the temperature dependences of the resistance in the resistive transition region.

Effect of the pH of Solutions on the Coercivity and Microstructure of Chemically Deposited CoP Films

Chzhan, A. V.; Podorozhnyak, S. A.; Volochaev, M. N.; Bondarenko, G. N.; Patrin, G. S. PHYSICS OF THE SOLID STATE, 59 (7):1440-1445; Doi: 10.1134/S1063783417070058 JUL 2017

Specific features of the variation in the microstructure and coercivity HC of chemically deposited CoP films with the pH of the solutions are determined. It is established that around pH ~ 8.5, the film undergoes the structural transition from the submicrocrystalline to nanocrystalline state, which is followed by the transition from the crystalline to amorphous phase. It is demonstrated that the observed transition is not accompanied by the change in the crystallographic structure and is caused by a decrease in the geometrical sizes due to embedding of P atoms. It is found that the CoP films fabricated at pH ~ 8.5 have the properties characteristic of compact nanocrystalline materials.

Bound states in the continuum with high orbital angular momentum in a dielectric rod with periodically modulated permittivity

Bulgakov, Evgeny N.; Sadreev, Almas F. PHYSICAL REVIEW A, 96 (1): Doi: 10.1103/PhysRevA.96.013841 JUL 20 2017

We report bound states in the radiation continuum (BICs) in a single infinitely long dielectric rod with periodically stepwise modulated permittivity alternating from ε1 to ε2. For ε2=1 in air the rod is equivalent to a stack of dielectric disks with permittivity ε1. Because of rotational and translational symmetries the BICs are classified by orbital angular momentum m and the Bloch wave vector β directed along the rod. For m=0 and β=0 the symmetry protected BICs have definite polarization and occur in a wide range of the radius of the rod and the dielectric permittivities. More involved BICs with m0,β=0 exist only for a selected radius of the rod at a fixed dielectric constant. The existence of robust Bloch BICs with β0,m=0 is demonstrated. Asymptotic limits to a homogeneous rod and to very thin disks are also considered.

Multilayered multiconductor stripline resonator and its application to bandpass filter with wide stopband

Belyaev, B. A.; Serzhantov, A. M.; Leksikov, A. A.; Bal'va, Y. F.; Leksikov, A. A. MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, 59 (9):2212-2216; Doi: 10.1002/mop.30706 SEP 2017

A multilayered, multi-conductor stripline resonator is proposed. It is shown that increase in the number of conductors leads to increase the unloaded Q-factor and decrease the resonant frequency, with increasing the effects for thinner dielectric interlayer. Application of the resonator to the bandpass filter enables designing bandpass filters with very wide and deep stopbands. To prove this, a 4-pole bandpass filter, having central frequency 360 MHz and an overall size of 15.5 × 31.75 × 8.45 mm3, was designed and fabricated.

On the Effect of an Inhomogeneous Magnetic Field and Many-body Localization on the Increase in the Second Moment of Multiple-Quantum NMR with Time

Zobov, V. E.; Lundin, A. A. JETP LETTERS, 105 (8):514-518; Doi: 10.1134/S0021364017080148 APR 2017

A change in the time dependence of the second moment of the distribution of intensities of coherences with various orders in the spectrum of multiple-quantum NMR in a solid at the inclusion of an inhomogeneous magnetic field in the effective interaction is studied. Both the secular dipole–dipole and nonspecular twoquantum interactions are considered as nucleus–nucleus interactions, which correspond to traditional experimental realizations. It is shown that, with an increase in the magnitude of the inhomogeneous field, an exponential increase in the second moment of multiple-quantum NMR with time changes to a power-law increase. The results obtained in this work indicate that this second moment, which determines the average number of dynamically correlated spins, can be used as a convenient characteristic for studying a transition to a many-body localized state.

Features of the intensity behavior of Kramers doublet components in NdFe3(BO3)(4) in the transverse Zeeman geometry

Kachur, I. S.; Kurnosov, V. S.; Piryatinskaya, V. G.; Yeremenko, A. V.; Gudim, I. A. LOW TEMPERATURE PHYSICS, 43 (5):590-596; Doi: 10.1063/1.4990018 MAY 2017
Nontrivial magnetic field dependence of the polarization of the Kramers doublet absorption lines (15 971–15 978 cm−1) was observed in the range of the 4I9/22H11/2 optical transition of Nd3+ ion in an easy-plane antiferromagnet NdFe3(BO3)4 in the transversal Zeeman effect geometry. Values of the transversal g factor and the effective exchange field with Fe3+ magnetic subsystem were determined for the excited state of Nd3+ from the field dependence of the doublet splitting. A semiempirical equation was proposed for the description of the field dependence of the intensities of the polarized components of the absorption lines corresponding to the Kramers doublet 15 971–15 978 cm−1. Besides the scaling factors, the equation contains only the independently determined magnitudes of exchange fields for the ground and excited states as parameters.

 

 

Low-temperature absorption spectra and electron structure of HoFe3(BO3)(4) single crystal

Malakhovskii, A. V.; Gnatchenko, S. L.; Kachur, I. S.; Piryatinskaya, V. G.; Gudim, I. A. LOW TEMPERATURE PHYSICS, 43 (5):610-616; Doi: 10.1063/1.4985208 MAY 2017
Polarized absorption spectra of HoFe3(BO3)4 single crystal in the range of 8500–24 500 cm−1 were studied as a function of temperature beginning from 2 K. The ground and excited electron states of Ho3+ were identified. The abrupt changes of the spectra at the reorientation phase transition at 4.7 K were observed. The exchange splitting of some excited states were revealed and measured. They changed at the reorientation phase transition. Several vibronic transitions were observed. The splitting of absorption lines corresponding to the C2 local symmetry of the Ho ion was not observed. Moreover, spectra of some absorption bands correspond to splitting in the cubic crystal field. There are some absorption lines, whose polarization cannot be explained both in D3 and C2 local symmetries. Some lines appear or disappear as a result of the transition from the easy axis to the easy plane state of the crystal. All these observations testify to the substantial changes of the local magnetic and structural properties in the excited states of the Ho3+ ion and to the strong influence of the magnetic moments orientation on the polarization of the electron transitions.

 

 

Rotational magnetocaloric effect in TbAl3(BO3)(4)

Pashchenko, M. I.; Bedarev, V. A.; Merenkov, D. N.; Bludov, A. N.; Pashchenko, V. A.; Gnatchenko, S. L.; Zajarniuk, T.; Szewczyk, A.; Temerov, V. L. LOW TEMPERATURE PHYSICS, 43 (5):631-635; Doi: 10.1063/1.4985220 MAY 2017
A rotational magnetocaloric effect is predicted in the TbAl3(BO3)4 crystal based on the results of measuring field dependences of magnetization and the temperature dependence of heat capacity. The effect is modeled using the quasi-doublet approximation. Changes to the crystal entropy at constant temperature are determined, as well as at varying temperature under adiabatic conditions. The refrigerant capacity of the crystal is estimated. It is shown that terbium aluminum borate is a promising material for magnetic cooling.

 

 

Microscopic models of source and sink for atomtronics

Kolovsky, Andrey R. PHYSICAL REVIEW A, 96 (1): Doi: 10.1103/PhysRevA.96.011601 JUL 10 2017

We analyze microscopic models of the particle source or sink which consist of a one- or two-site Bose-Hubbard model (the system) weakly coupled to a many-site Bose-Hubbard model (the reservoir). Assuming unequal filling factors for the system and reservoir, we numerically study equilibration dynamics and compare it with the solution of the master equation on the reduced density matrix of the system. Necessary conditions for the validity of the master equation approach are formulated.

Two-dimensional antiferromagnetic correlations in an La1.4Sr1.6(Mn0.9Co0.1)(2)O-7 single crystal

Bykov, A. A.; Zobkalo, I. A.; Dubrovskii, A. A.; Smirnov, O. P.; Nikitin, S. E.; Terent'ev, K. Yu.; Gavrilov, S. V.; Shaikhutdinov, K. A. JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 124 (5):786-791; Doi: 10.1134/S1063776117050120 MAY 2017

The temperature and field dependences of the magnetization, the electrical resistivity, and the magnetostriction of bilayer lanthanum manganite La1.4Sr1.6Mn2O7 single crystals and cobalt-doped La1.4Sr1.6(Mn0.9Cu0.1)2O7 are measured. The magnetostriction of the cobalt-doped compound increases as compared to the initial La1.4Sr1.6Mn2O7 compound, and the magnetization and the magnetoresistance of the former compound change substantially. Powder and single-crystal neutron diffraction patterns are used to detect ferromagnetic ordering in La1.4Sr1.6(Mn0.9Co0.1)2O7 at a temperature below TC ~ 45(2) K, and this ordering coexists with antiferromagnetic correlations, which develop at temperatures below TC ~ 80(5) K.

Magnetic resonance studies of three-layer FeNi/Bi/FeNi films

Patrin, K. G.; Yarikov, S. A.; Patrin, G. S.; Yakovchuk, V. Yu.; Lyamkin, A. I. JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 124 (5):779-785; Doi: 10.1134/S1063776117040069 MAY 2017

The interlayer coupling in three-layer FeNi/Bi/FeNi films is studied by electron magnetic resonance. The magnetic anisotropy at the permalloy–bismuth interface is shown to play a significant role in the formation of the magnetic state of the film structure. The interlayer coupling oscillation period is found to be about 8 nm. The interlayer coupling and the interface anisotropy and their temperature dependences are determined.

Analysis of the exchange magnetic structure in Pb3Mn7O15

Eremin, E. V.; Volkov, N. V.; Sablina, K. A.; Bayukov, O. A.; Molokeev, M. S.; Komarov, V. Yu. JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 124 (5):792-804; Doi: 10.1134/S1063776117040112 MAY 2017

The indirect-coupling model is used to analyze the exchange magnetic structure of Pb3Mn7O15 in the hexagonal setting. The ratios of manganese ions Mn4+/Mn3+ in each nonequivalent position are determined. Pb3(Mn0.95Ge0.05)7O15 and Pb3(Mn0.95Ga0.05)7O15 single crystals are grown by the solution–melt method in order to test the validity of the proposed model. The structural and magnetic properties of the single crystals are studied. The magnetic properties of the grown single crystals are compared with those of nominally pure Pb3Mn7O15.

Polarization of Light by a Polymer Film Containing Elongated Drops of Liquid Crystal with Inhomogeneous Interfacial Anchoring

Loiko, V. A.; Konkolovich, A. V.; Zyryanov, V. Ya.; Miskevich, A. A. OPTICS AND SPECTROSCOPY, 122 (6):984-994; Doi: 10.1134/S0030400X1706011X JUN 2017

An optico-mechanical model describing the coherent (directed) transmittance and the degree of polarization of forward-transmitted light by a polymer film with elongated liquid-crystal (LC) drops has been developed. This model, based on the Foldy–Twersky and anomalous-diffraction approximations, makes it possible to analyze the optical response of a film under extension as a function of the film thickness, refractive index of the polymer, the sizes and anisometry parameters of liquid-crystal drops, their concentration, internal structure, polydispersity, and orientation of optical axes. The model is verified based on the comparison of numerical and experimental data for the inverse modification of interfacial anchoring by an ion-forming surfactant. The internal drop structure is determined by solving the problem of minimizing the volume free energy density. A comparative analysis of the calculated transmittance and degree of polarization for films with uniform homeotropic and modified inhomogeneous interfacial anchoring is performed. The spectral polarization characteristics of a film with elongated LC drops and single-domain internal structure, formed under mechanical extension with the aid of surfactants, are investigated.

Structuring in Fast-Quenched Ferrite Compositions under Plasma Spraying

Lepeshev, A. A.; Karpov, I. V.; Ushakov, A. V.; Nagibin, G. E.; Dorozhkina, E. A.; Karpova, O. N.; Demin, V. G.; Shaikhadinov, A. A. TECHNICAL PHYSICS, 62 (6):911-914; Doi: 10.1134/S1063784217060196 JUN 2017

The influence of the quench rate on structuring in spinel ferrites has been studied. It has been found that, when the quench rate is increased, the equilibrium spinel structure gradually becomes disordered. At the first stage, the statistically homogeneous (or almost homogeneous) redistribution of cations over crystal lattice sites has been observed. Then, the fcc lattice of the anion framework breaks down, the translational symmetry disappears, and topological chaos arises. The resulting cluster structural state is thermodynamically unstable, and heating of quenched ferrites causes stepwise energy liberation. As a result, the activity of ferrite powders in solid-state and catalytic reactions rises.

Light enhancement by quasi-bound states in the continuum in dielectric arrays

Bulgakov, Evgeny N.; Maksimov, Dmitrii N. OPTICS EXPRESS, 25 (13):14134-14147; Doi: 10.1364/OE.25.014134 JUN 26 2017

The article reports on light enhancement by structural resonances in linear periodic arrays of identical dielectric elements. As the basic elements both subwavelength spheres and rods with circular cross section have been considered. In either case it has been demonstrated numerically that high-Q structural resonant modes originated from bound states in the continuum enable near-field amplitude enhancement by factor of 10–25 in the red-to-near infrared range in lossy silicon. The asymptotic behavior of the Q-factor with the number of elements in the array is explained theoretically by analyzing quasi-bound states propagation bands.

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Polymeric lithium(I) diaquabarbiturate: Crystal structure

Golovnev, N. N.; Molokeev, M. S.; Lesnikov, M. K.; Vereshchagin, S. N. RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 62 (6):746-750; Doi: 10.1134/S0036023617060092 JUN 2017

The lithium(I) catena-diaquabarbiturate complex [Li(H2O)2(HBA–O,O′)]n (I), where Н2ВА is barbituric acid, has been structurally characterized by X-ray diffraction (CIF file CCDC no. 1447689), and its thermal decomposition and IR spectrum have been studied. Crystals of complex I are monoclinic, a = 6.4306(7) Å, b = 16.720(1) Å, c = 7.1732(8) Å, β = 108.253(4)°, V = 732.5(1) Å3, space group P21/c, and Z = 4. One independent μ2-bridging HBA ligand is coordinated to two Li(I) ions via the two oxygen atoms of C4(6)=O carbonyl groups. Each Li+ ion is linked with two μ2-HBA ions and two terminal water molecules at tetrahedron vertices. μ2-HBA ions link tetrahedra into a chain. The structure is stabilized by multiple hydrogen bonds and π–π-interaction between HBA. The shift of ν(C=O) vibration bands in the IR spectrum of complex I in comparison with Н2ВА towards lower frequencies agrees with the coordination of HBA via oxygen atoms. The dehydration of complex I occurs in two stages in the regions of 100–150 and 150–240°C.

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Bis(mu(3)-barbiturato-O,O,O ')-(mu(2)-aqua)- aqua-barium(II): crystal structure, spectroscopic and thermal properties

Solovyov, Leonid A.; Golovnev, Nicolay N.; Molokeev, Maxim S.; Lesnikov, Maxim K. JOURNAL OF COORDINATION CHEMISTRY, 70 (12):1984-1993; Doi: 10.1080/00958972.2017.1319943 2017

A polymeric coordination compound, [Ba(H2O) 2(Hba)2] (1) (H2ba – barbituric acid, C4H4N2O3), was obtained. The structure of 1 was solved using powder X-ray diffraction methods. The Ba2+ ion in 1 formed a three-capped trigonal prism. The BaO9 polyhedra, connected with each other by the edges and faces, formed a chain. Several 4- and 12-membered cycles due to the bridging μ2-H2O and bridging μ3-Hba also formed implementing a 3-D polymer structure. The structures of 1 and other thiobarbiturate complexes were compared. The replacement of a S atom by an O atom in the heterocyclic ligand Htba (thiobarbiturate ion) of the compound Ba(H2O)2(Htba)2 resulted in changes of the coordination number Ba(II) and supramolecular structure. The intermolecular hydrogen bonds O–H⋯O and N–H⋯O formed a 3-D net where pronounced 2-D layers of Hba ions could be found. A new topological net in 1 was observed. The IR and thermal stability were investigated.

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Surface plasmon resonances in liquid metal nanoparticles

Ershov, A. E.; Gerasimov, V. S.; Gavrilyuk, A. P.; Karpov, S. V. APPLIED PHYSICS B-LASERS AND OPTICS, 123 (6): Doi: 10.1007/s00340-017-6755-2 JUN 2017

We have shown significant suppression of resonant properties of metallic nanoparticles at the surface plasmon frequency during the phase transition “solid–liquid” in the basic materials of nanoplasmonics (Ag, Au). Using experimental values of the optical constants of liquid and solid metals, we have calculated nanoparticle plasmonic absorption spectra. The effect was demonstrated for single particles, dimers and trimers, as well as for the large multiparticle colloidal aggregates. Experimental verification was performed for single Au nanoparticles heated to the melting temperature and above up to full suppression of the surface plasmon resonance. It is emphasized that this effect may underlie the nonlinear optical response of composite materials containing plasmonic nanoparticles and their aggregates.

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Comparative Analysis of Methods for Enhancement of the Photostability of CdTe@TGA QD Colloid Solutions

Tsipotan, Aleksey S.; Gerasimova, Marina A.; Polyutov, Sergey P.; Aleksandrovsky, Aleksandr S.; Slabko, Vitaliy V. JOURNAL OF PHYSICAL CHEMISTRY B, 121 (23):5876-5881; Doi: 10.1021/acs.jpcb.7b03166 JUN 15 2017

The employment of colloid quantum dots in a number of applications is limited by their instability under light irradiation. Additional methods of photostability enhancement of UV+visible-irradiated TGA-stabilized CdTe quantum dots are investigated. Photostability enhancement was observed via either addition of sodium sulphite in the role of chemical oxygen absorber or addition of 1% gelatin, or, finally, by additional stabilization by bovine serum albumine (BSA). The latter method is the most promising, since it not only enhances the quantum dots’ photostability but also makes them more biocompatible and extends the possibilities of their biological applications.

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Topological Bound States in the Continuum in Arrays of Dielectric Spheres

Bulgakov, Evgeny N.; Maksimov, Dmitrii N. PHYSICAL REVIEW LETTERS, 118 (26): Doi: 10.1103/PhysRevLett.118.267401 JUN 26 2017

We consider Bloch bound states in the radiation continuum in periodic arrays of dielectric spheres. It is demonstrated that the bound states are associated with phase singularities of the quasimode coupling strength. That makes the bound states topologically protected and, therefore, robust against any variation of parameters preserving the periodicity and rotational symmetry about the array axis. It is shown that under variation of parameters the bound states can only be destroyed by either annihilation of the topological charge or by migration to the sector of the parametric space where the second radiation channel is open.

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Formation of the atomically ordered L1(0) structure with the [001] orientation during the solid-state reaction in Fe/Pd bilayer thin films

Moiseenko, E. T.; Altunin, R. R.; Zharkov, S. M. PHYSICS OF THE SOLID STATE, 59 (6):1233-1237; Doi: 10.1134/S1063783417060154 JUN 2017

The formation of the atomically ordered L10-FePd structure during the solid-state reaction in Fe/Pd bilayer thin films is in situ investigated by electron microscopy and electron diffraction analysis. The initial iron and palladium layers were mainly coherently oriented crystallites with the orientation relationship α-Fe (001)[110] || Pd(001)[100]. It is established that the solid-state reaction between the iron and palladium layers upon heating at a rate of 4–8°C/min starts with the formation of the FePd solid solution at 390°C; at 430°C, the formation of the atomically ordered L10-FePd structure is observed. It is shown that at the low heating rate (4–8°C/min), the L10-FePd structure with the [001] orientation relative to the film plane forms, while at the high heating rate (50°C/min) it forms with the [100], [010], and [001] orientations.

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Electrocaloric effect in triglycine sulfate under equilibrium and nonequilibrium thermodynamic conditions

Bondarev, V. S.; Mikhaleva, E. A.; Flerov, I. N.; Gorev, M. V. PHYSICS OF THE SOLID STATE, 59 (6):1118-1126; Doi: 10.1134/S1063783417060051 JUN 2017

The direct and indirect measurements of intensive electrocaloric effect in a triglycine sulfate ferroelectric crystal are performed under equilibrium and nonequilibrium thermodynamic conditions implemented in the adiabatic calorimeter. The effect of the electric field parameters (frequency, profile, and strength) on the value of the effect and degree of its reversibility are studied. The difference between the temperature variation values in a switched-on and switched-off dc field under quasi-isothermal conditions is established. The low-frequency periodic electric field induces the temperature gradient along the electrocaloric element and heat flux from its free end to the thermostated base. A significant excess of the field switching-off rate over the switching-on rate leads to a noticeable intensification of the cooling effect.

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Effect of Deuteration on the Thermodynamic Properties of Dioxotetrafluoromolybdate(VI), (NH4)(2)MoO2F4

Bogdanov, Evgeniy V.; Pogoreltsev, Evgeniy I.; Gorev, Mikhail V.; Flerov, Igor N. INORGANIC CHEMISTRY, 56 (11):6706-6711; Doi: 10.1021/acs.inorgchem.7b00811 JUN 5 2017

Thermal and dielectric studies of (ND4)2MoO2F4 crystals undergoing successive phase transitions at T1 = 272 K and T2 = 181 K showed that deuteration is accompanied by an increase in the chemical pressure in the crystal lattice (Δp ≈ 0.02 GPa), which shifts the CmcmPnma transformation for the first order to the tricritical point. The direct participation of ammonium groups in the mechanism of structural distortions is demonstrated by a decrease in the entropy of the high-temperature phase transition (ΔS1 = R ln 6.0). An external hydrostatic pressure leads to an expansion of the temperature interval of the intermediate antiferroelectric Pnma phase. The triple point on the Tp phase diagram, where the Cmcm, Pnma, amd Pnma* phases coexist, can be realized at a negative pressure of ptrp ≈ −0.8 GPa.

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Electron spin resonance in Cu1-xFexCr2Se4 nanoparticles synthesized with the thermal decomposition method

Edelman, I. S.; Zharkov, S. M.; Pankrats, A. I.; Vorotynov, A. M.; Tugarinov, V. I.; Ivantsov, R. D.; Petrov, D. A.; Velikanov, D. A.; Lin, Chun-Rong; Chen, Chin-Chang; Tseng, Yaw-Teng; Hsu, Hua-Shu JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 436 21-30; Doi: 10.1016/j.jmmm.2017.04.006 AUG 15 2017

In this paper, we present a study of the electron spin resonance (ESR) of nanoparticles (NPs) of Cu1−xFexCr2Se4 chalcogenides with x = 0, 0.2, and 0.4. NPs were synthesized via the thermal decomposition of metal chloride salts and selenium powder in a high-temperature organic solvent. According to the XRD and HRTEM data, the NPs were single crystalline nearly hexagonal plates with the structure close to CuCr2Se4 (Fd-3m, a = 10.337 Å). For x = 0 and 0.2, the NPs tend to form long stacks consisting of the plates “face to face” attached to each other due to the magnetostatic interparticle interaction. Only separate NPs were observed in the case of x = 0.4. Peculiarities were revealed in the ESR temperature behavior for the NPs with x = 0 and 0.2 consistent with the features in the temperature dependences of the NPs magnetization. The non-monotonous dependence of the resonance field Hres on the temperature with a kink near 130 K and the energy gap in the resonance spectrum depending on the type of nanoparticle compacting are the distinct peculiarities. One of the main factors is discussed in order to explain the peculiarities: the coexistence of two types of anisotropy in the Cu1−xFexCr2Se4 NPs, in-plain shape anisotropy and magnetocrystalline anisotropy with four easy axes, which increases strongly with the temperature decrease.

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Origin of the giant circular dichroism of vibronic f-f transitions

Malakhovskii, A. V. MOLECULAR PHYSICS, 115 (14):1687-1690; Doi: 10.1080/00268976.2017.1317113 2017

Taking into account the space inhomogeneity of the light electromagnetic wave, a new quantum mechanical expression for the natural optical activity (NOA) of electron transitions has been obtained, which is consistent with the phenomenological theory. It is shown that properties of the NOA of parity forbidden f–f transitions substantially differ from those of allowed transitions. The experimentally observed large NOA of the f–f transitions and extremely large (close to unity) NOA of vibrational repetitions of the f–f transitions are qualitatively explained on the basis of the obtained theoretical expression.

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BIOMEDICAL APPLICATION OF BIOGENIC FERRIHYDRITE NANOPARTICLES

Chilom, C. G.; Gazdaru, D. M.; Balasoiu, M.; Bacalum, M.; Stolyar, S. V.; Popescu, A. I. ROMANIAN JOURNAL OF PHYSICS, 62 (3-4):2017

Magnetic Properties of Co-2 2+Co1-x3+Fex3+ BO5 (x=0.10) Single Crystals with a Ludwigite Structure

Knyazev, Yu. V.; Kazak, N. V.; Bayukov, O. A.; Platunov, M. S.; Velikanov, D. A.; Bezmaternykh, L. N.; Ivanova, N. B.; Ovchinnikov, S. G. JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 124 (4):623-627; Doi: 10.1134/S106377611703013X APR 2017

The investigation of mixed Co–Fe ludwigite single crystals shows that their magnetic properties are close to the magnetic properties of Fe3BO5 despite the predominance of cobalt ions. The magnetic properties of Co3 – xFexBO5 single crystals with x = 0.10 are studied in detail. Magnetometric measurements demonstrate a strong magnetic anisotropy with easy magnetization axis b, and the orbital magnetic moment of cobalt is in a frozen state. The detected temperature dependence of the absorption of Mössbauer spectra allowed us to determine the magnetic ordering temperature, which agrees with the results of magnetization measurements (TC = 84 K).

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GENERALIZED KONDO LATTICE MODEL AND ITS SPIN-POLARON REALIZATION BY THE PROJECTION METHOD FOR CUPRATES

Valkov, V. V.; Dzebisashvili, D. M.; Barabanov, A. F. THEORETICAL AND MATHEMATICAL PHYSICS, 191 (2):752-763; Doi: 10.1134/S0040577917050142 MAY 2017

The spin–fermion model, which is an effective low-energy realization of the three-band Emery model after passing to the Wannier representation for the px and py orbitals of the subsystem of oxygen ions, reduces to the generalized Kondo lattice model. A specific feature of this model is the existence of spin-correlated hoppings of the current carriers between distant cells. Numerical calculations of the spectrum of spin-electron excitations highlight the important role of the long-range spin-correlated hoppings.

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Phase formation of (Y,Ce)(2)BaAl4SiO12 yellow microcrystal-glass phosphor for blue LED pumped white lighting

Ji, Haipeng; Cho, Yujin; Wang, Le; Hirosaki, Naoto; Molokeev, Maxim S.; Huang, Zhaohui; Xie, Rong-Jun CERAMICS INTERNATIONAL, 43 (8):6425-6429; Doi: 10.1016/j.ceramint.2017.02.055 JUN 1 2017

The (Y,Ce)2BaAl4SiO12 phosphor, a garnet-structured blue-to-yellow color convertor for WLED, exhibits an interesting “microcrystal-glass powder” feature, which can be regarded as the 4th form for phosphor, in addition to the “ceramic powder phosphor”, the “single crystal phosphor” and the “glass-ceramic phosphor”. The structure exhibits luminescent microcrystals embedding in non-luminescent glass matrix: the spherical crystals are mainly arranged around the glass phase forming a “necklace” pattern, while the individual crystals show a “core-shell” architecture regarding the luminescence intensity variation. Further combining the phase evolution evidence evaluated by Rietveld refinement, we propose the formation mechanism for such unique morphology/structure as a two-stage process, including an initial nucleation by solid state reaction and following liquid-assisted crystal growth, instead of a precipitation-crystallization process.

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