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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Denisova L. T., Molokeev M. S., Kargin, Yu F., Ryabov V. V., Chumilina L. G., Belousova, N., V, Denisov V. M.
Заглавие : Structure and thermodynamic properties of the DyGaTi2O7 and EuGaTi2O7 titanates
Коллективы : Russian Federation Ministry of Science and Higher Education [FSRZ-2020-0013]
Место публикации : Inorg. Mater. - 2021. - Vol. 57, Is. 7. - P.733-740. - ISSN 0020-1685, DOI 10.1134/S0020168521070050. - ISSN 1608-3172(eISSN)
Примечания : Cited References: 26. - This work was supported by the Russian Federation Ministry of Science and Higher Education as part of the state research target for the Siberian Federal University federal state autonomous educational institution of higher education, project no. FSRZ-2020-0013
Предметные рубрики: CRYSTAL-STRUCTURE
MAGNETIC-PROPERTIES
STATE
Аннотация: The DyGaTi2O7 and EuGaTi2O7 titanates have been prepared by solid-state reactions in a starting mixture of Dy2O3 (Eu2O3), Ga2O3, and TiO2 via firing in air at temperatures of 1273 and 1573 K, and their crystal structure has been studied by X-ray diffraction. Their high-temperature heat capacity (350-1000 K) has been determined by differential scanning calorimetry. The Cp(T) experimental data have been used to calculate the thermodynamic functions of the titanates.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aksenov S. V., Zlotnikov A. O., Shustin M. S.
Заглавие : Strong Coulomb interactions in the problem of Majorana modes in a wire of the nontrivial topological class BDI
Коллективы : RAS Presidium programs for fundamental research [32, 12]; Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR) [18-32-00443, 19-02-00348]; Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science [19-42-240011]; Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific SchoolsLeading Scientific Schools Program [MK-1641.2020.2, MK-3594.2018.2]; Foundation for the Advancement of Theoretical Physics and Mathematics "BASIS" [18-46-007]
Место публикации : Phys. Rev. B. - 2020. - Vol. 101, Is. 12. - Ст.125431. - ISSN 2469-9950, DOI 10.1103/PhysRevB.101.125431. - ISSN 2469-9969(eISSN)
Примечания : Cited References: 60. - We acknowledge fruitful discussions with V. V. Valkov and V. A. Mitskan. The reported study was funded by the RAS Presidium programs for fundamental research Nos. 12 and 32, Russian Foundation for Basic Research (Projects No. 18-32-00443 and No. 19-02-00348), Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project: "Coulomb interactions in the problem of Majorana modes in low-dimensional systems with nontrivial topology" (Grant No. 19-42-240011). S.V.A. and A.O.Z. are grateful to the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools, Projects No. MK-1641.2020.2 and No. MK-3594.2018.2. S.V.A. acknowledges the support from the Foundation for the Advancement of Theoretical Physics and Mathematics "BASIS" (Grant No. 18-46-007).
Предметные рубрики: QUANTUM
POLARIZATION
TRANSITION
FERMIONS
SPECTRUM
STATE
Аннотация: In this study, the problem of strong Coulomb interactions in topological superconducting wire is analyzed by means of the density-matrix-renormalization-group (DMRG) approach. To analyze properties of edge states in the BDI-class structure, a quantity called Majorana polarization is used. From its dependence on wire length and an entanglement-spectrum degeneracy, topological phase diagrams are obtained. The DMRG calculations for the Shubin-Vonsovsky-type model of the wire show the transformation of phases with Majorana single and double modes (MSMs and MDMs, respectively) under the increase of onsite and intersite correlations. In particular, we demonstrate different scenarios including the possibilities of both induction and suppression of the MSMs and MDMs. It is shown that in the strongly correlated regime, the contributions of single-particle excitations to the Majorana-type states significantly decrease at low magnetic fxields. Moreover, the t-J*-V model is derived allowing to study the effective interactions and improve the DMRG numerics. It is found out that in the limiting case of the effective Hamiltonian with infinitely strong onsite repulsion, t model, the topological phases are destroyed. Finally, the ways to probe the MSMs and MDMs via the features of caloric functions are discussed.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Polukeev S. I., Ovchinnikov S. G.
Заглавие : Cation spin and superexchange interaction in oxide materials below and above spin crossover under high pressure
Коллективы : Russian Science FoundationRussian Science Foundation (RSF) [18-12-00022]
Место публикации : Phys. Rev. B. - 2020. - Vol. 101, Is. 9. - Ст.094409. - ISSN 2469-9950, DOI 10.1103/PhysRevB.101.094409. - ISSN 2469-9969(eISSN)
Примечания : Cited References: 65. - We acknowledge the support of the Russian Science Foundation through Grant No. 18-12-00022
Предметные рубрики: EXCHANGE INTERACTION
PHASE-TRANSITIONS
STATE
ELECTRON
IRON
Аннотация: We derived simple rules for the sign of 180° superexchange interaction based on the multielectron calculations of the superexchange interaction in the transition metal oxides that are valid both below and above spin crossover under high pressure. The superexchange interaction between two cations in dn configurations is given by a sum of partial contributions related to the electron-hole virtual excitations to the different states of the dn+1 and dn−1 configurations. Using these rules, we have analyzed the sign of the 180° superexchange interaction of a number of oxides with magnetic cations in electron configurations from d2 until d8: the iron, cobalt, chromium, nickel, copper, and manganese oxides with increasing pressure. The most interesting result concerns the magnetic state of cobalt and nickel oxides CoO, Ni2O3 and also La2CoO4, LaNiO3 isostructural to well-known high-TC and colossal magnetoresistance materials. These oxides have a spin 12 at the high pressure. Change of the interaction from antiferromagnetic below spin crossover to ferromagnetic above spin crossover is predicted for oxide materials with cations in d5(FeBO3) and d7(CoO) configurations, while for materials with the other dn configurations spin crossover under high pressure does not change the sign of the 180∘ superexchange interaction.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popkov S. I., Krasikov A. A., Semenov S. V., Dubrovskii A. A., Yakushkin S. S., Kirillov V. L., Mart'yanov O. N., Balaev D. A.
Заглавие : General regularities and differences in the behavior of the dynamic magnetization switching of ferrimagnetic (CoFe2O4) and antiferromagnetic (NiO) nanoparticles
Коллективы : Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR); Government of the Krasnoyarsk region; Krasnoyarsk Regional Foundation for Science [18-42-240012]
Место публикации : Phys. Solid State. - 2020. - Vol. 62, Is. 9. - P.1518-1524. - ISSN 1063-7834, DOI 10.1134/S1063783420090255. - ISSN 1090-6460(eISSN)
Примечания : Cited References: 46. - This work was supported by the Russian Foundation for Basic Research, the Government of the Krasnoyarsk region, and the Krasnoyarsk Regional Foundation for Science, project no. 18-42-240012: "Magnetization switching of magnetic nanoparticles in strong pulsed magnetic fields is a new approach to studying the dynamic effects related to the processes of magnetization of magnetic nanoparticles"
Предметные рубрики: PARTICLE-SIZE
EXCHANGE-BIAS
TEMPERATURE
STATE
COERCIVITY
Аннотация: In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe2O4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force HC at the dynamic magnetization switching is markedly higher than HC at quasi-static conditions. HC increases as the pulse duration τP decreases and the maximum applied field H0 increases. The dependence of HC on field variation rate dH/dt = H0/2τP is a unambiguous function for CoFe2O4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH/dt, and the value of applied field H0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Drokina T. V., Molokeev M. S., Velikanov D. A., Petrakovskii G. A., Bayukov O. A.
Заглавие : HoFeTi2O7: synthesis, peculiarities of the crystal structure, and magnetic properties
Место публикации : Phys. Solid State. - 2020. - Vol. 62, Is. 3. - P.464-471. - ISSN 1063-7834, DOI 10.1134/S1063783420030075. - ISSN 1090-6460(eISSN)
Примечания : Cited References: 23
Предметные рубрики: SPIN-GLASS
STATE
Аннотация: Polycrystalline samples of HoFeTi2O7 were obtained by solid-phase synthesis and investigated using X-ray diffraction, gamma resonance, and SQUID measurements. Characteristics of the structural properties are presented, which give an evidence of the distribution of iron atoms among nonequivalent crystallographic positions and of the nonuniform populating of positions mixed with titanium by the iron atoms. Spin disorder caused by mixing of magnetic and nonmagnetic ions, spatial nonuniformity of the interactions defining the magnetic structure in the crystal lead to formation of concurrent magnetic exchange interactions between the nearest neighbors, frustration of magnetic couplings, and loss of the long-range magnetic ordering. The temperature dependence of the magnetic susceptibility at low temperatures was shown to have some peculiarities typical of the magnetic state of spin glass.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhou, Guojun, Jiang, Xingxing, Molokeev M. S., Lin, Zheshuai, Zhao, Jing, Wang, Jing, Xia, Zhiguo
Заглавие : Optically Modulated Ultra-Broad-Band Warm White Emission in Mn2+-Doped (C6H18N2O2)PbBr4 Hybrid Metal Halide Phosphor
Место публикации : Chem. Mater. - 2019. - Vol. 31, Is. 15. - P.5788-5795. - ISSN 0897-4756, DOI 10.1021/acs.chemmater.9b01864. - ISSN 1520-5002(eISSN)
Примечания : Cited References: 47. - This work is supported by the National Natural Science Foundation of China (nos. 51722202 and 51572023), Natural Science Foundations of Beijing (2172036), the Fundamental Research Funds for the Central Universities (FRF-TP-18-002C1), and the Guangdong Provincial Science & Technology Project (no. 2018A050506004).
Предметные рубрики: LIGHT EMISSION
PEROVSKITE NANOCRYSTALS
ENERGY-TRANSFER
STATE
Br
Аннотация: Finding new low-dimensional metal halides with broad-band emission is attracting interest in single-component phosphor for white light-emitting diodes (WLEDs). The full-spectrum white light still remains a challenge as found in the two-dimensional hybrid material (C6H18N2O2)PbBr4 exhibiting the intrinsic free exciton (FE) and broad-band self-trap exciton (STE) emission upon 365 nm ultraviolet excitation, and a combined strategy has been proposed through doping the Mn2+ ions enabling a superposition of multiple emission centers toward the ultra-broad-band warm white light. The occupation of Mn2+ in (C6H18N2O2)PbBr4 has been discussed, and optical investigations verify that the warm white-light emission of Mn2+-doped (C6H18N2O2)PbBr4 originates from the coupling effects of the FE, STEs, and the 4T1–6A1 transition of the doped Mn2+. When the concentration of Mn2+ is 5%, the emission spectrum of the phosphor covers all visible-light areas with a full width at half maximum (FWHM) of about 230 nm. The high Ra (84.9) and warm light CCT (3577 K) values of the as-fabricated WLED lamp demonstrate that (C6H18N2O2)Pb1–xMnxBr4 can be promising as single-component white-light phosphor in solid-state lighting. Our work could provide a new understanding and perspective about hybrid metal halides for designing superior phosphor toward single-component white emission.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Golovnev N. N., Molokeev M. S., Sterkhova I. V., Lesnikov M. K.
Заглавие : Structure of Barbituratobis(2,2'-Dipyridyl)copper(II) Heptahydrate
Коллективы : Ministry of Education and Science of the Russian Federation [4.7666.2017/BCh]
Место публикации : Russ. J. Coord. Chem. - 2019. - Vol. 45, Is. 8. - P.569-572. - ISSN 1070-3284, DOI 10.1134/S1070328419080037. - ISSN 1608-3318(eISSN)
Примечания : Cited References: 25. - This work was supported by the Ministry of Education and Science of the Russian Federation in the framework of the state task for the Siberian Federal University for 2017-2019 (4.7666.2017/BCh).
Предметные рубрики: IONIC CO-CRYSTALS
BARBITURIC-ACID
COMPLEXES
STATE
Аннотация: The structure of the complex [Cu(Bipy)2(BA)] ∙ 7H2O (I), where Bipy is 2,2'-dipyridyl, and BA2– is the barbituric acid anion (H2BA), is determined (CIF file CCDC no. 1887338). The thermal decomposition and IR spectrum of complex I are studied. The crystals are orthorhombic: a = 26.118(3), b = 27.685(3), c = 15.683(2) Å, V = 11 370(2) Å3, space group Fdd2, Z = 16. The discrete structure of the polar crystal consists of neutral [Cu(Bipy)2(BA)] particles and molecules of crystallisation water . The Cu2+ ion is bound to the N atoms of two bidentate Bipy molecules and the N atom of the BA2− ion at the vertices of the trigonal bipyramid CuN5. Compound I is the first example of the metal complex only with the N-coordinated anions of barbituric acid (BA2−, НBA−). The structure is stabilized by hydrogen bonds O−H∙∙∙O and N−H∙∙∙O to form a three-dimensional network with the π–π interaction between the Bipy molecules. The compound begins to lose water at ~50°С and is completely dehydrated above 200°С.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min V. I., Orlov Yu. S., Zarubin A. E., Ovchinnikova T. M., Ovchinnikov S. G.
Заглавие : Magnetism in spin crossover systems: Short-range order and effects beyond the Heisenberg model
Коллективы : Russian Scientific FoundationRussian Science Foundation (RSF) [18-12-00022]
Место публикации : Phys. Rev. B. - 2019. - Vol. 100, Is. 14. - Ст.144429. - ISSN 2469-9950, DOI 10.1103/PhysRevB.100.144429. - ISSN 2469-9969(eISSN)
Примечания : Cited References: 72. - The authors thank the Russian Scientific Foundation for the financial support under Grant No. 18-12-00022.
Предметные рубрики: LOWER-MANTLE
STATE
TRANSITION
PRESSURE
IRON
SUSCEPTIBILITY
Аннотация: To study non-Heisenberg effects in the vicinity of spin crossover in strongly correlated electron systems we derive an effective low-energy Hamiltonian for the two-band Kanamori model. It contains a Heisenberg high-spin term proportional to exchange constant as well as a low-spin term proportional to spin gap parameter ɛs. Using cluster mean field theory we obtain several non-Heisenberg effects. Near the critical value of spin gap ɛcs there is a magnetic phase transition of first order. In the vicinity of ɛcs in the paramagnetic phase we observe nontrivial behavior of the Curie constant in the paramagnetic susceptibility in the wide range of temperature. Reentrant temperature behavior of nearest-neighbor spin-spin correlations is observed at ɛsɛcs. Finally, the pressure-temperature magnetic phase diagram for ferroperriclase is obtained using the effective Hamiltonian.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Drokina T. V., Petrakovskii G. A., Molokeev M. S., Velikanov D. A.
Заглавие : Synthesis, crystal structure, and magnetic properties of the YbFeTi2O7 compound
Место публикации : Phys. Solid State. - 2018. - Vol. 60, Is. 3. - P.532-536. - ISSN 1063-7834, DOI 10.1134/S1063783418030095. - ISSN 1090-6460(eISSN)
Примечания : Cited References:13
Предметные рубрики: STATE
Аннотация: We report on the synthesis conductions and results of experimental investigations of the crystal structure and magnetic properties of a new magnetic compound YbFeTi2O7. According to the X-ray diffractometry data, the crystal structure of the investigated compound is described by the rhombic space group Pcnb with unit cell parameters of a = 9.8115(1) Å, b = 13.5106(2) Å, and c = 7.31302(9) Å and atomic disordering in the distribution of iron ions Fe3+ over five structural sites. The magnetic measurements in the lowtemperature region revealed a kink in the temperature dependence of the magnetic moment and its dependence on the sample magnetic prehistory. The experimental results obtained suggest that with a decrease in temperature the sample passes from the paramagnetic state to the spin-glass-like magnetic state characterized by a freezing temperature of T f = 4.5 K at the preferred antiferromagnetic exchange coupling in the sample spin system. The chemical pressure variation upon replacement of rare-earth ion R by Yb in the RFeTi2O7 system does not change the crystal lattice symmetry and magnetic state.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Li O. A., Lin C. -R., Chen H. -Y., Hsu, Hua-Shu, Shih K. -Y., Edelman I. S., Wu K. -W., Tseng Y. -T., Ovchinnikov S. G., Lee J. -S.
Заглавие : Size dependent magnetic and magneto-optical properties of Ni0.2Zn0.8Fe2O4 nanoparticles
Место публикации : J. Magn. Magn. Mater.: Elsevier, 2016. - Vol. 408. - P.206-212. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2016.02.062
Примечания : Cited References: 51. - This work is supported by the Ministry of Science and Technology of Taiwan (MOST 103-2811-M-153 -001 and MOST 102-2112-M-153 -002 -MY3), and by the Russian Foundation for Basic Researches, grant No 14-02-01211.
Предметные рубрики: Zinc ferrite
Cation distribution
Sol-gel
Ni
ZnFe2O4
Spinel
Fe3O4
Particles
Spectra
State
Ключевые слова (''Своб.индексиров.''): nickel zinc ferrite--nanoparticles--magnetic properties--mcd
Аннотация: Ni0.2Zn0.8Fe2O4 spinel nanoparticles have been synthesized by combustion method. Average particles size varies from 15.5 to 50.0 nm depending on annealing temperature. Correlations between particles size and magnetic and magneto-optical properties are investigated. Magnetization dependences on temperature and external magnetic field correspond to the sum of paramagnetic and superparamagnetic response. Critical size of single-domain transition is found to be 15.9 nm. Magnetic circular dichroism (MCD) studies of nickel zinc spinel are presented here for the first time. The features in magnetic circular dichroism spectrum are assigned to the one-ion d-d transitions in Fe3+ and Ni2+ ions, as well to the intersublattice and intervalence charge transfer transitions. The MCD spectrum rearrangement was revealed with the change of the nanoparticles size. © 2016 Elsevier B.V. All rights reserved.
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