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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shneyder E. I., Ovchinnikov S. G., Shnurenko A. V.
Заглавие : Contribution of the non-Heisenberg ring exchange to the magnetic mechanism of high-Tc superconductivity
Место публикации : JETP Letters. - 2012. - Vol. 95, Is. 4. - P.193-197. - ISSN 0021-3640, DOI 10.1134/S0021364012040078
Примечания : Cited References: 44. - This work was supported by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project no. NSh-1044.2012.2), by the Russian Foundation for Basic Research (project no. 12-02-00040), by the Presidium of the Russian Academy of Sciences (program no. 20 "Quantum Mesoscopic and Disordered Systems"), jointly by the Siberian and Ural Branches of the Russian Academy of Sciences, by Siberian Federal University (project no. s/b S-11), and by the Ministry of Education and Science of the Russian Federation (state contract no. P891, federal program "Human Capital"). E.I.Sh. acknowledges the support of the Dynasty Foundation.
Предметные рубрики: BAND HUBBARD-MODEL
COPPER OXIDES
ELEMENTARY EXCITATIONS
SPIN
ELECTRON
STATE
T/U
Аннотация: The effect of non-Heisenberg four-spin ring exchange on the superconducting transition temperature in strongly correlated electron systems is studied. It is shown that the ring exchange can significantly suppress the contribution of the Heisenberg exchange to superconducting pairing.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Platunov M. S., Dudnikov V. A., Orlov Yu. S., Kazak N. V., Solovyov L. A., Zubavichus Y. V., Veligzhanin A. A., Dorovatovskii P. V., Vereshchagin S. N., Shaykhutdinov K. A., Ovchinnikov S. G.
Заглавие : Crystal structure and electronic states of Co and Gd ions in a Gd0.4Sr0.6CoO2.85 single crystal
Коллективы : Russian Foundation for Basic Research [13-02-00958, 13-02-00358, 14-02-31051, 16-32-60049]; Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools [SP-938.2015.5]; program "UMNIK"; Siberian Branch, Russian Academy of Sciences [V.45.3.1]
Место публикации : JETP Letters. - 2016. - Vol. 103, Is. 3. - P.196-200. - ISSN 0021-3640, DOI 10.1134/S0021364016030139. - ISSN 1090-6487(eISSN)
Примечания : Cited References:20. - This work was supported in part by the Russian Foundation for Basic Research (project nos. 13-02-00958, 13-02-00358, 14-02-31051, and 16-32-60049), by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project no. SP-938.2015.5), and by the program "UMNIK." The X-ray diffraction and thermochemical studies were supported by the Siberian Branch, Russian Academy of Sciences (project no. V.45.3.1).
Предметные рубрики: X-RAY-ABSORPTION
PROFILE REFINEMENT
PEROVSKITE
CHARGE
SPIN
Аннотация: X-ray diffraction and X-ray absorption near edge structure (XANES) spectra have been measured at the Со K-edge and Gd L3-edge in GdCoO3 and Gd0.4Sr0.6CoO2.85 cobaltites. The effect of Sr substitution on the crystal structure and electronic and magnetic states of Co3+ ions in a Gd0.4Sr0.6CoO2.85 single crystal has been analyzed. The XANES measurements at the Co K-edge have not showed a noticeable shift of the absorption edge with an increase in the concentration of Sr. This indicates that the effective valence of cobalt does not change. An increase in the intensity of absorption at the Gd L3-edge is due to an increase in the degree of hybridization of the Gd(5d) and O(2p) states. The effect of hole doping on the magnetic properties results in the appearance of the ferromagnetic component and in a significant increase in the magnetic moment.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kuz'min E. V., Ovchinnikov S. G., Singh D. J.
Заглавие : Effect of frustrations on magnetism in the Ru double perovskite Sr2YRuO6
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2003. - Vol. 68, Is. 2. - Ст.24409. - ISSN 1098-0121, DOI 10.1103/PhysRevB.68.024409
Примечания : Cited References: 24
Предметные рубрики: MOTT TRANSITION
LATTICE
SPIN
ANTIFERROMAGNETISM
SUPERCONDUCTIVITY
FERROMAGNETISM
Аннотация: Localized Ru5+ spins in Sr2YRuO6 form a fcc lattice with an antiferromagnetic (AFM) nearest-neighbor (NN) coupling J approximate to 25 meV and rather low Neel temperature T-N= 26 K. Analysis of the electronic structure of Sr2RuO4 results in the effective Heisenberg model. We have studied the effect of frustrations on the AFM type-I structure of Sr2YRuO6 in the spin-wave approximation. In the model with only NN coupling the AFM state is unstable due to frustrations, and T-N = 0. Stabilization of the AFM state occurs due to the next-nearest-neighbor coupling I or due to the magnetic anisotropy D. Very small values D/J similar to I/J less than or equal to 10(-3) are enough to obtain the experimental values of T-N and sublattice magnetization m = 1.85 mu(B) /Ru (62% from the nominal S = 3/2 value).
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Dudnikov V. A., Orlov Yu. S., Gavrilkin S. Yu., Gorev M. V., Vereshchagin S. N., Solovyov L. A., Perov N. S., Ovchinnikov S. G.
Заглавие : Effect of Gd and Sr ordering in a sites of doped Gd0.2Sr0.8CoO3-δ perovskite on its structural, magnetic, and thermodynamic properties
Место публикации : J. Phys. Chem. C: American Chemical Society, 2016. - Vol. 120, Is. 25. - P,13443-13449. - ISSN 19327447 (ISSN), DOI 10.1021/acs.jpcc.6b04810
Примечания : Cited References: 45. - The authors are thankful to the Russian Science Foundation (Project No. 16-13-00060) for financial support. The magnetic measurements were carried out in the Shared Facility Centre of P. N. Lebedev Physical Institute of RAS.
Предметные рубрики: Ln1-xSrxCoO(3-δ) Ln
PROFILE REFINEMENT
CRYSTAL-STRUCTURE
OXYGEN-CONTENT
COBALTITES
OXIDE
La1-xSrxCoO3-δ
Dy3+
SPIN
Ho3+
Аннотация: Magnetic and thermodynamic properties of perovskite Gd0.2Sr0.8CoO3−δ, with ordered and disordered states of Gd and Sr in the A-sites of the crystal lattice have been studied revealing remarkable differences in the physical properties of the ordered and disordered states. The ordered samples have larger oxygen nonstoichiometry, heat capacity, and thermal expansion anomalies, and abnormal temperature dependence of the magnetization around 350 K.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Troyanchuk I. O., Bushinsky M. V., Tereshko N. V., Lanovsky R. A., Sikolenko V. V., Ritter C., Orlov Yu. S., Ovchinnikov S. G.
Заглавие : Ferromagnet-antiferromagnet transition in layered perovskites of Sr3YCo4O10.5 type
Коллективы : Belarussian Foundation for Basic Research [F18R-159]; Russian Foundation Basic Research [18-52-00017 Bel_a, 16-02-00507, 18-52-00020]; Council on grants of the President of the Russian Federation [SP-1844.2016.1]
Место публикации : Mater. Res. Express. - 2019. - Vol. 6, Is. 2. - Ст.026105. - ISSN 2053-1591, DOI 10.1088/2053-1591/aaef21
Примечания : Cited References: 30. - This work was supported by the Belarussian Foundation for Basic Research (project F18R-159) and Russian Foundation Basic Research (contract no. 18-52-00020). Yu S Orlov and SG Ovchinnikov are grateful Russian Foundation Basic Research (contracts no. 18-52-00017 Bel_a, 16-02-00507) and Council on grants of the President of the Russian Federation (SP-1844.2016.1) for the support.
Предметные рубрики: SPIN
NANOWIRES
Ключевые слова (''Своб.индексиров.''): neutron diffraction--orbital ordering--spin state
Аннотация: 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 4√2a p × 2√2a 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.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ignatchenko V. A., Polukhin D. S.
Заглавие : Fine structure of the crossing resonance spectrum of wavefields in an inhomogeneous medium
Место публикации : J. Exp. Theor. Phys. - 2020. - Vol. 130, Is. 3. - P.358-369. - ISSN 1063-7761, DOI 10.1134/S1063776120010033. - ISSN 1090-6509(eISSN)
Примечания : Cited References: 37
Предметные рубрики: SUPERCONDUCTING CRITICAL-TEMPERATURE
ELECTRON
BREAKDOWN
SPIN
Аннотация: The crossing resonance of two wavefields m(x, t) and u(x, t) of different natures in an inhomogeneous medium with zero mean value of the coupling parameter η between fields has been studied. The stages of formation of the fine structure of the crossing resonance have been analyzed. It has been shown within the model of independent crystallites that the removal of the degeneracy of eigenfrequencies of these fields at the crossing resonance point has a threshold character in the coupling parameter and occurs under the condition η ηc, where ηc = |Γu – Γm|/2, Γu and Γm are the relaxation parameters of the corresponding wavefields. At η ηc, each random implementation of the Green’s functions G~′′mm and G~′′uu of wavefields has the form of two resonance peaks with the same half-width (Γu + Γm)/2 spaced by the interval 2η; this form is standard for crossing resonances. At η ηc, the functions G~′′mm and G~′′uu are different: if Γu Γm, the function G~′′mm has the form of a narrow resonance peak at ω = ωr, whereas the function G~′′uu has the form of a broader resonance peak split at the top by a narrow antiresonance. Averaging over regions where η ηc leads to the formation of a broad resonance with a resonance line half-width of about η2〉1/2 on the both averaged Green’s functions, which is due to the stochastic distribution of resonance frequencies. Averaging over regions where η ηc results in the sharpening of a resonance peak on the function G′′mm and an antiresonance peak on the function G′′uu at the same frequency ω vu at the first and second crossing points, respectively.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Val'kova T. A., Mitskan V. A.
Заглавие : Gapless chiral superconducting (d + id)-wave phase in strongly correlated layered material with a triangular lattice
Коллективы : Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR) [19-02-00348, 18-42240014]; Krasnoyarsk Kray Science Foundation [18-42-240014]; Administration of the Krasnoyarsk Kray
Место публикации : J. Exp. Theor. Phys. - 2020. - Vol. 130, Is. 2. - P.235-246. - ISSN 1063-7761, DOI 10.1134/S1063776120010197. - ISSN 1090-6509(eISSN)
Примечания : Cited References: 44. - This study was supported by the Russian Foundation for Basic Research (project nos. 19-02-00348 and 18-42240014), the Administration of the Krasnoyarsk Kray, the Krasnoyarsk Kray Science Foundation within research project "Single-orbital Effective Model of Ensemble of Spin-Polaron Quasiparticles in the Problem of Description of the Intermediate State and Pseudogap Behavior of Cuprate Superconductors" (project no. 18-42-240014).
Предметные рубрики: TRANSITIONS
SPIN
Аннотация: It is shown that interlayer electron tunneling in the quasi-two-dimensional ensemble of Hubbard fermions leads to the realization of the gapless superconducting phase with the chiral (d + id)-wave order parameter symmetry, not for a single value of sodium ion concentration, but in a wide range of concentrations. Precisely this situation corresponds to experimental data on the layered sodium cobaltite intercalated by water (NaxCoO2 · yH2O). Intra-atomic electron repulsion that determines the strong electron correlation regime leads to the representation of Hubbard fermions, the interaction of which ensures Cooper instability. Intersite intralayer interactions between fermions considerably affect the positions of nodal points of the chiral order parameter and change the critical concentration at which a topological transition occurs in the 2D system of Hubbard fermions.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Dzebisashvili D. M., Klyuchantsev, Andrey B.
Заглавие : London Penetration Depth as a Test of Order Parameter Symmetry in Sodium Cobaltate Superconductors
Коллективы : Russian Foundation for Basic Research (RFBR) [18-02-00837]; Presidium of the Russian Academy of Sciences [12]
Место публикации : Symmetry-Basel. - 2019. - Vol. 11, Is. 5. - Ст.633. - ISSN 2073-8994, DOI 10.3390/sym11050633
Примечания : Cited References: 43. - The work was financially supported by the Russian Foundation for Basic Research (RFBR) (project no. 18-02-00837) and by the program of the Presidium of the Russian Academy of Sciences No. 12 "Fundamental problems of high-temperature superconductivity".
Предметные рубрики: SPIN
DEPENDENCE
POWDER
CHARGE
PHASE
GAP
Аннотация: Temperature dependence of the magnetic field penetration depth λ was calculated for water intercalated sodium cobaltate superconductor NaxCoO2⋅yH2O. Assuming that the system is in the chiral d+id–wave superconducting state, it was shown that the shifting of the excitation spectrum nodal points off the normal phase Fermi surface due to variation of the sodium content x changes the functional form of the temperature dependence of λ−2 from exponential to linear in the low temperatures region. It is argued that this change in the functional form of T–dependence of the λ−2 can serve as a proof for the chiral symmetry of the superconducting order parameter in the sodium cobaltate.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Ovchinnikov S. G., Balaev A. D., Ivanova N.B., Pashkevich, Yu. G., Michel C.R., Bondarenko G. V.
Заглавие : Magnetic and transport properties of Gd(0.9)A(0.1)CoO(3-delta) (A = Ba, Sr)
Место публикации : J. Magn. Magn. Mater. - 2009. - Vol. 321, Is. 9. - P.1266-1271. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2008.11.087
Примечания : Cited Reference Count: 31. - Гранты: This study was supported by the Rosnauka (Project no. MK-4278.2008.2), Russian Foundation for Basic Research (Project no. 08-02-90708 mob_st) and "Strongly correlated electrons'' program of the Department of Physical Sciences of RAS.Финансирующая организация: Rosnauka [MK-4278.2008.2]; Russian Foundation for Basic Research [08-02-90708 mob_st]; "Strongly correlated electrons'' program of the Department of Physical Sciences of RAS
Предметные рубрики: PEROVSKITE
PR
LA
EU
ND
LN
TRANSITION
SPIN
GD
SM
Ключевые слова (''Своб.индексиров.''): perovskite structure--doped cobaltite--magnetic susceptibility--metal-insulator transition--doped cobaltite--magnetic susceptibility--metal-insulator transition--perovskite structure--antiferromagnetism--barium--cobalt compounds--electric conductivity--ferromagnetic materials--ferromagnetism--gadolinium--magnetic susceptibility--metal insulator boundaries--oxide minerals--paramagnetic materials--perovskite--phase separation--semiconductor insulator boundaries--transport properties--antiferromagnetic--doped cobaltite--doped samples--electrical conductivity measurements--ferromagnetic transitions--insulator-metal transitions--magnetic and transport properties--magnetic behaviors--perovskite structure--temperature ranges--transport datum--x- ray diffractions--metal insulator transition
Аннотация: The X-ray diffraction, magnetization and electrical conductivity measurements for Gd(0.9)A(0.1)CoO(3-delta) (A = Ba, Sr) have been made. The complicated magnetic behavior, including the paramagnetic-ferromagnetic-antiferromagnetic and paramagnetic-ferromagnetic transitions, was found for Ba- and Sr-doped samples. The gradual insulator-metal transitions were observed in a wide temperature range T = 600-800 K. The complex magnetic and transport data could be explained on the basis of the structural phase separation. (C) 2009 Elsevier B.V. All rights reserved.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : Magnetic ordering and phase transitions in planar antiferromagnetic systems with a Kagome lattice
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1998. - Vol. 86, Is. 6. - P1209-1215. - ISSN 1063-7761, DOI 10.1134/1.558592
Примечания : Cited References: 23
Предметные рубрики: TRIANGULAR LATTICE
2 DIMENSIONS
SPIN
MODEL
Аннотация: We study the process of magnetic ordering in planar antiferromagnetic systems with a Kagome lattice. It is found that if the interaction between next-nearest-neighbor spins is taken into account, the heat capacity of such systems has a singularity at a finite temperature T. On the basis of a scaling analysis of finite-size systems we study the behavior of thermodynamic quantities in the neighborhood of a phase transition. We find that the phase transition at the critical point is due to discrete- and continuous-symmetry breaking, in which the long-range chiral order and the power-law translational spin order emerge simultaneously. Finally, we calculate the temperatures of the transition to different (with three and nine spins per unit cell) ordered states. (C) 1998 American Institute of Physics.
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