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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Martynov S. N.
Заглавие : The incommensurate magnetic structure of a tetragonal antiferromagnet with antisymmetric exchange
Место публикации : J. Exp. Theor. Phys. - 2009. - Vol. 109, Is. 6. - P.979-988. - ISSN 1063-7761, DOI 10.1134/S1063776109120097
Примечания : Cited References: 34
Предметные рубрики: FLUCTUATION-INDUCED PHASE
FIELD-INDUCED GAP
COPPER METABORATE
WEAK FERROMAGNETISM
SOLITON LATTICE
SPIN-WAVES
CUB2O4
BA2CUGE2O7
CSCUCL3
CHAINS
Ключевые слова (''Своб.индексиров.''): anti-symmetric--antiferromagnetic sublattices--antiferromagnets--antisymmetric exchange--exchange bonds--ferromagnetic component--ferromagnetic moments--ginzburg-landau functional--incommensurate magnetic structures--mean field approximation--modulation vectors--polarization planes--polarization vectors--symmetry groups--antiferromagnetic materials--antiferromagnetism--crystal orientation--crystal symmetry--ferromagnetic materials--ferromagnetism--magnetic devices--magnetic structure--modulation--polarization--vector spaces--vectors--crystallography
Аннотация: Analysis of the incommensurate magnetic structure that emerges for two coexisting types of the antisymmetric Dzyaloshinski-Moriya exchange interaction (the weakly ferromagnetic component of vector D along the tetragonal axis and the helicoidal component distributed in the tetragonal plane) is carried out for the first time for a tetragonal antiferromagnet. The helicoidal component for each pair of interacting spins has a 2D distribution; its direction in the tetragonal plane depends on the direction of the exchange bond in each pair. The Lifshits invariant of the Ginzburg-Landau functional is obtained, which is responsible for the formation of an incommensurate magnetic structure for such a distribution. It is shown in the mean field approximation that the incommensurate magnetic structure that forms in this case is a nonlinear double helicoid with a modulation vector lying in the tetragonal plane and with a varying angle between the polarization planes of quasi-antiferromagnetic sublattices. The ground state of the magnet is degenerate in the orientation of the modulation vector in the tetragonal plane. The rate of variation in the orientations of moments in the polarization planes passing through the tetragonal axis is controlled by the angle between the directions of the moments and the tetragonal axis. The local weakly ferromagnetic moment remaining in the polarization plane varies in magnitude and sign. The relation between the orientations of the modulation and polarization vectors is derived for the cases of simple and inversion tetragonal axes in the space symmetry group of the crystal.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Belobrov P. I., Tretyakov A. G., Zaslavsky G. M.
Заглавие : Methods of nonlinear dynamics and equilibrium structures of magnetoelastic chains
Разночтения заглавия :авие SCOPUS: Methods of nonlinear dynamics and equilibrium structures of magnetoelastic chains
Место публикации : J. Stat. Phys. - 1985. - Vol. 38, Is. 1-2. - P.393-404. - ISSN 0022-4715, DOI 10.1007/BF01017869
Примечания : Cited References: 22
Ключевые слова (''Своб.индексиров.''): chaos--incommensurate structure--magnetoelastic interaction--nonlinear resonance
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : The study of magnetic properties of the quasi-one-dimensianal spin-1/2 antiferromagnet by Monte-Carlo method
Место публикации : Phys. Low-Dimens. Struct.: V S V CO. LTD, 2000. - Vol. 07.08.2013. - P37-46. - ISSN 0204-3467
Примечания : Cited References: 15
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
SYSTEMS
CHAINS
CA2CUO3
Аннотация: The thermodynamic quantities, two- and four-spin correlation functions as well as the correlation radius for weakly coupled antiferromagnetic spin chains with S = 1/2 are calculated using the mean-field approximation for the interchain coupling (J(2)) for longitudinal and transverse spin components by quantum Monte Carlo method. Results for the staggered magnetization and Neel temperature are in agreement with general scaling arguments. The value of triplet DeltaS(z) =1 gp in the spectrum of excitations is estimated. The transverse staggered field was found to induce an additional maximum in the correlation radius of the four spin correlation function around T/J(1) approximate to [0.05 divided by 0.075), J(2)/J(1) 0.03.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Martynov S. N.
Заглавие : Antisymmetric Exchange in the CuB2O4 A Subsystem
Место публикации : JETP Letters. - 2009. - Vol. 90, Is. 1. - P.55-58. - ISSN 0021-3640, DOI 10.1134/S0021364009130116
Примечания : Cited References: 31
Предметные рубрики: TRANSVERSE MAGNETIC-FIELD
FLUCTUATION-INDUCED PHASE
COPPER METABORATE
ANTIFERROMAGNETIC CHAINS
SOLITON LATTICE
INDUCED GAP
SPIN-WAVES
BA2CUGE2O7
CSCUCL3
MNSI
Аннотация: The space distribution of the components of the microscopic Hamiltonian of the antisymmetric Dzyaloshinskii-Moriya exchange with respect to the exchange bond pairs of the A subsystem of Cu2+ ions in the crystallographic 4b positions of CuB2O4 has been obtained using symmetry analysis. The possibility of the coexistence of two different types of the exchange spatial distribution is demonstrated. The component of the anti-symmetric exchange vector D parallel to the tetragonal axis has a weakly ferromagnetic distribution for all of the directions of the bonds between the nearest magnetic neighbors. Each exchange bond has an additional component of the antisymmetric exchange parallel to the bond projection on the tetragonal plane. The spatial distribution of these components is helicoidal with the modulation vector in the tetragonal crystal plane.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the magnetic properties of weakly interacting antiferromagnetic chains with an alternating exchange interaction with spin S=1/2
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2000. - Vol. 90, Is. 1. - P194-201. - ISSN 1063-7761, DOI 10.1134/1.559075
Примечания : Cited References: 35
Предметные рубрики: PEIERLS COMPOUND CUGEO3
MAGNON DISPERSION
BI2CUO4
EXCITATIONS
RESONANCE
SYSTEMS
SCATTERING
DYNAMICS
NEUTRON
PHASE
Аннотация: An approximation dependence of the spontaneous magnetic moment at a site, sigma/sigma(0) - 1 = 0.71(6)delta(2.5(2)), and the antiferromagnet-singlet state phase boundary, J(2)/J(1) = 0.52(3)delta, are determined by the quantum Monte Carlo method in the self-consistent sublattice molecular field approximation for weakly interacting (J(2)) antiferromagnetic chains with spin S = 1/2 and alternating exchange interaction (J(1) +/- delta). The Neel temperature and a number of critical temperatures which could be related with the filling energy of two singlets (Delta S-z = 0) and one triplet (Delta S-z= 1) spin bands, each of which is split by the sublattice field (h(x,y)not equal h(z)) into two subbands, are determined on the basis of the computed correlation radii of the two- and four-spin correlation function, the squared total spin (S-z)(2) with respect to the longitudinal components, the dimerization parameter, and the correlation functions between the nearest neighbors with respect to longitudinal and transverse spin components. On the basis of the Monte Carlo calculations, the critical temperatures and possible energy gaps at the band center are determined for the antiferromagnets CuWO4 and Bi2CuO4 and for the singlet compounds (VO)(2)P2O7 and CuGeO3 , agreeing satisfactorily with existing results, and new effects are also predicted. (C) 2000 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Static and dynamic magnetic properties of coupled spin-1/2 antiferromagnetic chains
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2000. - Vol. 12, Is. 37. - P.8191-8207. - ISSN 0953-8984, DOI 10.1088/0953-8984/12/37/316
Примечания : Cited References: 21
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
SYSTEMS
SUSCEPTIBILITY
EXCITATIONS
SR2CUO3
CA2CUO3
KCUF3
Ключевые слова (''Своб.индексиров.''): computational methods--copper compounds--correlation methods--functions--magnetic field effects--magnetic properties--magnetization--monte carlo methods--quantum theory--specific heat--thermal effects--excitation spectroscopy--interchain coupling--intrachain couplings--mean-field approximation--spin-spin correlation function--spinons--antiferromagnetic materials
Аннотация: Calculations of the thermodynamic quantities, and the spectra of spinons, triplet excitations, and two-particle spin-singlet (Delta S-z = 0, +/- 1) excitations for a weakly coupled antiferromagnetic S = 1/2 spin chain are made using a mean-field approximation for the interchain couplings (J(2)) by the quantum Monte Carlo method. The mass gaps in these excitation spectra are estimated as functions of the interchain coupling. The critical held H-c, and the temperatures at which the spinon and singlet gaps close (T-1 and T-2, respectively) are obtained. Some peculiarities of the staggered magnetization, the specific heat, and the spin-spin correlation function are found at T-1 = 0.9J(2), T-2 = 1.5J(2), H-c = 3.8J(2), as determined by linear function fitting for J(2)/J(1) 0.15 The intrachain and interchain couplings, and the staggered magnetization for KCuF3, Sr2CuO3, and Ca2CuO3 are estimated, and mass gaps are predicted to exist in the spectra of the spinons and the singlet two-particle excitations.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Roessli B., Fischer P., Schefer J., Buhrer W., Furrer A., Vogt T., Petrakovskii G. A., Sablina K. A.
Заглавие : Elastic and inelastic neutron study of CuGeO3
Место публикации : J. Phys.: Condens. Matter. - 1994. - Vol. 6, Is. 41. - P.8469-8477. - ISSN 0953-8984, DOI 10.1088/0953-8984/6/41/009
Примечания : Cited References: 18
Предметные рубрики: SPIN-PEIERLS TRANSITION
CHAINS
Аннотация: Elastic and inelastic neutron scattering was used to probe the structural and magnetic properties of polycrystalline CuGeO3. The diffraction data show that the chemical lattice remains stable in the measured temperature range 1.5 K less-than-or-equal-to T less-than-or-equal-to 296 K. At low temperature the inelastic experiments revealed a well defined magnetic excitation at 15 meV, which persists up to T = 50 K. The analysis of the spin-wave spectrum is based on a one-dimensional Heisenberg model within the spin-wave theory. On the other hand, no evidence of energy-gap opening, which would result from a dimerization of the Cu chains, could be found at low temperature.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S., Petrakovskii G. A.
Заглавие : Investigation of the magnetic properties of chains with alternating ferro- and antiferromagnetic exchange interactions in the Heisenberg model with spin S=1/2
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 1999. - Vol. 41, Is. 9. - P1511-1512. - ISSN 1063-7834, DOI 10.1134/1.1131042
Примечания : Cited References: 11
Предметные рубрики: HALDANE-GAP
SYSTEMS
Аннотация: The quantum Monte Carlo method is used to calculate the susceptibility and pairwise spin-spin correlation functions of chains with alternating ferro (K)- and antiferromagnetic (J)-exchange interactions within the Heisenberg model with spin S=1/2. From the susceptibility, the energy gap between the ground state and excited triplet states is determined for arbitrary ratios K/J. The value of the gap coincides with the Haldane gap for spin S=1 when K/J 1.25. (C) 1999 American Institute of Physics. [S1063-7834(99)02409-0].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Аверьянов, Евгений Михайлович
Заглавие : Изменения температуры фазового перехода нематик – изотропная жидкость в гомологических рядах каламитных жидких кристаллов и конформационная подвижность концевых молекулярных цепей
Место публикации : Жидк. крист. и их практич. использ. - 2018. - Т. 18, № 1. - С. 37-46. - ISSN 1991-3966, DOI 10.18083/LCAppl.2018.1.37; Liq. Cryst. Appl. - ISSN 2499–9644
Примечания : Библиогр.: 16. - Данная работа выполнена в рамках проекта 0356-2015-0411 Комплексной программы Сибирского отделения РАН № II.2П.
Ключевые слова (''Своб.индексиров.''): фазовый переход нематик – изотропная жидкость--гомологические ряды жидких кристаллов--конформационная подвижность молекулярных цепей--nematic – isotropic liquid phase transition--homologous series of liquid crystals--conformational mobility of molecular chains
Аннотация: Для каламитных нематиков (холестериков) различных химических классов показано, что монотонно возрастающие зависимости tс(np) температуры перехода нематик – изотропная жидкость от номера np четных (ne) или нечетных (no) гомологов хорошо аппроксимируются функциями Fp(n) = tlp + Dpexp(–λpn). Две ветви tс(no) и tс(ne) описываются одной функцией F(n) = Fs(n) + Fa(n) с гладкой частью Fs(n) = [Fe(n) + Fo(n)]/2 и альтернацией Fa(n) =(–1)n[Fe(n) – Fo(n)]/2. Выведена зависимость Fs(n) = tl + Dexp(–λn), где коэффициент λ = –ln(q) определяется отношением q = Sk/Sk–1 (k ≥ 2) параметров ориентационного порядка Sk = S1exp[–(k–1)/ζ] для метиленовых фрагментов алифатических цепей молекул в нематической фазе. Значения λ и ζ = 1/λ связаны выражением q = [4–exp(–ε)]/[4+8exp(–ε)] с эффективной разностью энергий ε = Egt/RT для гош(g±)- и транс(t)-ориентаций k–го фрагмента цепи относительно (k–1)-го. Прослежена связь величин λp, ζp, λ, ζ, q, ε и функции Fa(n) с химической структурой молекул.For calamitic nematics (cholecterics) of various chemical classes it was shown that monotonous increasing dependences tс(np) of the nematic – isotropic liquid transition temperature on the number np of even (ne) or odd (no) homologues are well approximated by functions Fp(n) = tlp + Dpexp(–λpn). Two branches tс(no) and tс(ne) are described by one function F(n) = Fs(n) + Fa(n) with smooth part Fs(n) = [Fe(n) + Fo(n)]/2 and alternating part Fa(n) =(–1)n[Fe(n) – Fo(n)]/2. The dependence Fs(n) = tl + Dexp(–λn) was derived, in which coefficient λ = –ln(q) is determined by the ratio q = Sk/Sk–1 (k ≥ 2) of the orientational order parameters Sk = S1exp[–(k–1)/ζ] for methylene fragments of aliphatic molecular chains in the nematic phase. The values of λ and ζ = 1/λ are related by the expression q = [4–exp(–ε)]/[4+8exp(–ε)] with effective difference ε = Egt/RT between the energies of gosh(g±)- and trans(t)-orientations of k-th methylene fragment of the chain relative to (k–1)-th one. A connection between the values λp, ζp, λ, ζ, q, ε with function Fa(n) and chemical structure of molecules was observed.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Shustin M. S.
Заглавие : Effect of intersite repulsion on the correlation functions and thermodynamics of an Ising chain with annealed magnetic disorder
Место публикации : Bull. Russ. Acad. Sci. Phys.: Allerton Press, 2016. - Vol. 80, Is. 11. - P.1335-1337. - ISSN 10628738 (ISSN), DOI 10.3103/S1062873816110290
Примечания : Cited References: 6. - This work was supported by the Russian Foundation for Basic Research, project nos. 13-02-00073, 14-02-31237, and 15-42-04372.
Ключевые слова (''Своб.индексиров.''): chains--magnetic susceptibility--temperature distribution--thermodynamics--transfer matrix method--correlation function--equilibrium behavior--equilibrium distributions--non-magnetic impurities--quantum phase transitions--repulsion parameter--temperature dependence--transfer matrix technique--phase transitions
Аннотация: An exact solution for a model describing the equilibrium behavior of an ensemble of Ising chains with nonmagnetic intersite repulsion of nearest neighbors and an equilibrium distribution of nonmagnetic impurities is obtained using the transfer matrix technique. The possibility of exciting quantum phase transitions using the intersite repulsion parameter in a system is demonstrated. Proximity to the critical points of these transitions has a substantial effect on the temperature dependence of a system’s magnetic susceptibility. © 2016, Allerton Press, Inc.
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