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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Аверьянов, Евгений Михайлович
Заглавие : Молекулярно-оптическая и структурная анизотропия нематической смеси Е7
Место публикации : Жидк. крист. и их практич. использ. - 2019. - Т. 19, № 1. - С. 42-51. - ISSN 1991-3966, DOI 10.18083/LCAppl.2019.1.42; Liq. Cryst. Appl. - ISSN 2499–9644
Примечания : Библиогр.: 20
Предметные рубрики: LIQUID
ORDER
POLARIZABILITY
Ключевые слова (''Своб.индексиров.''): нематические смеси--ориентационный порядок нематических смесей--анизотропия локального поля в нематических смесях--свойства молекул в нематических смесях--нематические смеси, ориентационный порядок нематических смесей, анизотропия локального поля в нематических смесях, свойства молекул в нематических смесях--nematic mixtures--orientational order of nematic mixtures--local-field anisotropy in nematic mixtures--molecular properties in nematic mixtures
Аннотация: Для нематической смеси E7 производных цианобифенила исследована связь показателей преломления nj при поляризациях световой волны вдоль (j = ||) и нормально оптической оси (j = ⊥) с параметрами поляризуемости (компонентами γjα, средним значением γmα = (γ||α + 2γ⊥α)/3, анизотропией δγα = γ||α - γ⊥α) и ориентационным порядком молекул типа α, составляющих смесь. Для смеси введен тензор локального поля с компонентами fj =1+Lj(nj2 – 1). Получена связь компонент тензора Лорентца Lj с компонентами Ljα. Температурные зависимости Lj(Т) для смеси Е7 определены с использованием экспериментальных зависимостей nj(λ,Т) от длины световой волны λ. Подтверждена связь Lj(Ljα). Получена температурная зависимость S(Т) материального параметра порядка смеси. Обнаружено изменение среднего значения γm(Т) = ((γ|| + 2γ⊥)/3 для исследованной смеси за счет изменения S(Т). Показано, что зависимость γm(S) обусловлена противоположными по знаку вкладами от изменения конформации бифенильных остовов молекул и межмолекулярных взаимодействий. Полученные результаты сопоставлены со следствиями использования модельных тензоров fj, известных в литературе для смесей.The relation of the refractive indices nj of the nematic mixture E7 consisting of cyanobiphenyl derivatives for the light-wave polarization along (j = ||) and across (j = ⊥) the optical axis with the polarizability parameters (components γjα, mean value γmα = (γ||α + 2γ⊥α)/3, anisotropy δγα = γ||α - γ⊥α) and orientational order of α-type molecules comprising the mixture was investigated. The local-field tensor with components fj =1+Lj(nj2 – 1) was introduced for the mixture and the relationship between the Lorentz-tensor components Lj and the components Ljα was established. The temperature dependences Lj(Т) for the E7 mixture were obtained using experimental dependences nj(λ,T). The relationship Lj(Ljα) was confirmed. The temperature dependence of the material order parameter S(T) was obtained. The change of the mean value γm(Т) = ((γ|| + 2γ⊥)/3 for the studied mixture due to changing of S(Т) was observed. The dependence γm(S) was shown to be caused by two opposite-sign contributions due to changing conformation of molecular biphenyl cores and intermolecular interactions. The obtained results were compared with the consequences of using model tensors fj, which literature data are known for mixtures.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zhandun V. S., Zamkova N. G., Zinenko V. I.
Заглавие : Lattice dynamics, ferroelectric and antiferroeelctric instabilities, and the ferroelectric phase transition in disordered PbB(1/2)' B(1/2)'' O(3) (B ' = Ga, In, Lu; B '' = Nb, Ta) solid solutions
Разночтения заглавия :авие SCOPUS: Lattice dynamics, ferroelectric and antiferroeelctric instabilities, and the ferroelectric phase transition in disordered PbB′ 1/2B″1/2O3 (B′ = Ga, In, Lu; B″ = Nb, Ta) solid solutions
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 106, Is. 6. - P1109-1117. - ISSN 1063-7761, DOI 10.1134/S1063776108060101
Примечания : Cited References: 29
Предметные рубрики: STATISTICAL-MECHANICS
PEROVSKITES
CRYSTALS
ORDER
RELAXOR
BATIO3
PBTIO3
Ключевые слова (''Своб.индексиров.''): crystal lattices--ferroelectricity--lattice vibrations--solids--ferroelectric (barium strontium titanate)--ferroelectric phase transitions--lattice (co)--lattice dynamics--vibration spectrum--ferroelectric materials
Аннотация: The lattice vibration spectra, rf permittivity, and dynamic Born charges of disordered PbB(1/2)'B(1/2)'' O(3) (B' = Ga, In, Lu; B '' = Nb, Ta) solid solutions are calculated in terms of the generalized Gordon-Kim model. All the compounds are found to have soft modes related to the center (Gamma(15)) and boundary point R (R(15)) of the Brillouin zone; the frequencies of these modes are close. The ferroelectric phase transition temperatures and the spontaneous polarization in the ferroelectric phase are calculated for the solid solutions using a model Hamiltonian in the local mode approximation and the Monte Carlo method. These temperatures for the tantalum compounds are found to be higher than for the niobium compounds, and temperature t(s) increases with the atomic number of ion B'. A model where the antiferroelectric state is related to the condensation of modes Gamma(15) and R(15) is proposed. It is found that, for all compounds except for PbSc(1/2)Nb(1/2)O(3) and PbSc(1/2)Ta(1/2)O(3), the ferroelectric phase, which is only related to the condensation of mode R(15), and the antiferroelectric phase have similar energies. In PbIn(1/2)Ta(1/2)O(3), the antiferroelectric phase turns out to be energetically favorable.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sukhinin Y. V.
Заглавие : Ising-like model of tilted phase transitions in Langmuir monolayers
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2006. - Vol. 74, Is. 19. - Ст.195423. - ISSN 1098-0121, DOI 10.1103/PhysRevB.74.195423
Примечания : Cited References: 27
Предметные рубрики: MONTE-CARLO-SIMULATION
FATTY-ACID MONOLAYERS
AIR-WATER-INTERFACE
AMPHIPHILE MONOLAYERS
ROTATOR PHASES
ALKANES
DIAGRAM
POTENTIALS
ORDER
Аннотация: Two Ising models on a rectangular lattice (sigma(1) model and sigma(2) model) linked to three- and four-spin interactions are used to describe the sequence of tilted phase transitions in monolayers of amphiphilic long-chain molecules on an air-water surface. Starting from Morse atom-atom potentials self-consistent equations for basic thermal averages are derived in terms of a mean-field approximation. We employ the model for CH3(CH2)(18)COOH at two values of the molecule density and obtain all known tilted phases, including an intermediate one.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Janoschek M., Fischer P., Schefer J., Roessli B., Pomjakushin V., Meven M., Petricek V., Petrakovskii G. A., Bezmaternykh L. N.
Заглавие : Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Разночтения заглавия :авие SCOPUS: Single magnetic chirality in the magnetoelectric NdFe3( 11BO3 )4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2010. - Vol. 81, Is. 9. - Ст.94429. - ISSN 1098-0121, DOI 10.1103/PhysRevB.81.094429
Примечания : Cited References: 55
Предметные рубрики: NEUTRON-DIFFRACTION
PHASE-TRANSITIONS
SLOW-NEUTRONS
CRYSTAL
NDFE3(BO3)(4)
EXTINCTION
NUCLEAR
ORDER
MNSI
ANTIFERROMAGNETS
Аннотация: We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Flerov I. N., Tressaud A., Molokeev M. S., Kartashev A. V., Pogoreltsev E. I., Bayukov O. A.
Заглавие : Phase transitions in fluoride KFe2F6 with tetragonal tungsten bronze structure
Коллективы : RFBR [12-02-00056]; Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation [NSh-924.2014.2]
Место публикации : J. Fluor. Chem.: Elsevier Science, 2014. - Vol. 168. - P.204-211. - ISSN 0022-1139, DOI 10.1016/j.jfluchem.2014.09.031. - ISSN 1873-3328
Примечания : Cited References: 14. - This work was supported by RFBR, project no. 12-02-00056, and the Council on Grants from the President of the Russian Federation for the Support of Leading Scientific Schools of the Russian Federation (grant NSh-924.2014.2).
Предметные рубрики: K3FE5F15
490-K
ORDER
Ключевые слова (''Своб.индексиров.''): tetragonal tungsten bronze structure--phase transition--charge ordering--thermal properties
Аннотация: Heat capacity, thermal dilatation, structure, Mossbauer spectra and dielectric permittivity of fluoride KFe2F6 with tetragonal tungsten bronze crystal structure were studied. The as-made sample undergoes two structural phase transitions P4/mbm (T-1 approximate to 340 K) - Pbam (T-2 approximate to 250 K) - G(2) and magnetic phase transformation at T-m approximate to 133 K. Heating up to 600-700 K and subsequent cooling in helium atmosphere leads to a change of phase transition temperatures and diffused anomalies in thermal expansion. The results obtained and influence of thermal prehistory of the sample on its physical properties are discussed in the context of previous studies on related fluorides KFe2F6, which sometimes suggest conflicting structural details. (C) 2014 Elsevier B.V. All rights reserved.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : GOREV M. V., FLEROV I. N., VORONOV V. N., MISYUL S. V.
Заглавие : P = T-PHASE DIAGRAMS OF ELPASOLITES RB2KB3+F6(B3+ = HO,DY,TB)
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1993. - Vol. 35, Is. 4. - P1022-1027. - ISSN 0367-3294
Примечания : Cited References: 16
Предметные рубрики: RIGID SPHERE MODEL
RB2KMIIIF6 ELPASOLITES
TRANSITIONS
ORDER
WOS
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Martynov S. N., Tugarinov V. I.
Заглавие : Ground state of an antiferromagnet with uniform antisymmetric exchange in a magnetic field
Место публикации : JETP Letters. - 2010. - Vol. 92, Is. 2. - P.115-119. - ISSN 0021-3640, DOI 10.1134/S0021364010140092
Примечания : Cited References: 12
Предметные рубрики: INCOMMENSURATE
TRANSITION
ORDER
Аннотация: A system of two nonlinear differential equations for sublattice angles is proposed to describe the spin orientation distribution in a planar antiferromagnet with uniform antisymmetric exchange in a magnetic field. This system involves the initial symmetry of the problem and is reduced to a single delay differential equation. The solutions of this system are parameterized by the initial condition imposed on the angle of one sublattice at the hyperbolic singular point of the phase space. The numerical analysis of the stability boundary of soliton solutions demonstrates that the transition to the commensurate phase takes place outside the region where the stochastic solutions appear and is accompanied by the magnetization jump Delta m similar to 10(-1) m.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Makarov I. A., Ovchinnikov S. G.
Заглавие : Temperature dependence of the electronic structure of La2CuO4 in the multielectron LDA+GTB approach
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2015. - Vol. 121, Is. 3. - P.457-464. - ISSN 1063-7761, DOI 10.1134/S1063776115090174
Примечания : Cited References: 38. - The work was supported by the Russian Science Foundation (project no. 14-12-00061)
Предметные рубрики: Copper oxides
Model
Superconductivity
Excitations
Instability
Spectrum
States
Order
Аннотация: The band structure of La2CuO4 in antiferromagnetic and paramagnetic phases is calculated at finite temperatures by the multielectron LDA+GTB method. The temperature dependence of the band spectrum and the spectral weight of Hubbard fermions is caused by a change in the occupation numbers of local multielectron spin-split terms in the antiferromagnetic phase. A decrease in the magnetization of the sublattice with temperature gives rise to new bands near the bottom of the conduction band and the top of the valence band. It is shown that the band gap decreases with increasing temperature, but La2CuO4 remains an insulator in the paramagnetic phase as well. These results are consistent with measurements of the red shift of the absorption edge in La2CuO4 with increasing temperature. © 2015, Pleiades Publishing, Inc.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Parshin A. M., Nazarov V. G., Zyryanov V. Ya., Shabanov V. F.
Заглавие : Magnetic-field-induced structural transition in polymer-dispersed liquid crystals
Место публикации : Mol. Cryst. Liquid Cryst. - 2012. - Vol. 557, Is. 1. - P.50-59. - ISSN 1542-1406, DOI 10.1080/15421406.2011.632237
Примечания : Cited References: 19. - This study was supported by the Presidium of the Russian Academy of Sciences (Project no. 24.1) and the Siberian Branch of the Russian Academy of Sciences (grant no. 43).
Предметные рубрики: FRANK CONSTANTS
ELECTRIC-FIELD
NEMATIC DROPS
ANISOTROPY
ALIGNMENT
FILMS
ORDER
Ключевые слова (''Своб.индексиров.''): anchoring energy--magnetic field--polymer-dispersed liquid crystals--structural transition--temperature fluctuations
Аннотация: The structural transition occurring in droplets of nematic liquid crystals formed in a polymer in magnetic field is studied. The transition is caused by field-driven weakening of tangential surface anchoring and develops following two scenarios: bipolar structure/homogeneous structure or bipolar structure/radial structure. The first scenario suggests a cyclic transition occurring upon thermal fluctuations without field. The structural transition is considered within a model of the biaxial liquid crystal/polymer interface. The model describes tendency of the nematic director to align tangentially on a droplet's surface, normally under the action of flexoelectric polarization, and axially along the magnetic-field-imposed easy orientation axis.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Krasikov A. A., Dubrovskii A. A., Semenov S. V., Bayukov O. A., Stolyar S. V., Iskhakov R. S., Ladygina V. P., Ishchenko L. A.
Заглавие : Magnetic properties and the mechanism of formation of the uncompensated magnetic moment of antiferromagnetic ferrihydrite nanoparticles of a bacterial origin
Коллективы : Ministry of Education and Science of the Russian Federation; Siberian Branch of the Russian Academy of Sciences
Место публикации : J. Exp. Theor. Phys.: Pleiades Publishing, 2014. - Vol. 119, Is. 3. - P.479-487. - ISSN 1063-7761, DOI 10.1134/S1063776114080044. - ISSN 1090-6509
Примечания : Cited References: 42. - This work was supported by the Ministry of Education and Science of the Russian Federation (state contract in 2014-2016) and a program of the Siberian Branch of the Russian Academy of Sciences.
Предметные рубрики: NIO NANOPARTICLES
EXCHANGE BIAS
HYSTERESIS ANOMALIES
FERRITIN
SURFACE
MOSSBAUER
ORDER
SIZE
Аннотация: The magnetic properties of the superparamagnetic ferrihydrite nanoparticles that form as a result of the vital activity of Klebsiella oxytoca bacteria are studied. Both an initial powder with an average number of iron atoms N Fe ∼ 2000–2500 in a particle and this powder after annealing at 140°C for 3 h in air are investigated. The following substantial modifications of the magnetic properties of the ferrihydrite nanoparticles are detected after annealing: the superparamagnetic blocking temperature increases from 23 to 49.5 K, and the average magnetic moment of a particle increases (as follows from the results of processing of magnetization curves). The particles have antiferromagnetic ordering, and the magnetic moment resulting in the superparamagnetism of the system appears due to random spin decompensation inside the particle. For this mechanism, the number of uncompensated spins is proportional to the number of magnetically active atoms raised to the one-half power, and this relation holds true for the samples under study at a good accuracy. The possible causes of the detected shift of magnetic hysteresis loops at low temperatures upon field cooling are discussed.
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