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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Jorio A., Currat R., Myles DAA, McIntyre G. J., Aleksandrova I. P., Kiat J. M., Saint-Gregoire P.
Заглавие : Ferroelastic phase transition in Cs3Bi2I9: A neutron diffraction study
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2000. - Vol. 61, Is. 6. - P3857-3862. - ISSN 1098-0121, DOI 10.1103/PhysRevB.61.3857
Примечания : Cited References: 16
Предметные рубрики: CRYSTAL
SCATTERING
CS3SB2I9
Аннотация: Crystalline Cs3Bi2I9, With the P6(3)/mmc symmetry at room temperature was studied by Laue and four-circle neutron diffractometry from room temperature down to 50 K. At T-0 = 220 K the crystal undergoes a second-order proper ferroelastic phase transition to a polydomain structure with a nonprimitive monoclinic C12/m1 space group. Satellites were not found below T-0, indicating that the continuous distribution of sites observed in previous I-127 nuclear quadrupole resonance experiments is due either to an undetected incommensurate phase characterized by a very small displacement amplitude, or due to the fraction of the crystal volume occupied by domain walls. We argue that thick domain walls are expected in the present structure due to the absence of mechanical compatibility between domains.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Roessli B., Staub U., Amato A., Herlach D., Pattison P., Sablina K. A., Petrakovskii G. A.
Заглавие : Magnetic phase transitions in the double spin-chains compound LiCu2O2
Место публикации : Physica B. - 2001. - Vol. 296, Is. 4. - P.306-311. - ISSN 0921-4526, DOI 10.1016/S0921-4526(00)00574-3
Примечания : Cited References: 17
Предметные рубрики: ORDERED MOMENT
COPPER
CRYSTAL
LI2CUO2
Ключевые слова (''Своб.индексиров.''): muon-spin rotation--spin ladder--magnetic ordering--licu2o2--crystal structure--lithium compounds--magnetic anisotropy--magnetic field effects--magnetic relaxation--magnetization--order disorder transitions--specific heat of solids--x ray diffraction analysis--anisotropic line broadening--muon spin rotation--spin ladder--antiferromagnetic materials
Аннотация: We report high-resolution X-ray diffraction, muon-spin-rotation spectroscopic and specific heat measurements in the double spin-chains compound LiCu2O2. The X-ray diffraction results show that the crystal structure of LiCu2O2 is orthorhombic down to T = 10 K. Anisotropic line-broadening of the diffraction peaks is observed, indicating disorder along the spin chains. Muon-spin relaxation and specific heat measurements show that LiCu2O2 undergoes a phase transition to a magnetic ordered state at T-1 similar to 24 K. The specific heat data exhibits a second lambda -like peak at T-2 similar to 32.5 K, which increases with increasing magnetic field in a similar way to that found in spin-ladder compounds. (C) 2001 Elsevier Science B.V. All rights reserved.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Lundin A. A.
Заглавие : Second moment of multiple-quantum NMR and a time-dependent growth of the number of multispin correlations in solids
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 103, Is. 6. - P904-916. - ISSN 1063-7761, DOI 10.1134/S1063776106120089
Примечания : Cited References: 39
Предметные рубрики: NUCLEAR-MAGNETIC-RESONANCE
LINE-SHAPE
SPIN SYSTEMS
DYNAMICS
SPECTRA
COHERENCES
STATE
BEHAVIOR
CRYSTAL
MODEL
Ключевые слова (''Своб.индексиров.''): correlation methods--mathematical models--nuclear magnetic resonance spectroscopy--spectrum analysis--time series analysis--four-spin time correlation--multispin correlations--second moment--time power series--quantum theory
Аннотация: The time evolution of multispin correlations (the growth of the number of correlated spins as a function of time) can be observed directly using the multiple-quantum nuclear magnetic resonance spectroscopy of solids. A quantity related to this number, namely, the second moment n(2)(t) of the intensity distribution of coherences of different orders in the multiple-quantum spectrum can be calculated using the theory proposed in this work. An approach to the calculation of the four-spin time correlation function through which this moment is expressed is developed. The main sequences of contributions in the expansion of this function into a time power series are summed using the approximation of a large number of neighbors both for systems with a secular dipole-dipole interaction and for systems with a nonsecular effective interaction. An exponential dependence of n(2)(t) is obtained. The value of n(2)(t) is additionally calculated using an expansion in terms of orthogonal operators for three model examples corresponding to different limiting realizations of spin systems. It is shown that the results of the microscopic theory at least qualitatively agree with both the results obtained for model examples and experimental results obtained recently for adamantane.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zinenko V. I., Pavlovskii M. S.
Заглавие : Lattice dynamics of BiFeO3 under hydrostatic pressure
Место публикации : Phys. Solid State. - 2009. - Vol. 51: 18th All-Russia Conference on Physics of Ferroelectrics (VKS-XVIII) (JUN 09-14, 2008, St Petersburg, RUSSIA), Is. 7. - P.1404-1408. - ISSN 1063-7834, DOI 10.1134/S1063783409070208
Примечания : Cited References: 10
Предметные рубрики: CRYSTAL
Аннотация: The vibrational frequencies of the BiFeO3 crystal lattice in the cubic phase (Pm3m) and the rhombohedral paraelectric phase (R3c) are calculated in terms of the ab initio model of an ionic crystal with the inclusion of the dipole and quadrupole polarizabilities. In the ferroelectric phase with the symmetry R3c, the calculated spontaneous polarization of 136 mu C cm(-2) agrees well with the experimental data. The dependences of the unit cell volume, the elastic modulus, and the vibrational frequencies on the pressure are calculated. It is found that the frequency of an unstable ferroelectric mode in both the cubic (Pm3m) and rhombohedral (R3c) phases are almost independent of the applied pressure, in contrast to classical ferroelectrics with a perovskite structure, where the ferroelectric instability is very sensitive to a variation in the pressure.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Isaenko L. I., Pashkov V. M., Pevnev I. V.
Заглавие : Search for and study of phase transitions in some representatives of the APb(2)X(5) family
Разночтения заглавия :авие SCOPUS: Search for and study of phase transitions in some representatives of the APb2X5 family
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 48, Is. 11. - P2152-2156. - ISSN 1063-7834, DOI 10.1134/S1063783406110217
Примечания : Cited References: 5
Предметные рубрики: CRYSTAL
Аннотация: Single crystals of KPb2Cl5, RbPb2Cl5, and RbPb2Br5 are grown and studied using optical polarization methods. The heat capacity of the crystals is investigated by differential scanning microcalorimetry, and the birefringence and the angle of rotation of the optical indicatrix are measured. The measurements are performed in the temperature range 270-640K. It is found that KPb2Cl5 undergoes a first-order ferroelastic phase transition at T-0 up arrow=530K, T-0 down arrow=528K, and Delta H=1000 +/- 200 J/mol. The transition is accompanied by twinning and a change in symmetry mmm reversible arrow P2(1)/c. The RbPb2Cl5 crystal remains monoclinic up to the melting temperature. The RbPb2Br5 compound belongs to the I4/mcm tetragonal modification and does not undergo structural transformations.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krylova S. N., Vtyurin A. N., Bulou A., Krylov A. S., Zamkova N. G.
Заглавие : Lattice dynamics and raman scattering spectrum of elpasolite Rb2KScF6: Comparative analysis
Разночтения заглавия :авие SCOPUS: Lattice dynamics and Raman scattering spectrum of elpasolite Rb 2KScF6: Comparative analysis
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2004. - Vol. 46, Is. 7. - P1311-1319. - ISSN 1063-7834, DOI 10.1134/1.1778457
Примечания : Cited References: 18
Предметные рубрики: STRUCTURAL PHASE-TRANSITION
LIGHT-SCATTERING
OPTICAL PHONONS
SOFT-MODE
CRYSTAL
Аннотация: Raman scattering spectra of elpasolite Rb2KScF6 are studied in a wide temperature range including two phase transitions: from the cubic to the tetragonal phase and then to the monoclinic phase. The experimental Raman scattering spectrum is compared with the lattice vibration spectra of these phases calculated using an ab initio approach. A number of anomalies (caused by structural rearrangement during the phase transitions) are revealed and quantitatively analyzed in the ranges of both the intramolecular vibrations of the octahedron molecular ScF6 ions and low-frequency intermolecular lattice vibrations. The interaction between low-frequency intramolecular vibrations and the intermolecular modes is found to be significant, and strong resonance interaction of the rotational soft modes (which are recovered below the phase transition points) with hard low-frequency vibrations of the rubidium ion sublattice is detected. These interactions are shown to substantially complicate the spectra. (C) 2004 MAIK "Nauka / Interperiodica".
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zvyagina G. A., Zhekov K. R., Bilych I. V., Zvyagin A. A., Bezmaternykh L. N., Gudim I. A.
Заглавие : Low-temperature behavior of the magnetoelastic characteristics of praseodymium ferroborate
Место публикации : Low Temp. Phys. - 2010. - Vol. 36, Is. 4. - P.296-302. - ISSN 1063-777X, DOI 10.1063/1.3420962; \b Физика низких температур
Примечания : Cited References: 16
Предметные рубрики: CRYSTAL
STATE
ND
Аннотация: The behavior of the elastic moduli and sound absorption in a PrFe(3)(BO(3))(4) single crystal at low temperatures is studied. A transition of the magnetic subsystem into an antiferromagnetically ordered state is manifested in the temperature behavior of the sound velocities and absorption. The characteristic behavior of the elastic properties of PrFe(3)(BO(3))(4) in an external magnetic field is observed. A phenomenological theory that gives a qualitative description of the observed features is constructed. It is proposed that a weak magnetic moment exists in the crystal. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3420962]
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ritter C., Vorotynov A. M., Pankrats A. I., Petrakovskii G. A., Temerov V. L., Gudim, I. A., Szymczak R.
Заглавие : Magnetic structure in iron borates RFe3(BO3)(4) (R = Er, Pr): a neutron diffraction and magnetization study
Коллективы :
Разночтения заглавия :авие SCOPUS: Magnetic structure in iron borates RFe3(BO3) 4 (R = Er, Pr): A neutron diffraction and magnetization study
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2010. - Vol. 22, Is. 20. - Ст.206002. - ISSN 0953-8984, DOI 10.1088/0953-8984/22/20/206002
Примечания : Cited References: 22. - This work was supported by RFBR, grant no. 10-02-00765, and by the Physical Sciences Department of RAS, project no. 1.1.1.1.
Предметные рубрики: GDFE3(BO3)(4)
DYFE3(BO3)(4)
CRYSTAL
Ключевые слова (''Своб.индексиров.''): antiferromagnetics--crystallographic structure--iron borate--low temperatures--magnetic ordering--magnetic propagation--magnetization measurements--rare-earth sublattices--space groups--spin reorientation--sub-lattices--temperature range--unit cells--anisotropy--antiferromagnetic materials--antiferromagnetism--erbium--erbium compounds--magnetic devices--magnetic properties--magnetic structure--magnetization--neutron diffraction--rare earths--single crystals--crystallography
Аннотация: Neutron diffraction, susceptibility and magnetization measurements (for R = Er only) were performed on iron borates RFe3(BO3)(4) (R = Pr, Er) to investigate details of the crystallographic structure, the low temperature magnetic structures and transitions and to study the role of the rare earth anisotropy. PrFe3(BO3)(4), which crystallizes in the spacegroup R32, becomes antiferromagnetic at T-N = 32 K, with t = [0 0 3/2], while ErFe3(BO3)(4), which keeps the P3(1)21 symmetry over the whole studied temperature range 1.5 K T 520 K, becomes antiferromagnetic below T-N
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9.

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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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Mel'nikova S. V., Laptash N. M., Zhogal' A. L.
Заглавие : Phase transitions in the oxyfluoride (NH4)(3)NbOF6
Разночтения заглавия :авие SCOPUS: Phase transitions in the oxyfluoride (NH4)3NbOF 6
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 5. - P958-962. - ISSN 1063-7834, DOI 10.1134/S1063783407050253
Примечания : Cited References: 11
Предметные рубрики: RAY-DIFFRACTION INVESTIGATIONS
DISTORTED PHASES
SYMMETRY
DISORDER
CRYSTAL
Аннотация: (NH4)(3)NbOF6 single crystals were grown, polarization-optical studies were performed, and birefringence was measured over the temperature range 90-500 K. A sequence of first-order structural phase transitions was found at temperatures T (1 down arrow) = 259.7 K and T (2 down arrow) = 257.7 K with temperature hysteresis delta T-1 = 0.9 K and delta T-2 = 1.9 K. The transitions are accompanied by twinning and the following change in the crystal symmetry: cubic paired left right arrows tetragonal paired left right arrows monoclinic. Optical second harmonic generation is found to occur at room temperature, which indicates that the cubic phase is not centrosymmetric. It is assumed that the phase transitions are ferroelastic and ferroelectric in nature.
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