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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Valkov V. V., Valkova T. A.
Заглавие : Application of indefinite metric for transition to bose description of Su(3) hamiltonians - excitation spectrum of spin nematics
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz. - 1991. - Vol. 99, Is. 6. - P.1881-1897. - ISSN 0044-4510
Примечания : Cited References: 37
Предметные рубрики: BIQUADRATIC EXCHANGE
PHASE-TRANSITIONS
DIAGRAM TECHNIQUE
MAGNETISM
FIELD
STATE
Аннотация: A procedure is developed for a correct transition to the Bose representation for quantum SU(3) Hamiltonians. The analysis is carried out for a spin nematic by applying the indefinite metric formalism and pseudo-Hubbard operators. An important aspect of the theory is that the finiteness of the number of physical states is taken into account. This is attained by introducing and consistently taking into account the metric operator for which purpose a simple expression in terms of Bose operators is suggested. It is shown that in this approach the quantum Bose analog of the Hamiltonian is an Hermitian operator. This circumstance removes a number of principle contradictions which appeared previously on application of the Bose analog of the Hamiltonian derived by virtually identifying the Hubbard and pseudo-Hubbard operators and ignoring the finiteness of the number of physical states. The integral equations defining the chief characteristics of the system are obtained and solved analytically for the spin-nematic state of a magnet with S = 1 and by taking into account anharmonic effects. This permits one to write down in nonlinear theory explicit expressions for the two branches of the quantum excitation spectrum. The character of the renormalization of the spectrum parameters due to the presence of zero-point quantum oscillations is studied. The renormalization of the critical field on transition of the system from the spin nematic state is calculated analytically.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : GEKHT R. S.
Заглавие : MAGNETIC-STRUCTURES AND PROPERTIES OF STATES IN STRONGLY FRUSTRATED HEISENBERG ANTIFERROMAGNETS
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1992. - Vol. 102, Is. 6. - P1968-1982. - ISSN 0044-4510
Примечания : Cited References: 23
Предметные рубрики: PHASE-TRANSITIONS
SPIN
LATTICE
MODELS
LONG
Аннотация: The magnetic structures and properties of states in frustrated Heisenberg antiferromagnets are analyzed. It is shown that frustrations induced due to additional spins in the system lead to a large variety of phase with the commensurable and uncommensurable periods and also to arising nonperiodical phases. The energy spectrum of states is studied. It is found that in the large region of the frustration parameter variation the modulated phase (0, Q) is unstable. The phase diagram of states is found and the region of local degeneration for some structures is indicated.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : GEKHT R. S., GRISHIN V. V.
Заглавие : ON MAGNETIC STATES IN STRONGLY FRUSTRATED 2-DIMENSIONAL ANTIFERROMAGNETICS
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1992. - Vol. 34, Is. 11. - P3557-3559. - ISSN 0367-3294
Примечания : Cited References: 5
Предметные рубрики: PHASE-TRANSITIONS
LATTICE
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : GEKHT R. S., PONOMAREV V. I.
Заглавие : LOW-TEMPERATURE PROPERTIES OF QUASI-2-DIMENSIONAL FRUSTRATED ANTI-FERROMAGNETICS
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1994. - Vol. 36, Is. 11. - P3394-3397. - ISSN 0367-3294
Примечания : Cited References: 8
Предметные рубрики: PHASE-TRANSITIONS
MAGNETIC STATES
ANTIFERROMAGNETS
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zeer E. P., Falaleev O. V., Ivanov Y. N., Petrakovskaya E. A.
Заглавие : Study of molecular mobility in ABF6-center-dot-6H2O crystal family
Место публикации : Fiz. Tverd. Tela. - 1994. - Vol. 36, Is. 8. - P.2210-2220. - ISSN 0367-3294
Примечания : Cited References: 21
Предметные рубрики: PHASE-TRANSITIONS
NMR
SYSTEM
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Epikhin A. M., Ponomarev V. I.
Заглавие : Helicoidal magnetic structure in frustrated antiferromagnetics
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1995. - Vol. 37, Is. 6. - P.1891-1893. - ISSN 0367-3294
Примечания : Cited References: 6
Предметные рубрики: QUANTUM FLUCTUATIONS
PHASE-TRANSITIONS
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ivanov Y. N., Totz J., Michel D., Klotzsche G., Sukhovsky A. A., Aleksandrova I. P.
Заглавие : Chemical exchange in NH4HSeO4 single crystals studied by two-dimensional H-2 nuclear magnetic resonance
Разночтения заглавия :авие SCOPUS: Chemical exchange in NH4HSeO4 single crystals studied by two-dimensional 2H nuclear magnetic resonance
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 1999. - Vol. 11, Is. 18. - P.3751-3760. - ISSN 0953-8984, DOI 10.1088/0953-8984/11/18/310
Примечания : Cited References: 16
Предметные рубрики: PHASE-TRANSITIONS
CONDUCTIVITY PROCESSES
AMMONIUM
Ключевые слова (''Своб.индексиров.''): hydrogen bonds--nuclear magnetic resonance--single crystals--thermal effects--ammonium hydrogen selenate--ammonium compounds
Аннотация: Processes of chemical exchange of deuterons in partially deuterated ammonium hydrogen selenate, NH4HSeO4 (AHSe), crystals are investigated by means of H-2 nuclear magnetic resonance (NMR) experiments over a wide temperature range. The temperature dependencies of the quadrupole line splittings in the one-dimensional spectra of AHSe above 350 K revealed lineshape changes which are characteristic for chemical exchange processes. A detailed study of these exchange processes in AHSe is achieved by means of two-dimensional H-2 NMR experiments. In the temperature range investigated, a chemical exchange occurs only between those deuteron (proton) sites which are involved in hydrogen bonds (alpha- and beta-positions). It was established that the rates of exchange between all types of hydrogen-bound deuteron are approximately the same. Exchange between these positions and the deuterons in the ND4 groups could not be detected. On the basis of our findings, we finally discuss a model for the microscopic mechanism of hydrogen transport in AHSe.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Application of synchrotron radiation to the study of magnetic materials
Место публикации : Uspekhi Fiz. Nauk: MEZHDUNARODNAYA KNIGA, 1999. - Vol. 169, Is. 8. - P.869-887. - ISSN 0042-1294
Примечания : Cited References: 93
Предметные рубрики: X-RAY-SCATTERING
RESONANCE EXCHANGE SCATTERING
RARE-EARTH-METALS
CIRCULAR-DICHROISM
VALENCE STATES
CO/PD(111) MULTILAYERS
ABSORPTION-SPECTRA
PHASE-TRANSITIONS
SPIN POLARIZATION
EDGE STRUCTURE
Аннотация: The recent results of the studies of magnetic materials using synchrotron irradiation are reviewed. The influence of magnetic effects on X-ray scattering is studied for linearly and circularly polarized photons, and effects of magnetic circular dichroism on the spectra of X-ray absorption and photoelectron emission are discussed. It is shown that X-ray magnetooptics techniques provide fine details of crystal and magnetic structures and also make it possible to separate the spin and orbital contributions to the total moment; to obtain element- and position-sensitive information on the magnetic properties of the material; to visualize domains and domain walls; and to probe magnetization reversal dynamics. A comparison of magnetic neutron and X-ray methods is given.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Afanas'ev M. L., Ushakova T. V.
Заглавие : Thermodynamic properties of (NH4)(2)KGaF6 elpasolite
Разночтения заглавия :авие SCOPUS: Thermodynamic properties of (NH4)2KGaF6 elpasolite
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2001. - Vol. 43, Is. 12. - P2301-2306. - ISSN 1063-7834, DOI 10.1134/1.1427960
Примечания : Cited References: 19
Предметные рубрики: NUCLEAR MAGNETIC-RESONANCE
PHASE-TRANSITIONS
CRYOLITE (NH4)(3)SCF6
MOTIONS
F-19
H-1
Аннотация: The heat capacity of (NH4)(2)KGaF6 elpasolite is measured in the temperature range from 80 to 350 K. A sequence of three phase transitions at T-1 = 288.5 K, T-2 = 250 K, and T-3 = 244.5 K is revealed, and the thermodynamic characteristics of these transitions are determined. The influence of hydrostatic pressure on the phase transition temperature is investigated. The results obtained are discussed within the model of orientational ordering of NH4+ and GaF63- ionic groups. (C) 2001 MAIK "Nauka/Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Burriel R., Gorev M. V., Isla P., Voronov V. N.
Заглавие : Low-temperature specific heat of the Rb2KScF6 elpasolite
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2003. - Vol. 45, Is. 1. - P167-170. - ISSN 1063-7834, DOI 10.1134/1.1537430
Примечания : Cited References: 9
Предметные рубрики: PHASE-TRANSITIONS
CRYOLITE (NH4)(3)SCF6
DISTORTED PHASES
SYMMETRY
Аннотация: The specific heat of single-crystal Rb2KScF6 is measured using ac calorimetry in the range 4-280 K. The results are discussed in the context of a group-theoretical analysis of possible distortions of the elpasolite structure and of experimental data obtained earlier with an adiabatic calorimeter in a narrower temperature region. (C) 2003 MAIK "Nauka/Interperiodica".
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