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Вид документа : Однотомное издание
Шифр издания : В37/П 58 рукописный текст
Автор(ы) : Попов, Михаил Александрович
Заглавие : Влияние внутренней подвижности твердых тел на высокотемпературную динамику ядерных спинов : дис. на соиск. уч. степени д-ра физ.-мат. наук : 01.04.07
Выходные данные : Красноярск, 2000
Колич.характеристики :143 л.
Коллективы : Красноярский государственный университет, Российская академия наук, Сибирское отделение РАН, Институт физики им. Л.В. Киренского Сибирского отделения РАН
Примечания : Библиогр.: 153 назв.
ГРНТИ : 29.19.37 + 29.19.49
ББК : В373.3я031
Экземпляры :ДС(1)
Свободны : ДС(1)
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Вид документа : Однотомное издание
Шифр издания : В37/П 58 рукописный текст
Автор(ы) : Попов, Михаил Александрович
Заглавие : Ядерная спин-решеточная релаксация в кристаллах со структурными фазовыми переходами : дис. на соиск. уч. степени канд. физ.-мат. наук : 01.04.03 : защищена 14.06.1985
Выходные данные : Красноярск, 1985
Колич.характеристики :94 л.
Коллективы : Академия наук СССР, Сибирское отделение АН СССР, Институт физики им. Л.В. Киренского Сибирского отделения АН СССР
Примечания : Библиогр.: 84 назв.
ГРНТИ : 29.19.15 + 29.19.37
ББК : В373.3я031 + В375.1я031
Экземпляры :ДС(1)
Свободны : ДС(1)
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popov M. A., Zavislyak I. V., Movchan N. N., Gudim, I. A., Srinivasan G.
Заглавие : Mode splitting in 37-42 GHz barium hexaferrite resonator: Theory and device applications
Место публикации : IEEE Trans. Magn.: IEEE-Institute Electrical and Electronics Engineers, 2014. - Vol. 50, Is. 6. - Ст.4004507. - ISSN 0018-9464, DOI 10.1109/TMAG.2014.2298498. - ISSN 1941-0069
Примечания : Cited References: 34
Предметные рубрики: MILLIMETER-WAVE APPLICATIONS
GUIDE JUNCTION CIRCULATORS
FERRITE
MICROWAVE
PROPAGATION
CYLINDERS
Ключевые слова (''Своб.индексиров.''): dielectric resonance--ferromagnetic resonance (fmr)--hexagonal ferrite--isolator--phase shifter
Аннотация: Dielectric resonances in the 37-42 GHz frequency band in the single crystal barium hexaferrite that occur well below the ferromagnetic resonance (FMR) have been investigated. Sample dimensions have been chosen so that the mode frequency is lower than the spin-wave excitation (in this case, the natural domain resonance) frequency. Such dielectric mode frequencies, being a function of both permittivity and permeability, are magnetic field H tunable. Here, we report on below-FMR magnetodielectric resonance (MDR) axially magnetized barium hexaferrites and their H-tuning characteristics. Our studies reveal H-tuning by up to 2.5 GHz and the tuning is the largest when the ferrite is in a magnetically unsaturated state. A theory for the MDR is presented and a fairly good agreement between experimental data and theory has been obtained. Tunable millimeter wave phase shifters and isolators utilizing the below-FMR dielectric resonances have been demonstrated.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popov M. A., Petrakovskii G. A., Bolsunovskaya O. A.
Заглавие : On the magnetic phase diagram of copper metaborate
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2008. - Vol. 50, Is. 5. - P909-912. - ISSN 1063-7834, DOI 10.1134/S106378340805017X
Примечания : Cited References: 6
Предметные рубрики: SOLITON LATTICE
CUB2O4
Аннотация: A stepwise transition from one incommensurate state of the spin system of a copper metaborate crystal to another incommensurate state was previously revealed using neutron scattering in an applied magnetic field. In this paper, the new state is interpreted as a combination of a commensurate state of one spin subsystem and an incommensurate state of another spin subsystem of the crystal.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Petrakovskii G. A., Bezmaternykh L. N., Bayukov O. A., Popov M. A., Schefer J., Neidermayer C., Aleshkevich P., Szymczak R.
Заглавие : Magnetic structure and magnetic excitations in the two-dimensional spin system of the Cu3B2O6 compound
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 49, Is. 7. - P1315-1320. - ISSN 1063-7834, DOI 10.1134/S1063783407070207
Примечания : Cited References: 21
Предметные рубрики: LONG-RANGE ORDER
HEISENBERG-MODEL
GROUND-STATE
GAP
ANTIFERROMAGNET
SRCU2(BO3)(2)
CUGEO3
CHAINS
CAV4O9
Аннотация: This paper reports on the results of measurements of the magnetic susceptibility, heat capacity, neutron scattering, muon spin relaxation, and electron paramagnetic resonance in Cu3B2O6 for the study of the ground state of the spin system of this compound. The results obtained suggest that, at a temperature of 10 K, the spin subsystem of the crystal, which consists of single spins and clusters of pairs and fours of spins interacting with one another, undergoes a transition to a state representing a superposition of the singlet (for clusters) and magnetically ordered (for single spins) states.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Yasuda Y., Nakamura H., Fujii Y., Kikuchi H., Chiba M., Yamamoto Y., Hori H., Petrakovskii G. A., Popov M. A., Bezmaternykh L. N.
Заглавие : B-11-NMR study of low-temperature phase transition in CuB2O4
Разночтения заглавия :авие SCOPUS: 11B-NMR study of low-temperature phase transition in CuB 2O4
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2007. - Vol. 19: International Conference on Highly Frustrated Magnetism (AUG 15-19, 2006, Osaka, JAPAN), Is. 14. - Ст.145277. - ISSN 0953-8984, DOI 10.1088/0953-8984/19/14/145277
Примечания : Cited References: 10
Предметные рубрики: COPPER METABORATE
Ключевые слова (''Своб.индексиров.''): copper compounds--low temperature effects--magnetic field effects--nuclear magnetic resonance--b t phase diagram--dzialoshinskii moriya interaction--phase transitions
Аннотация: The material CuB2O4 presents a variety of phases in the B - T phase diagram, caused by the frustration and the Dzialoshinskii - Moriya interaction. In order to investigate the nature of the phase transitions, a B-11- NMR experiment on CuB2O4 has been performed under an applied magnetic field along the a- axis down to 0.4 K. A new incommensurate - incommensurate phase transition has been found at 0.8 K under a field of 0.5 T. Further, another phase transition has been observed at 4.7 K under a field of about 2 T, which is consistent with the transition reported by the neutron diffraction experiment.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : Tree growth parameter in the Eden model on face-centered hypercubic lattices
Место публикации : Theor. Math. Phys. - 2005. - Vol. 144, Is. 3. - P.1361-1371. - ISSN 0040-5779, DOI 10.1007/s11232-005-0165-z
Примечания : Cited References: 19
Предметные рубрики: BRANCHED POLYMERS
HIGH-TEMPERATURES
EXPANSION
CLUSTERS
SYSTEMS
TIME
Ключевые слова (''Своб.индексиров.''): eden model--number of lattice trees--monte carlo method--growth parameter--singular points of generating function--large-dimension expansion--face-centered hypercubic lattice--eden model--face-centered hypercubic lattice--growth parameter--large-dimension expansion--monte carlo method--number of lattice trees--singular points of generating function
Аннотация: In the Eden model, we investigate how the tree growth parameter depends on the space dimension d for face-centered hypercubic lattices. We find the first three terms of the 1/d-expansion for this parameter directly from the generating function without calculating the number of trees because the growth parameter is the reciprocal coordinate of the singular point of the tree generating function. The same growth parameter was calculated by computer experiment where the ratios between the numbers of trees without intersections and trees without restrictions in the dimensions 3, 4, 6, 8, and 10 were estimated by the Monte Carlo method on face-centered cubic lattices. The results of the two methods agree well. Comparing with the previously performed computer experiment for simple hypercubic lattices, we observe that the values of the singular exponents for the tree generating functions are close for two different types of lattices.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : The coordinate of a singular point of the time correlation functions for a heteronuclear spin system of a crystal
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 100, Is. 4. - P775-783. - ISSN 1063-7761, DOI 10.1134/1.1926438
Примечания : Cited References: 24
Предметные рубрики: FLUCTUATION SPECTRUM
CROSS-RELAXATION
NMR ABSORPTION
SHAPE
WINGS
LINE
Ключевые слова (''Своб.индексиров.''): correlation methods--crystal lattices--crystallography--functions--integral equations--lithium compounds--nuclear magnetic resonance--quantum theory--random processes--autocorrelation functions (acf)--dipole-dipole interactions (ddi)--heteronuclear spin systems--self-consistent fluctuating field (scff)--crystals
Аннотация: The singularities of the time autocorrelation functions (ACFs) for a heteronuclear spin system of a crystal are investigated. Exact expressions are obtained for ten moments of the spectra of ACFs in the approximation of a self-consistent fluctuating field (SCFF) with arbitrary axial symmetry. These expressions are applied to determine the coordinate of the lowest singular point of these functions on the imaginary-time axis for a spin system with a dipole-dipole interaction (DDI). The leading corrections to this coordinate due to the correlation of local fields in real crystals are calculated. These corrections are determined by lattice sums with triangles of four bonds and pairs of four bonds. Numerical values of the coordinate are obtained for a LiF crystal in a magnetic field directed along three crystallographic axes. An increase in the coordinate of the singular point, which follows from the theory and leads to a faster falloff of the wings of the ACF spectra, qualitatively agrees with experiment. © 2005 Pleiades Publishing, Inc.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popov M. A., Petrakovskii G. A., Zinenko V. I.
Заглавие : Magnetic properties of copper metaborate: Two-parameter phenomenological model
Разночтения заглавия :авие SCOPUS: Magnetic Properties of Copper Metaborate: Two-Parameter Phenomenological Model
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 3. - P491-497. - ISSN 1063-7834, DOI 10.1134/1.1687867
Примечания : Cited References: 9
Предметные рубрики: SOLITON LATTICE
CUB2O4
FIELD
Аннотация: Symmetry analysis is performed for the magnetic subsystem of copper metaborate, and a phenomenological model is proposed with two two-component order parameters that correspond to ferromagnetism and antiferromagnetism vectors lying in the tetragonal plane of this crystal. Owing to the I (4) over bar 2d space group of symmetry of this crystal, the thermodynamic potential contains the Lifshitz invariant having the form of an antisymmetric product of the order parameters and their spatial derivatives. Analysis of this model shows that the temperatures of ordering in the magnetic subsystem and of the formation of a spiral structure in it can be different. This fact allows numerical calculation of the temperature dependences of the spiral wave vector, magnetization, and intensities of first- and third-order magnetic satellites in the incommensurate phase that arise in neutron elastic scattering, as well as the field dependence of the magnetization. The experimental data, including a magnetic-field-temperature phase diagram, are satisfactorily described. The parameters of the phenomenological thermodynamic potential of the magnetic subsystem of copper metaborate are estimated. (C) 2004 MAIK "Nauka / Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : The coordinate of the singular point of generating functions of clusters in the high-temperature dynamics of spin lattice systems with axially symmetric interaction
Место публикации : Theor. Math. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2003. - Vol. 136, Is. 3. - P1297-1311. - ISSN 0040-5779, DOI 10.1023/A:1025603416535
Примечания : Cited References: 25
Предметные рубрики: CONSISTENT FLUCTUATING FIELD
NUCLEAR-DOUBLE-RESONANCE
HEISENBERG PARAMAGNET
LINE SHAPE
RELAXATION
SPECTRUM
APPROXIMATION
CRYSTALS
MOMENT
CAF2
Ключевые слова (''Своб.индексиров.''): spin dynamics--singular points--expansion over the reciprocal space dimension--expansion over the reciprocal space dimension--singular points--spin dynamics
Аннотация: We investigate generating functions for equipped trees composed of double bonds of two sorts on a hypercubic lattice of dimension d with built-in fragments. Rules for constructing these clusters are chosen to ensure the estimate for coefficients of power series in time for the longitudinal and transverse autocorrelation functions of the spin system with axially symmetric interaction. We derive a system of two equations for the tree-generating functions and an equation for the generating functions of chains leading from the root to a fragment in a tree using the Bethe approximation and under the condition that mainly bonds of one sort are taken into account. For the face-centered hypercubic lattice, we find the First terms of the 1/d expansion for the coordinate of the singular point of the generating function in both the anisotropic and the isotropic cases taking fragments in the forms of a triangle from four bonds and a four-fold bound pair into account. The obtained result is written in terms of ratios of lattice sums and is generalized to nuclear spin systems with dipole-dipole interaction. The theoretical value of the singular-point coordinate agrees well with the experimental value calculated from the tail of the absorption spectrum of the nuclear magnetic resonance in a barium fluoride monocrystal.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Petrakovskii G. A., Popov M. A., Sablina K. A., Prozorova L. A., Sosin S. S., Szimczak G., Szimczak R., Baran M.
Заглавие : New magnetic states in copper metaborate CuB2O4
Место публикации : JETP Letters. - 2003. - Vol. 78, Is. 9. - P.569-573. - ISSN 0021-3640, DOI 10.1134/1.1641486
Примечания : Cited References: 15
Предметные рубрики: SOLITON LATTICE
FIELD
Аннотация: The static and resonance properties of copper metaborate CuB2O4 were experimentally studied in a magnetic field applied in the crystal tetragonal plane. The field-induced second-order phase transition to a weakly ferromagnetic state was observed in the temperature range 10-20 K. The low-field state is characterized by the absence of spontaneous moment, and it represents, presumably, a long-period helicoid. At temperatures below 2 K, two sequential first-order phase transitions were observed. They were accompanied by jumps in resonance absorption with a hysteresis upon changing field-scan direction. These transitions can be caused by the transformation of the incommensurate spin structure into the helicoidal states with periods commensurate with the lattice translation period. (C) 2003 MAIK "Nauka / Interperiodica".
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : On the coordinate of a singular point of time correlation functions for the system of nuclear magnetic moments of a crystal
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2003. - Vol. 97, Is. 1. - P78-84. - ISSN 1063-7761, DOI 10.1134/1.1600799
Примечания : Cited References: 22
Предметные рубрики: DIPOLAR FLUCTUATION SPECTRUM
FREE-INDUCTION DECAY
CROSS-RELAXATION
DOUBLE-RESONANCE
SPIN SYSTEMS
NMR-SPECTRA
LINE SHAPE
IRREVERSIBILITY
ABSORPTION
CAF2
Ключевые слова (''Своб.индексиров.''): absorption spectroscopy--barium compounds--crystallography--lattice constants--magnetic fields--nuclear magnetic resonance--absorption spectrum--dipole-dipole interaction--magnetic field directions--nuclear magnetic moments--magnetic moments
Аннотация: The hypothesis concerning the existence of singular points on the imaginary time axis for a correlation function of a system with the dipole-dipole interaction of nuclear spins of a crystal is verified. Within the framework of the self-consistent fluctuating field theory taking into account the principal corrections related to the correlation of local fields, a result for this coordinate is obtained in terms of the ratios of lattice sums. Experimental values of this coordinate are calculated from the wings of the nuclear magnetic resonance absorption spectrum of a BaF2 crystal for the magnetic field directions along the three crystallographic axes. Good agreement of the theoretical and experimental results justifies this hypothesis. (C) 2003 MAIK "Nauka / Interperiodica".
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Petrakovskii G. A., Pankrats A. I., Popov M. A., Balaev A. D., Velikanov D. A., Vorotynov A. M., Sablina K. A., Roessli B., Schefer J., Amato A., Staub U., Boehm M., Ouladdiaf B.
Заглавие : Magnetic properties of copper metaborate CuB2O4
Место публикации : Low Temp. Phys. - 2002. - Vol. 28, Is. 8-9. - P.606-612. - ISSN 1063-777X, DOI 10.1063/1.1511704; \b Физика низких температур
Примечания : Cited References: 17
Предметные рубрики: SINGLE-CRYSTALS
RESONANCE
STATE
Аннотация: The results of experimental research on the magnetic and resonance properties, heat capacity, muon spin relaxation, and neutron scattering of single-crystal copper metaborate CuB2O4 are reviewed. The results of a symmetry analysis and of modeling by the method of the phenomenological thermodynamic potential are presented. The magnetic structure of the crystal in various temperature intervals of the magnetic ordering region is discussed. (C) 2002 American Institute of Physics.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : On the coordinate of a singular point of the time correlation function for a spin system on a simple hypercubic lattice at high temperatures
Место публикации : Theor. Math. Phys. - 2002. - Vol. 131, Is. 3. - P.862-872. - ISSN 0040-5779, DOI 10.1023/A:1015935809388
Примечания : Cited References: 19
Предметные рубрики: NUCLEAR-DOUBLE-RESONANCE
HEISENBERG MAGNET
DEPENDENCE
MODEL
Ключевые слова (''Своб.индексиров.''): spin dynamics--correlation functions--power series in time--frequency moments--singular points--generated functions--lattice trees--multidimensional expansion--correlation functions--frequency moments--generated functions--lattice trees--multidimensional expansion--power series in time--singular points--spin dynamics
Аннотация: Using the d(-1) expansion method (d is the space dimension), we estimate the coordinate of the time-dependent autocorrelation function singular point on the imaginary time axis for the spin 1/2 Heisenberg model on a simple hypercubic lattice at high temperatures. We represent the coefficients of the time expansion (the spectral moments) for the autocorrelation function as the sums of the weighted lattice figures in which the trees constructed from the double bonds give the leading contributions with respect to d(-1) and the same trees with the built-in squares from six bonds or diagrams with the fourfold bonds give the contribution of the next-to-leading order. We find the corrections to the coordinate of the autocorrelation function singular point that are due to the latter contributions.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : A Monte Carlo study of the dependence of the growth parameter for trees on the lattice dimension in the Eden model
Место публикации : Theor. Math. Phys. - 2001. - Vol. 126, Is. 2. - P.270-279. - ISSN 0040-5779, DOI 10.1023/A:1005260114182
Примечания : Cited References: 17
Предметные рубрики: DIFFUSION-LIMITED AGGREGATION
BRANCHED POLYMERS
HIGH-TEMPERATURES
EXPANSION
TIME
Аннотация: We use the Monte Carlo method to compute the number of trees with n edges in the Eden model on d-dimensional simple cubic lattices for d = 2, 3, 4, 6, 8, 10. We compare these numbers with the exact data derived by the enumeration method up to n = 12 on the square lattice and up to n = 10 on the cubic lattice. We find that for d greater than or equal to 3, the computed values of the growth parameter for trees agree with the values that we derived earlier by the expansion in inverse powers of 2d - 1.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Petrakovskii G. A., Popov M. A., Roessli B., Ouladdiaf B.
Заглавие : Incommensurate magnetic structure in copper metaborate
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2001. - Vol. 93, Is. 4. - P809-814. - ISSN 1063-7761, DOI 10.1134/1.1420450
Примечания : Cited References: 10
Предметные рубрики: CUB2O4
Аннотация: Based on the experimental data on copper metaborate single crystals obtained in X-ray and neutron diffraction studies and heat capacity, magnetic susceptibility, and muon spin relaxation measurements, a phenomenological theory of the incommensurate magnetic structure of this crystal was developed. Considering the space group of the crystal, I (4) over bar 2d, Lifshits invariants were included into its thermodynamic potential. An analysis showed that magnetic structure formation at 10-20 K was dominated by the subsystem of copper spins in 4b unit cell sites. Below 10 K, the role played by the magnetic subsystem of copper spins in 8d unit cell sites in the formation of the magnetic structure of copper metaborate substantially increased. This caused a sharp increase in the wave vector of the incommensurate structure as temperature lowered. Numerical simulation of the temperature dependence of the wave vector of the helix and the heat capacity of the crystal gave a satisfactory description of the experimental data. This simulation was used to estimate the parameters of the phenomenological thermodynamic potential of the magnetic system of copper metaborate. (C) 2001 MAIK "Nauka/Interperiodica".
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : Excluded volume effects for frequency moments of the spin autocorrelation function of the Heisenberg model on a square lattice at high temperatures
Место публикации : J. Stat. Phys. - 1999. - Vol. 97, Is. 3-4. - P.793-802. - ISSN 0022-4715, DOI 10.1023/A:1004675527713
Примечания : Cited References: 17
Предметные рубрики:
Ключевые слова (''Своб.индексиров.''): spin dynamics--frequency moments--excluded volume--singular points
Аннотация: The expansion coefficients in powers of time (or frequency moments) of the spill autocorrelation Function are represented at the simple self-consistent approximation as a sum of weighted trees on a Bethe lattice. Using the computer numeration and the Monte Carlo method for self-avoidingly embedding these trees on the square lattice, we estimate the moments and the convergence radius of the expansion. We show that the moments decrease and the radius increases in consequence of the volume exclusion.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Ivanov Y. N., Popov M. A., Livshits A. I.
Заглавие : Orientational dependence of the tails of dipole-broadened NMR spectra in crystals
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 1999. - Vol. 88, Is. 1. - P157-167. - ISSN 1063-7761, DOI 10.1134/1.558778
Примечания : Cited References: 36
Предметные рубрики: NUCLEAR-DOUBLE-RESONANCE
FLUCTUATION SPECTRUM
CROSS-RELAXATION
SOLIDS
DIFFUSION
MEMORY
SHAPE
Аннотация: This paper describes experimental and theoretical studies of the tails of the dipole-broadened nuclear magnetic resonance (NMR) absorption spectra of F-19 in isomorphic single crystals of BaF2 and CaF2 with the magnetic field directed along three crystallographic axes. The results obtained by directly measuring the derivative of the tail of the NMR absorption spectrum and the falloffs of the Engelsberg-Lowe free precession after Fourier transformation qualitatively agree. It is shown that the shape of the tail is well described by an exponential function in which the orientational dependence of the exponent does not reduce to variation of the second moment. The observed shape of the tail and the orientational dependence of its parameters are explained on the basis of a self-consistent fluctuating-local-field theory. Nonlinear integral equations are derived for the correlation functions, taking into account the changes of the actual number of nearest neighbors caused by the anisotropy of the dipole-dipole interaction and the contribution of lattice sums with loops. The equations are solved numerically. Good agreement is obtained for the computed dropoffs of the free precession, the NMR spectra, and the cross-polarization rates with the experimental results. (C) 1999 American Institute of Physics. [S1063-7761(99)02401-4].
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Zobov V. E., Popov M. A.
Заглавие : On the radius of convergence of series in powers of time for spin correlation functions of the Heisenberg magnet at high temperature
Место публикации : Theor. Math. Phys.: PLENUM PUBL CORP, 1997. - Vol. 112, Is. 3. - P1182-1191. - ISSN 0040-5779, DOI 10.1007/BF02583049
Примечания : Cited References: 22
Предметные рубрики: AUTO-CORRELATION FUNCTION
INFINITE-TEMPERATURE
PARAMAGNET
DYNAMICS
MODEL
Аннотация: The convergence of series in powers of time for spin autocorrelation functions of the Heisenberg magnet are investigated at infinite temperatures on lattices of different dimensions d. The calculation data available at the present time for the coefficients of these series are used to estimate the corresponding radii of convergence, whose growth with decreasing d is revealed and explained in a self-consistent approximation. To this end, a simplified nonlinear equation corresponding to this approximation is suggested and solved for the autocorrelation function of a system with an arbitrary number Z of nearest neighbors. The coefficients of the expansion in powers of time for the solution are represented in the form of trees on the Bethe lattice with the coordination number Z. A computer simulation method is applied to calculate the expansion coefficients for trees embedded in square, triangular, and simple cubic lattices under the condition that the intersection of tree branches is forbidden. It is found that the excluded volume effect that manifests itself in a decrease in these coefficients and in an increase in the coordinate and exponent of the singularity of the autocorrelation function on the imaginary time axis is intensified with decreasing lattice dimensions.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popov M. A.
Заглавие : Gaussian approximation in the ising-model with long-range interaction
Место публикации : Theor. Math. Phys. - 1990. - Vol. 83, Is. 3. - P.658-663. - ISSN 0040-5779, DOI 10.1007/BF01018036
Примечания : Cited References: 7
Аннотация: The infinite hierarchy of equations for the cumulants of the correlation functions of the longitudinal spin components in the Ising model with long-range interaction corresponding to a Gaussian form of the spectral density is investigated. The invariance of the cumulants with respect to permutation of the vertices is used to decouple the hierarchy. A phase transition of the second kind is described by the obtained system of equations for the cumulants of the first three orders in a three-dimensional model.
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