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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bondarenko I. N., Gekht R. S., Ponomarev V. I.
Заглавие : Magnetic transitions in layered triangular antiferromagnets
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 1996. - Vol. 222, Is. 4. - P269-274. - ISSN 0375-9601, DOI 10.1016/0375-9601(96)00635-4
Примечания : Cited References: 22
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
PHASE-TRANSITION
VBR2
SYSTEMS
FIELD
VCL2
Ключевые слова (''Своб.индексиров.''): triangular antiferromagnets--quantum and thermal fluctuations--successive phase transitions--quantum and thermal fluctuations--successive phase transitions--triangular antiferromagnets
Аннотация: Magnetic states and phase transitions of the layered triangular antiferromagnets in an applied field are studied. It is shown that in compounds like VBr2 and VCl2 quantum effects change the ground state structure and cause successive phase transitions as the magnetic field increases. Coplanar structures of different spin configuration are realized far from the saturation field and a noncoplanar structure of umbrella-type configuration is realized near this field. The ground-state phase diagram is constructed, and a finite region of fields where the collinear phase is also possible is indicated.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aronov I. E., Berman G. P., Campbell D. K., Dudiy S. V.
Заглавие : Wigner function description of ac transport through a two-dimensional quantum point contact
Разночтения заглавия :авие SCOPUS: Wigner function description of a.c. transport through a two-dimensional quantum point contact
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 1997. - Vol. 9, Is. 24. - P.5089-5103. - ISSN 0953-8984, DOI 10.1088/0953-8984/9/24/009
Примечания : Cited References: 45
Предметные рубрики: QUANTIZED CONDUCTANCE
BALLISTIC-RESISTANCE
CONSTRICTION
CAPACITANCE
ADMITTANCE
ELECTRONS
SYSTEMS
FIELD
PUMP
Аннотация: We have calculated the admittance of a two-dimensional quantum point contact (QPC) using a novel variant of the Wigner distribution function (WDF) formalism. In the semiclassical approximation, a Boltzmann-like equation is derived for the partial WDF describing both propagating and non-propagating electron modes in an effective potential generated by the adiabatic QPC. We show that this quantum kinetic approach leads to the well known stepwise behaviour of the real part of the admittance (the conductance), and of the imaginary part of the admittance (the emittance), in agreement with the latest results derived by Christen and Buttiker, which is determined by the number of propagating electron modes. It is shown that the emittance is sensitive to the geometry of the QPC, and can be controlled by the gate voltage. We have established that the emittance has contributions corresponding to both quantum inductance and quantum capacitance. Stepwise oscillations in the quantum inductance are determined by the harmonic mean of the velocities for the propagating modes, whereas the quantum capacitance is a significant mesoscopic manifestation of the nonpropagating (reflecting) modes.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Alekseev K. N., Erementchouk M. V., Kusmartsev F. V.
Заглавие : Direct-current generation due to wave mixing in semiconductors
Место публикации : Europhys. Lett. - 1999. - Vol. 47, Is. 5. - P.595-600. - ISSN 0295-5075, DOI 10.1209/epl/i1999-00430-0
Примечания : Cited References: 34
Предметные рубрики: BLOCH OSCILLATOR
SUPERLATTICES
PHOTOCURRENT
TRANSPORT
FREQUENCY
FIELD
RECTIFIERS
EMISSION
CHAOS
GAAS
Аннотация: We describe an effect of the generation of direct current which may arise in semiconductors or semiconductor microstructures due to a mixing of coherent electromagnetic radiations of commensurate frequencies. The effect is, in essence, due to a nonparabolicity of the electron energy bands and is stronger in systems where this nonparabolicity is greater. We have made exact calculations in the framework of the Kane model, applicable to narrow-gap semiconductors and the tight-binding model which we employ for a description of a semiconductor superlattice.
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shaikhutdinov K. A., Balaev D. A., Popkov S. I., Petrov M. I.
Заглавие : Transport and magnetic properties of Y3/4Lu1/4Ba2Cu3O7+Y3Fe5O12 composites representing a Josephson-type superconductor-ferrimagnet-superconductor weak-link network
Разночтения заглавия :авие SCOPUS: Transport and Magnetic Properties of Y3/4Lu1/4Ba 2Cu3O7 + Y3Fe5O 12 Composites Representing a Josephson-Type Superconductor-Ferrimagnet-Superconductor Weak-Link Network
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2003. - Vol. 45, Is. 10. - P1866-1873. - ISSN 1063-7834, DOI 10.1134/1.1620087
Примечания : Cited References: 36
Предметные рубрики: RESISTIVE PROPERTIES
JUNCTION NETWORK
SYSTEM
TRANSITION
CURRENTS
VOLTAGE
STATE
FIELD
Аннотация: Y3/4Lu1/4Ba2Cu3O7 + Y3Fe5O12 composites with different volume ratios of the starting components were synthesized. The composites model an S-F-S Josephson junction network, where S stands for a superconductor and F, for a ferrimagnet. A study of the transport characteristics of the composites revealed that the temperature behavior of the electrical resistivity rho(T) below the superconducting transition point T-C is different in two regions separated by a temperature T-m. Below T-m, the current-voltage characteristics of the composites are nonlinear, while in the interval from T-C to T-m the values of rho(T) do not depend on the transport current j and magnetic field H. This behavior of rho(T, j ) and rho(T, H) is assigned to specific features of the tunneling of superconducting carriers through the ferrimagnetic layers separating HTSC grains in the composite. Magnetic measurements showed the diamagnetic response of HTSC grains to be lower in composites with a ferrimagnet. (C) 2003 MAIK "Nauka / Interperiodica".
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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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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bayukov O. A., Abd-Elmeguid M. M., Ivanova N. B., Kazak N. V., Ovchinnikov S. G., Rudenko V. V.
Заглавие : Mossbauer effect study in Fe1-xVxBO3 solid solutions
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 6. - P1088-1094. - ISSN 1063-7834, DOI 10.1134/1.1767250
Примечания : Cited References: 28. - One of the authors (M.M. A.-E.) would like to thank the Deutsche Forschungsgemeinschaft for financial support (SFB 608). This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286) and the federal program “Integration” (project no. Б0017)
Предметные рубрики: MAGNETO-OPTICAL PROPERTIES
FEBO3 SINGLE-CRYSTALS
FERRIC BORATE
CALCITE STRUCTURE
IRON BORATE
TEMPERATURE
FIELD
SPECTRA
FE3BO6
CRBO3
Аннотация: The Mossbauer effect in the Fe1 - xVxBO3 solid solutions has been measured at 130 and 300 K. The Fe0.05V0.95BO3 composition was studied in the interval 4.2-300 K. The experimental data obtained are described in terms of the model of a dilute magnetic insulator in which atoms of the first coordination sphere provide a major contribution to the hyperfine field at iron nucleus sites. It was found that, at low temperatures, the field H-hf is generated primarily by the iron ion itself and depends only weakly on substitution. The hyperfine interaction parameters in the discrete configuration series 6Fe, 5Fe1V, 4Fe2V, 3Fe3V, and 2Fe4V were determined. The magnitude of the isomer shift suggests that iron in the crystal resides in the trivalent state. (C) 2004 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aver'yanov E. M.
Заглавие : Correlation of the molecular structure of discotic nematic liquid crystals with their orientational order and specific features of the nematic-isotropic phase transition
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 8. - P1554-1559. - ISSN 1063-7834, DOI 10.1134/1.1788794
Примечания : Cited References: 32
Предметные рубрики: MONTE-CARLO
ANISOTROPIC SYSTEMS
COMPUTER-SIMULATION
BEHAVIOR
TRIPHENYLENE
DISCOGEN
MESOGEN
FIELD
Аннотация: The orientational order parameter S of molecules in high-temperature discotic nematic liquid-crystal phases of triphenylene derivatives is investigated as a function of the length of side flexible molecular chains at different temperatures. It is established that the orientational order parameters S in the range of the transition from the nematic phase to the isotropic liquid phase (the N-D-I transition) are smaller than those predicted from the molecular-statistical theory and computer simulation. It is shown that the N-D-I transition is close to both the isolated Landau point and the tricritical point (regardless of the chemical structure of the molecules and the anisotropy of dispersion intermolecular interactions). Consistent explanations are offered for a number of experimental findings, such as the anomalously small changes in the enthalpy and entropy upon the N-D-I transition (as compared to those revealed upon the N-I transition in calamitic nematic liquid crystals), the anomalously strong response of the isotropic phase of discotic nematic liquid crystals to external fields (thermodynamically conjugate to the order parameter S) and the long relaxation times of this response, and the formation of cybotactic discotic molecular clusters in the isotropic phase in the vicinity of the N-D-I transition. (C) 2004 MAIK "Nauka / Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Erkaev N. V., Shaidurov V. A., Semenov V. S., Langmayr D., Biernat H. K.
Заглавие : Peculiarities of Alfven wave propagation along a nonuniform magnetic flux tube
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2005. - Vol. 12, Is. 1. - Ст.12905. - ISSN 1070-664X, DOI 10.1063/1.1833392
Примечания : Cited References: 18
Предметные рубрики: HYDROMAGNETIC-WAVES
TRANSFER EVENTS
FIELD
SLOW
Ключевые слова (''Своб.индексиров.''): algebra--approximation theory--boundary conditions--electric conductivity--electric field effects--integral equations--magnetic flux--magnetohydrodynamics--perturbation techniques--polarization--vectors--velocity measurement--alfven wave propagation--axial symmetry--magnetic flux tubes--magnetosonic pulses--wave propagation
Аннотация: Within the framework of the assumption of large azimuthal wave numbers, the equations for Alfven and slow magnetosonic waves are obtained using frozen-in material coordinates. These equations are specified for the case of a nonuniform magnetic field with axial symmetry. Assuming a meridional polarization of the magnetic field and velocity perturbations, the effects of Alfven wave propagation are analyzed which are related to geometric characteristics of a nonuniform magnetic field: (a) A finite curvature radius of the magnetic field lines and (b) convergence of magnetic field lines. The interaction between the Alfven and magnetosonic waves is found to be strongly dependent on the curvature radius of the magnetic tube and the local plasma beta parameter. The electric field amplitude and the length scale of a wave front are found to increase very strongly in the course of the Alfven wave propagation along a converging magnetic flux tube. Also studied is a temporal decrease of the wave perturbations which is caused by dissipation at the conducting boundary. (C) 2005 American Institute of Physics.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S.
Заглавие : Magnetization curve and magnetic correlations in a nanochain of ferromagnetic grains with random anisotropy
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P495-501. - ISSN 1063-7834, DOI 10.1134/1.1884711
Примечания : Cited References: 31
Предметные рубрики: NANOCRYSTALLINE FERROMAGNETS
AMORPHOUS FERROMAGNETS
FIELD
MODEL
MICROSTRUCTURE
SIMULATIONS
DEPENDENCE
SYMMETRY
SYSTEM
MEDIA
Аннотация: The magnetization curve and magnetization correlation function are calculated for a ferromagnetic chain of single-domain nanoparticles with a randomly oriented anisotropy axis for different ratios between the exchange correlation and anisotropy energies. It is shown that the coercive force decreases as the exchange correlations increase. For strong exchange correlations, the magnetization curve is described by the following three successive magnetization processes as the applied field is increased: (i) nonuniform rotation of the magnetization of stochastic domains, (ii) collapse of the magnetic solitons, and (iii) nonuniform rotation of exchange-correlated magnetization vectors of the nanoparticles. For high fields, the calculated correlation function of the transverse magnetization components coincides with that predicted from linear theory. At low and zero fields, the main parameters of the correlation function (the variance and correlation radius) tend to certain finite values rather than diverge (as is the case in linear theory). The irreversible variation in the magnetization at low fields (the hysteresis loop) and the hysteresis of the main parameters of the correlation function are calculated. (c) 2005 Pleiades Publishing, Inc.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kliava J., Malakhovskii A. V., Edelman I. S., Potseluyko A. M., Petrakovskaja E. A., Melnikova S.V., Zarubina T. V., Petrovskii G., Bruckental Y., Yeshurun Y.
Заглавие : Unusual magnetic transitions and nature of magnetic resonance spectra in oxide glasses containing gadolinium
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2005. - Vol. 71, Is. 10. - Ст.104406. - ISSN 1098-0121, DOI 10.1103/PhysRevB.71.104406
Примечания : Cited References: 40
Предметные рубрики: ELECTRON-PARAMAGNETIC-RESONANCE
BORATE GLASSES
IONS
BEHAVIOR
GD3+
SPECTROSCOPY
SYSTEMS
GD-3+
FIELD
SHAPE
Ключевые слова (''Своб.индексиров.''): gadolinium--glass--lanthanide--oxide--anisotropy--article--chemical structure--concentration response--electron spin resonance--energy--magnetism--molecular physics--nanoparticle--phase transition--refraction index--temperature sensitivity
Аннотация: Magnetic susceptibility, electron paramagnetic resonance (EPR), and optical properties have been studied in a glass system {20La(2)O(3)-22Al(2)O(3)-23B(2)O(3)-35(SiO2+GeO2)} with a part of La2O3 substituted by Gd2O3 in different concentrations. Positive Weiss constants have been found in the more heavily doped glasses and ascribed to clustering of Gd3+ ions. Two magnetic phase transitions at 55 and 12 K were detected and ascribed, respectively, to ferromagnetic and antiferromagnetic clusters containing Gd ions. The overall shape of the EPR spectra shows the presence of clustering at the higher Gd contents. At low temperatures the cluster-related resonance signal is altered in shape, indicating an onset of magnetic anisotropy field. This signal is convincingly fitted to superparamagnetic resonance arising from ferromagnetic nanoparticles. The clustering, depending on the Gd concentration, correlates with a significant shift to lower energies of the strong optical absorption band edge, ascribed to a charge transfer transition between Gd ions. A nonmonotonous change of refractive index with the increase of the Gd content indicates changes in the glass matrix and in Gd cluster structure.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M. V., Bondarev V. S., Flerov I. N., Sciau P., Savariault J. M.
Заглавие : Heat capacity study of double perovskite-like compounds BaTi1-xZrxO3
Разночтения заглавия :авие SCOPUS: Heat capacity study of double perovskite-like compounds BaTi 1 - XZrxO3
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 12. - P2304-2308. - ISSN 1063-7834, DOI 10.1134/1.2142895
Примечания : Cited References: 19
Предметные рубрики: BATIO3
BA(TI1-XZRX)O-3
FERROELECTRICS
CERAMICS
STATE
FILMS
FIELD
Аннотация: The temperature dependence of the heat capacity of two compositions in the solid solution system BaTi1 - xZrxO3 (x = 0.25, 0.35) was measured using adiabatic calorimetry. In the T-x phase diagram, these compounds occupy positions near the crossover from conventional ferroelectric behavior to the relaxor state. Both compounds reveal diffuse heat capacity anomalies: two anomalies in the temperature ranges 250-350 and 150-200 K at x = 0.35 and one anomaly within the range similar to 150-320 K at x = 0.25. The results obtained are discussed together with structural and dielectric measurements. (c) 2005 Pleiades Publishing, Inc.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Popkov S. I., Shaikhutdinov K. A., Petrov M. I.
Заглавие : Investigation of the Josephson coupling through a magnetoactive barrier (ferrimagnet, paramagnet) in Y3/4Lu1/4Ba2Cu3O7+Y-3(Al1-xFex)(5)O-12 composites
Разночтения заглавия :авие SCOPUS: Investigation of the Josephson coupling through a magnetoactive barrier (ferrimagnet, paramagnet) in Y3/4Lu1/4Ba 2Cu3O7 + Y3(Al1 - X Fe x )5O12 composites
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 48, Is. 11. - P2046-2055. - ISSN 1063-7834, DOI 10.1134/S1063783406110023
Примечания : Cited References: 41
Предметные рубрики: S-F-S
MAGNETIC-PROPERTIES
RESISTIVE PROPERTIES
JUNCTION NETWORK
SUPERCONDUCTOR
Y3FE5-XALXO12
TRANSITION
TRANSPORT
METAL
FIELD
Аннотация: The transport properties of two-phase composites consisting of a high-temperature superconductor and a nonsuperconducting component with magnetic ordering are analyzed. These composites are considered as a network of "superconductor-magnetoactive insulator-superconductor" weak links of the Josephson type. Substituted garnets Y-3(Al1 - x Fe (x) )(5)O-12 (x = 0, ..., 1.0) are used as a magnetoactive component. The composites under investigation contain 92.5 vol % Y3/4Lu1/4Ba2Cu3O7 (the high-temperature superconductor) and 7.5 vol % Y-3(Al1 - x Fe (x) )(5)O-12 (x = 0, ..., 1.0). It is shown that an increase in the iron content in the Y-3(Al1 - x Fe (x) )(5)O-12 garnet leads to a reduction of the Josephson coupling strength: the temperature range in which the electrical resistance of the composites is equal to zero is reduced, and the critical current density at a temperature of 4.2 K decreases exponentially. For composites in which the iron content in the Y-3(Al1 - x Fe (x) )(5)O-12 garnet is higher than 0.1, the temperature dependence of the electrical resistance R(T) at temperatures below the transition point T-C of high-temperature superconductor crystallites has a portion in the range T-m -T-C where the resistance R(T) is independent of the transport current and the magnetic field strength. Below the temperature T-m , the dependences of the electrical resistance R(T) of the composites are nonlinear functions of the current and involve a considerable contribution from magnetoresistance. This behavior is characteristic of a network of Josephson junctions. The temperature T-m decreases with an increase in the iron content in the Y-3(Al1 - x Fe (x) )(5)O-12 garnet. The appearance of the above feature in the temperature dependences of the electrical resistance R(T) is interpreted as complete suppression of the Josephson coupling in the temperature range above T (m) due to the interaction of supercurrent carrier pairs with magnetic moments of iron atoms in the dielectric barriers separating high-temperature superconductor grains.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Patrin G. S., Vas'kovskii V. O., Svalov A. V., Eremin E. V., Panova M. A., Vasil'ev V. N.
Заглавие : Magnetic resonance in multilayer Gd/Si/Co magnetic films
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 1. - P131-136. - ISSN 1063-7761, DOI 10.1134/S1063776106010158
Примечания : Cited References: 9
Предметные рубрики: FIELD
Ключевые слова (''Своб.индексиров.''): magnetic properties--molecular dynamics--paramagnetic resonance--thin films--exchange parameters--gyromagnetic ratios--interlayer coupling--magnetic dynamics--resonance
Аннотация: The magnetic properties of multilayer Gd/Si/Co magnetic films are experimentally studied by electron magnetic resonance and analyzed theoretically. The introduction of a semiconductor silicon interlayer is found to substantially affect the magnetic interlayer coupling and the magnetic dynamics of the system. The interlayer coupling is shown to be ferromagnetic for the (Gd/Si)(n) films and to be antiferromagnetic for the (Gd/Si/Co/Si)(n) films. The temperature dependences of the exchange parameters and the gyromagnetic ratios are determined. Possible mechanisms responsible for the formation of the interlayer coupling are discussed.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Gokhfeld D. M., Dubrovskii A. A., Popkov S. I., Shaikhutdinov K. A., Petrov M. I.
Заглавие : Magnetoresistance hysteresis in granular HTSCs as a manifestation of the magnetic flux trapped by superconducting grains in YBCO+CuO composites
Разночтения заглавия :авие SCOPUS: Magnetoresistance hysteresis in granular HTSCs as a manifestation of the magnetic flux trapped by superconducting grains in YBCO + CuO composites
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2007. - Vol. 105, Is. 6. - P1174-1183. - ISSN 1063-7761, DOI 10.1134/S1063776107120084
Примечания : Cited References: 53
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTOR
CRITICAL-CURRENT-DENSITY
CURRENT-VOLTAGE CHARACTERISTICS
BA-CU-O
TRANSPORT-PROPERTIES
FIELD
YBA2CU3O7-DELTA
FLUCTUATIONS
FINGERPRINT
NETWORK
Ключевые слова (''Своб.индексиров.''): critical currents--hysteresis--hysteresis loops--josephson junction devices--magnetic flux--magnetoresistance--yttrium barium copper oxides--granular superconductors--hysterestic dependence--negative magnetoresistance--transport current--composite materials
Аннотация: Hysterestic behavior of the magnetoresistance of granular HTSCs and its interaction with the magnetic hysteresis are studied by measuring magnetoresistance R(H) and critical current I-c(H) of composites formed by HTSC Y0.75Lu0.25Ba2CU3O7 and CuO. A network of Josephson junctions is formed in such composites, in which the nonsuperconducting component plays the role of barriers between HTSC grains. Hysteretic dependences R(H) of magnetoresistance are studied in a wide range of transport current density j and are analyzed in the framework of the two-level model of a granular superconductor, in which dissipation takes place in the Josephson medium and the magnetic flux can be pinned both in grains and in the Josephson medium. The interrelation between the hysteresis of critical current I-c(H) and the evolution of the hysterestic dependence R(H) of the magnetoresistance upon transport current variation is demonstrated experimentally. The effect of the magnetic past history on the hysteretic behavior of R(H) and the emergence of a segment with a negative magnetoresistance are analyzed. It is shown for the first time that the R(H) dependences are characterized by a parameter that is independent of the transport current, viz., the width of the R(H) hysteresis loop.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Eremin I., Shorikov A., Anisimov V. I., Renner M., Brenig W.
Заглавие : Itinerant in-plane magnetic fluctuations and many-body correlations in NaxCoO2
Разночтения заглавия :авие SCOPUS: Itinerant in-plane magnetic fluctuations and many-body correlations in Nax Co O2
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2007. - Vol. 75, Is. 9. - Ст.94511. - ISSN 1098-0121, DOI 10.1103/PhysRevB.75.094511
Примечания : Cited References: 47
Предметные рубрики: TRANSITION-METALS
WAVE-FUNCTIONS
HUBBARD-MODEL
FERMI-SURFACE
ENERGY-BANDS
FERROMAGNETISM
APPROXIMATION
DIMENSIONS
SYSTEMS
FIELD
Аннотация: Based on the ab initio band structure for NaxCoO2, we derive the single-electron energies and the effective tight-binding description for the t(2g) bands using projection procedure. Due to the presence of the next-nearest-neighbor hoppings, a local minimum in the electronic dispersion close to the Gamma point of the first Brillouin zone forms. Correspondingly, in addition to a large Fermi surface, an electron pocket close to the Gamma point emerges at high doping concentrations. The latter yields a scattering channel, resulting in a peak structure of the itinerant magnetic susceptibility at small momenta. This indicates dominant itinerant in-plane ferromagnetic fluctuations above a certain critical concentration x(m), in agreement with neutron scattering data. Below x(m), the magnetic susceptibility shows a tendency toward the antiferromagnetic fluctuations. We further analyze the many-body effects on the electronic and magnetic excitations using various approximations applicable for different U/t ratios.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Divin A., Markidis S., Lapenta G., Semenov V. S., Erkaev N. V., Biernat H. K.
Заглавие : Model of electron pressure anisotropy in the electron diffusion region of collisionless magnetic reconnection
Коллективы :
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2010. - Vol. 17, Is. 12. - Ст.122102. - ISSN 1070-664X, DOI 10.1063/1.3521576
Примечания : Cited References: 42. - The present work is supported partially by the Onderzoekfonds KU Leuven (Research Fund KU Leuven) and by the European Commission's Seventh Framework Programme (FP7/2007-2013) under grant Agreement No. 218816 (SOTERIA project, www.soteria- space.eu). Additional support is provided by RFBR (Grant No. 09-05-91000-ANF-a). V.S.S. thanks ISSI for hospitality and financial support. The simulations were conducted on the resources of the Vlaams Supercomputer Centrum (VSC) at the Katholieke Universiteit Leuven.
Предметные рубрики: CURRENT SHEETS
X-LINE
PLASMA
DISSIPATION
FIELD
SIMULATIONS
ACCELERATION
TRANSPORT
Ключевые слова (''Своб.индексиров.''): analytical results--antiparallel configuration--collisionless--electron diffusion--electron population--electron pressures--magnetic reconnections--neutral line--new model--particle-in-cell simulations--two particles--anisotropy--astrophysics--collisionless plasmas--computer simulation--diffusion--geophysics--magnetic fields--magnetic properties--plasma simulation--electrons
Аннотация: A new model of the electron pressure anisotropy in the electron diffusion region in collisionless magnetic reconnection is presented for the case of antiparallel configuration of magnetic fields. The plasma anisotropy is investigated as source of collisionless dissipation. By separating electrons in the vicinity of the neutral line into two broad classes of inflowing and accelerating populations, it is possible to derive a simple closure for the off-diagonal electron pressure component. The appearance of these two electron populations near the neutral line is responsible for the anisotropy and collisionless dissipation in the magnetic reconnection. Particle-in-cell simulations verify the proposed model, confirming first the presence of two particle populations and second the analytical results for the off-diagonal electron pressure component. Furthermore, test-particle calculations are performed to compare our approach with the model of electron pressure anisotropy in the inner electron diffusion region by Fujimoto and Sydora [Phys. Plasmas 16, 112309 (2009)]. (C) 2010 American Institute of Physics. [doi:10.1063/1.3521576]
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Popkov S. I., Semenov S. V., Bykov A. A., Shaykhutdinov K. A., Gokhfeld D. M., Petrov M. I.
Заглавие : Magnetoresistance hysteresis of bulk textured Bi1.8Pb0.3Sr1.9Ca2Cu3Ox + Ag ceramics and its anisotropy
Коллективы :
Место публикации : Physica C. - 2010. - Vol. 470, Is. 1. - P.61-67. - ISSN 0921-4534, DOI 10.1016/j.physc.2009.10.007
Примечания : Cited References: 24. - Authors thanks to I.L. Belozerova for help in preparation of textured ceramics. This work was supported by program N5 of RAS, project N7, and in part in frames of young scientist projects of Siberian Federal University, project N6.
Предметные рубрики: CRITICAL-CURRENT ANISOTROPY
HIGH-TEMPERATURE SUPERCONDUCTOR
CRITICAL-CURRENT DENSITY
MAGNETIC HYSTERESIS
TAPES
FLUX
YBA2CU3O7-DELTA
FIELD
Ключевые слова (''Своб.индексиров.''): magnetoresistance--anisotropy--scaling--magnetization--bi2223--bscco--anisotropy--bi2223--bscco--magnetization--magnetoresistance--scaling--bi-2223--bscco--external fields--granular superconductors--magnetic induction--parameters characterizing--anisotropy--calcium--ceramic materials--crystallites--electric resistance--hysteresis--lead--magnetic moments--magnetoelectronics--magnetoresistance--nanocrystalline alloys--silver--superconducting materials--superconductivity--magnetic field effects
Аннотация: Magnetoresistance of bulk textured Bi1.8Pb0.3Sr1.9Ca2Cu3Ox + Ag ceramics has been studied in the magnetic fields applied parallel and perpendicular to a-b planes of Bi2223 crystallites. Besides well known anisotropy of magnetoresistance of textured superconductors (R-H parallel to c RH parallel to a-b), anisotropic hysteresis of R(H) dependences was investigated. Parameters characterizing hysteretic R(H) curves differ for the cases H parallel to c and H parallel to a-b. This behavior is explained within the model of a granular superconductor where the total magnetic induction in the intercrystallite boundaries is superposition of the external field and the magnetic field induced by dipole magnetic moments of neighbor crystallites. (C) 2009 Elsevier B.V. All rights reserved.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Rudenko V. V., Tugarinov V. I.
Заглавие : Temperature dependence of the uniaxial magnetic anisotropy of rhombohedral antiferromagnetic crystals with ions in the S state
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2010. - Vol. 52, Is. 1. - P112-116. - ISSN 1063-7834, DOI 10.1134/S1063783410010191
Примечания : Cited References: 19
Предметные рубрики: ALPHA-FE2O3
RESONANCE
FIELD
MNF2
Аннотация: The contributions of the anisotropic exchange to the firstand second-order uniaxial anisotropy constants have been calculated for hematite at T = 0 K and arbitrary temperatures. The results of the calculations and the most significant mechanisms are taken into account in interpreting the temperature dependence of the anisotropy in rhombohedral antiferromagnetic crystals. The first-order anisotropy constant for hematite is described by the dipole interaction, contributions of the "single-ion" nature, and relatively small contributions of the anisotropic exchange. The second-order constant for hematite includes the "single-ion" contribution and the contribution of the anisotropic exchange. For FeBO(3) and MnCO(3) crystals, the main contributions to the first-order anisotropy constant come from the dipole and single-ion mechanisms.
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