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1.

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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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Altin E., Gokhfeld D. M., Demirel S., Oz E., Kurt F., Altin S., Yakinci M.E.
Заглавие : Vortex pinning and magnetic peak effect in Eu(Eu,Ba)2.125Cu3Ox
Место публикации : J. Mater. Sci.-Mater. Electron.: Springer, 2014. - Vol. 25, Is. 3. - P.1466-1473. - ISSN 0957-4522, DOI 10.1007/s10854-014-1753-1. - ISSN 1573-482X
Примечания : Cited References: 30
Предметные рубрики: SUPERCONDUCTORS
FIELD
NANOCRYSTALLINE
TEMPERATURE
LOOP
Аннотация: Eu–Ba–Cu–O composition was synthesized by solid state reaction technique. To determine optimum growth temperature, heat treatment was examined on the material at 880–1,100 °C. Microstructural evolution, phase formation and elemental distribution depending on heat treatments were examined by using X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope analysis. Optimum fabrication conditions were determined as 1,020 °C for 24 h under oxygen atmosphere and detailed characterization of corresponding compound was performed. The magnetization hysteresis loops are expounded to be the product of superconducting Eu-123 grains and magnetic Eu2+ ions. The peak effect on the magnetization curves was described by the extended critical state model. Scaling of the pinning force was found such that the peak position is proportional to the irreversibility field H irr and the maximum pinning force is proportional to H irr 2 .
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3.

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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4.

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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5.

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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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Yakushkin S. S., Dubrovskii A. A., Bukhtiyarova G. A., Shaikhutdinov K. A., Martyanov O. N.
Заглавие : Study of the high-coercivity material based on ε-Fe2O3 nanoparticles in the silica gel matrix
Место публикации : Tech. Phys. Lett.: MAIK Nauka-Interperiodica / Springer, 2016. - Vol. 42, Is. 4. - P.347-350. - ISSN 10637850 (ISSN), DOI 10.1134/S1063785016040039
Примечания : Cited References: 17. - This study was supported by the Federal Agency for Scientific Organizations of Russia (base budget financing no. V.44.1.15), the Scientific and Educational Center of Energy-Efficient Catalysis at the Novosibirsk State University, and the Russian Foundation for Basic Research (project no. 15-32-50919).
Предметные рубрики: Phase
Field
State
Oxide
Iron
Аннотация: We report the results of investigations of ε-Fe2O3 magnetic nanoparticles obtained by incipient wetness impregnation of silica gel. It was established that the obtained samples with an iron content of 12‒16% mass % containing ε-Fe2O3 nanoparticles with an average size of 10 nm on the silica gel surface exhibit a room-temperature coercivity of about 10 kOe. Along with fabrication simplicity, this fact makes the prepared samples promising for application as a magnetically hard material. © 2016, Pleiades Publishing, Ltd
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pachauri, Neha, Khodadadi B., Althammer M., Singh A.V., Loukya B., Datta R., Iliev M., Bezmaternykh L. N., Gudim I. A., Mewes T., Gupta A.
Заглавие : Study of structural and ferromagnetic resonance properties of spinel lithium ferrite (LiFe5O8) single crystals
Коллективы : NSF [ECCS-1102263], NSF-CAREER [0952929], ICMS
Место публикации : J. Appl. Phys.: American Institute of Physics, 2015. - Vol. 117, Is. 23. - Ст.233907. - ISSN 0021, DOI 10.1063/1.4922778. - ISSN 10897550(eISSN)
Примечания : Cited References:32. - This work has been supported by NSF Grant No. ECCS-1102263. Tim Mewes and Behrouz Khodadadi would like to acknowledge support by the NSF-CAREER Award No. 0952929. R. Datta and B. Loukya sincerely acknowledge ICMS for providing advanced microscopy facility and funding. We thank Sahar Keshavarz, Archana Panikar, Stefan Kingler, and Jamileh Beik Mohammadi for help with the experimental work.
Предметные рубрики: EFFECTIVE LINEWIDTH
MAGNETIC-PROPERTIES
FIELD
TEMPERATURE
DEPENDENCE
Аннотация: The effect of B-site cation ordering on the room temperature structural and ferromagnetic resonance (FMR) properties of single crystal spinel lithium ferrite (LiFe5O8, LFO) have been investigated. A detailed microstructural analysis is done through X-ray diffraction, polarized Raman spectroscopy, and transmission electron microscopy (TEM) to examine the effect of post-annealing on the B-site cation ordering. The X-ray diffraction pattern of the as-grown crystal indicates a disordered state of the crystal. However, the annealed sample shows additional superlattice reflections corresponding to the ordered phase. This ordering is further confirmed by Raman spectra and TEM images, which reveal ordering of Li and Fe ions at the octahedral sites contrasting with the relatively high degree of octahedral site disorder in the as-grown crystal. To study the effect of B-site ordering on the magnetic properties and FMR linewidth, vibrating sample magnetometry and broadband FMR measurements have been performed for both the ordered and disordered phases of lithium ferrite. The value of saturation magnetization for both phases is ∼290 emu/cm3. A single mode FMR profile is observed for both phases with little distortion. The linewidth characteristics of the ordered and disordered phases of lithium ferrite phases are compared, and it is observed that the linewidth is independent of the cation ordering. Both the phases exhibit a low linewidth (∼26 Oe at 30 GHz) and the effective damping parameter for the as-grown and annealed samples is determined to be 0.0021 ± 0.0001.Влияние катионного упорядочения в Б-позициях при комнатной температуре на структурные свойства и ферромагнитный резонанс (ФМР) монокристалла литий железной шпинели (LiFe5O8, LFO) были исследованы. Подробный анализ микроструктуры делается с использованием рентгеновской дифракции, спектроскопии комбинационного рассеяния поляризованного света и просвечивающей электронной микроскопии (ПЭМ), чтобы изучить влияние после отжига на катионное упорядочение в B-позиции. Рентгеновская дифракционная картина, так выращенных кристаллов указывает на беспорядочное состояние кристалла. Тем не менее, пример показывает дополнительные индексы, соответствующие сверхрешетчатой упорядоченной фазы, при отжиге. Этот порядок подтверждается также спектрами комбинационного рассеяния и ТЕМ изображений, которые показывают порядок ионов Li и Fe в октаэдрических контрастными с относительно высокой степенью восьмигранной расстройства позиций в выращенных кристаллах. Для изучения влияния упорядочения В-позиций на магнитные свойства и ширины линии ФМР, вибрационные образцы магнитометрии и широкополосных ФМР измерений были выполнены как для упорядоченных и неупорядоченных фаз литиевого феррита. Значение намагниченности насыщения для обоих фаз ~290 emu / см3. Одиночный профиль в режиме ФМР наблюдается для обеих фаз с небольшим искажением. Ширина линии характеристики упорядоченной и неупорядоченной фаз литиевых ферритов сравниваются, и следует отметить, что ширина линии не зависит от катионного упорядочения. Оба фазы проявляют малую ширину линии (Э около 26 на 30 ГГц) и эффективный параметр демпфирования, как, для только выращенных, так и для отожженных образцов, определяется как 0,0021 ± 0,0001.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Dubrovskiy A. A., Balaev A. D., Shaykhutdinov K. A., Bayukov O. A., Pletnev O. N., Yakushkin S. S., Bukhtiyarova G. A., Martyanov O. N.
Заглавие : Size effects in the magnetic properties of ε-Fe2O3 nanoparticles
Место публикации : J. Appl. Phys.: American Institute of Physics, 2015. - Vol. 118, Is. 21. - Ст.213901. - ISSN 00218979 (ISSN), DOI 10.1063/1.4936838
Примечания : Cited References: 41. - We are grateful to Professor Yu. L. Raikher for useful discussions and M. A. Kazakova for the help in sample preparationThis work was supported by Russian Federal Agency of Scientific Organizations (Project No. V.44.1.15) and scientific and educational center of energy-efficient catalysis of NSU
Предметные рубрики: FERROMAGNETIC-RESONANCE
OXIDE NANOPARTICLES
WAVE ABSORBER
IRON
TRANSITION
TEMPERATURE
PARTICLES
PHASE
FNANOWIRES
FIELD
Аннотация: We report the results of comparative analysis of magnetic properties of the systems based on ε-Fe2O3, nanoparticles with different average sizes (from ∼3 to 9 nm) and dispersions. The experimental data for nanoparticles higher than 6-8 nm in size are consistent with the available data, specifically, the transition to the magnetically ordered state occurs at a temperature of ∼500 K and the anomalies of magnetic properties observed in the range of 80-150 K correspond to the magnetic transition. At the same time, Mossbauer and ferromagnetic resonance spectroscopy data as well as the results of static magnetic measurements show that at room temperature all the investigated samples contain ε-Fe2O3 particles that exhibit the superparamagnetic behavior. It was established that the magnetic properties of nanoparticles significantly change with a decrease in their size to ∼6 nm. According to high-resolution electron microscopy and Mossbauer spectroscopy data, the particle structure can be attributed to the ε-modification of trivalent iron oxide; meanwhile, the temperature of the magnetic order onset in these particles is increased, the well-known magnetic transition in the range of 80-150 K does not occur, the crystallographic magnetic anisotropy constant is significantly reduced, and the surface magnetic anisotropy plays a decisive role. This is apparently due to redistribution of cations over crystallographic positions with decreasing particle size, which was established using Mössbauer spectra. As the particle size is decreased and the fraction of surface atoms is increased, the contribution of an additional magnetic subsystem formed in a shell of particles smaller than ∼4 nm becomes significant, which manifests itself in the static magnetic measurements as paramagnetic contribution. © 2015 AIP Publishing LLC.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sadreev A. F.
Заглавие : Feshbach projection formalism for transmission through a time-periodic potential
Место публикации : Phys. Rev. E: American Physical Society, 2012. - Vol. 86, Is. 5. - Ст.56211. - ISSN 1539-3755, DOI 10.1103/PhysRevE.86.056211
Примечания : Cited References: 33
Предметные рубрики: NUCLEAR REACTIONS
UNIFIED THEORY
QUANTUM
FIELD
SCATTERING
SYSTEM
STATES
Аннотация: The Feshbach projection formalism is applied to consider quantum transmission through a tight-binding wire subject to a time-periodic potential. The wire is coupled with two leads via the coupling constant v(C). The periodicity of the potential implies an additional temporal dimension that reduces the problem to stationary transmission through an effectively two-dimensional lattice system. The non-Hermitian effective Hamiltonian is formulated. Thist allows us to trace the redistribution of resonance positions and resonance widths with the growth of v(C) from the weak-coupling to the strong-coupling regime.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Rasskazov I. L., Karpov S. V., Markel V. A.
Заглавие : Surface plasmon polaritons in curved chains of metal nanoparticles
Коллективы : US National Science Foundation [DMS1216970]; Russian Academy of Sciences [24.29, 24.31, III. 9.5, 43, SFU (101)]; Russian Ministry of Education and Science [1792]
Место публикации : Phys. Rev. B: American Physical Society, 2014. - Vol. 90, Is. 7. - Ст.75405. - ISSN 1098-0121, DOI 10.1103/PhysRevB.90.075405. - ISSN 1550-235X
Примечания : Cited References: 34. - This research was supported in part by the US National Science Foundation under Grant DMS1216970, by the Russian Academy of Sciences under the Grants 24.29, 24.31, III. 9.5, 43, SFU (101), and also by the Russian Ministry of Education and Science under the Contract 1792.
Предметные рубрики: LINEAR-CHAINS
DISPERSION-RELATIONS
ARRAYS
RESONANCES
FIELD
Аннотация: We investigate numerically the propagation of steady-state monochromatic surface plasmon polaritons (SPPs) in curved chains of metal nanoparticles of various spheroidal shapes. We discuss the SPP propagation (decay of the amplitude), the polarization conversion due to coupling of orthogonally polarized SPPs, and the electromagnetic field localization in the near-field vicinity of a chain.
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