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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Semenov S. V., Gokhfeld D. M.
Заглавие : New evidence of interaction between grain and boundaries subsystems in granular high-temperature superconductors
Место публикации : J. Supercond. Novel Magn. - 2021. - Vol. 34. Is. 4. - P.1067-1075. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-021-05812-2
Примечания : Cited References: 62
Аннотация: Granular high-temperature superconductors (HTSs) exhibit magnetotransport properties, including the clockwise magnetoresistance hysteresis. The hysteresis is explained by the concept of an effective field in the subsystem of grain boundaries, where the observed dissipation occurs. The effective field in the intergrain medium is determined by a superposition of the external field H and the field induced by the magnetic response of HTS grains. The magnetic flux compression in the intergrain medium provides an increase of the effective field. The magnetoresistance hysteresis of polycrystalline YBa2Cu3O7-δ has a bright feature: In a fairly wide external field range, the hysteresis width ΔH(H) is found to be almost linear, ΔH ≈ H. This behavior is considered to be universal over the entire temperature range corresponding to the superconducting state (the investigations have been carried out at temperatures of 77 K and 4.2 K). The analysis of the magnetoresistive and magnetic properties has shown that the upper boundary of the field range of the ΔH ≈ H regime is consistent with the field of complete penetration into HTS grains. This is indicative of the strong interrelation between the magnetotransport and magnetic properties of granular HTSs.
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2.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Bolyachkin A. S., Dengina E., Komogortsev S. V.
Заглавие : Magnetic Correlations and Coercivity in Nanocrystalline Alloys With Grain-Size Distribution.
Коллективы : Annual conference on мagnetism and мagnetic мaterials
Место публикации : 65th Annual conference on мagnetism and мagnetic мaterials (MMM-2020): abstract book. - 2020. - Ст.R5-01. - P.564
Примечания : Cited References: 1
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Belyaev B. A., Boev N. M., Gorchakovskii A. A., Izotov A. V., Solovev P. N.
Заглавие : Structure constant and grain size determination by ferromagnetic resonance in thin magnetic films
Место публикации : Russ. Phys. J. - 2021. - Vol. 64, Is. 1. - P.1-8. - ISSN 10648887 (ISSN), DOI 10.1007/s11182-021-02293-7
Примечания : Cited References: 28. - This work was financially supported by Project N 20-42-24290 from the Russian Foundation for Basic Research, administrative support from Krasnoyarsk Krai, Scientific Foundation of Krasnoyarsk Krai, and AO "Radiosvyaz"
Аннотация: The paper shows that the structure constant and the average crystal grain size of anisotropic nanocrystalline magnetic film can be determined by analyzing the shape of the microwave absorption peak in sweeping the external magnetic field along the hard magnetization axis. In the theory of magnetization ripple, the surface energy density of the local magnetic anisotropy is connected with the structure constant, which can be used to determine the quality of nanocrystalline films. The effectiveness of the structure constant measurements is demonstrated on a 300-nm-thick nanocrystalline Co–P film. Spectral data on the microwave absorption are collected in the ~1 mm2 region of the film using a scanning ferromagnetic resonance spectrometer. The structure constant obtained from the spectral analysis allows detecting the average grain size of the magnetic film, which is in good agreement with transmission electron microscopy observations.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Izotov A. V., Belyaev B. A., Solovev P. N., Boev N. M.
Заглавие : Grain-size dependence of magnetic microstructure and high-frequency susceptibility of nanocrystalline thin films: A micromagnetic simulation study
Место публикации : J. Magn. Magn. Mater. - 2021. - Vol. 529. - Ст.167856. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2021.167856
Примечания : Cited References: 73. - The reported study was funded by RFBR, the Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund and JSC «NPP «Radiosviaz», project number 20-42-242901
Аннотация: The size of crystallites is one of the most important factors that determine the key characteristics of nanocrystalline thin magnetic films that make them very promising media for various applications. In this paper, using micromagnetic simulation, we study in detail the influence of the grain size on the magnetic microstructure of the films and its relation with high-frequency dynamics of magnetization. When the grain size exceeds some critical value Dcr, a sharp broadening and shift of the ferromagnetic resonance line are observed at certain frequencies of the alternating magnetic field. Using a two-magnon scattering model, it is shown that these effects are caused by the scattering of spin waves on the inhomogeneous stochastic magnetic structure—magnetization ripple. An expression for the determination of the critical size Dcr is obtained. The micromagnetic simulation results agree with the main conclusions of the static and dynamic theories of magnetization ripple and also confirmed by experimental data reported by other authors.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Semenov S. V., Balaev D. A.
Заглавие : Model of the behavior of a granular HTS in an external magnetic field: temperature evolution of the magnetoresistance hysteresis
Место публикации : Phys. Solid State. - 2020. - Vol. 62, Is. 7. - P.1136-1144. - ISSN 10637834 (ISSN), DOI 10.1134/S1063783420070239
Примечания : Cited References: 61. - The authors are grateful to D.M. Gokhfeld for discussion of the results. The measurements of the transport properties were performed in part on a PPMS-6000 facility at the Krasnoyarsk Territorial Center of Collective Use, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences
Аннотация: A model for describing the magnetoresistance behavior in a granular high-temperature superconductor (HTS) that has been developed in the last decade explains a fairly extraordinary form of the hysteretic R(H) dependences at T = const and their hysteretic features, including the local maximum, the negative magnetoresistance region, and the local minimum. In the framework of this model, the effective field Beff in the intergrain medium has been considered, which represents a superposition of the external field and the field induced by the magnetic moments of HTS grains. This field can be written in the form Beff(H) = H + 4παM(H), where M(H) is the experimental field dependence of the magnetization and α is the parameter of crowding of the magnetic induction lines in the intergrain medium. Therefore, the magnetoresistance is a function of not simply an external field, but also the “internal” effective field R(H) = f(Beff(H)). The magnetoresistance of the granular YBa2Cu3O7 – δ HTS has been investigated in a wide temperature range. The experimental hysteretic R(H) dependences obtained in the high -temperature range (77–90 K) are well explained using the developed model and the parameter α is 20–25. However, at a temperature of 4.2 K, no local extrema are observed, although the expression for Beff(H) predicts them and the parameter α somewhat increases (~30–35) at this temperature. An additional factor that must be taken into account in this model can be the redistribution of the microscopic current trajectories, which also affects the dissipation in the intergrain medium. At low temperatures under the strong magnetic flux compression (α ~ 30–35), the microscopic trajectories of the current Im can change and tunneling through the neighboring grain is preferred, but the angle between Im and Beff will be noticeably smaller than 90°, although the external (and effective) field direction is perpendicular to the macroscopic current direction.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Koblischka, Michael R., Naik, Sugali Pavan Kumar, Koblischka-Veneva, Anjela, Murakami, Masato, Gokhfeld D. M., Reddy, Eddula Sudhakar, Schmitz, Georg J.
Заглавие : Superconducting YBCO Foams as Trapped Field Magnets
Коллективы : ANR [ANR-17-CE05-0030]; DFG [DFG-ANR Ko2323-10]; SIT start-up grant
Место публикации : Materials. - 2019. - Vol. 12, Is. 6. - Ст.853. - ISSN 1996-1944, DOI 10.3390/ma12060853
Примечания : Cited References: 62. - This work is part of the SUPERFOAM international project funded by ANR and DFG under the references ANR-17-CE05-0030 and DFG-ANR Ko2323-10, respectively. Further funding by a SIT start-up grant is also gratefully acknowledged.
Предметные рубрики: CRITICAL CURRENT-DENSITY
TRANSPORT-PROPERTIES
SINGLE-GRAIN
BULK
Ключевые слова (''Своб.индексиров.''): high-tc superconductors--ybco--foam--trapped fields--current flow
Аннотация: Superconducting foams of YBa2Cu3Oy (YBCO) are proposed as trapped field magnets or supermagnets. The foams with an open-porous structure are light-weight, mechanically strong and can be prepared in large sample sizes. The trapped field distributions were measured using a scanning Hall probe on various sides of an YBCO foam sample after field-cooling in a magnetic field of 0.5 T produced by a square Nd-Fe-B permanent magnet. The maximum trapped field (TF) measured is about 400 G (77 K) at the bottom of the sample. Several details of the TF distribution, the current flow and possible applicatons of such superconducting foam samples in space applications, e.g., as active elements in flux-pinning docking interfaces (FPDI) or as portable strong magnets to collect debris in space, are outlined.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bykov A. A., Terent'ev K. Yu., Gokhfeld D. M., Savitskaya N. E., Popkov S. I., Petrov M. I.
Заглавие : Superconductivity on interfaces of nonsuperconducting granules La2CuO4 and La1.56Sr0.44CuO4
Место публикации : J. Supercond. Nov. Magn. - 2018. - Vol. 31, Is. 12. - P.3867–3874. - ISSN 15571939 (ISSN), DOI 10.1007/s10948-018-4668-x
Примечания : Cited References: 19. - The authors are grateful to D.A. Balaev for fruitful discussions, and I.V. Nemtsev for electronic microscope measurements in the center for shared use, KSC SB RAS. The work is supported by the Russian Science Foundation (project No. 17-72-10067).
Ключевые слова (''Своб.индексиров.''): magnetic properties--superconductivity--oxide superconductors--grain boundaries--lco--lsco--josephson media
Аннотация: Composite materials fabricated by annealing of nonsuperconducting ceramics La2CuO4 and La1.56Sr0.44CuO4 at 910 °C during various time are investigated. Areas of superconducting La1.85Sr0.15CuO4 phase arises at boundaries of contacting nonsuperconducting granules. The volume fraction of the superconducting phase increases with increasing annealing time. A model describing the magnetic and transport properties of the samples at low magnetic fields is constructed. The magnetotransport characteristics of obtained samples at low magnetic fields (∼ 100 Oe) are defined by weak links network formed by superconducting areas. At high fields, behavior of the system is defined by a magnetization of the disconnected superconducting islands. The average size of the superconducting areas has been estimated from an extended critical state model.
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8.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Bolyachkin A. S., Komogortsev S. V.
Заглавие : Power-law behavior of coercivity in nanocrystalline alloys with grain-size distribution
Коллективы : Российская академия наук, Уральское отделение РАН, Институт физики металлов им. М. Н. Михеева Уральского отделения РАН, Уральский федеральный университет им. первого Президента России Б.Н. Ельцина, Российский фонд фундаментальных исследований, Euro-Asian Symposium "Trends in MAGnetism", "Trends in MAGnetism", Euro-Asian Symposium
Место публикации : Euro-asian symposium "Trends in magnetism" (EASTMAG-2019): Book of abstracts/ чл. конс. ком.: S. G. Ovchinnikov, N. V. Volkov [et al.] ; чл. прогр. ком. D. M. Dzebisashvili [et al.]. - 2019. - Vol. 2. - Ст.J.P3. - P.195-196. - ISBN 978-5-9500855-7-4 (Шифр В33/E12-125657784)
Примечания : Cited References: 4
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bykova L. E., Zharkov S. M., Myagkov V. G., Zhigalov V. S., Patrin G. S.
Заглавие : In situ electron diffraction investigation of solid state synthesis of Co-In2O3 ferromagnetic nanocomposite thin films
Место публикации : JOM. - 2020. - Vol. 72, Is. 6. - P.2139–2145. - ISSN 10474838 (ISSN), DOI 10.1007/s11837-019-03919-5
Примечания : Cited References: 52. - The investigation was conducted under the partial financial support of the Russian Foundation for Basic Research (Grants #18-03-01173 and #19-43-240003).
Аннотация: In situ electron diffraction was used to study structural transformations during the formation of Co-In2O3 ferromagnetic nanocomposite thin films in a thermite reaction of In/Co3O4 bilayer thin films. Heating was performed from room temperature to 600°C at a rate of 4°C/min, while simultaneously electron diffraction patterns were recorded at a speed of 4 frames/min. This made it possible to determine the initiation, 185°C, and finishing, 550°C, temperatures of the solid-state synthesis, as well as the change in the phase composition during the thermite reaction. The synthesized Co-In2O3 film nanocomposite contained ferromagnetic cobalt nanoclusters surrounded by an In2O3 layer, with an average size of 20 nm, and had a magnetization of 400 emu/cm3 and a coercivity of 50 Oe at room temperature. The estimate of the effective interdiffusion coefficient of the reaction suggests that the main mechanism for the formation of the Co-In2O3 nanocomposite is diffusion along the grain boundaries and dislocations.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Чжан А. В., Дрокин, Николай Александрович, Ничкова Н. М., Мороз Ж. М.
Заглавие : Особенности спектральных характеристик электрического импеданса увлажненных зерен пшеницы
Место публикации : Усп. совр. естествознания. - 2022. - № 5. - С. 34-38. - ISSN 1681-7494, DOI 10.17513/use.37821; Adv. curr. nat. sci.
Примечания : Библиогр.: 9
Аннотация: Целью работы является определение особенностей спектральных характеристик электрического импеданса зерен пшеницы. Исследованы электрофизические свойства цельных спрессованных, а также размолотых образцов зёрен пшеницы с различной влажностью в диапазоне частот от 1 Гц до 100 МГц. Исходная партия зерен предварительно высушивалась в нагревательном шкафу при температуре 60 °С и затем насыщалась влагой в паровой бане при той же температуре. Влажность оценивалась по разнице веса между исходным и подвергнутым воздействию образцами (сушке или увлажнению). Исследовались образцы двух типов, отличающихся способом подготовки и структурой. Образцы первого типа состояли из цельных зерен, которые помещались в пресс-форму и подвергались всестороннему сжатию небольшим давлением, что исключало наличие воздушных промежутков между зернами. В образцах второго типа зерна предварительно размалывались в ступе и затем в виде порошка помещались в измерительную ячейку. Измерительная ячейка с образцом при комнатной температуре подключалась к анализаторам спектров Elins 1500J и Agilent E5061B, которые позволяют получать частотные зависимости импеданса и фазы. Согласно полученным данным, область низких частот (до 10 кГц) характеризуется преобладающим влиянием активной составляющей полного сопротивления, в то время как выше этой частоты преобладает реактивная часть. Выявлены процессы накопления электрических зарядов у поверхности металлических электродов, которые экранируют внешнее электрическое поле и приводят к аномальному увеличению диэлектрической проницаемости и тангенса угла потерь в области низких частот. Полученные спектры сопоставлялись со спектрами наиболее подходящих эквивалентных электрических схем, радиотехнические компоненты которых помогают понять основные механизмы прохождения переменного электрического тока через неоднородную структуру зерна.The aim of this work is to determine the features of the spectral characteristics of the electrical impedance of wheat grains. The electrophysical properties of whole pressed and ground samples of wheat grains with different moisture content in the frequency range from 1 Hz to 100 MHz have been studied. The initial batch of grains was preliminarily dried in a heating cabinet at a temperature of 60°C and then saturated with moisture in a steam bath at the same temperature. Moisture was estimated from the difference in weight between the original and exposed samples (drying or wetting). Samples of two types were studied, differing in the method of preparation and structure. Samples of the first type consisted of whole grains, which were placed in a mold and subjected to all-round compression by a small pressure, which excluded the presence of air gaps between the grains. In samples of the second type, the grains were preliminarily ground in a mortar and then placed in the form of a powder into a measuring cell. The measuring cell with the sample at room temperature was connected to the Elins 1500J and Agilent E5061B spectrum analyzers, which make it possible to obtain the frequency dependences of the impedance and phase. According to the data obtained, the low-frequency region (up to 10 kHz) is characterized by the predominant influence of the active component of the impedance, while above this frequency, the reactive part predominates. The processes of accumulation of electric charges near the surface of metal electrodes, which shield the external electric field and lead to an anomalous increase in the permittivity and loss tangent in the low-frequency region are revealed. The obtained spectra were compared with the spectra of the most suitable equivalent electrical circuits, the radio engineering components of which help to understand the main mechanisms of the passage of an alternating electric current through a heterogeneous grain structure.
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