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Иванов, Андрей Анатольевич

Организационные подразделения

Организационная единица

Институт лазерных и плазменных технологий

Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.

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Иванов

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Андрей Анатольевич

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Теперь показываю 1 - 10 из 46

Только метаданные
Magnetic susceptibility of pyrochlores R2Ti2O7: R = Gd, Dy, Tb
(2020) Kuznetsov, A. V.; Churkin, O. A.; Ivanov, A. A.; Popov, V. V.; Alekseev, P. A.; Menushenkov, A. P.; Кузнецов, Алексей Владимирович; Чуркин, Олег Алексеевич; Иванов, Андрей Анатольевич; Попов, Виктор Владимирович; Алексеев, Павел Александрович; Менушенков, Алексей Павлович
© 2019We present the study of magnetic susceptibility of pyrochlores Gd2Ti2O7, Dy2Ti2O7 and Tb2Ti2O7 which belong to frustrated magnets. The temperature dependence of the susceptibility χ(T) of powder samples was measured in the temperature range from 4.2 to 300 K and analyzed in the framework of mean field approximation taking into account both crystal field effects and anisotropy of the exchange interaction. We developed a simple approach allowing us to estimate interaction energies of magnetic ions from χ(T) dependences and data on wave functions of the crystal-field states of the ions using a minimum number of fitting parameters. We revealed a strong anisotropy of the exchange interaction in the paramagnetic state of Gd2Ti2O7 and obtained nearest-neighbor effective bond energies of the magnetic ions in Tb2Ti2O7 and Dy2Ti2O7 which are in good agreement with the temperatures of formation of the spin-ice state in these compounds.
Только метаданные
Rearrangement in the local, electronic and crystal structure of europium titanates under reduction and oxidation
(2020) Khramov, E. V.; Svetogorov, R. D.; Kurilkin, V. V.; Murzin, V. Y.; Popov, V. V.; Menushenkov, A. P.; Molokova, A. Y.; Ivanov, A. A.; Rudakov, S. G.; Boyko, N. V.; Yastrebtsev, A. A.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Иванов, Андрей Анатольевич; Рудаков, Сергей Геннадьевич; Бойко, Надежда Владимировна; Ястребцев, Алексей Алексеевич
© 2020 Elsevier B.V.We studied powder samples of europium titanates Eu1−x 2+Eux 3+TiO3+x/2 prepared by sol-gel and coprecipitation methods with subsequent thermal treatment of precursors at different conditions (reducing or oxidizing atmosphere, temperature, exposure time). We have revealed a radical rearrangement in the local, electronic and crystal structure of europium titanates depending on synthesis conditions. The combination of synchrotron X-ray diffraction (s-XRD), X-ray absorption (XANES and EXAFS), infrared and Raman spectroscopies supplemented by photoluminescence and simultaneous thermal analysis was used in our study. It is shown that the combined XANES and thermogravimetric analysis gives clear evidence of a change in the oxidation state of europium cations from Eu2+ to Eu3+. The comparison of s-XRD, XANES, and EXAFS data allowed us to explain the local structure rearrangement during the phase transition from cubic perovskite Eu2+TiO3 (space group Pm3¯m) to pyrochlore phase Eu2 3+Ti2O7 (space group Fd3¯m) through intermediate layered perovskite Eu2 3+Ti2O7 with monoclinic structure (space group P21) under annealing in oxidizing atmosphere. The Raman spectroscopy study pointed to significant changes in the local structure of the anionic sublattice upon the observed phase transitions. The analysis of luminescence spectra has shown that Eu3+ cations occupy positions with low local site symmetry in all synthesized compounds regardless of the type of the crystal structure.
Только метаданные
Memristive Properties of Oxide-based High-Temperature Superconductors
(2020) Tulina, N. A.; Ivanov, A. A.; Иванов, Андрей Анатольевич
© 2020, Springer Science+Business Media, LLC, part of Springer Nature.The study of memristive properties or effect of resistive switchings in four classes of high-temperature superconductors (HTSC), namely Bi2Sr2CaCu2O8+y (BSCCO), YBa2Cu3O7−y (YBCO), Ba0.6K0.4BiO3−y (BKBO), and Nd2−xCexCuO4−y (NCCO), is presented. The purpose of this study is to reveal functional properties of HTSC which become apparent in the effects under discussion, prospects of usage of HTSC-based memristors in applications, and search for new mechanisms of strongly correlated nature to realize new-generation memristors (Tulina 1). The properties are as follows: undergoing the metal-insulator transition at oxygen doping, transport anisotropy, and existence of charge reservoirs through which doping of conductive copper–oxygen layers is carried out. These are the main functional properties of HTSC which allows their usage in memristors. By the example of study of bipolar effect of resistive switching in HTSC-based heterojunctions, it is shown how one can form memristor structures based on HTSC using their functional properties.
Только метаданные
A XAFS investigation of amorphous-to-crystalline and fluorite-to-pyrochlore phase transitions in Ln2M2O7 (Ln = Gd, Tb, Dy; M = Ti, Zr)
(2020) d'Acapito, F.; Puri, A.; Popov, V. V.; Menushenkov, A. P.; Ivanov, A. A.; Yastrebtsev, A. A.; Gaynanov, B. R.; Попов, Виктор Владимирович; Менушенков, Алексей Павлович; Иванов, Андрей Анатольевич; Ястребцев, Алексей Алексеевич; Гайнанов, Булат Радикович
© 2019 Elsevier LtdAmorphous-to-crystalline and fluorite-to-pyrochlore phase transitions in complex oxides Ln2M2O7 (Ln = Gd, Tb, Dy; M = Ti, Zr) prepared by sol-gel and coprecipitation methods were studied using x-ray absorption spectroscopy in combination with x-ray diffraction and Raman spectroscopy. The Ln titanates crystallize directly from the amorphous state to the pyrochlore structure, while the Ln zirconates form the intermediate fluorite phase first. We have found that both XANES and EXAFS data reflect the considerable difference between the crystallization processes of Ln titanates and zirconates. In particular the evolution of the K–Ti pre-edge features is a good indicator of the phase transition from amorphous to crystalline state. The splitting of the first Ln-O shell in the FT modulus of L3-Ln edge EXAFS spectra in Ln titanates can be regarded as a fingerprint of the ordered pyrochlore structure formation which is accompanied also by specific changes in the main features of the XANES spectra. For the Ln zirconates these features are less pronounced.
Только метаданные
Relationship between the Surface Morphology of Thin YBa2Cu3O7 –x Films Obtained by Pulsed Laser Deposition and the Endset Temperature of Superconducting Transition
(2020) Il'in, A. I.; Trofimov, O. V.; Ivanov, A. A.; Иванов, Андрей Анатольевич
© 2020, Pleiades Publishing, Ltd.Abstract: A correlation was found between the endset temperature of the superconducting transition T(R = 0) of YBa2Cu3O7 – x films 100–200 nm thick, obtained by pulsed laser deposition on SrTiO3(100) substrates with a temperature of ~740°C, and the regimes of high-speed filtering of the erosion plume formed upon ablation of the material the target. Under deposition conditions, we changed the width of the filtering window, the repetition rate of the atomized material passing through the filter onto the substrate, and the radiation energy density of the KrF excimer laser on the target surface. At deposition rates of less than 0.1 nm s–1, the values of T(R = 0) did not exceed 77 K, and pyramids were formed on the surface of the films up to 80 nm in height along the c axis in the form of spirals with rectangular bases and steps of 1–2 nm along the lateral faces. With an increase in the deposition rate from 0.1 to 0.6 nm s–1, T(R = 0) increased to 86 K. These regimes corresponded to a wavy pyramid surface up to 40 nm in height with rounded bases up to 1500 nm in diameter and irregular steps 1–4 nm on the side slopes. Faceted crystals with a width from 20–30 to 500 nm in the base grew along the boundaries between the pyramids during the deposition. This morphology of the growth surface was explained by the high flow rate of the sputtered material, which is determined by the frequency filtering of the erosion plume and the energy density in the pulse upon predominantly surface diffusion.
Только метаданные
Magnetization of Crystalline and Amorphous Phases of R(2)Ti(2)O(7)and R2Zr2O7(R = Gd, Dy, Tb)
(2020) Kuznetsov, A. V.; Churkin, O. A.; Popov, V. V.; Shchetinin, I. V.; Ivanov, A. A.; Yaroslavtsev, A. A.; Gaynanov, B. R.; Yastrebtsev, A. A.; Chernysheva, O. V.; Alekseev, P. A.; Menushenkov, A. P.; Кузнецов, Алексей Владимирович; Чуркин, Олег Алексеевич; Попов, Виктор Владимирович; Иванов, Андрей Анатольевич; Гайнанов, Булат Радикович; Ястребцев, Алексей Алексеевич; Чернышева, Ольга Викторовна; Алексеев, Павел Александрович; Менушенков, Алексей Павлович
We present the study of frustrated magnets R2M2O7, where R = Gd, Dy, Tb and M = Ti, Zr. Magnetic susceptibility chi and low-temperature magnetization of perfectly ordered pyrochlores R2Ti2O7, partially disordered fluorites R2Zr2O7, and their completely disordered amorphous phases were measured and analyzed. We have found that structural disorder weakens the exchange interaction of the rare-earth ions. Magnetic moments of dysprosium and terbium, obtained from nearly saturated magnetization, are slightly affected by the disorder while the gadolinium moment is completely independent of it. The local structure of the compounds, including oxygen environment of the rare-earth ions, is discussed in terms of the influence of the crystal electric field on the magnetic properties of R2M2O7.
Только метаданные
The Study of Switching Dynamics in Planar Structures Based on Epitaxial Films of YBa2Cu3O7-δ High-Temperature Superconductor
(2020) Tulina, N. A.; Borisenko, I. Y.; Shmytko, I. M.; Rossolenko, A. N.; Ivanov, A. A.; Иванов, Андрей Анатольевич
© 2020, Springer Science+Business Media, LLC, part of Springer Nature.We have been studying the dynamic effects of bipolar resistive switching (BERS) in memristive planar heterostructures based on c-oriented epitaxial films of the high-temperature superconductor YBa2Cu3O7 (YBCO). We have been observing the suppression of the memristive properties of the structures under sinusoidal and pulse loads and the nucleation and the evolution of the regions of current density and electric field in the structures under study. We found that the limiting frequencies of a sinusoidal type load for observing the switching effect are frequencies of about 104 Hz. It has been shown that the percolation channel is formed by the appearance of electric field domains in which the electric field threshold is reached. The switchings are controlled by two processes, with time t < ms and a longer time of the order of a few seconds. Possible physical models of the observed phenomena are being discussed.
Только метаданные
Lateral vortex motion in highly layered electron-doped superconductor Nd2−xCexCuO4
(2020) Petukhova, O. E.; Popov, M. R.; Klepikova, A. S.; Shelushinina, N. G.; Ivanov, A. A.; Иванов, Андрей Анатольевич
© 2020 Elsevier B.V.The carrier transport and the motion of a vortex system in the electron-doped high-temperature superconductors Nd2−xCexCuO4 in underdoped and optimally doped (x = 0.135, 0.145, 0.15) regions, in the area of the evolution from antiferromagnetic to superconducting order were investigated. To study the anisotropy of the transport properties of highly layered NdCeCuO system we have synthesized Nd2−xCexCuO4+δ/SrTiO3 epitaxial films of three types with different orientations of the c-axis and conductive CuO2 layers relative to the substrate. Such a set of samples allowed us to study the processes of both standard (in the CuO2 layers) and lateral (across the CuO2 layers) carrier transfer in the normal and the mixed states of a superconductor. In a flux-flow regime, in magnetic field B, the dynamics of Abrikosov (B ∥ c-axis) and Josephson (B ∥ ab-plane) vortices are thoroughly investigated and analyzed which is perspective for scientific purposes and for practical applications in measurement technology.
Только метаданные
Properties of percolation channels in planar memristive structures based on epitaxial films of a YBa2Cu3O7-delta high temperature superconductor
(2019) Tulina, N. A.; Rossolenko, A. N.; Shmytko, I. M.; Sirotkin, V. V.; Ivanov, A. A.; Иванов, Андрей Анатольевич
The transport properties of the percolation channels of memristive structures based on YBa2Cu3O7-delta epitaxial films were studied. Molecular electronics and Andreev reflection spectroscopy were utilised, and the influence of the superconductive transition of electrodes on resistive switching effects in these structures was examined. Based on the analysis of the conductivity mechanisms in the obtained heterostructures, it is assumed that percolation channels form through a chain of domains disordered by oxygen about 10 nm in diameter, with a maximum T-c of 60 K. Zero-bias anomalies of the dynamic resistance of the studied structures display temperature dependence of the critical current of typical superconductor-normal-superconductor weak links within the framework of Kulik-Omel' yanchuk theory in the dirty limit. A simulation was used to determine the physical parameters of the studied heterostructures.
Только метаданные
Fabrication and Electrical Characteristics of Asymmetric Rings Made of HTS YBCO Films Obtained by Pulsed Laser Deposition
(2019) Il'in, A. I.; Trofimov, O. V.; Firsov, A. A.; Nikulov, A. V.; Ivanov, A. A.; Иванов, Андрей Анатольевич
© 2019, Pleiades Publishing, Ltd. Abstract: HTS YBCO films 200–400 nm thick are fabricated by pulsed laser deposition, both without filtration and in the regimes of velocity filtration of particles of an ablation plume. Using AFM and SEM, it is established that the size of large particles in the plane of films during deposition without filtration ranges from 60 to 1000 nm. After filtration, the maximum particle size in the film plane is less than 500 nm. Two types of irregularities are found on the surface after deposition: irregularities obtained from rounded particles and irregularities from faceted crystals. Using the methods of electron lithography and etching with argon ions through a mask, micro- and nanostructures are fabricated from HTS films. A correlation has been found between the characteristic dimensions of the irregularities on the surface of the films and the available lateral resolution of the microstructures obtained. For structures from HTS films that are asymmetric rings with a characteristic line width of 800 nm, the temperature dependences of the superconducting transition are determined and their asymmetric I–V characteristics are observed.