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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krasikov A. A., Balaev D. A., Balaev A. D., Stolyar S. V., Yaroslavtsev R. N., Iskhakov R. S.
Заглавие : Separating the contributions of the magnetic subsystems in antiferromagnetic ferrihydrite nanoparticles by analyzing the magnetization in fields of up to 250 kOe
Колич.характеристики :8 с
Место публикации : J. Magn. Magn. Mater. - 2024. - Vol. 592. - Ст.171781. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2024.171781. - ISSN 18734766 (eISSN)
Примечания : Cited References: 84. - This study was supported by his work was supported by the Russian Science Foundation, project no. 22–72-00134Authors thank to D.A. Velikanov, S.V. Komogortsev for fruitful discussions
Аннотация: Contributions of different magnetic subsystems formed in the systems of synthetic ferrihydrite nanoparticles (characterized previously) with an average size of ˂d˃ ≈ 2.7 nm coated with polysaccharide arabinogalactan in different degrees have been separated by measuring the dependences of their magnetization M on magnetic field H of up to 250 kOe on vibrating sample and pulsed magnetometers. The use of a wide measuring magnetic field range has been dictated by the ambiguity in identifying a linear M(H) portion for such antiferromagnetic nanoparticle systems within the conventional field range of 60–90 kOe. The thorough analysis of the magnetization curves in the temperature range of 100–250 K has allowed the verification of the contributions of (i) uncompensated magnetic moments µun in the superparamagnetic subsystem, (ii) the subsystem of surface spins with the paramagnetic behavior, and (iii) the antiferromagnetic susceptibility of the antiferromagnetically ordered ferrihydrite particle core. As a result, a model of the magnetic state of ferrihydrite nanoparticles has been proposed and the numbers of spins corresponding to magnetic subsystems (i)–(iii) have been estimated. An average magnetic moment μun of ∼ 145 μB (μB is the Bohr magneton) per particle corresponds approximately to 30 decompensated spins of iron atoms in a particle (about 3 % of all iron atoms), which, according to the Néel’s hypothesis μun ∼ ˂d˃3/2, are localized both on the surface and in the bulk of an antiferromagnetically ordered particle. The fraction of free (paramagnetic) spins is minimal in the sample without arabinogalactan coating of the nanoparticle surface (7 %) and is attained 20 % of all iron atoms in the sample with the highest degree of spatial separation of particles. According to this estimation, paramagnetic spins are located mainly on the edges and protruding areas of particles. Most magnetic moments of iron atoms are ordered antiferromagnetically and the corresponding magnetic susceptibility of this subsystem behaves as in an antiferromagnet with the randomly distributed crystallographic axes, i.e., increases with temperature.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Krasikov A. A., Balaev D. A.
Заглавие : Analysis of magnetization processes in antiferromagnetic nanoparticles in strong pulse fields (Brief review)
Коллективы : Eurasian Symposium “Trends in Magnetism”
Место публикации : J. Exp. Theor. Phys. - 2023. - Vol. 136, Is. 1. - P.97-105. - ISSN 10637761 (ISSN), DOI 10.1134/S1063776123010132. - ISSN 10906509 (eISSN)
Примечания : Cited References: 43. - The authors are grateful to V.L. Kirillov for synthesis of a set of NiO samples, O.N. Mart’yanov for cooperation and discussion of results for NiO nanoparticles, V.P. Ladygina for synthesis of nanoferrihydrite, S.V. Stolyar and R.S. Iskhakov for cooperation and discussion of results for ferrihydrite, and A.D. Balaev, K.A. Shaikhutdinov, and S.I. Popkov for the decisive contribution to the realization of pulse field setup
Аннотация: We present a brief review of investigations and analysis of magnetization curves M(H) for NiO and ferrihydrite antiferromagnetic nanoparticles in external fields up to 250 kOe. For correct interpretation of magnetic properties of systems of antiferromagnetic nanoparticles, it is important to take into account the segment of M(H) dependences, which corresponds to high fields (exceeding 100 kOe). We analyze the regularities in the formation of additional magnetic subsystems in antiferromagnetically ordered nanoparticles due to the influence of size effects. These additional subsystems (the ferromagnetic subsystem associated with uncompensated magnetic moment and the subsystem of surface free spins) are estimated quantitatively. It is shown that antiferromagnetic nanoparticles with a size of 5 nm acquire the properties of “nanomagnets,” which are not inferior to those for iron-oxide ferromagnetic nanoparticles of the same size.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V.
Заглавие : Antiferromagnetic excitonic insulator
Колич.характеристики :12 с
Место публикации : J. Exp. Theor. Phys. - 2023. - Vol. 137, Is. 4: Special Issue dedicated to the 95th Anniversary of L. A. Prozorova. - P.474-485. - ISSN 1063-7761 (ISSN), DOI 10.1134/S1063776123100138. - ISSN 10906509 (eISSN)
Примечания : Cited References: 39
Аннотация: The effective the two-band Hamiltonian is obtained for iridium oxides with account for strong electron correlations (SEC) and the spin–orbit interaction. The intraatomic electron correlations in iridium ions induce the formation of Hubbard fermions (HF) filling the states in the valence band. Another consequence of SEC is associated with the emergence of the antiferromagnetic (AFM) exchange interaction between HF in accordance with the Anderson mechanism. As a result, a long-range antiferromagnetic order is established in the system, and in the conditions of band overlapping, the intersite Coulomb interaction induces a phase transition to the excitonic insulator (EI) state with a long-range AFM order. The system of integral self-consistent equations, the solution to which determines the excitonic order parameter components Δi, j(k), sublattice magnetization M, Hubbard fermion concentration nd, and chemical potential μ, is obtained using the atomic representation, the method of two-time temperature Green’s functions, and the Zwanzig–Mori projection technique. The symmetry classification of AFM EI phases is performed, and it is shown that in the nearest neighbor approximation, state Δi, j(k) with the s-type symmetry corresponds to the ground state, while the phases with the d- and p-symmetries are metastable.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Zharkov S. M., Zeer G. M., Gudim I. A.
Заглавие : Antiferromagnetic resonance and magnetic anisotropy in PrxY1−xFe3(BO3)4 crystals in the region of the magnetic structure transformation “easy axis – easy plane”
Место публикации : J. Alloys Compd. - 2022. - Vol. 909. - Ст.164821. - ISSN 09258388 (ISSN), DOI 10.1016/j.jallcom.2022.164821
Примечания : Cited References: 37. - The authors acknowledge the assistance of R. Mironov in some resonance measurements. The SEM and EDS investigations were conducted in the SFU Joint Scientific Center supported by the State assignment (#FSRZ-2020–0011) of the Ministry of Science and Higher Education of the Russian Federation
Аннотация: The spin dynamics, magnetic structures and magnetic anisotropy of single crystals PrxY1−xFe3(BO3)4 have been studied using antiferromagnetic resonance (AFMR) in a wide range of frequencies, magnetic fields, and temperatures. The frequency-field dependences of AFMR for the crystals with x = 0.25 and 0.45 are characteristic of antiferromagnets with the easy plane (EP) anisotropy. The crystals with x = 0.75 and 1.0 exhibit frequency-field dependences that are typical for antiferromagnets with the easy axis (EA) anisotropy. In these crystals, a significant decrease in the effective anisotropy fields of praseodymium upon the transition to the spin-flop state has been found. It is shown that this is the main reason for the large lability intervals, within which the regions of coexistence of the collinear and spin-flop states overlap. In the crystal with x = 0.67, the magnetic field applied along the trigonal axis of the crystal leads to the spin reorientation transition from the EA to the EP state. A magnetic phase diagram of the states on the plane "magnetic field - temperature" is built. In this crystal, the effective anisotropy field of praseodymium also decreases upon the transition to the field-induced EP state. Diamagnetic dilution of the praseodymium subsystem leads to the contribution of this subsystem to the total anisotropy field depending almost linearly on the praseodymium concentration.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kurilova A. V., Sokolov A. Е., Sukhachev A. L., Ivanova O. S., Bogdanov K. V., Baranov M. A., Dubavik A. Y.
Заглавие : Synthesizing antiferromagnetic α-Fe2O3–rGO discs: Their magnetic and magneto-optical properties
Место публикации : Bull. Russ. Acad. Sci. Phys. - 2022. - Vol. 86, Is. 5. - P.610-613. - ISSN 10628738 (ISSN), DOI 10.3103/S106287382205015X
Примечания : Cited References: 26
Аннотация: A comprehensive study is performed of the properties of hybrid structures of iron oxide and reduced graphene oxide α-Fe2O3/rGO synthesized via “wet mixing.” It is shown that hematite nanoparticles with a comparatively uniform distribution can be encapsulated in graphene layers, and the way of preparing precursors is of critical importance in shaping the magneto-optical properties of α-Fe2O3/rGO hybrid structures.
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6.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Pankrats A. I., Zharkov S. M., Zeer G. M., Gudim I. A.
Заглавие : Magnetic anisotropy and “easy axis-easy plane” transformation in PrxY1–xFe3(BO3)4 single crystals studied by antiferromagnetic resonance
Коллективы : Российская академия наук, Физико-технический институт им. Е.К. Завойского ФИЦ Казанского научного центра РАН, Казанский (Приволжский) федеральный университет, Euro-Asian Symposium "Trends in MAGnetism", "Trends in MAGnetism", Euro-Asian Symposium
Место публикации : VIII Euro-Asian symposium "Trends in magnetism" (EASTMAG-2022): Book of abstracts/ program com. S. G. Ovchinnikov [et al.]. - 2022. - Vol. 1, Sect.: Spin dynamics and magnetic resonances. - Ст.B.P14. - P.284-286. - ISBN 978-5-94469-051-7
Примечания : Cited References: 4
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popova M. N., Chukalina E. P., Erofeev D. A., Gudim I. A., Golosovsky I. V., Gukasov A., Mukhin A. A., Malkin B. Z.
Заглавие : High-resolution optical spectroscopy, magnetic properties, and single-crystal neutron diffraction of multiferroic HoFe3(BO3)4: Magnetic structure
Место публикации : Phys. Rev. B. - 2021. - Vol. 103, Is. 9. - Ст.094411. - ISSN 24699950 (ISSN), DOI 10.1103/PhysRevB.103.094411
Примечания : Cited References: 65. - Financial support of the Russian Science Foundation under Grant No. 19-12-00413 is acknowledged. I.V.G. acknowledges financial support of the neutron scattering studies from the Russian Foundation for Basic Research under Grant No. 20-02-00109. The analysis of the measured neutron diffraction data was performed by A.A.M. with support of the Russian Science Foundation under Grant No. 16-12-10531
Аннотация: The magnetic structure is usually determined by the neutron diffraction measurements. However, in the case of complex multisublattice magnetics, this method fails to give an unambiguous result. Here, on the example of multiferroic HoFe3(BO3)4, we show that in the case of rare-earth (RE) compounds the right magnetic structure can be determined by additionally using optical spectroscopy and a theoretical analysis based on spectroscopic data. HoFe3(BO3)4 demonstrates a series of phase transitions and interesting magnetic and magnetoelectric properties. The available information on the magnetic structure of the compound, necessary for understanding and utilizing these properties, is contradictory. To resolve the existing ambiguities, we apply a combined approach. The high-resolution spectroscopy data deliver a set of the Ho3+ crystal-field (CF) levels in the paramagnetic and both easy-plane and easy-axis magnetic phases. These data are used to determine CF and Ho3+-Fe3+ exchange parameters and, then, to calculate the temperature dependencies of the magnetic susceptibility tensor of HoFe3(BO3)4. Based on these calculations, we suggest an easy-plane antiferromagnetic structure with a collinear arrangement of the Fe spins along the a axis and induced noncolinear moments of magnetically nonequivalent Ho ions. The suggested structure is further confirmed by single-crystal elastic neutron scattering experiments. We argue that specific features of the magnetic properties of RE iron borates isostructural to HoFe3(BO3)4 are governed by the energy patterns and the symmetry properties of the wave functions of the lower CF levels of the RE ground multiplet in the crystal field of the C2 symmetry.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kulbakov A. A., Sarkar R., Janson O., Dengre S., Weinhold T., Moshkina E. M., Portnichenko P. Y., Luetkens H., Yokaichiya F., Sukhanov A. S., Eremina R. M., Schlender P., Schneidewind A., Klauss H. -H., Inosov D. S.
Заглавие : Destruction of long-range magnetic order in an external magnetic field and the associated spin dynamics in Cu2GaBO5 and Cu2AlBO5 ludwigites
Место публикации : Phys. Rev. B. - 2021. - Vol. 103, Is. 2. - Ст.024447. - ISSN 24699950 (ISSN), DOI 10.1103/PhysRevB.103.024447
Примечания : Cited References: 46. - We thank U. Nitzsche for technical assistance. This project was funded in part by the German Research Foundation (DFG) under Grant IN 209/9-1, via Project C03 of the Collaborative Research Center SFB 1143 (project-id 247310070) at the TU Dresden, and the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter—ct.qmat (EXC 2147, project-id 390858490). O.J. was supported by the Leibniz Association through the Leibniz Competition
Аннотация: The quantum spin systems Cu2M′BO5 (M′=Al,Ga) with the ludwigite crystal structure consist of a structurally ordered Cu2+ sublattice in the form of three-leg ladders, interpenetrated by a structurally disordered sublattice with a statistically random site occupation by magnetic Cu2+ and nonmagnetic Ga3+ or Al3+ ions. A microscopic analysis based on density-functional-theory calculations for Cu2GaBO5 reveals a frustrated quasi-two-dimensional spin model featuring five inequivalent antiferromagnetic exchanges. A broad low-temperature 11B nuclear magnetic resonance points to a considerable spin disorder in the system. In zero magnetic field, antiferromagnetic order sets in below TN≈4.1 K and ∼2.4 K for the Ga and Al compounds, respectively. From neutron diffraction, we find that the magnetic propagation vector in Cu2GaBO5 is commensurate and lies on the Brillouin-zone boundary in the (H0L) plane, qm=(0.45,0,−0.7), corresponding to a complex noncollinear long-range ordered structure with a large magnetic unit cell. Muon spin relaxation is monotonic, consisting of a fast static component typical for complex noncollinear spin systems and a slow dynamic component originating from the relaxation on low-energy spin fluctuations. Gapless spin dynamics in the form of a diffuse quasielastic peak is also evidenced by inelastic neutron scattering. Most remarkably, application of a magnetic field above 1 T destroys the static long-range order, which is manifested in the gradual broadening of the magnetic Bragg peaks. We argue that such a crossover from a magnetically long-range ordered state to a spin-glass regime may result from orphan spins on the structurally disordered magnetic sublattice, which are polarized in magnetic field and thus act as a tuning knob for field-controlled magnetic disorder.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Krasikov A. A., Popkov S. I., Semenov S. V., Volochaev M. N., Velikanov D. A., Kirillov V. L., Martyanov O. N.
Заглавие : Uncompensated magnetic moment and surface and size effects in few-nanometer antiferromagnetic NiO particles
Место публикации : J. Magn. Magn. Mater. - 2021. - Vol. 539. - Ст.168343. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2021.168343
Примечания : Cited References: 98. - The TEM study was carried out on the equipment of the Krasnoyarsk Territorial Center for Collective Use, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences
Аннотация: The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60–90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments μun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the μun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of d ~ 4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is ~130 μB (μB is the Bohr magneton) per particle, which corresponds to 60–70 decompensated spins of nickel atoms localized, according to the Néel hypothesis (μun ~ d3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Martynov S. N.
Заглавие : Ground State of a Two-Sublattice Anisotropic Ferromagnet in a Magnetic Field
Коллективы : Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR); Krasnoyarsk Territorial Foundation [20-42-240006]
Место публикации : Phys. Solid State. - 2021. - Vol. 63, Is. 8. - P.1253-1261. - ISSN 1063-7834, DOI 10.1134/S1063783421080199. - ISSN 1090-6460(eISSN)
Примечания : Cited References: 38. - This study was supported by the Russian Foundation for Basic Research and the Krasnoyarsk Territorial Foundation for Support of Scientific and R&D Activities, project no. 20-42-240006 "Synthesis and Study of Pb2+-and Bi3+Containing Oxide Single Crystals with Partial Substitution in One of the Subsystems: Magnetic Structures and Magnetodielectric Effect"
Предметные рубрики: ANTIFERROMAGNETIC-RESONANCE
SUPEREXCHANGE INTERACTION
WEAK FERROMAGNETISM
Аннотация: The ground state of a classical two-sublattice ferromagnet with the noncollinear single-ion anisotropy axes of the sublattices and the antisymmetric and anisotropic symmetric exchanges between them has been investigated in a magnetic field applied along the hard magnetization directions in the crystal. The threshold relations for the parameters of the anisotropic interactions have been obtained, which determine the choice of the ground state among the three possible magnetic phases. Depending on the ground state type and the field direction, the transition between the phases is a first- or second-order phase transition. The antisymmetric exchange value above which the reorientation between the noncollinear phases ends with a second-order transition depends on the angle between the local easy axes and the single-ion anisotropy value. Field dependences of the magnetization and susceptibility for different ground states have been calculated. A comparison with the results of the magnetic measurements in the highly anisotropic PbMnBO4 ferromagnet has been made.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Orlov Yu. S., Nikolaev S. V., Dudnikov V. A., Ovchinnikov S. G.
Заглавие : Forming a dielectric exciton phase in strongly correlated systems with spin crossover
Место публикации : Phys. Rev. B. - 2021. - Vol. 104, Is. 19. - Ст.195103. - ISSN 24699950 (ISSN), DOI 10.1103/PhysRevB.104.195103
Примечания : Cited References: 46. - The authors thank the Russian Scientific Foundation for financial support under Grant No. 18-12-00022
Аннотация: Formation of the magnetic structure and exciton condensate of local magnetic excitons in strongly correlated systems near the spin crossover under high pressure is considered in terms of the effective Hamiltonian obtained from a two-band Hubbard model in the regime of strong electron correlations. The coexistence of the long-range antiferromagnetic order and exciton condensate and the occurrence of the magnetization caused by the condensation of local magnetic excitons are demonstrated. Transformation of the electronic structure of the antiferromagnetic high-spin insulator into the paramagnetic two-band correlated metal via a narrow-gap antiferromagnetic excitonic semiconductor is obtained.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popkov S. I., Krasikov A. A., Semenov S. V., Dubrovskii A. A., Yakushkin S. S., Kirillov V. L., Mart'yanov O. N., Balaev D. A.
Заглавие : General regularities and differences in the behavior of the dynamic magnetization switching of ferrimagnetic (CoFe2O4) and antiferromagnetic (NiO) nanoparticles
Коллективы : Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR); Government of the Krasnoyarsk region; Krasnoyarsk Regional Foundation for Science [18-42-240012]
Место публикации : Phys. Solid State. - 2020. - Vol. 62, Is. 9. - P.1518-1524. - ISSN 1063-7834, DOI 10.1134/S1063783420090255. - ISSN 1090-6460(eISSN)
Примечания : Cited References: 46. - This work was supported by the Russian Foundation for Basic Research, the Government of the Krasnoyarsk region, and the Krasnoyarsk Regional Foundation for Science, project no. 18-42-240012: "Magnetization switching of magnetic nanoparticles in strong pulsed magnetic fields is a new approach to studying the dynamic effects related to the processes of magnetization of magnetic nanoparticles"
Предметные рубрики: PARTICLE-SIZE
EXCHANGE-BIAS
TEMPERATURE
STATE
COERCIVITY
Аннотация: In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe2O4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force HC at the dynamic magnetization switching is markedly higher than HC at quasi-static conditions. HC increases as the pulse duration τP decreases and the maximum applied field H0 increases. The dependence of HC on field variation rate dH/dt = H0/2τP is a unambiguous function for CoFe2O4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH/dt, and the value of applied field H0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Krasikov A. A., Popkov S. I., Dubrovskiy A. A., Semenov S. V., Velikanov D. A., Kirillov V. L., Martyanov O. N.
Заглавие : Features of the quasi-static and dynamic magnetization switching in NiO nanoparticles: Manifestation of the interaction between magnetic subsystems in antiferromagnetic nanoparticles
Место публикации : J. Magn. Magn. Mater. - 2020. - Vol. 515. - Ст.167307. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2020.167307
Примечания : Cited References: 89. - We are grateful to A.D. Balaev for fruitful discussions. The TEM study and magnetic measurements using a PPMS-6000 facility were carried out on the equipment of the Krasnoyarsk Territorial Center for Collective Use, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences
Аннотация: We report on the investigations of a system of 8-nm NiO particles representing antiferromagnetic (AFM) materials, which are weak magnetic in the form of submicron particles, but can be considered to be magnetoactive in the form of nanoparticles due to the formation of the uncompensated magnetic moment in them. The regularities of the behavior of magnetization switching in AFM nanoparticles are established by studying the magnetic hysteresis loops under standard quasi-static conditions and in a quasi-sinusoidal pulsed field of up to 130 kOe with pulse lengths of 4–16 ms. The magnetic hysteresis loops are characterized by the strong fields of the irreversible magnetization behavior, which is especially pronounced upon pulsed field-induced magnetization switching. Under the pulsed field-induced magnetization switching conditions, which are analogous to the dynamic magnetic hysteresis, the coercivity increases with an increase in the maximum applied field H0 and a decrease in the pulse length. This behavior is explained by considering the flipping of magnetic moments of particles in an external ac magnetic field; however, in contrast to the case of single-domain ferro- and ferrimagnetic particles, the external field variation rate dH/dt is not a universal parameter uniquely determining the coercivity. At the dynamic magnetization switching in AFM nanoparticles, the H0 value plays a much more important role. The results obtained are indicative of the complex dynamics of the interaction between magnetic subsystems formed in AFM nanoparticles.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Balaev D. A., Krasikov A. A., Balaev A. D., Stolyar S. V., Ladygina V. P., Iskhakov R. S.
Заглавие : Features of relaxation of the remanent magnetization of antiferromagnetic nanoparticles by the example of ferrihydrite
Место публикации : Phys. Solid State. - 2020. - Vol. 62, Is. 7. - P.1172-1178. - ISSN 10637834 (ISSN), DOI 10.1134/S1063783420070033
Примечания : Cited References: 53
Аннотация: The relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles at the exchange bias effect implemented in these systems has been investigated. The magnetization relaxation depends logarithmically on time, which is typical of the thermally activated hoppings of particle magnetic moments through the potential barriers caused by the magnetic anisotropy. The barrier energy obtained by processing of the remanent magnetization relaxation data under the field cooling conditions significantly exceeds the barrier energy under standard (zero field cooling) conditions. The observed difference points out the possibility of using the remanent magnetization relaxation to analyze the mechanisms responsible for the exchange bias effect in antiferromagnetic nanoparticles and measure the parameters of the exchange coupling of magnetic subsystems in such objects.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Patrin G. S., Mataev M. M., Seitbekova, K. Zh., Shiyan Ya. G., Yarikov S. A., Zharkov S. M.
Заглавие : Magnetic and resonance properties of the Y0.5Sr0.5Cr0.5Mn0.5O3 polycrystal
Коллективы : Ministry of Education and Science of the Republic of KazakhstanGovernment of the Republic of KazakhstanMinistry of Education and Science of the Republic of Kazakhstan [05130165]
Место публикации : Phys. Solid State. - 2020. - Vol. 62, Is. 8. - P.1350-1354. - ISSN 1063-7834, DOI 10.1134/S1063783420080272. - ISSN 1090-6460(eISSN)
Примечания : Cited References: 20. - This study was supported by the Ministry of Education and Science of the Republic of Kazakhstan, project no. 05130165 and carried out in the framework of the cooperation agreement between the Siberian Federal University and the Kazakh National Women's Teacher Training University
Предметные рубрики: CHROMIUM
TRANSITION
Аннотация: The magnetostatic and magnetic resonance properties of the Y0.5Sr0.5Cr0.5Mn0.5O3 polycrystalline system have been experimentally investigated. The predominance of the intracrystalline ferromagnetic interaction and the antiferromagnetic character of the intercrystallite interaction have been established. The magnetic resonance spectrum in the magnetically ordered region consists of two lines. The high-field line corresponds to the interacting parts of polycrystal shells and the low-field peak is related to the disordered system of ferromagnetic particles.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Eremina R. M., Gavrilova T. P., Moshkina E. M., Gilmutdinov I. F., Batulin R. G., Gurzhiy V. V., Grinenko V., Inosov D. S.
Заглавие : Structure, magnetic and thermodynamic properties of heterometallic ludwigites: Cu2GaBO5 and Cu2AlBO5
Место публикации : J. Magn. Magn. Mater. - 2020. - Vol. 515. - Ст.167262. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2020.167262
Примечания : Cited References: 42. - The reported study was supported by the Russian Foundation for Basic Research (RFBR), grant No 17-02-00953. T.P.G., R.M.E. acknowledge the financial support from the government assignment for FRC Kazan Scientific Center of RAS. D.S.I. acknowledges funding from the German Research Foundation through the Collaborative Research Center SFB 1143 in Dresden (project C03) and the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter – ct.qmat (EXC 2147, project-id 39085490). The XRD and EDX measurements have been performed at the X-ray Diffraction Centre and Centre for Microscopy and Microanalysis of the St. Petersburg State University. The magnetometer studies were performed by the subsidy allocated to Kazan Federal University for the state assignment in the sphere of scientific activities (Project No. 0671-2020-0050)
Аннотация: +We present an extensive study of the structural, magnetic and thermodynamic properties of high-quality monocrystals of two heterometallic oxyborates from the ludwigite family: Cu2GaBO5 and Cu2AlBO5 in the temperature range above 2 K. The distinctive feature of the investigated structures is the selective distribution of Cu and Ga/Al cations. The unit cell of Cu2GaBO5 and Cu2AlBO5 contains four nonequivalent crystallographic sites of metal ions. Two sites in the structure of Cu2GaBO5 are fully occupied by Cu atoms which form the quasi one-dimensional chains along the a-axis. For Cu2AlBO5 all sites are partially occupied by Al and Cu atoms. The joint analysis of low-temperature data on magnetic susceptibility and magnetic contribution to the specific heat showed that Cu2AlBO5 and Cu2GaBO5 exhibit an antiferromagnetic transition at TN=2.4 and 4.1 K, respectively. The magnetic response below TN can be represented as the sum of two contributions: the ordered component and the paramagnetic contribution from defects of the same relative weight. It is shown that the external magnetic field above 2.5 T and 2.8 T for Cu2GaBO5 and Cu2AlBO5, respectively, leads to a broadening of the magnetic phase transition indicating suppression of the long-range antiferromagnetic order.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popkov S. I., Krasikov A. A., Velikanov D. A., Kirillov V. L., Martyanov O. N., Balaev D. A.
Заглавие : Formation of the magnetic subsystems in antiferromagnetic NiO nanoparticles using the data of magnetic measurements in fields up to 250 kOe
Место публикации : J. Magn. Magn. Mater. - 2019. - Vol. 483. - P.21-26. - ISSN 03048853 (ISSN) , DOI 10.1016/j.jmmm.2019.03.004
Примечания : Cited References: 76. - We are grateful S.V. Semenov and A.A. Dubrovskiy for their help, S.V. Komogortsev and A.D. Balaev for fruitful discussions, and M.N. Volochaev for the TEM measurements. The TEM investigations were carried out on the equipment of the Center of Collective Use of the Federal Research Center “Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences”.The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science, to the research project: «Magnetic reversal of magnetic nanoparticles in strong pulsed magnetic fields - a new approach to the study of dynamic effects associated with the magnetization of magnetic nanoparticles» (project no. 18-42-240012).
Ключевые слова (''Своб.индексиров.''): antiferromagnetic nanoparticle--external magnetic field--low temperature regions--magnetic subsystems--magnetically actives--magnetization curves--paramagnetic subsystems--pulsed magnetic fields--magnetic bubbles
Аннотация: It is well-known that the fraction of surface atoms and the number of defects in an antiferromagnetic particle increase with a decrease in the particle size to tens of nanometers, which qualitatively changes the properties of the particle. Specifically, in antiferromagnetic nanoparticles, spins in the ferromagnetically ordered planes can partially decompensate; as a result, an antiferromagnetic particle acquires a magnetic moment. As a rule, uncompensated chemical bonds of the surface atoms significantly weaken the exchange coupling with the antiferromagnetic particle core, which can lead to the formation of an additional magnetic subsystem paramagnetic at high temperatures and spin-glass-like in the low-temperature region. The existence of several magnetic subsystems makes it difficult to interpret the magnetic properties of antiferromagnetic nanoparticles. It is shown by the example of NiO nanoparticles with an average size of 8 nm that the correct determination of the contributions of the magnetic subsystems forming in antiferromagnetic nanoparticles requires magnetic measurements in much stronger external magnetic fields than those commonly used in standard experiments (up to 60–90 kOe). An analysis of the magnetization curves obtained in pulsed magnetic fields up to 250 kOe allows one to establish the contributions of the uncompensated particle magnetic moment μun, paramagnetic subsystem, and antiferromagnetic particle core. The μun value obtained for the investigated NiO particles is consistent with the Néel model, in which μun ∼ N1/2 (N is the number of magnetically active atoms in a particle), and thereby points out the existence of defects on the surface and in the bulk of a particle. It is demonstrated that the anomalous behavior of the high-field susceptibility dM/dH of antiferromagnetic NiO nanoparticles, which was observed by many authors, is caused by the existence of a paramagnetic subsystem, rather than by the superantiferromagnetism effect.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Eremina R. M., Moshkina E. M., Muftakhutdinov A. R., Gilmutdinov I. F., Lyadov N. M.
Заглавие : Magnetic properties of the warwickite MnMgBO4
Место публикации : Solid State Commun. - 2019. - Vol. 290. - P.64-66. - ISSN 00381098 (ISSN) , DOI 10.1016/j.ssc.2018.12.019
Примечания : Cited References: 13. - This work was carried out with the financial support of the RFBR , the government of the Krasnoyarsk Region, the Krasnoyarsk Regional Fund of Science and Technology Support in the framework of the scientific project 18 - 42 - 243007 . The work of GIF was funded by a subsidy allocated to Kazan Federal University for state assignments in the sphere of scientific activities (project No. 3.8138.2017/8.9).
Ключевые слова (''Своб.индексиров.''): warwickite--short range order--antiferromagnetic--frustration
Аннотация: Magnetic properties of a new single crystal MnMgBO4 have been studied. It was determined that below 16 K antiferromagnet spin order was observed with the axis of easy magnetization along the c axis crystal. The short antiferromagnetic range order was observed below 100 K. The Curie–Weiss temperature has been determined in single crystal MnMgBO4 as θCW = −98 K and the frustration parameter has been estimated as 6.125.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Balaev D. A., Nikitin S. E., Freydman A. L., Krasikov A. A., Balaev A. D., Popkov S. I., Kolkov M. I.
Заглавие : Magnetic and thermodynamic properties and spin-flop-driven magnetodielectric response of the antiferromagnetic Pb2Fe2Ge2O9 single crystals
Коллективы : Russian Foundation for Basic Research [16-02-00563]; RFBR; Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science [18-42-240008]; International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM)
Место публикации : J. Magn. Magn. Mater. - 2019. - Vol. 479. - P.114-120. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2019.02.026. - ISSN 1873-4766(eISSN)
Примечания : Cited References: 23. - This study was supported by the Russian Foundation for Basic Research, project no. 16-02-00563; the reported study was also funded by RFBR and the Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science, to the research project no. 18-42-240008 "Effect of magnetic structure on the magnetodielectric properties of oxide crystals containing stereoactive ions Pb2+ and Bi3+". S.E.N. acknowledges the support of the International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM).
Предметные рубрики: FERROMAGNETISM
TRANSITION
Аннотация: Orthorhombic Pb2Fe2Ge2O9 antiferromagnetic single crystals have been synthesized by a modified pseudo-flux technique and their magnetic, thermodynamic, and magnetodielectric properties have been investigated. It has been found that, below the Ned temperature (45.2 K), iron moments are arranged in a canted antiferromagnetic structure with a weak ferromagnetic moment parallel to the a axis. According to the specific heat measurement data, the T-N value remains invariable in applied magnetic fields of up to 50 kOe within the experimental accuracy. The magnetic entropy in the investigated crystals attains 2Rln(2S + 1) right above T-N, which is indicative of a purely magnetic nature of the transition. It has been shown that the weak ferromagnetic moment is induced by the interplay between the single-ion anisotropy and antisymmetric Dzyaloshinskii-Moriya exchange interaction, with the latter contribution being dominant. It has been established from the angular dependences of the magnetization in three orthorhombic planes that the symmetries of the magnetic and crystal structure are identical. The magnetodielectric properties of the Pb2Fe2Ge2O9 single crystals have been studied at different mutual orientations of the electric and magnetic fields. The most prominent anomalies have been observed in the vicinity of the spin-flop transition in a magnetic field applied along the c axis.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gnatchenko S. L., Kachur I. S., Kurnosov V. S., Piryatinskaya V. G., Malakhovskii A. V., Gudim I. A.
Заглавие : Specific features of Nd3+ Kramers doublets' splitting in an antiferromagnetic crystal NdFe3(BO3)4 in an external magnetic field
Место публикации : Low Temp. Phys. - 2019. - Vol. 45, Is. 8. - P.928-933. - ISSN 1063777X (ISSN), DOI 10.1063/1.5116545
Примечания : Cited References: 27. - A. V. Malakhovskii is grateful for the financial support provided by the RFBR Grant No. 19-02-00034.
Аннотация: The optical absorption spectra of an easy-plane NdFe3(BO3)4 antiferromagnet are measured in the region of the 4I9/2 → 2H11/2 transition of the of Nd3+ ion. The study is performed in the 2-35 K temperature range, in external magnetic fields of up to 65 kOe directed both along the C3 axis and the basal plane of the crystal. The splitting values of the Nd3+ excited states in the exchange field of the Fe3+ subsystem and the g-factors of the 2H11/2 multiplet states are determined. The nontrivial dependences of the splitting of some Nd3+ states in a magnetic field indicate that these states have anisotropic Fe-Nd exchange interaction. © 2019 Author(s).
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