Библиотека института физики им. Л.В. Киренского СО РАН

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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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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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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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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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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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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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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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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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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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