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Uncompensated magnetic moment and surface and size effects in few-nanometer antiferromagnetic NiO particles / D. A. Balaev, A. A. Krasikov, S. I. Popkov [et al.] // J. Magn. Magn. Mater. - 2021. - Vol. 539. - Ст. 168343, DOI 10.1016/j.jmmm.2021.168343. - 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 . - ISSN 0304-8853
Кл.слова (ненормированные):
Antiferromagnetic NiO nanoparticles -- Uncompensated magnetic moment -- Superparamagnetism -- Surface magnetic anisotropy
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 ~ 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 ~ 3/2), 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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Держатели документа:
Kirensky Institute of Physics, Federal Research Center “Krasnoyarsk Scientific Center”, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036, Russian Federation
Siberian Federal University, Krasnoyarsk, 660041, Russian Federation
Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russian Federation

Доп.точки доступа:
Balaev, D. A.; Балаев, Дмитрий Александрович; Krasikov, A. A.; Красиков, Александр Александрович; Popkov, S. I.; Попков, Сергей Иванович; Semenov, S. V.; Семёнов, Сергей Васильевич; Volochaev, M. N.; Волочаев, Михаил Николаевич; Velikanov, D. A.; Великанов, Дмитрий Анатольевич; Kirillov, V. L.; Martyanov, O. N.
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Interparticle magnetic interactions in synthetic ferrihydrite: Mossbauer spectroscopy and magnetometry study of the dynamic and static manifestations / Y. V. Knyazev, D. A. Balaev, S. V. Stolyar [et al.] // J. Alloys Compd. - 2022. - Vol. 889. - Ст. 161623, DOI 10.1016/j.jallcom.2021.161623. - Cited References: 84. - This study was supported by the Russian Foundation for Basic Research, the Government of the Krasnoyarsk Territory, and the Krasnoyarsk Territorial Foundation for Support of Scientific and R&D Activities, project no. 19–42–240012 R-A “Magnetic Resonance in Ferrihydrite Nanoparticles: Effects Related to the Core-Shell Structure” . - ISSN 0925-8388
Кл.слова (ненормированные):
Ferrihydrite nanoparticles -- Superparamagnetism -- Interparticle magnetic interactions
Аннотация: Samples of synthetic ferrihydrite with an average nanoparticle size of 2.7 nm have been examined by magnetometry and Mossbauer spectroscopy. Ferrihydrite is characterized by the antiferromagnetic interactions between the magnetic moments of iron atoms. In ferrihydrite nanoparticles, as in any other antiferromagnetic ones, structural defects induce the formation of an uncompensated magnetic moment, which determines the magnetic properties typical of single-domain ferro- and ferrimagnetic particles. The manifestation of the magnetic interactions between ferrihydrite nanoparticles in the magnetic properties of the material and in the temperature evolution of Mossbauer spectra has been in focus. The results obtained on synthetic ferrihydrite have been compared with the data for the biogenic ferrihydrite sample with a similar average size of particles surrounded by a polysaccharide shell, which weakens and screens the interparticle magnetic interactions. A clear manifestation of the effect of the interparticle magnetic interactions on the transition to the blocked state is the presence of a significant contribution of the relaxation component in the Mossbauer spectra at temperatures of the transition from the superparamagnetic to blocked state. The temperature dependence of the particle relaxation time obtained from the Mossbauer spectra points out the collective effect of freezing of the magnetic moments of particles due to the magnetic interactions between them.

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Держатели документа:
Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Akademgorodok 50, bld. 38, Krasnoyarsk, 660036, Russian Federation
Siberian Federal University, Svobodniy 79, Krasnoyarsk, 660041, Russian Federation
Krasnoyarsk Scientific Center, Federal Research Center KSC SB RAS, Akademgorodok 50, Krasnoyarsk, 660036, Russian Federation

Доп.точки доступа:
Knyazev, Yu. V.; Князев, Юрий Владимирович; Balaev, D. A.; Балаев, Дмитрий Александрович; Stolyar, S. V.; Столяр, Сергей Викторович; Krasikov, A. A.; Красиков, Александр Александрович; Bayukov, O. A.; Баюков, Олег Артемьевич; Volochaev, M. N.; Волочаев, Михаил Николаевич; Yaroslavtsev, R. N.; Ярославцев, Роман Николаевич; Ladygina, V. P.; Velikanov, D. A.; Великанов, Дмитрий Анатольевич; Iskhakov, R. S.; Исхаков, Рауф Садыкович
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Dynamic remagnetisation of CoFe2O4 nanoparticles: thermal fluctuational thawing of anisotropy / D. A. Balaev, I. S. Poperechny, A. A. Krasikov [et al.] // J. Phys. D. - 2021. - Vol. 54, Is. 27. - Ст. 275003, DOI 10.1088/1361-6463/abf371. - Cited References: 63. - Experimental measurements were supported by Project No. AAAA-A17-117103050081-1. I S P and Yu L R acknowledge the support of ICMM in the framework of topical task AAAAA20-120020690030-5. The numerical calculations were performed on the Uran supercomputer (Ural Branch, Russian Academy of Sciences, Ekaterinburg) . - ISSN 0022-3727. - ISSN 1361-6463

РУБ Physics, Applied
Рубрики:
COBALT-FERRITE NANOPARTICLES
   MAGNETIC-PROPERTIES
   SIZE
   COERCIVITY
Кл.слова (ненормированные):
nanoparticles -- cobalt ferrite -- magnetodynamics -- superparamagnetism -- effective anisotropy
Аннотация: We report a study of the magnetodynamics of cobalt ferrite (CoFe2O4) nanoparticles with an average diameter of ~6 nm. Hysteresis loops were measured under quasi-static conditions and in pulse fields with amplitudes H0 of up to 130 kOe and for durations τP of 8 and 16 ms. The growth of coercivity Hc observed with an increase in the magnetic field variation rate dH/dt (determined by the values of H0 and τP) and the reduction of Hc with temperature is ascribed to the superparamagnetic effect. The proposed theoretical model explains the observed dependences fairly well. Notably, the effective magnetic anisotropy constant obtained exceeds the value for bulk crystals and might be indicative of the contribution of surface magnetic anisotropy.

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Держатели документа:
Russian Acad Sci, Inst Phys, Siberian Branch, Krasnoyarsk 660000, Russia.
Russian Acad Sci, Inst Continuous Media Mech, Ural Branch, Perm 614068, Russia.
Perm State Natl Res Univ, Dept Phase Transit Phys, Perm 614990, Russia.
Russian Acad Sci, Boreskov Inst Catalysis, Siberian Branch, Novosibirsk 630090, Russia.

Доп.точки доступа:
Balaev, D. A.; Балаев, Дмитрий Александрович; Poperechny, I. S.; Krasikov, A. A.; Красиков, Александр Александрович; Semenov, S. V.; Семёнов, Сергей Васильевич; Popkov, S. I.; Попков, Сергей Иванович; Knyazev, Yu. V.; Князев, Юрий Владимирович; Kirillov, V. L.; Yakushkin, S. S.; Martyanov, O. N.; Raikher, Y. L.; [AAAA-A17-117103050081-1]; [AAAAA20-120020690030-5]
}
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    Yurkin, G. Yu.
    Magnetic Properties of Fe1-xCoxSi Single Crystals at Low Co Impurity Concentrations / G. Yu. Yurkin, G. S. Patrin, S. A. Yarikov // J. Sib. Fed. Univ. Math. Phys. - 2019. - Vol. 12, Is. 6. - P. 756-771 ; Журн. СФУ. Матем. и физика, DOI 10.17516/1997-1397-2019-12-1-1-6. - Cited References: 17 . - ISSN 1997-1397. - ISSN 2313-6022
   Перевод заглавия: Магнитные свойства монокристаллов Fe1-xCoxSi
Кл.слова (ненормированные):
Co impurities -- iron Silicide -- superparamagnetism -- силицид железа -- примесь Co -- суперпарамагнетизм
Аннотация: Velocity of bulk acoustic waves in base and rotated cuts have been measured by the ultrasonic pulse-echo method and values of CE ijkl and eijk in single crystals YAl3(BO3)4 have been calculated. The value of dijk piezoelectric modulus of these single crystals have been determined by quasistatic measurements, and εσ ij dielectric constants have been determined by the flat capacitor method. Experimental values of material constants have been applied for the study of Magnetostatic properties of FeSi and Fe0;98Co0;02Si single crystals have been studied. It has been found that the temperature and field dependences of the magnetization of monocrystal FeSi are strongly affected by introduction of a small amount of Co (2 %). A description of the results were provided by a model accounting for the formation of superparamagnetic iron clusters, as well as Fe-Co complexes. It is assumed that Fe-Co complexes form a ferromagnetic phase, which is approximately 0.6% of the Fe0;98Co0;02Si sample weight
В работе представлено исследование магнитостатических характеристик образцов FeSi и Fe0;98Co0;02Si. Обнаружено, что внесение небольшого количества примести Co (2 %) значительно влияет на температурные и полевые зависимости намагниченности монокристалла FeSi. Результаты обрабобтаны в рамках модели, учетывающей образование суперпарамагнитных кластеров железа, а также комплексов Fe-Co. Предполагается, что комплексы Fe-Co образуют ферромагнитную фазу, которая составляет примерно 0,6 % от массы образца Fe0;98Co0;02Si.

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Держатели документа:
Institute of Engineering Physics and Radioelectronics Siberian Federal University Svobodny, 79, Krasnoyarsk, 660041 Russia
Kirensky Institute of Physics Federal Research Center KSC SB RAS Akademgorodok, 50/38, Krasnoyarsk, 660036 Russia

Доп.точки доступа:
Patrin, G. S.; Патрин, Геннадий Семёнович; Yarikov, S. A.; Яриков, Станислав Алексеевич; Юркин, Глеб Юрьевич

}
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Magnetic anisotropy and core-shell structure origin of the biogenic ferrihydrite nanoparticles / Y. V. Knyazev, D. A. Balaev, S. V. Stolyar [et al.] // J. Alloys Compd. - 2021. - Vol. 851. - Ст. 156753, DOI 10.1016/j.jallcom.2020.156753. - Cited References: 82. - The electron microscopy study was carried out on the equipment of the Krasnoyarsk Territorial Center for Collective Use, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences. This study was supported by the Russian Foundation for Basic Research, the Government of the Krasnoyarsk Territory, and the Krasnoyarsk Territorial Foundation for Support of Scientific and R & D Activities, project no. 19-42-240012 p-a “Magnetic Resonance in Ferrihydrite Nanoparticles: Effects Related to the Core–Shell Structure” . - ISSN 0925-8388
Кл.слова (ненормированные):
Ferrihydrite -- Core-shell nanoparticles -- Superparamagnetism -- Surface magnetic anisotropy
Аннотация: Ferrihydrite is a low-crystalline nanoscale matter. The uncompensated magnetic moment of the ferrihydrite caused by the antiferromagnetic ordering of the magnetic moments of iron atoms and leads to the magnetic properties very similar to those of ferro- and ferrimagnetic nanoparticles. In this study, we investigated the biogenic ferrihydrite nanoparticles with the narrow size distribution and an average diameter of ≈2 nm obtained by the bacteria life cycle. The features caused by the surface effects and the inhomogeneous structure of ferrihydrite have been examined in the temperature range of 4–300 K using Mossbauer spectroscopy and magnetometry. Based on the Mossbauer data, we identified the superparamagnetic blocking temperature at the temperature of 30 K for the largest ferryhidrite particles. We established that the exceptional magnetic anisotropy of ferrihydrite (KV=1.2∙105 erg/cm3 and KS=0.1 erg/cm2) is reached because of the highly developed ferrihydrite nanoparticles’ surface. According to the Mossbauer data, we propose a core-shell structural model of the biogenic ferrihydrite particles. We found that the size of the dense core depends on the particle size. The well-crystallized core is formed only for nanoparticles larger than ≈2 nm, whereas smaller particles consist entirely of a matter with a lower density of iron atoms.

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Держатели документа:
Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Akademgorodok 50, Bld. 38, Krasnoyarsk, 660036, Russian Federation
Siberian Federal University, Svobodniy 79, Krasnoyarsk, 660041, Russian Federation
Krasnoyarsk Scientific Center, Federal Research Center KSC SB RAS, Akademgorodok 50, Krasnoyarsk, 660036, Russian Federation

Доп.точки доступа:
Knyazev, Yu. V.; Князев, Юрий Владимирович; Balaev, D. A.; Балаев, Дмитрий Александрович; Stolyar, S. V.; Bayukov, O. A.; Баюков, Олег Артемьевич; Yaroslavtsev, R. N.; Ярославцев, Роман Николаевич; Ladygina, V. P.; Velikanov, D. A.; Великанов, Дмитрий Анатольевич; Iskhakov, R. S.; Исхаков, Рауф Садыкович
}
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Transport properties of FeSi with cobalt impurities / G. Y. Yurkin [et al.] // TRENDS IN MAGNETISM. - 2011. - Vol. 168-169. - P493-496, DOI 10.4028/www.scientific.net/SSP.168-169.493 . - ISSN 1012-0394
Кл.слова (ненормированные):
iron monosilicide -- kondo effect -- magnetization -- resistivity -- spindependent scattering -- superparamagnetic cluster -- cobalt -- crystals -- electric resistance -- electron energy loss spectroscopy -- kondo effect -- magnetic field effects -- magnetic properties -- magnetization -- magnetoresistance -- scattering -- superparamagnetism -- transport properties -- cobalt -- electric conductivity -- electron scattering -- impurities -- kondo effect -- magnetism -- magnetization -- experimental investigations -- kondo models -- magnetoresistance properties -- resistivity -- si crystals -- spin dependent scattering -- superparamagnetic clusters -- crystal impurities -- crystal impurities
Аннотация: The results of experimental investigations of Fe1-xCo xSi crystals in the impurity limit are presented in this article. We made an attempt to study changes of magnetic properties and conductivity in mixed Fe1-xCoxSi crystals in the impurity limit. Magnetoresistance properties are well described in the framework of Kondo model. The presence of Co-subsystem leads to the occurrence of spin-dependent channel in electron scattering conduction.

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Держатели документа:
Kirensky Institute of Physics, SB, RAS, 660036, Krasnoyarsk, Russian Federation
Siberian Federal University, 660041, Krasnoyarsk, Russian Federation

Доп.точки доступа:
Yurkin, G. Yu.; Юркин, Глеб Юрьевич; Patrin, G. S.; Патрин, Геннадий Семёнович; Velikanov, D. A.; Великанов, Дмитрий Анатольевич; Beletsky, V. V.
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Study of magnetic iron oxide nanoparticles coated with silicon oxide by ferromagnetic method / I. G. Vazhenina, S. V. Stolyar, A. V. Tyumentsev [et al.] // Phys. Solid State. - 2023. - Vol. 65, Is. 6. - P. 884-888, DOI 10.21883/PSS.2023.06.56095.01H. - Cited References: 20. - The study was supported by grant No. 22-14-20020 provided by the Russian Science Foundation, Krasnoyarsk Regional Science Foundation . - ISSN 1063-7834. - ISSN 1090-6460
Кл.слова (ненормированные):
iron oxide nanoparticles -- ferromagnetic resonance -- superparamagnetism -- blocking temperature
Аннотация: agnetic nanoparticles of magnetite with a size of ~8 nm synthesized with a different type of coating were studied by ferromagnetic resonance in the temperature range from 7 to 300 K. The features of the experimental temperature dependences of the parameters of the ferromagnetic resonance curve (the magnitude of the resonant field, line width and intensity) and their approximation allowed us to estimate the values of characteristic temperatures. Firstly, the value of the Vervey temperature and the dependence of its value on the type of coating were determined. Secondly, the temperature of transition of nanoparticles to the superparamagnetic state (blocking temperature) and the temperature range within which the magnetic structure of the outer shell of the magnetic nanoparticle is in the spin glass state are established.

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Публикация на русском языке Исследование магнитных наночастиц оксида железа, покрытых оксидом кремния, методом ферромагнитного резонанса [Текст] / И. Г. Важенина, С. В. Столяр, А. В. Тюменцева [и др.]. - 5 с. // Физ. твердого тела. - 2023. - Т. 65 Вып. 6. - С. 923-927

Держатели документа:
Kirensky Institute of Physics, Federal Research Center KSC SB, Russian Academy of Sciences, Krasnoyarsk, Russia
Siberian Federal University, Krasnoyarsk, Russia
Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia
Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia
Krasnoyarsk State Medical University named after Prof. V.F. Voyno-Yasenetsky, Ministry of Health of Russia, Krasnoyarsk, Russia

Доп.точки доступа:
Vazhenina, I. G.; Важенина, Ирина Георгиевна; Stolyar, S. V.; Tyumentsev, A. V.; Volochaev, M. N.; Волочаев, Михаил Николаевич; Iskhakov, R. S.; Исхаков, Рауф Садыкович; Komogortsev, S. V.; Комогорцев, Сергей Викторович; Pyankov, V. F.; Nikolaeva, E. D.; Nanophysics and Nanoelectronics, International Symposium(27 ; 13-16 March 2023 ; Nizhny Novgorod, Russia)
}
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Superparamagnetic relaxation in ensembles of ultrasmall ferrihydrite nanoparticles / Yu. V. Knyazev, D. A. Balaev, S. A. Skorobogatov [et al.] // Phys. Met. Metallogr. - 2024. - Vol. 125, Is. 4. - P. 377-385, DOI 10.1134/S0031918X23603025. - Cited References: 56. - The work was conducted as part of the state assignment of the Kirensky Institute of Physics SB RAS, while the synthesis of biogenic ferrihydrite was carried out as part of the state assignment of the Krasnoyarsk Scientific Center SB RAS . - ISSN 0031-918X. - ISSN 1555-6190
Кл.слова (ненормированные):
superparamagnetism -- relaxation -- ferrihydrite
Аннотация: The paper examines the impact of interparticle interactions on the superparamagnetic relaxation of ultrasmall nanoparticle ensembles, using Fe2O3•nH2O iron oxyhydroxide (ferrihydrite) nanoparticles as an example. Two samples were analyzed: ferrihydrite of biogenic origin (with an average particle size of ≺d≻ ≈ 2.7 nm) with a natural organic shell, and a sample (with ≺d≻ ≈ 3.5 nm) that underwent low-temperature annealing, during which the organic shell was partially removed. The DC and AC magnetic susceptibilities (χ'(T), χ''(T)) in a small magnetic field in the superparamagnetic (SPM) blocking region of the nanoparticles were measured. The results show that an increase in interparticle interactions leads to an increase in the SPM blocking temperature from 28 to 52 K according to DC magnetization data. It is shown that below the SPM blocking temperature, magnetic interactions of nanoparticles lead to the formation of a collective state similar to spin glass in bulk materials. The scaling approach reveals that the dynamics of correlated magnetic moments on the particle surface slow down with increasing interparticle interactions. Simulation of χ''(T) dependence has shown that the dissipation of magnetic energy occurs in two stages. The first stage is directly related to the blocking of the magnetic moment of nanoparticles, while the second stage reflects the spin-glass behavior of surface spins and strongly depends on the strength of interparticle interactions.

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Держатели документа:
Kirensky Institute of Physics, Federal Research Center (FRC), KSC SB RAS, Krasnoyarsk, 660036 Russia
FRC Krasnoyarsk Scientific Center (KSC), Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, 660036 Russia

Доп.точки доступа:
Knyazev, Yu. V.; Князев, Юрий Владимирович; Balaev, D. A.; Балаев, Дмитрий Александрович; Skorobogatov, S. A.; Скоробогатов, Станислав Алексеевич; Velikanov, D. A.; Великанов, Дмитрий Анатольевич; Bayukov, O. A.; Баюков, Олег Артемьевич; Stolyar, S. V.; Столяр, Сергей Викторович; Ladygina, V. P.; Krasikov, A. A.; Красиков, Александр Александрович; Iskhakov, R. S.; Исхаков, Рауф Садыкович
}
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Magneto-optical spectroscopy of nanocomposites (CoFeZr)x(Al2O3)100-x / E. A. Gan’shina, A. B. Granovsky, V. V. Garshin [et al.] // SPIN. - 2023. - Vol. 13, Is. 1. - Ст. 2340006, DOI 10.1142/S2010324723400064. - Cited References: 17. - This work was supported in part by the Russian Foundation for Basic Research under Grant 22-29-00392. Magnetic and MO studies were performed using equipment purchased at the expense of the MSU The authors thank the Krasnoyarsk Regional Center of Research Equipment of Federal Research Center “Krasnoyarsk Science Center SB RAS” for assistance . - ISSN 2010-3247. - ISSN 2010-3255
Кл.слова (ненормированные):
Superparamagnetism -- superferromagnetism -- nanocomposites -- magneto-optical spectra
Аннотация: We present results of magneto-optical investigations of (CoFeZr)x(Al2O3)100-x film nanocomposites in transverse Kerr effect (TKE) geometry in the spectral range 0.5-4.0eV and magnetic field up to 3.0kOe. Nanocomposites were deposited onto a glass-ceramic substrate by ion-beam sputtering. The TKE response at room temperature strongly depends on the wavelength of light, applied magnetic field H and the volume metallic fraction. From the analysis of the field dependences of TKE at different wavelengths, it follows that in the as-deposited samples, the interaction between nanoparticles at x<30at.% is small and the nanocomposite is an ensemble of superparamagnetic particles; as x increases to 32at.%, a superspinglass-type state arises, then, in the vicinity of 34at.%, along with individual superparamagnetic particles, superferromagnetic regions appear. Long-range ferromagnetic order arises at concentrations x less than the percolation threshold for conductivity xper=42.6at.%. In the presence of two different magnetic states in the samples, TKE is not proportional to the magnetization. Both the field dependences at near-infrared region and the spectral dependences of TKE change significantly after annealing of the samples, while the changes in the field dependences of the magnetization are almost imperceptibly.

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Держатели документа:
Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
Voronezh State Technical University, Voronezh 394026, Russia
Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk 660036, Russia
National Research Centre “Kurchatov Institute”, Moscow 123182, Russia

Доп.точки доступа:
Gan’shina, Elena A.; Granovsky, Alexandr B.; Garshin, Vladimir V.; Pripechenkov, Ilya M.; Sitnikov, Alexandr V.; Volochaev, M. N.; Волочаев, Михаил Николаевич; Ryl’kov, Vladimir V.; Nikolaev, Sergey N.
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10.

Role of the surface effects and interparticle magnetic interactions in the temperature evolution of magnetic resonance spectra of ferrihydrite nanoparticle ensembles / D. A. Balaev, S. V. Stolyar, Y. V. Knyazev [et al.] // Results Phys. - 2022. - Vol. 35. - Ст. 105340, DOI 10.1016/j.rinp.2022.105340. - Cited References: 119. - Authors thank to A.D. Balaev, S.V. Komogortsev for fruitful discussions and M.N. Volochaev for TEM studies. The TEM study and measurements of X-band FMR spectra were carried out on the equipment of the Krasnoyarsk Territorial Center for Collective Use, Krasnoyarsk Scientific Center, Siberian Branch, Russian Academy of Sciences. This study was supported by the Russian Science Foundation, project no. 21-72-00025 (https://rscf.ru/project/21-72-00025/) "Tuning the Magnetic Properties of Ultrafine Biocompatible Ferrihydrite Nanoparticles through Interparticle Interactions" . - ISSN 2211-3797
Кл.слова (ненормированные):
Ferrihydrite nanoparticles -- Superparamagnetism -- Interparticle magnetic interactions -- Ferromagnetic resonance
Аннотация: Ferrihydrite is characterized by the antiferromagnetic ordering and, in ferrihydrite nanoparticles, as in nanoparticles of any antiferromagnetic material, an uncompensated magnetic moment is formed. We report on the investigations of ferrihydrite powder systems with an average particle size of ∼ 2.5 nm obtained (i) as a product of the vital activity of bacteria (sample FH-bact) and (ii) by a chemical method (sample FH-chem). In the first approximation, these samples can be considered to be identical. However, in sample FH-chem, particles contact directly, while in sample FH-bact, they have organic shells; therefore, the interparticle magnetic interactions in these samples have different degrees. The main goal of this work has been to establish the effects of the interparticle magnetic interactions and individual characteristics of ferrihydrite nanoparticles on ferromagnetic resonance (FMR) spectra. The FMR spectra have been measured at different (9.4–75 GHz) frequencies in a wide temperature range. It has been found that, at low temperatures, the field-frequency dependence ν(HR) of the investigated systems has a gap ν/γ = HR + HA, where HR is the resonance field and HA is the induced anisotropy, which decreases with increasing temperature. To estimate a degree of the effect of interparticle interactions on the results obtained and to correctly determine the temperature range of the superparamagnetic (or blocked) state, the static magnetic measurement and Mössbauer spectroscopy data have been obtained and analyzed. It has been shown that the most striking feature of the FMR spectra - a gap in the field-frequency dependences - is a manifestation of individual characteristics of ferrihydrite nanoparticles. The induced anisotropy is caused by freezing of a subsystem of surface spins and its coupling with the particle core, which is observed in both samples at a temperature of ∼80 K. The temperature range (below 80 K) in which the gap exists corresponds to the blocked state in the FMR technique. In sample FH-bact, the ratio between the FMR parameters HA and linewidth ΔH obeys the standard expression HA ∼ (ΔH)3. In sample FH-chem, however, the interparticle magnetic interactions dramatically affect the behavior of parameters of the FMR spectra, which change nonmonotonically upon temperature variation. This fact is attributed to the collective freezing of the magnetic moments of particles under the conditions of sufficiently strong interactions, which follows from the temperature dependence of the particle magnetic moment relaxation time determined from the Mössbauer spectroscopy and static magnetometry data obtained in weak magnetic fields.

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Держатели документа:
Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Akademgorodok 50, bld. 38, Krasnoyarsk, 660036, Russian Federation
Siberian Federal University, Svobodniy 79, Krasnoyarsk, 660041, Russian Federation
Krasnoyarsk Scientific Center, Federal Research Center KSC SB RAS, Akademgorodok 50, Krasnoyarsk, 660036, Russian Federation

Доп.точки доступа:
Balaev, D. A.; Балаев, Дмитрий Александрович; Stolyar, S. V.; Столяр, Сергей Викторович; Knyazev, Yu. V.; Князев, Юрий Владимирович; Yaroslavtsev, R. N.; Ярославцев, Роман Николаевич; Pankrats, A. I.; Панкрац, Анатолий Иванович; Vorotynov, A. M.; Воротынов, Александр Михайлович; Krasikov, A. A.; Красиков, Александр Александрович; Velikanov, D. A.; Великанов, Дмитрий Анатольевич; Bayukov, O. A.; Баюков, Олег Артемьевич; Ladygina, V. P.; Iskhakov, R. S.; Исхаков, Рауф Садыкович
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