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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ivanova N. B., Kazak N. V., Markov V. V., Ovchinnikov S. G., Rudenko V. V., Abd-Elmeguid M. M.
Заглавие : Analysis of the electrical and optical properties of VBO3 single crystals and Fe1-xVxBO3 solid solutions on the basis of a many-electron model of energy band structure
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 8. - P1462-1468. - ISSN 1063-7834, DOI 10.1134/1.1788779
Примечания : Cited References: 32. - One of the authors (M.M.A.) would like to thank the Deutsche Forschungsgemeinschaft (SFB608) for financial support. This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286), the program "Integration" (project no. B0017), and the program of the Division of Physical Sciences of the Russian Academy of Sciences "Strongly Correlated Electrons"
Предметные рубрики: MAGNETIC-PROPERTIES
CALCITE STRUCTURE
PHASE-TRANSITION
FERRIC BORATE
HIGH-PRESSURE
FEBO3
FE1-XCRXBO3
FERROMAGNET
MOSSBAUER
SPECTRA
Аннотация: A many-electron model of the energy band structure of VBO3 and of Fe1 - xVxBO3 solid solutions is proposed with strong electron correlations taken into account. Experimental optical absorption spectra and data on the resistivity are discussed in the framework of the suggested model. Variation in the magnetic and electronic properties of VBO3 and Fe1 - xVxBO3 under high pressure is predicted. For VBO3, a Mott-Hubbard (insulator-metal) transition is expected in the high-pressure phase. In Fe1 - xVxBO3 solid solutions, a nontrivial variation in the properties is predicted, leading to the appearance of a different magnetic state. (C) 2004 MAIK "Nauka / Interperiodica".
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavrichkov V. A., Ivanova N. B., Ovchinnikov S. G., Balaev A. D., Aminov T. G., Shabunina G. G., Chernov V. K., Petukhov M. V.
Заглавие : Comparison of negative magnetoresistance mechanisms in manganese perovskites and chromium spinels
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1999. - Vol. 41, Is. 10. - P1652-1655. - ISSN 1063-7834, DOI 10.1134/1.1131064
Примечания : Cited References: 17
Предметные рубрики: ANISOTROPIC MAGNETORESISTANCE
TRANSPORT-PROPERTIES
THIN-FILMS
ALLOYS
Аннотация: A transition of the field dependence of the electrical resistivity from a square law (similar to H-2) above T-c to a linear function (similar to H) below T-c is observed in the degenerate ferromagnetic semiconductor HgCr2Se4(n). Together with the large negative magnetoresistance, these magnetoelectric effects correspond to effects observed in the perovskite-type oxides La1-xCaxMnOdelta. Inasmuch as the undoped semiconductor HgCr2Se4 is a ferromagnet with approximately the same critical temperature as the doped semiconductor and in view of the total lack of data on the Jahn-Teller effect in this compound, we infer that our results cast doubt on existing hypotheses (polaron and binary exchange) regarding the origin of the giant magnetoresistance in La1-xCaxMnOdelta. Impurity sd scattering is discussed as a possible magnetoresistance mechanism for both compounds. (C) 1999 American Institute of Physics. [S1063-7834(99)01710-4].
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Ivanova N. B., Rudenko V. V., Ovchinnikov S. G., Vasil'Ev A. D., Knyazev Yu. V.
Заглавие : Conductivity study of Co3O2BO3 and Co 3-xFexO2BO3 oxyborates
Коллективы : Moscow International Symposium on Magnetism
Место публикации : Solid State Phenomena. - 2009. - Vol. 152-153. - С. 104-107. - ISSN 10120394 (ISSN); 390845168X (ISBN); 9783908451686 (ISBN), DOI 10.4028/www.scientific.net/SSP.152-153.104
Ключевые слова (''Своб.индексиров.''): doped cobaltite--electrical conductivity--ludwigite--variable-range hopping--crystal structure--electric conductivity--magnetic materials--single crystals--crystal structure--electric conductivity--magnetic materials--magnetism--single crystals--electrical conductivity--electrical resistivity--experimental data--mott variable-range hopping--oxyborates--temperature regions--variable-range hopping--doped cobaltite--ludwigite--variable range hopping--cobalt--cobalt
Аннотация: Single crystals of cobalt oxyborates Co3O2BO 3 and Co3-xFexO2BO3 were synthesized. The crystal structure and electric properties were investigated. The difference in the electrical resistivity behaviors was found. For parent Co3O2BO3 nor simple activation law, nor Mott variable range hopping (VRH) are acquirable to describe the experimental data in wide temperature region. In contrast for Co3-xFex O 2BO3 Mott's variable-range hopping conductivity clearly dominates.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Loseva G. V., Ovchinnikov S. G., Chernov V. K., Ivanova N. B., Kiselev N. I., Bovina A. V.
Заглавие : Correlation between the magnetic and electrical properties of the (VS)(x)(Fe2O3)(2-x) oxysulfide system
Разночтения заглавия :us: Correlation between the magnetic and electrical properties of the (VS)x(Fe2O3)2-x oxysulfide system
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2000. - Vol. 42, Is. 4. - P730-733. - ISSN 1063-7834, DOI 10.1134/1.1131281
Примечания : Cited References: 7
Аннотация: The correlation between the magnetic and electrical properties of the (VS)(x)(Fe2O3)(2-x) (0.9 x 1.25) oxysulfide solid solutions has been studied. The crossover of conductivity from the semimetallic to semiconducting type is accompanied by changes in the magnetic susceptibility, which are characteristic of the transition from delocalized to localized electrons. For x
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Platunov M. S., Knyazev Yu. V., Ivanova N. B., Zubavichus Y. V., Veligzhanin A. A., Vasiliev A. D., Bezmaternykh L. N., Bayukov O. A., Arauzo A., Bartolome J., Lamonova K. V., Ovchinnikov S. G.
Заглавие : Crystal and local atomic structure of MgFeBO4,Mg0.5Co0.5FeBO4, and CoFeBO4: effects of Co substitution
Место публикации : Phys. Status Solidi B. - 2015. - Vol. 252, Is. 10. - P.2245-2258. - ISSN 0370, DOI 10.1002/pssb.201552143. - ISSN 15213951 (eISSN)
Примечания : Cited References: 46. - This work has been financed by the MECOM Project MAT11/23791, and DGA IMANA project E-34, Council for Grants of the President of the Russian Federation (project nos. NSh-2886.2014.2, SP-938.2015.5), and Russian Foundation for Basic Research (project nos. 13-02-00958-a, 13-02-00358-a, 14-02-31051-mol-a). The work of one of the coauthors (M.S.P.) was supported by the program of Foundation for promoting the development of small enterprises in scientific and technical sphere ("UMNIK" program).
Предметные рубрики: SPIN-GLASS BEHAVIOR
MAGNETIC WARWICKITES
SINGLE-CRYSTALS
PHASE-RELATIONS
OXYBORATE
SYSTEM
SPECTROSCOPY
ANISOTROPY
MN2OBO3
FE2OBO3
Ключевые слова (''Своб.индексиров.''): crystal structure--xanes--exafs--magnetic semiconductor--oxyborate
Аннотация: Single-crystalline MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 have been grown by the flux method. The samples have been characterized by X-ray spectral analysis, X-ray diffraction, and X-ray absorption spectroscopy. The X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra have been measured at the Fe and Co K-edges over a wide temperature range (6.5– 300 K). The composition, the charge state, and local environ- ment of both Fe and Co atoms have been determined. The effects of Co substitution for Mg on the local structural distortions have been revealed experimentally and the M–O bond anisotropy has been found.Монокристаллические образцы CoFeBO4 были выращены раствор-расплавным методом. Образцы были охарактеризованы с помощью рентгеноспектрального анализа, рентгеновской дифракции и спектроскопии поглощения рентгеновских лучей. Спектры вблизи K-края поглощения рентгеновского излучения структуры (XANES) и далее рентгеновского поглощения тонкой структуры (EXAFS) были измерены для Fe и Co в широком диапазоне температур (6.5- 300К). Состав, состояние заряда, и локальная положение и Fe и Co атомов были определены. Эффекты замещения Co магнием Mg на местные структурные искажения были выявлены экспериментально и анизотропия связи М-О была найдена.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ivanova N. B., Kazak N. V., Knyazev Yu.V., Velikanov D. A., Bezmaternykh L. N., Ovchinnikov S. G., Vasiliev A. D., Platunov M. S., Bartolomé J., Patrin G. S.
Заглавие : Crystal structure and magnetic anisotropy of ludwigite Co2FeO2BO3
Место публикации : J. Experim. Theor. Phys. - 2011. - Vol. 113, Is. 6. - P.1015-1024. - DOI 10.1134/S1063776111140172
Примечания : Cited References: 14. - This work was supported by the Russian Founda tion for Basic Research (project no. 090200171a), the Russian Science Foundation (President project no. MK5632.2010.2), and the program of the Divi sion of Physical Sciences of the Russian Academy of Sciences “Strong Electronic Correlations.” REFE
Аннотация: Co3O2BO3 and Co2FeO2BO3 single crystals with a ludwigite structure are fabricated, and their crystal structure and magnetic properties are studied in detail. Substituted ludwigite Co2FeO2BO3 undergoes two-stage magnetic ordering at the temperatures characteristic of Fe3O2BO3 (T N1 ≈ 110 K, T N2 ≈ 70 K) rather than Co3O2BO3 (T N = 42 K). This effect is explained in terms of preferred occupation of nonequivalent crystallographic positions by iron, which was detected by X-ray diffraction. Both materials exhibit a pronounced uniaxial magnetic anisotropy. Crystallographic direction b is an easy magnetization axis. Upon iron substitution, the cobalt ludwigite acquires a very high magnetic hardness.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Knyazev Yu.V., Ivanova N. B., Kazak N. V., Platunov M. S., Bezmaternykh L. N., Velikanov D. A., Vasiliev A. D., Ovchinnikov S. G., Yurkin G. Yu.
Заглавие : Crystal structure and magnetic properties of Mn substituted ludwigite Co3O2BO3
Место публикации : J. Magn. Magn. Mater.: Elsevier Science BV, 2012. - Vol. 324, Is. 6. - P.923-927. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2011.07.044
Примечания : Cited References: 15. - The study was supported by the Russian Foundation for Basic Research (Project no. 09-02-00171-a), the Federal Agency for Science and Innovation (Rosnauka) (Project no. MK-5632.2010.2), the Physical Division of the Russian Academy of Science, the program "Strongly Correlated Electrons", Project 2.3.1.
Предметные рубрики: BOND VALENT SUMS
COORDINATION CHEMISTRY
OXIDATION -STATE
O BONDS
COMPLEXES
MANGANESE
COBALT
Ключевые слова (''Своб.индексиров.''): transition metal oxyborate--distinct crystallographic position--spin glass magnetic ordering
Аннотация: The needle shape single crystals Co3−x MnxO2BO3 with ludwigite structure have been prepared. According to the X-ray diffraction data the preferable character of distinct crystallographic positions occupation by Mn ions is established. Magnetization field and temperature dependencies are measured. Paramagnetic Curie temperature value Θ=−100 K points out the predominance of antiferromagnetic interactions. Spin-glass magnetic ordering takes the onset at TN=41 K. The crystallographic and magnetic properties of Co3O2BO3:Mn are compared with the same for the isostructural analogs Co3O2BO3 and CoO2BO3:Fe.
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8.

Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Platunov M. S., Ivanova N. B., Kazak N. V., Bezmaternykh L. N., Vasil'ev A. D., Eremin E. V., Ovchinnikov S. G.
Заглавие : Crystal structure and magnetism OF Co2-xNixB2O5 pyroborate
Коллективы : Moscow International Symposium on Magnetism
Место публикации : Moscow Int. Symp. on Magnet. (MISM-2011): Book of abstracts. - 2011. - Ст.22PO-I-59 . - P.158
Аннотация: The crystal structure and magnetic properties of Co3B2O6 single crystals are studied. Orthorhombic symmetry with space group Pnnm is detected at room temperature. The measurements of static magnetization and dynamic magnetic susceptibility reveal two magnetic anomalies at T 1 = 33 K and T 2 = 10 K and an easy-axis magnetic anisotropy. The effective magnetic moment indicates a high-spin state of the Co2+ ion. A spin-flop transition is found at low temperatures and H sf = 23 kOe. EXAFS spectra of the K-edge absorption of Co are recorded at various temperatures, the temperature-induced changes in the parameters of the local environment of cobalt are analyzed, and the effective Co-Co and Co-O distances are determined. The magnetic interactions in the crystal are analyzed in terms of an indirect coupling model.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Platunov M. S., Ivanova N. B., Knyazev Yu. V., Bezmaternykh L. N., Eremin E. V., Vasil'ev A. D., Bayukov O. A., Ovchinnikov S. G., Velikanov D. A., Zubavichus Y. V.
Заглавие : Crystal structure and magnetization of a Co3B2O6 single crystal
Место публикации : J. Exp. Theor. Phys.: MAIK Nauka-Interperiodica / Springer, 2013. - Vol. 117, Is. 1. - P.94-107. - ISSN 1063-7761, DOI 10.1134/S1063776113060186
Примечания : Cited References: 43. - The synchrotron measurements were performed at the Kurchatov Center of Synchrotron Radiation and Nanotechnologies (state contract no. 16.552.11.7055).This work was supported by the Russian Foundation for Basic Research (project nos. 12-02-00175-a, 12-02-90410-Ukr_a, 12-02-31543mol_a, 13-02-00958-a), the President of the Russian Federation (grant no. NSh-1044.2012.2), the Siberian Branch of the Russian Academy of Sciences (project no. 38), the Ministry of Education and Science of the Russian Federation (project no. 8365), and an integration project of SO RAN-NAN of Belarus (project no. 29).
Предметные рубрики: ABSORPTION FINE-STRUCTURE
NICKEL ORTHOBORATE
RAY
GDFE3(BO3)(4)
LUDWIGITE
NI3(BO3)2
NI3B2O6
SPECTRA
Аннотация: The crystal structure and magnetic properties of Co3B2O6 single crystals are studied. Orthorhombic symmetry with space group Pnnm is detected at room temperature. The measurements of static magnetization and dynamic magnetic susceptibility reveal two magnetic anomalies at T (1) = 33 K and T (2) = 10 K and an easy-axis magnetic anisotropy. The effective magnetic moment indicates a high-spin state of the Co2+ ion. A spin-flop transition is found at low temperatures and H (sf) = 23 kOe. EXAFS spectra of the K-edge absorption of Co are recorded at various temperatures, the temperature-induced changes in the parameters of the local environment of cobalt are analyzed, and the effective Co-Co and Co-O distances are determined. The magnetic interactions in the crystal are analyzed in terms of an indirect coupling model.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Knyazev, Yu. V., Kazak N. V., Platunov M. S., Ivanova N. B., Bezmaternykh L. N., Arauzo A., Bartolome J., Ovchinnikov S. G.
Заглавие : Disorder- and correlation-induced charge carriers localization in oxyborate MgFeBO4, Mg0.5Co0.5FeBO4, CoFeBO4 single crystals
Место публикации : J. Alloys Compd.: Elsevier Science, 2015. - Vol. 642. - P.232-237. - ISSN 0925, DOI 10.1016/j.jallcom.2015.04.056. - ISSN 18734669(eISSN)
Примечания : Cited References:32. - This work has been financed by Council for Grants of the President of the Russian Federation (Project Nos. NSh-2886.2014.2, SP-938.2015.5), Russian Foundation for Basic Research (Project Nos. 13-02-00958-a, 13-02-00358-a, 14-02-31051-mol-a). The work of one of coauthors (M.S.P.) was supported by the grant of KSAI "Krasnoyarsk Regional Fund of Supporting Scientific and Technological Activities'' and by the Program of Foundation for Promoting the Development of Small Enterprises in Scientific and Technical Sphere ("UMNIK'' program). Financial support from the Spanish MINECO MAT11/23791 and DGA IMANA project E-34 is acknowledged.
Предметные рубрики: WARWICKITE
Fe2OBO3
FeBO3
Ключевые слова (''Своб.индексиров.''): transition metal alloys and compounds--disordered system--semiconductors--electrical transport
Аннотация: The temperature dependence of the resistivity of single crystalline Mg1−xCoxFeBO4 samples with x = 0.0, 0.5, 1.0 is investigated for the temperature range (210–400 K). The conduction was found to be governed by Mott variable-range hopping (VRH) in the low-temperature range (T = 210–270 K) and by thermo-activation mechanism in the high-temperature range (T = 280–400 K). Microscopic electronic parameters, such as the density of the localized states near the Fermi level, localization length, the hopping length, and the activation energy have been obtained. The change of the activation energy observed at high-temperature range was attributed to local structure distortions around Fe and Co atoms. The complicated behavior of charge transfer mechanisms is discussed based on two approaches: atomic disorder and electron correlations.Температурная зависимость сопротивления монокристаллических образцов Mg1- XCoxFeBO4 с х = 0,0; 0.5, 1.0 исследована в интервале температур (210-400 К). Было установлено, что проводимость регулируется Мотт-переменной длиной прыжка (VRH) в области низких температур (T = 210-270 К) и термо-активационным механизмом в области высоких температур (Т = 280-400 К). Микроскопические электронные параметры, такие как плотность локализованных состояний вблизи уровня Ферми, длины локализации, длина прыжка, и энергия активации были получены. Изменение энергии активации наблюдается при высокой температурном Диапазоне, что было связано с локальными искажениями структуры вокруг Fe и Co атомов. Сложный механизм поведения переноса заряда обсуждается на основе двух подходов: атомный беспорядок и электронная корреляция.
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