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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Starchikov S. S., Lin Chun-Rong, Lu Shin-Zong, Shaikh M. O., Funtov K. O., Dmitrieva T. V., Ovchinnikov S. G., Edelman I. S., Ivantsov R. D.
Заглавие : Magnetic, structural, and electronic properties of iron sulfide Fe3S4 nanoparticles synthesized by the polyol mediated process
Место публикации : J. Nanopart. Res.: Springer, 2013. - Vol. 15. - P.1397. - DOI 10.1007/s11051-012-1397-0
Аннотация: Iron sulfide nanoparticles Fe3S4 with the spinel-type crystal structure were synthesized by the polyol mediated process. The particle size depends on preparation conditions and varies from 9 to 20 nm. Mössbauer data have revealed that the dominating fraction of iron ions in the 9-nm sample is in the high-spin ferric state. This implies an occurrence of the cation vacancies in nonstoichiometric greigite. The stoichiometric phase of greigite Fe3S4 dominates in the 18-nm-size nanoparticles. Magnetic measurements have shown a ferrimagnetic behavior of all samples at temperatures between 78 and 300 K. The estimated value of magnetic moment of the stoichiometric greigite nanoparticles is about 3.5 μB per Fe3S4 unit. The Mössbauer spectra indicate a superparamagnetic behavior of small particles, and some fraction of superparamagnetic phase is observed in all samples synthesized which may be caused by the particle size distribution. The blocking temperatures of T B ≈ 230 and 250 K are estimated for the 9 and 14 nm particles, respectively. The Mössbauer parameters indicate a great degree of covalency in the Fe–S bonds and support the fast electron Fe3+ ⇆ Fe2+ exchange in the B-sites of greigite. An absence of the Verwey transition at temperatures between 90 and 295 K is established supporting a semimetal type of conductivity. The temperature and magnetic field dependences of the magnetic circular dichroism (MCD) of optical spectra were measured in Fe3S4 for the first time. The spectra differ substantially from that of the isostructural oxide Fe3O4. It is supposed that the MCD spectra of greigite nanoparticles result from the collective electron excitations in a wide band with superimposed peaks of the d–d transitions in Fe ions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Struzhkin V. V., Mironovich A. A., Gavriliuk A. G., Naumov P. G., Jung-Fu Lin, Ovchinnikov S. G., Sinogeikin S., Chow P., Hemley R. J.
Заглавие : Quantum critical point and spin fluctuations in lower-mantle ferropericlase
Место публикации : Proc. Nat. Acad. Sci. USA. - 2013. - Vol. 110, No. 18. - P.7142-7147. - DOI 10.1073/pnas.1304827110. - P.Supporting information - 4 pp.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Struzhkin V. V., Jung-Ho Kim, Shvydko Yuri, Gavriliuk A. G., Lyubutin I. S., Ovchinnikov S. G.
Заглавие : Strongly correlated systems with spin-crossover effects
Коллективы : Euro-Asian Symposium "Trends in MAGnetism": Nanomagnetism
Место публикации : V Euro-Asian simposium "Trend in MAGnetism": Nanomagnetism. [[b]]EASTMAG – 2013[[/b]]: abstracts. - Vladivostok: FEFU, 2013. - С. 113. - ISBN 978-5-7444-3124-2
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Lyubutin I. S., Starchikov S. S., Mironovich A. A., Ovchinnikov S. G., Trojan I. A., Xiao, Yuming, Chow P., Sinogeikin S. V., Struzhkin V. V.
Заглавие : The magnetic P-T phase diagram of langasite Ba3TaFe 3Si2O14 at high hydrostatic pressures up to 38 GPa
Место публикации : Applied Physics Letters. - 2013. - Vol. 103, Is. 16. - Ст.162402. - P. - ISSN 0003-6951, DOI 10.1063/1.4822422
Аннотация: The langasite-type crystals with 3d ions are considered as a class of multiferroics in which ferroelectricity can be induced by the magnetic ordering. In this paper, the high-pressure magnetic states of the langasite-type powdered sample Ba3TaFe3Si2O14 have been investigated in a diamond anvil cell by the nuclear forward scattering of synchrotron radiation technique at different temperatures in hydrostatic conditions. In the pressure range of 0 < P < 19.5 GPa, an increase of the Neel temperature TN from 27 to 41 K was observed in the antiferromagnetic phase of the material. At pressures ?19.5 GPa, a transition to another magnetic phase with huge increase in the Neel temperature to ?120 K was found. We attribute this change to the structural transition at ?19.5 GPa which is evidenced by a drastic change of Raman spectra at this pressure. A tentative magnetic P-T phase diagram of Ba3TaFe 3Si2O14 is proposed. В© 2013 AIP Publishing LLC.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Chun-Rong Lin, Shin-Zong Lu, Yu-Jhan Siao, Lyubutin I.S., Ivantsov R.D., Starchikov S.S., Funtov K.O., Ovchinnikov S. G., Edelman I.S.
Заглавие : Experimental study of iron sulfide Fe[[d]]3[[/d]]S[[d]]4[[/d]] nanoparticles synthesized by the polyolmediated process
Коллективы : Российская академия наук, Научный совет по физике конденсированных сред РАН, Институт физики твердого тела РАН, Московский государственный университет им. М.В. Ломоносова, Астраханский государственный университет , "Новое в магнетизме и магнитных материалах", международная конференция (22; 2012 ; сент. ; 17-23; Астрахань)
Место публикации : Новое в магнетизме и магнитных материалах : сборник трудов XXII международной конференции. - Астрахань, 2012. - С. 470-472
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Ovchinnikov S. G.
Заглавие : Spin crossovers in Mott-Hubbard insulators at high pressures
Коллективы : Moscow International Symposium on Magnetism
Место публикации : J. Magn. Magn. Mater.: Elsevier Science BV, 2012. - Vol. 324, Is. 21. - P.3538-3541. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2012.02.084
Примечания : Cited References: 16. - We acknowledge the help and discussions with Drs. A.G. Gavriliuk, V.V. Struzkin and J.F. Lin. Supports by RFBR (Grants # 09-02-00171, 10-02-00251, # 11-02-00636, # 11-02-00291, # 11-02-12089) and by the RAS Program "Strongly correlated electronic systems" are acknowledged.
Предметные рубрики: ELECTRONIC-TRANSITION
MAGNETIC COLLAPSE
PHASE-TRANSFORMATIONS
BIFEO3 CRYSTAL
METAL-OXIDES
METALLIZATION
Ключевые слова (''Своб.индексиров.''): electronic structure--spin crossover--high pressure--magnetic transition
Аннотация: The high-pressure induced phase transitions initiated by electronic transition in 3d ions from the high-spin (HS) to the low-spin (LS) state (HS-LS spin-crossover) are considered. Behavior of the system with d(6) electronic configuration is investigated in the ground state of zero temperature and critical pressure P-c. Magnetic properties of the Mott-Hubbard insulator (Mg1-xFex)O are studied in the vicinity of the quantum critical point (T=0, P-c). At the critical pressure of spin crossover P-c, the spin gap energy epsilon(S) between HS and LS states is zero. The quantum spins fluctuations HS double left right arrow LS do not require any energy, and the antiferromagnetism is destroyed in the quantum critical point by the first order transition. (C) 2012 Published by Elsevier B.V.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Troyan I. A., Gavrilyuk A. G., Ovchinnikov S. G., Lyubutin I. S., Kazak N. V.
Заглавие : Electron transport in FeBO3 ferroborate at ultrahigh pressures
Место публикации : JETP Letters. - 2012. - Vol. 94, Is. 10. - P.748-752. - ISSN 0021-3640, DOI 10.1134/S0021364011220115
Примечания : Cited References: 22. - This work was supported by the Russian Foundation for Basic Research (project nos. 09-02-01527-a, 09-02-00127-a, 09-02-00171-a, 11-02-00291-a, and 11-02-00636-a), by the Ministry of Education and Science of the Russian Federation (state contract nos. 16.518.11.7021 and MK-5632.2010.2), and by the Division of Physical Sciences, Russian Academy of Sciences (program "Strong Electron Correlations").
Предметные рубрики: MAGNETIC COLLAPSE
TRANSITION
STATE
Аннотация: The electrical resistance of FeBO3 crystals at high and ultrahigh pressures (up to 198 GPa) and low temperatures has been measured using diamond anvil cells. It has found that in the high-pressure phase, 46 GPa ‹ P‹ 100 GPa, the activation energy E-ac decreases gradually from 0.55 to 0.3 eV according to a linear law. Its extrapolation to zero gives an estimated value of about 210 GPa for the pressure at which complete metallization is expected. However, above 100 GPa, the linear E-ac(P) dependence smoothly transforms to a nonlinear one. At the same time, the temperature dependence of the electrical resistance at fixed pressure significantly deviates from the Arrhenius activation law and does not obey the Mott law for the hopping conductivity. Experimental data demonstrate the dependence of the activation energy E-ac both on pressure and temperature. At T = 0, the gap tends to zero. Theoretical analysis shows that the decrease in E-ac upon cooling can be interpreted in terms of the transition of the low-spin FeBO3 phase to the magnetically ordered (anti-ferromagnetic) state.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lin C.-R., Tseng Y.-T., Ovchinnikov S. G., Ivantsov R. D., Edelman I. S., Fedorov A. S., Kuzubov A. A., Fedorov D. A., Starchikov S. S., Lyubutin I. S.
Заглавие : Fe3S4 and Fe3O4 magnetic nanocrystals: magnetooptical and Mössbauer spectroscopy study
Место публикации : Mater. Research Express. - 2014. - Vol. 1, Is. 2. - P.025033. - DOI 10.1088/2053-1591/1/2/025033
Примечания : We thank the National Science Council of Taiwan (NSC 100-2923-M-153-001-MY3 and NSC 102-2112-M-153-002-MY3) for financial support. Support by the Russian Foundation for Basic Research (Grants #14-12-00848 and 14-02-0121) is acknowledged. This work was also supported by the Russian Federation President Grant NSh-2886.2014.2.
Ключевые слова (''Своб.индексиров.''): iron sulfide fe3s4--iron oxide fe3o4--magnetic nanoparticles--mössbauer spectroscopy--magnetic circular dichroism--ab-initio band structure--calculations
Аннотация: Iron oxide magnetite (Fe3O4) should be a reasonable analog for conception and understanding of the magnetic properties of iron sulfide greigite (Fe3S4)—one of the most required magnetic materials having numerous applications but being far from the complete understanding now. We present here a comparative study of the Mössbauer effect (ME) and the magnetic circular dichroism (MCD) spectroscopy of Fe3O4 and Fe3S4 nanoparticles. The ME spectrum parameters of Fe3S4 are shown to distinguish strongly from that of Fe3O4, and the MCD spectrum shapes are shown to be absolutely different for two compounds. To clarify the origin of the Fe3S4 MCD spectrum we have performed ab initio band structure calculations and identified the MCD spectrum features with the transitions between calculated energy states.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Arauzo A., Kazak N. V., Ivanova N. B., Platunov M. S., Knyazev Yu. V., Bayukov O. A., Bezmaternykh L. N., Lyubutin I. S., Frolov K. V., Ovchinnikov S. G., Bartolome J.
Заглавие : Spin-glass behavior in single crystals of hetero-metallic magnetic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4
Коллективы : MINECO Project [MAT11/23791, MAT2014-53921-R], DGA IMANA project [E-34], Russian Foundation for Basic Research [13-02-00958, 13-02-00358, 14-02-31051-mol-a], Council for Grants of the President of the Russian Federation [NSh-2886.2014.2, SP-938.2015.5], program of Foundation for Promotion of Small Enterprises in Science and Technology ("UMNIK" program)
Место публикации : J. Magn. Magn. Mater.: Elsevier Science, 2015. - Vol. 392. - P.114-125. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2015.05.006. - ISSN 18734766(eISSN)
Примечания : Cited References:36. - This work has been financed by the MINECO Project MAT11/23791, MAT2014-53921-R and DGA IMANA project E-34, Russian Foundation for Basic Research (project Nr. 13-02-00958, 13-02-00358 and 14-02-31051-mol-a), Council for Grants of the President of the Russian Federation (project Nr. NSh-2886.2014.2 and SP-938.2015.5). The work of one of coauthors (M.S.P.) was supported by the program of Foundation for Promotion of Small Enterprises in Science and Technology ("UMNIK" program).
Предметные рубрики: SYSTEMS
CHAIN
Fe
SUSCEPTIBILITY
Fe2OBO3
ENERGY
Ключевые слова (''Своб.индексиров.''): warwickites--spin glass--entanglement--exchange interaction
Аннотация: Magnetic properties of heterometallic warwickites MgFeBO4, Mg0.5Co0.5FeBO4, and CoFeBO4 are presented, highlighting the effect of Co substitution on the magnetic properties of these compounds. The analysis of magnetization and heat capacity data has shown that these compounds exhibit a spin-glass transition below TSG=10, 20 and 22 K, respectively. Using zero field ac susceptibility as entanglement witness we find that the low dimensional magnetic behavior above TSG show quantum entanglement behavior χ(Τ)∝T−α(Τ) up to TE≈130 K. The α parameters have been deduced as a function of temperature and Co content, indicating the existence of random singlet phase in this temperature region. Above TE the paramagnetism is interpreted in terms of non-entangled spins giving rise to Curie–Weiss paramagnetism. The different intra- and inter-ribbon exchange interaction pathways have been calculated within a simple indirect coupling model. It is determined that the triangular motifs in the warwickite structure, together with the competing interactions, induce frustration. The spin-glass character is explained in terms of the substitutional disorder of the Mg, Fe and Co atoms at the two available crystallographic sites, and the frustration induced by the competing interactions. The Co substitution induces uniaxial anisotropy, increases the absolute magnetization and increases the spin-glass freezing temperature. The entanglement behavior is supported in the intermediate phase irrespective of the introduction of anisotropy by the Co substitution.Представлены магнитные свойства гетерометаллических варвикитов MgFeBO4, Mg0.5Co0.5FeBO4 и CoFeBO4, с выделением эффекта замещения Co на магнитные свойства этих соединений. Анализ данных намагниченности и теплоемкости показал, что эти соединения обладают спин-стекольным переходом ниже TSG=10, 20 и 22 К соответственно. Используя нулевого поля для переменной восприимчивости, мы находим, что низкоразмерных магнитное поведение выше TSG показать квантовая запутанность поведение χ (Τ) αT? α (Τ) до TEE130 К. Параметры α были выведены в зависимости от температуры и содержание Со, что указывает на существование случайного синглетного фазы в этой области температур. Над TE в Парамагнетизм интерпретируется в терминах перепутывания спинов, приводящих к парамагнетизму Кюри-Вейсса. Различные внутри- и обменного взаимодействия между направлениями были рассчитаны в модели простой косвенной связи. Установлено, что треугольные мотивы в структуре варвикита, вместе с конкурирующими взаимодействиями, вызывают фрустрацию. Характер спинового стекла объясняется в условиях беспорядка замещения атомов Mg, Fe и Co в двух доступных кристаллографических позициях, и фрустрацию, индуцированную конкурирующими взаимодействиями. Замена Со вызывает одноосную анизотропию, увеличивает абсолютную намагниченность и повышает температуру замерзания спинового стекла. Запутанность Поведения поддерживается в промежуточной фазе, независимо от анизотропии из-за введения замещения Со.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Korotkov, N. Yu., Frolov K. V., Kazak N. V., Platunov M. S., Knyazev, Yu. V., Bezmaternykh L. N., Ovchinnikov S. G., Arauzo A., Bartolome J.
Заглавие : Spin-glass behavior of warwickite MgFeBO4 and CoFeBO4 crystals observed by Mössbauer spectroscopy
Место публикации : J. Alloys Compd.: Elsevier Science, 2015. - Vol. 642. - P.204-209. - ISSN 0925, DOI 10.1016/j.jallcom.2015.04.067. - ISSN 18734669(eISSN)
Примечания : Cited References:29. - This study was supported by the Russian Foundation for Basic Research (Grants # 14-02-00483a, 14-02-31051-mol-a, 13-02-00958- a, and 13-02-00358-a), by the Council for Grants of the President of the Russian Federation (Project Nos. NSh-2886.2014.2 and SP-938.2015.5), by the Grant of KSAI, Krasnoyarsk regional fund of supporting scientific and technological activities and by the program of Foundation for Promotion of Small Enterprises in Science and Technology (''UMNIK'' program). The Spanish MINECO project MAT2011/23791, MAT2014/53921 and DGA E-34 are acknowledged.
Предметные рубрики: SOLVABLE MODEL
SPECTRA
Ключевые слова (''Своб.индексиров.''): warwickites--spin-glass--mossbauer spectroscopy
Аннотация: Single crystals of MgFeBO4 and СоFeBO4 warwickites were obtained. The effects of charge ordering and magnetic properties were investigated by Mössbauer spectroscopy. Cation distribution over M1 and M2 nonequivalent sites and the average charge at the metal positions were established. Low temperature Mössbauer spectra reveal spin-glass behavior, with spin-freezing temperatures TSG of 15.2 and 33.2 K for Mg- and Co-warwickites, respectively, higher than that observed from the d.c. and a.c. magnetic susceptibility measurements. The difference is explained in terms of dynamical scaling theory. The specific shape of the Mössbauer spectra in the vicinity of the magnetic transition at TSG shows the difference between spin-glass and superparamagnetic behavior and demonstrates an overwhelming role of the exchange anisotropy in the properties of Mg-warwickite. In Co-warwickite the increase of magnetocrystalline anisotropy provokes an increase in magnetic viscosity.Были получены монокристаллы MgFeBO4 и CoFeBO4 warwickites. Эффекты упорядочения зарядов и магнитные свойства были исследованы методом мессбауэровской спектроскопии. Было определено распределение катионов на М1 и M2 неэквивалентных позициях и средний заряд на металлических позициях. При низкой температуре Мессбауэровские спектры показывают поведение типа спинового стекла, с температурой замораживания спинов TSG 15.2 и 33.2 K для MG-и Co-warwickites, соответственно, более высокие, чем наблюдалось от постоянного тока и на ~ измерениях магнитной восприимчивости. Разница объясняется в терминах динамической теории подобия. Удельный форма спектров Мессбауэра в непосредственной близости от магнитного перехода на TSG показывает разницу между спин-стекольным и суперпарамагнитным поведением и демонстрирует подавляющее роль обменной анизотропии в свойствах Mg-warwickite. В Co-warwickite увеличение магнитокристаллической анизотропия провоцирует увеличение магнитной вязкости.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Frolov K. V., Lyubutin I. S., Smirnova E. S., Alekseeva O. A., Verin I. A., Artemov V. V., Kharlamova S. A., Bezmaternykh L. N., Gudim, I. A.
Заглавие : Low-temperature structural and magnetic phase transitions in multiferroic GdFe3(BO3)4
Коллективы : Russian Foundation for Basic Research [14-02-00483a, 13-02-12442]; Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools [NSh-1130.2014.5, NSh-924.2014.2]; Russian Ministry of Education and Science [RFMEFI62114X0005]
Место публикации : J. Alloys Compd.: Elsevier Science, 2016. - Vol. 671. - P.545-551. - ISSN 0925-8388, DOI 10.1016/j.jallcom.2016.02.083. - ISSN 1873-4669(eISSN)
Примечания : Cited References:36. - We thank Dr. A.P. Dudka for help in the low temperature XRD measurements. This study was supported in part by the Russian Foundation for Basic Research (projects # 14-02-00483a and 13-02-12442), and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools (grant # NSh-1130.2014.5 and # NSh-924.2014.2). This work was performed using the equipment of the Shared Research Center IC RAS and was supported by the Russian Ministry of Education and Science (project RFMEFI62114X0005).
Предметные рубрики: IRON BORATE GDFE3(BO3)4
BIFEO3 THIN-FILMS
MAGNETOELASTIC PROPERTIES
RM3(BO3)4 CRYSTALS
TRIGONAL GDFE3(BO3)4
ENHANCED POLARIZATION
HIGH-PRESSURES
CRYSTALLIZATION
BEHAVIOR
GROWTH
Ключевые слова (''Своб.индексиров.''): multiferroics--rare earth compounds--x-ray diffraction--mossbauer--spectroscopy--crystal structure--spin dynamics
Аннотация: X-ray analysis revealed that at temperature decreasing from room temperature to Tstr = 155 K the crystal unit cell GdFe3(BO3)4 is reduced only along the c axis (at 0.01 Å), while the a and b axes are unchanged within the error limits. The volume of the crystal decreases uniformly in the direction of all three axes at 155–80 K. At 80–30 K the crystal volume is decreased only by reduction of the parameters a and b, while the parameter c increases conversely. In the paramagnetic region Mössbauer spectra do not distinguish between the two structural positions of iron ions Fe1 and Fe2, appearing at T < Tstr. Below the temperature of the magnetic phase transition at TN = 38.0(1) K the Mössbauer data indicate quasi-one-dimensional magnetic ordering of iron moments in the sublattice Fe2 and a two-dimensional one in the iron sublattice Fe1. The dynamics of spin reorientation in sublattices Fe1 and Fe2 is studied in detail.Рентгеновский анализ показал, что при уменьшении температуры от комнатной до Tstr = 155 K изменение параметра элементарной ячейки кристалла GdFe3(BO3)4 происходит лишь вдоль оси с (при 0,01 Å), в то время как а и b оси остаются неизменными в пределах погрешности измерений. Объем кристалла уменьшается равномерно в направлении всех трех осей при 155-80 K. При 80-30 K объем кристалла уменьшается только уменьшением параметров a и b, в то время как параметр с наоборот увеличивается. В парамагнитной области Мессбауэровские спектры не различают двух структурных позиций ионов железа Fe1 и Fe2, появляющиеся при Т˂Tstr. Ниже температуры магнитного фазового перехода при TN = 38,0(1) К Мёссбауэрские данные указывают на квази-одномерный магнитное упорядочение моментов железа в подрешетке Fe2 и двумерное в железной подрешетке Fe1. Динамика спиновой переориентации в подрешетках Fe1 и Fe2 подробно изучается.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bartolome J., Arauzo A., Kazak N. V., Ivanova N. B., Ovchinnikov S. G., Knyazev Yu. V., Lyubutin I. S.
Заглавие : Uniaxial magnetic anisotropy in Co2.25Fe0.75O2BO3 compared to Co3O2BO3 and Fe3O2BO ludwigites
Разночтения заглавия :авие SCOPUS: Uniaxial magnetic anisotropy in Co2.25Fe0.75O 2BO3 compared to Co3O2BO3 and Fe3O2BO ludwigites
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2011. - Vol. 83, Is. 14. - Ст.144426. - ISSN 1098-0121, DOI 10.1103/PhysRevB.83.144426
Примечания : Cited References: 25. - The authors acknowledge V. V. Rudenko for the oxyborate samples they made and O. A. Bayukov for fruitful discussion. The financial support of Spanish MINCYT, Grant No. MAT08/1077, and the Aragonese E-34 project are acknowledged. Fruitful discussions with F. Bartolome and P. Bordet are acknowledged. The latter is thanked for providing the FeINF3/INFOINF2/INFBOINF3/INF single crystal. Also this 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), and the Physical Division of the Russian Academy of Science (Program "Strongly Correlated Electrons," Project No. 2.3.1).
Предметные рубрики: CRYSTAL-STRUCTURE
MOSSBAUER
CO3BO5
Аннотация: Magnetic and Mossbauer spectroscopy (MS) measurements have been performed on a single crystal of Co2.25Fe0.75O2BO3 with ludwigite structure. Two magnetic transitions (T-N = 115 K and T-C = 70 K) were traced from the ac susceptibility temperature dependence. The MS spectra as a function of temperature clearly show the onset of magnetic ordering below 115 K. Magnetization measurements on the parent Co3O2BO3 and Fe3O2BO3 compounds have been done for comparison. In Fe3O2BO3 the anisotropy of the different phases has been determined, showing that the anisotropy axis changes from the a to the b axis in the low-temperature antiferromagnetic phase. High magnetic uniaxial anisotropy has been detected for both Co3O2BO3 and Co2.25Fe0.75O2BO3. From the angle-dependent magnetization measurements it is found that in both compounds the easy axis of magnetization is the b [010] axis, where an antiferromagnetic component is superimposed on the main ferromagnetic component. In the c direction the behavior is purely antiferromagnetic. In Co2.25Fe0.75O2BO3 a strong reduction of the remanent magnetization and a very strong increase in coercive field along the b axis with respect to those found in Co3O2BO3 were observed from magnetic hysteresis cycles measured below T-C. The increase of coercive field is caused by the increase of defects upon Co substitution by Fe.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Kazak N. V., Ovchinnikov S. G., Lyubutin I. S.
Заглавие : Electronic Transitions in the VBO3 Single Crystal at High Pressures
Коллективы :
Разночтения заглавия :авие SCOPUS: Electronic transitions in the VBO3 single crystal at high pressures
Место публикации : JETP Letters. - 2008. - Vol. 88, Is. 11. - P.762-766. - ISSN 0021-3640, DOI 10.1134/S0021364008230136
Примечания : Cited References: 19. - We are grateful to V.V. Rudenko for the samples provided for this study and to I.S. Edelman for discussions of the results. This work was supported by the Russian Foundation for Basic Research (project nos. 07-02-00490a, 08-02-00897a, and 08-02-90708mob_st); by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (project no. MK-4278.2008.2); and by the Division of Physical Sciences, Russian Academy of Sciences (program "Strongly Correlated Electrons").
Предметные рубрики: FEBO3
Ключевые слова (''Своб.индексиров.''): 74.62.fj--75.50.-y--78.70.en--81.40.rs
Аннотация: Optical absorption spectra of single crystals of the ferromagnetic semiconductor VBO3 are studied at high pressures up to 70 GPa achieved in a diamond-anvil cell. An electronic transition accompanied by sharp changes in the optical parameters and a decrease in the optical gap from E-0 = 3.02 eV to 2.25 eV is found at the pressure P-C = 30 GPa. The gap does not disappear in the high-pressure phase and its value becomes typical of semiconductors. This is indicative of a semiconductor-semiconductor transition. The transition to the metallic state may occur at the critical pressure P-met similar to 290 GPa.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Struzhkin V. V., Lyubutin I. S., Ovchinnikov S. G., Hu M. Y., Chow P.
Заглавие : Another mechanism for the insulator-metal transition observed in Mott insulators
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2008. - Vol. 77, Is. 15. - Ст.155112. - ISSN 1098-0121, DOI 10.1103/PhysRevB.77.155112
Примечания : Cited References: 26
Предметные рубрики: ELECTRONIC-STRUCTURE
SPIN TRANSITION
HIGH-PRESSURES
GDFE3(BO3)(4)
Аннотация: The two widely accepted mechanisms of the insulator-metal Mott-Hubbard transitions which have been considered up until now are driven by the band-filling or bandwidth effects. We found a different mechanism of the Mott-Hubbard insulator-metal transition, which is controlled instead by the changes in the Mott-Hubbard energy U. In contrast to the changes in the bandwidth W in the "bandwidth control" scenario or to the variations of the band-filling n parameter in the "band-filling" scenario, a dramatic decrease in the Mott-Hubbard energy U plays the key role in this mechanism. We have experimentally observed this type of the insulator metal transition in the transition metal oxide BiFeO(3). The decrease in the Mott-Hubbard energy is caused by the high-spin-low-spin crossover in the electronic d shell of 3d transition metal ion Fe(3+) with d(5) configuration under high pressure. The pressure-induced spin crossover in BiFeO(3) was investigated and confirmed by synchrotron x-ray diffraction, nuclear forward scattering, and x-ray emission methods. The insulator-metal transition at the same pressures was found by the optical absorption and dc resistivity measurements.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Berry F. J., Dmitrieva T. V., Ovanesyan N. S., Lyubutin I. S., Thomas M. F., Sarkisyan V. A., Ren X., Aminov T. G., Shabunina G. G., Rudenko V., Vorotynov A. M., Dubinskaya Y. L.
Заглавие : Magnetic order in FeCr2S4-type chalcogenide spinels
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2007. - Vol. 19, Is. 26. - Ст.266204. - ISSN 0953-8984, DOI 10.1088/0953-8984/19/26/266204
Примечания : Cited References: 15
Предметные рубрики: COLOSSAL-MAGNETORESISTANCE
TRANSITION
Ключевые слова (''Своб.индексиров.''): doping (additives)--iron compounds--magnetization--magnetoresistance--mossbauer spectroscopy--x ray absorption fine structure spectroscopy--chalcogenide spinels--low temperature magnetic behaviour--magnetic ordering temperature--thiospinels--chalcogenides
Аннотация: The thiospinels of composition FeCr2S4 and Fe1+xCr2-2xSnxS4 with 0 x 0.1 have been examined by means of extended x- ray absorption fine structure, Mossbauer spectroscopy and magnetoresistance techniques. The structural characterization shows that tin enters the spinel- related lattice as Sn4+ and occupies the octahedral B site. Appreciable magnetoresistance is observed in the temperature range 160 - 185 K which includes the magnetic ordering temperature. The effect of slight non- stoichiometry in FeCr2S4 and of tin doping is observed in the M r ossbauer spectra which show the Fe2+ ions to occupy the tetrahedral A sites. The M r ossbauer spectra recorded around the magnetic ordering temperature are sensitive to small ( 0.03 T) applied magnetic fields. The influence of tin on the low temperature magnetic behaviour is associated with the distribution of Cr3+, Sn4+ and Fe3+ ions around tetrahedral Fe2+ sites and vacancies in the anionic sublattice. An interpretation of the colossal magnetoresistance phenomena below TN is suggested.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Kharlamova S. A., Lyubutin I. S., Ovchinnikov S. G., Potseluyko A. M., Trojan I. A., Zabluda V. N.
Заглавие : Optical transitions in GdFe3(BO3)(4) and FeBO3 under high pressures
Разночтения заглавия :авие SCOPUS: Optical transitions in GdFe3(BO3)4 and FeBO3 under high pressures
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2005. - Vol. 17: 2nd International Symposium on Physics of Solids Under High Presure Using Nuclear Probes (JUL 22-25, 2004, Cologne, GERMANY), Is. 48. - P7599-7604. - ISSN 0953-8984, DOI 10.1088/0953-8984/17/48/011
Примечания : Cited References: 8
Предметные рубрики: ELECTRONIC-STRUCTURE
Ключевые слова (''Своб.индексиров.''): band structure--coulomb blockade--high pressure effects--iron compounds--magnetic moments--mathematical models--optical properties--relaxation processes--coulomb correlations--electron correlations--insulator-semiconductor transitions--optical transitions--gadolinium compounds
Аннотация: The optical properties of GdFe3(BO3)(4) under high pressures have been investigated experimentally and theoretically, and the results are compared with the properties of FeBO3. A model of the GdFe3(BO3)(4) band structure is derived within the multielectron model taking into account the strong electron correlations. Crossover of the Fe3+ ion high-spin and low-spin states, collapse of the magnetic moment, the relaxation Coulomb correlations, and insulator-semiconductor transition are predicted. Optical transitions in GdFe3(BO3)(4) and FeBO3 under high pressures were discovered.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bayukov O. A., Gavrilyuk A. M., Zabluda V. N., Lyubutin I. S., Ovchinnikov S. G., Potseluyko A. M., Tomas M., Trojan I. A., Kharlamova S. A.
Заглавие : Studies of magnetic and optic properties of rare-earth gallo-ferroborates by Mossbauer and optical spectroscopy
Место публикации : Physica B: ELSEVIER SCIENCE BV, 2005. - Vol. 359: International Conference on Strongly Correlated Electron Systems (SCES 04) (JUL 26-30, 2004, Karlsruhe, GERMANY). - P1321-1323. - ISSN 0921-4526, DOI 10.1016/j.physb.2005.01.397
Примечания : Cited References: 3
Ключевые слова (''Своб.индексиров.''): strongly correlated electron system--antiferromagnets--borates--antiferromagnets--borates--strongly correlated electron system--antiferromagnetism--cryostats--energy gap--magnetic moments--magnetic properties--mossbauer spectroscopy--optical properties--single crystals--borates--coulomb correlations--liquid helium--strongly correlated electron systems--gadolinium compounds
Аннотация: Magnetic and optical properties of GdFe3-xGax(BO3)(4) single crystals are investigated by Mossbauer and optical spectroscopy. The GdFe3(BO3)(4) multielectron band structure model is derived. A high- and low-spin crossover of Fe3+ ion, a collapse of the magnetic moment, the suppression of Coulomb correlations, and insulator-semiconductor transition are predicted. The jump of an energy gap is measured at pressure 43 GPa. (c) 2005 Elsevier B.V. All rights reserved.
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kharlamova S. A., Ovchinnikov S. G., Balaev A. D., Thomas M. F., Lyubutin I. S., Gavriliuk A. G.
Заглавие : Spin reorientation effects in GdFe3(BO3)(4) induced by applied field and temperature
Разночтения заглавия :авие SCOPUS: Spin reorientation effects in GdFe3(BO3)4 induced by applied field and temperature
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 6. - P1098-1105. - ISSN 1063-7761, DOI 10.1134/1.2163925
Примечания : Cited References: 14
Предметные рубрики: RM(3)(BO3)(4) CRYSTALS
GROWTH
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--ground state--magnetic moments--magnetic properties--mossbauer spectroscopy--single crystals--temperature distribution--spin orientation--static magnetic measurements--gadolinium compounds
Аннотация: Magnetic properties of GdFe3(BO3)(4) single crystals were investigated by Fe-57-Mossbauer spectroscopy and static magnetic measurements. In the ground state, the GdFe3(BO3)(4) crystal is an easy-axis compensated antiferromagnet, but the easy axis of iron moments does not coincide with the crystal C-3 axis, deviating from it by about 20 degrees. The spontaneous and field-induced spin reorientation effects were observed and studied in detail. The specific directions of iron magnetic moments were determined for different temperatures and applied fields. Large values of the angle between the Fe3+ magnetic moments and the C-3 axis in the easy-axis phase and between Fe3+ moments and the a(2) axis in the easy-plane phase reveal the tilted antiferromagnetic structure. (c) 2005 Pleiades Publishing, Inc.
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Trojan I. A., Lyubutin I. S., Ovchinnikov S. G., Sarkissian V. A.
Заглавие : High-pressure magnetic properties and P-T phase diagram of iron borate
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 100, Is. 4. - P688-696. - ISSN 1063-7761, DOI 10.1134/1.1926429
Примечания : Cited References: 24
Предметные рубрики: FEBO3 SINGLE-CRYSTALS
NUCLEAR-RESONANCE
BAND-STRUCTURE
TRANSITION
TEMPERATURE
SCATTERING
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--diamonds--ferromagnetic materials--high pressure effects--low temperature effects--magnetic moments--magnetic properties--magnetization--phase diagrams--powders--single crystals--synchrotron radiation--diamond anvil cells--electronic transition--iron borate--nuclear forward scattering (nfs)--iron compounds
Аннотация: The high-pressure magnetic states of iron borate (FeBO3)-Fe-57 single-crystal and powder samples have been investigated in diamond anvil cells by nuclear forward scattering (NFS) of synchrotron radiation at different temperatures. In the low-pressure (0 < P < 46 GPa) antiferromagnetic phase, an increase of the Neel temperature from 350 to 595 K induced by pressure was found. At pressures 46-49 GPa, a transition from the antiferromagnetic to a new magnetic state with a weak magnetic moment (magnetic collapse) was discovered. It is attributed to the electronic transition in Fe3+ ions from the high-spin 3d(5) (S = 5/2, (6)A(1g)) to the low-spin (S = 1/2, T-2(2g)) state (spin crossover) due to the insulator-semiconductor-type transition with extensive suppression of strong d-d electron correlations. At low temperatures, NFS spectra of the high-pressure phase indicate magnetic correlations in the low-spin system with a magnetic ordering temperature of about 50 K. A tentative magnetic P-T phase diagram of FeBO3 is proposed. An important feature of this diagram is the presence of two triple points where magnetic and paramagnetic phases of the high-spin and low-spin states coexist. © 2005 Pleiades Publishing, Inc.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Kharlamova S. A., Lyubutin I. S., Troyan I. A., Ovchinnikov S. G., Potseluiko A. M., Eremets M. I., Boehler R.
Заглавие : Structural and electronic transitions in gadolinium iron borate GdFe3(BO3)(4) at high pressures
Место публикации : JETP Letters. - 2004. - Vol. 80, Is. 6. - P.426-432. - ISSN 0021-3640, DOI 10.1134/1.1830662
Примечания : Cited References: 20
Предметные рубрики: TRIGONAL GDFE3(BO3)(4)
RM(3)(BO3)(4) CRYSTALS
OPTICAL-SPECTRA
BAND-STRUCTURE
FEBO3
GROWTH
Аннотация: The optical properties and structure of gadolinium iron borate GdFe3(BO3)(4) crystals are studied at high pressures produced in diamond-anvil cells. X-ray diffraction data obtained at a pressure of 25.6 GPa reveal a first-order phase transition retaining the trigonal symmetry and increasing the unit cell volume by 8%. The equation of state is obtained and the compressibility of the crystal is estimated before and after the phase transition. The optical spectra reveal two electronic transitions at pressures similar to26 GPa and similar to43 GPa. Upon the first transition, the optical gap decreases jumpwise from 3.1 to similar to2.25 eV. Upon the second transition at P = 43 GPa, the optical gap deceases down to similar to0.7 eV, demonstrating a dielectric-semiconductor transition. By using the theoretical model developed for a FeBO3 crystal and taking into account some structural analogs of these materials, the anomalies of the high-pressure optical spectra are explained. (C) 2004 MAIK "Nauka/Interperiodica".
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