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1.

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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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gavriliuk A. G., Trojan I. A., Ovchinnikov S. G., Lyubutin I. S., Sarkisyan V. A.
Заглавие : The mechanism of suppression of strong electron correlations in FeBO3 at high pressures
Разночтения заглавия :авие SCOPUS: The mechanism of suppression of strong electron correlations in FeBO 3 at high pressures
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2004. - Vol. 99, Is. 3. - P566-573. - ISSN 1063-7761, DOI 10.1134/1.1809686
Примечания : Cited References: 18
Предметные рубрики: MAGNETIC COLLAPSE
TRANSITION
SPECTRA
ABSORPTION
STATE
Ключевые слова (''Своб.индексиров.''): crystal structure--high pressure effects--light absorption--parameter estimation--phase transitions--spectrum analysis--crystal field--electron correlations--generalized tight binding method--hybridization--iron compounds
Аннотация: The optical absorption spectra of iron borate (FeBO3) are measured at high pressures up to P = 82 GPa. A mechanism of suppression of strong electron correlations is proposed within the framework of the generalized tight binding method, which leads to the experimentally observed magnetic, electronic, and structural phase transitions. Taking into account peculiarities of the crystal structure of FeBO3 and the strong s-p hybridization of boron and oxygen, it is established that, as the distance between ions varies with increasing pressure, the crystal field parameter begins to play a decisive role in the electron transitions, while the influence of the d band broadening is negligibly small. Parameters of the theory are calculated as functions of the pressure. (C) 2004 MAIK "Nauka / Interperiodica".
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3.

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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4.

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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5.

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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6.

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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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Lyubutin I. S., Gavriliuk A. G., Struzhkin V. V., Ovchinnikov S. G., Kharlamova S. A., Bezmaternykh L. N., Hu M., Chow P.
Заглавие : Pressure-induced electron spin transition in the paramagnetic phase of the GdFe3(BO3)(4) Heisenberg magnet
Разночтения заглавия :авие SCOPUS: Pressure-induced electron spin transition in the paramagnetic phase of the GdFe3(BO3)4 Heisenberg magnet
Место публикации : JETP Letters. - 2006. - Vol. 84, Is. 9. - P.518-523. - ISSN 0021-3640, DOI 10.1134/S0021364006210119
Примечания : Cited References: 26
Предметные рубрики: TRIGONAL GDFE3(BO3)(4)
NUCLEAR
FEBO3
STATE
SCATTERING
COLLAPSE
Аннотация: The HS - LS spin crossover effect (high-spin - low-spin transition) induced by high pressure in the range 45-53 GPa is observed in trivalent Fe3+ ions in the paramagnetic phase of a (GdFe3)-Fe-57(BO3)(4) gadolinium iron borate crystal. This effect is studied in high-pressure diamond-anvil cells by two experimental methods using synchrotron radiation: nuclear resonant forward scattering (NFS) and Fe K-beta high-resolution x-ray emission spectroscopy (YES). The manifestation of the crossover in the paramagnetic phase, which has no order parameter to distinguish between the HS and LS states, correlates with the optical-gap jump and with the insulator-semiconductor transition in the crystal. Based on a theoretical many-electron model, an explanation of this effect at high pressures is proposed.
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8.

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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9.

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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10.

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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