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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Volkov N. V., Tarasov A. S., Eremin E. V., Eremin A. V., Varnakov S. N., Ovchinnikov S. G.
Заглавие : Frequency-dependent magnetotransport phenomena in a hybrid Fe/SiO2/p-Si structure
Место публикации : J. Appl. Phys.: American Institute of Physics, 2012. - Vol. 112, Is. 12. - Ст.123906. - ISSN 0021-8979, DOI 10.1063/1.4769788
Примечания : Cited References: 31. - This study was supported by the Russian Foundation for Basic Research, Project No. 11-02-00367-a; the Presidium of the Russian Academy of Sciences, program Quantum Mesoscopic and Disordered Structures, Project No. 20.8; the Division of Physical Sciences of the Russian Academy of Sciences, program Spin Phenomena in Solids Nanostructures and Spintronics, Project No. II.4.3; the Siberian Branch of the Russian Academy of Sciences, Integration Projects Nos. 85 and 102, and the Federal target program Scientific and Pedagogical Personnel of Innovative Russia (State Contract No. NK-556P_15).
Предметные рубрики: SILICON
IRON
SPINTRONICS
PAIRS
Аннотация: We report the large magnetoimpedance effect in a hybrid Fe/SiO2/p-Si structure with the Schottky barrier. The pronounced effect of magnetic field on the real and imaginary parts of the impedance has been found at temperatures 25-100K in two relatively narrow frequency ranges around 1 kHz and 100MHz. The observed frequency-dependent magnetotransport effect is related to the presence of localized "magnetic" states near the SiO2/p-Si interface. In these states, two different recharging processes with different relaxation times are implemented. One process is capture-emission of carriers that involves the interface levels and the valence band; the other is the electron tunneling between the ferromagnetic electrode and the interface states through SiO2 potential barrier. In the first case, the applied magnetic field shifts energy levels of the surface states relative to the valence band, which changes recharging characteristic times. In the second case, the magnetic field governs the spin-dependent tunneling of carriers through the potential barrier. The "magnetic" interface states originate, most likely, from the formation of the centers that contain Fe ions, which can easily diffuse through the SiO2 layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769788]
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Maiti S., Korshunov M. M., Chubukov A.V.
Заглавие : Gap symmetry in KFe2As2 and the cos 4θ gap component in LiFeAs
Место публикации : Phys. Rev. B: American Physical Society, 2012. - Vol. 85, Is. 1. - Ст.14511. - ISSN 1098-0121, DOI 10.1103/PhysRevB.85.014511
Примечания : Cited References: 49. - We are thankful to S. Borisenko, S. Davis, R. Fernandes, P. Hirschfeld, I. Eremin, D. Evtushinsky, A. Kordyuk, K. Kuroki, Y. Matsuda, A. Rost, M. Vavilov, and V. Zabolotnyy for useful discussions. This work was supported by NSF-DMR-0906953 (SM and AVC) and by the Humboldt Foundation (AVC). MMK is grateful for support from RFBR (Grant No. 09-02-00127), the Presidium of RAS program N5.7, the FCP Scientific and Research and Educational Personnel of Innovative Russia for 2009-2013 (GK P891 and GK16.740.12.0731), and the President of Russia (Grant No. MK-1683.2010.2).
Предметные рубрики: SUPERCONDUCTING GAPS
IRON
Аннотация: We revisit the issue of the gap symmetry in KFe2As2, which is an Fe pnictide superconductor with only hole pockets. Previous theoretical studies mostly argued for a d−wave gap in KFe2As2 since transport and thermodynamic measurements point to the presence of the gap nodes. However, a d-wave gap is inconsistent with recent laser-based angle-resolved photoemission measurements. We propose a scenario for a nodal s−wave superconductivity induced by a nonmagnetic intraband and interband interactions between fermions near hole pockets. The superconducting gap changes sign between the hole pockets and has cos4θ angular dependence and accidental nodes on one or several hole pockets. We argue that strong angle dependence is the consequence of near-degeneracy between interpocket and intrapocket interaction on the hole pockets. We also analyze the cos4θ angular dependence of the gap in other Fe pnictides and compare theoretical results with the photoemission experiments of LiFeAs.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shukla D. K., Francoual S., Skaugen A., von Zimmermann M., Walker H. C., Bezmaternykh L. N., Gudim, I. A., Temerov V. L., Strempfer J.
Заглавие : Ho and Fe magnetic ordering in multiferroic HoFe3(BO3)4
Место публикации : Phys. Rev. B: American Chemical Society, 2012. - Vol. 86, Is. 22. - Ст.224421. - ISSN 1098-0121, DOI 10.1103/PhysRevB.86.224421
Примечания : Cited References: 32
Предметные рубрики: X-RAY SCATTERING
POLARIZATION DEPENDENCE
IRON
Аннотация: Resonant and nonresonant x-ray scattering studies on HoFe3(BO3)4 reveal competing magnetic ordering of Ho and Fe moments. Temperature and x-ray polarization dependent measurements employed at the Ho L3 edge directly reveal a spiral spin order of the induced Ho moments in the ab plane propagating along the c axis, a screw-type magnetic structure. At about 22.5 K the Fe spins are observed to rotate within the basal plane inducing spontaneous electric polarization, P. Components of P in the basal plane and along the c axis can be scaled with the separated magnetic x-ray scattering intensities of the Fe and Ho magnetic sublattices, respectively.
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4.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Yakushkin S. S., Dubrovskiy A. A., Balaev A. D., Shaykhutdinov K. A., Bukhtiyarova G. A., Martyanov O. N.
Заглавие : Magnetic properties of few nanometers ɛ-Fe2O3 nanoparticles supported on the silica
Место публикации : J. Appl. Phys.: American Institute of Physics, 2012. - Vol. 111, Is. 4. - Ст.44312. - ISSN 0021-8979, DOI 10.1063/1.3686647
Примечания : Cited References: 27. - authors thank A. D. Balaev and N. V. Volkov for fruitful discussions and comments. This work was supported by Program of RAS No. 27.46.
Предметные рубрики: HIGH-TEMPERATURE
IRON
STABILIZATION
OXIDE
GEL
Аннотация: Magnetic properties of ɛ-Fe2O3nanoparticles supported on silica with the average size of few nanometers, narrow size distribution and no admixture of any other iron oxide polymorphs are investigated. The investigation of the temperature behavior of magnetization within the temperature range from 4.2 to 1000 K revealed the presence of several magnetic subsystems in the species under study. The temperatures’ behavior of the magnetic moment value indicates ferrimagnetic ordering in the ɛ-Fe2O3nanoparticles with a Curie temperature of about 800 K and points to the existence of a significant paramagnetic contribution becoming apparent at low temperatures. According to the electron spin resonance data, the particles possess superparamagnetic behavior at temperature higher ∼120 K. The model of the magnetic structure of monophase system of few nanometers ɛ-Fe2O3nanoparticles supported on silica is proposed.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sofronova S. N., Gerasimova Y. V., Vtyurin A. N., Gudim, I. A., Shestakov N. P., Ivanenko A. A.
Заглавие : Infrared absorption spectrum of HoFe3(BO3)4 crystal
Коллективы : RFBR [13-02-00825, 13-02-98041, SS-4828.2012.2]
Место публикации : Vib. Spectrosc.: Elsevier Science, 2014. - Vol. 72. - P.20-25. - ISSN 0924-2031, DOI 10.1016/j.vibspec.2014.02.005. - ISSN 1873-3697
Примечания : Cited References: 18. - The work was partially supported by the RFBR through Grants No. 13-02-00825 and 13-02-98041, SS-4828.2012.2.
Предметные рубрики: MAGNETOELASTIC INTERACTIONS
IRON
GDFE3(BO3)4
Ключевые слова (''Своб.индексиров.''): holmium ferroborate--infrared absorption
Аннотация: Infrared (IR) absorption spectra of HoFe3(BO3)4 crystal have been obtained in spectral range 30–7000 cm−1 at temperatures from 4 to 423 K. Vibrational frequencies have been simulated with ‘Lady’ software package both for high-temperature and low-temperature phases. The experimental spectra have been analyzed on the basis of calculated data, and interpreted within the framework of internal vibrations of ionic complexes of HoFe3(BO3)4 crystal lattice. The spectral range under study was observed to have no Davydov splitting of internal vibrational modes due to unit cell multiplication. No effects of magnetic ordering on the IR spectra of the crystal under study were observed in the low-temperature range.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Efremov D. V., Golubov A. A., Dolgov O. V.
Заглавие : Unexpected impact of magnetic disorder on multiband superconductivity
Коллективы : Dynasty Foundation; ICFPM; Ministry of Education and Science of the Russian Federation [14Y26.31.0007]; RFBR [12-02-31534, 13-02-01395]; Leading Scientific Schools of the Russian Federation [NSh-2886.2014.2]; DFG [1458]; EU-Japan
Место публикации : Phys. Rev. B: American Physical Society, 2014. - Vol. 90, Is. 13. - ISSN 1098-0121, DOI 10.1103/PhysRevB.90.134517. - ISSN 1550-235X
Примечания : Cited References: 41. - The authors are grateful to S.-L. Drechsler, P.J. Hirschfeld, K. Kikoin, and S.G. Ovchinnikov for useful discussions. We acknowledge partial support by the Dynasty Foundation and ICFPM (MMK), the Ministry of Education and Science of the Russian Federation (Grant No. 14Y26.31.0007), RFBR (Grant Nos. 12-02-31534 and 13-02-01395), President Grant for Government Support of the Leading Scientific Schools of the Russian Federation (NSh-2886.2014.2), DFG Priority Program 1458, and FP7 EU-Japan program IRON SEA.
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTIVITY
PARAMAGNETIC IMPURITIES
IRON
CONDUCTIVITY
ALLOYS
Аннотация: We analyze how the magnetic disorder affects the properties of the two-band s± and s++ models, which are the subject of discussions regarding iron-based superconductors and other multiband systems like MgB2. We show that there are several cases when the transition temperature Tc is not fully suppressed by magnetic impurities in contrast to the Abrikosov-Gor'kov theory, but a saturation of Tc takes place in the regime of strong disorder. These cases are: (1) the purely interband impurity scattering and (2) the unitary scattering limit. We show that in the former case the s± gap is preserved, while the s++ state transforms into the s± state with increasing magnetic disorder. For case (2), the gap structure remains intact.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Anshits A. G., Bayukov O. A., Anshits N. N., Pletnev O. N., Rabchevskii E. V., Vereshchagin S. N., Kondratenko E. V.
Заглавие : Nature of the active sites of ferrospheres in the oxidative condensation of methane
Коллективы : Russian Science Foundation [4-13-00289], Russian Congress on Catalysis (2; 2014 ; Oct. ; 2–5; Samara)
Место публикации : Kinet. Catal.: MAIK Nauka-Interperiodica / Springer, 2015. - Vol. 56, Is. 4. - P.523-531. - ISSN 0023, DOI 10.1134/S0023158415040023. - ISSN 16083210(eISSN)
Примечания : Cited References:37. - This work was supported by the Russian Science Foundation (grant no. 14-13-00289).
Предметные рубрики: GLASS CRYSTAL CATALYSTS
HIGH-TEMPERATURE
MOSSBAUER
MAGNETITES
MICROSPHERES
SELECTIVITY
CONVERSION
FERRITES
ASHES
IRON
Ключевые слова (''Своб.индексиров.''): oxidative condensation of methane--ferrospheres--iron spinel--mossbauer spectroscopy--structural defects
Аннотация: The catalytic properties of ferrospheres containing 76–97 wt % Fe2O3 in the oxidative condensation of methane were compared with their phase composition and the distribution of iron cations over the crystallographic positions of iron-containing phases in a steady state. It was established that the reaction route of methane oxidation changed at a Fe2O3 content of 89 wt %. Deep oxidation was the main reaction route on ferrospheres with a Fe2O3 content of 88.8 wt %. At a Fe2O3 content of ≥89 wt %, the yield of C2 hydrocarbons sharply increased and the contribution of deep oxidation decreased. The yield of C2 hydrocarbons correlated with the amount of defects in the structure of iron spinel, which are iron ions with the tetrahedral cation of Ca2+ and the octahedral cation vacancy among the nearest neighbors.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S., Zimin A. A., Filatov E. Y., Korenev S. V., Shubin Yu. V., Chizhik N. A., Yurkin G. Yu., Eremin E. V.
Заглавие : The exchange interaction effects on magnetic properties of the nanostructured CoPt particles
Место публикации : J. Magn. Magn. Mater.: Elsevier, 2016. - Vol. 401. - P.236-241. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2015.10.041
Примечания : Cited References: 55. - The work has been partially supported by RFBR Grants 15-08-06673, 14-03-00411, 14-03-00129, 15-42-0417115 and it is partly performed in Siberian Federal University within the state contract of the Russian Federation Ministry of Education and Science for 2014-2016 (project number 1792)
Предметные рубрики: CLUSTER BEAM DEPOSITION
BULK MAGNETS
NANOCRYSTALLINE FERROMAGNETS
REMANENCE ENHANCEMENT
THIN-FILMS
COERCIVITY
MICROSTRUCTURE
NANOPARTICLES
IRON
SYSTEM
Аннотация: Various manifestations of the exchange interaction effects in magnetization curves of the CoPt nanostructured particles are demonstrated and discussed. The inter-grain exchange constant A in the sponge-like agglomerates of crystallites is estimated as A=(7±1) pJ/m from the approach magnetization to saturation curves that is in good agreement with A=(6.6±0.5) pJ/m obtained from Bloch T 3/2 law. The fractal dimensionality of the exchange coupled crystallite system in the porous media of the disordered CoPt alloy d=(2.60±0.18) was estimated from the approach magnetization to saturation curve. Coercive force decreases with temperature as Hc~T 3/2 which is assumed to be a consequence of the magnetic anisotropy energy reduction due to the thermal spin wave excitations in the investigated CoPt particles. © 2015 Elsevier B.V. All rightsreserved.Демонстрируются и обсуждаются различные проявления эффектов обменного взаимодействия в кривых намагниченности наноструктуированных частиц CoPt. Межзеренная обменная константа А в агломератах губчатой структуры кристаллитов оценивается как /A/=(7±1) pJ/m из кривых приближения намагниченности к насыщению, это значение находится в хорошем согласии с /A/=(6.6±0.5) pJ/m, полученным из закона /T/. /2 Блоха. Размерность фрактала обменно-соединенных кристаллических систем в пористой среды неупорядоченного сплава CoPt /d/=(2.60±0.18) оценивалась из кривых приближения намагниченности к насыщению. Коэрцитивная сила уменьшается с температурой по закону /H_c /~/T/. /2 , который, как предполагается, есть следствие уменьшения энергии магнитной анизотропии из-за теплового возбуждения спиновых волн в изучаемых частицах CoPt.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Dubrovskiy A. A., Balaev A. D., Shaykhutdinov K. A., Bayukov O. A., Pletnev O. N., Yakushkin S. S., Bukhtiyarova G. A., Martyanov O. N.
Заглавие : Size effects in the magnetic properties of ε-Fe2O3 nanoparticles
Место публикации : J. Appl. Phys.: American Institute of Physics, 2015. - Vol. 118, Is. 21. - Ст.213901. - ISSN 00218979 (ISSN), DOI 10.1063/1.4936838
Примечания : Cited References: 41. - We are grateful to Professor Yu. L. Raikher for useful discussions and M. A. Kazakova for the help in sample preparationThis work was supported by Russian Federal Agency of Scientific Organizations (Project No. V.44.1.15) and scientific and educational center of energy-efficient catalysis of NSU
Предметные рубрики: FERROMAGNETIC-RESONANCE
OXIDE NANOPARTICLES
WAVE ABSORBER
IRON
TRANSITION
TEMPERATURE
PARTICLES
PHASE
FNANOWIRES
FIELD
Аннотация: We report the results of comparative analysis of magnetic properties of the systems based on ε-Fe2O3, nanoparticles with different average sizes (from ∼3 to 9 nm) and dispersions. The experimental data for nanoparticles higher than 6-8 nm in size are consistent with the available data, specifically, the transition to the magnetically ordered state occurs at a temperature of ∼500 K and the anomalies of magnetic properties observed in the range of 80-150 K correspond to the magnetic transition. At the same time, Mossbauer and ferromagnetic resonance spectroscopy data as well as the results of static magnetic measurements show that at room temperature all the investigated samples contain ε-Fe2O3 particles that exhibit the superparamagnetic behavior. It was established that the magnetic properties of nanoparticles significantly change with a decrease in their size to ∼6 nm. According to high-resolution electron microscopy and Mossbauer spectroscopy data, the particle structure can be attributed to the ε-modification of trivalent iron oxide; meanwhile, the temperature of the magnetic order onset in these particles is increased, the well-known magnetic transition in the range of 80-150 K does not occur, the crystallographic magnetic anisotropy constant is significantly reduced, and the surface magnetic anisotropy plays a decisive role. This is apparently due to redistribution of cations over crystallographic positions with decreasing particle size, which was established using Mössbauer spectra. As the particle size is decreased and the fraction of surface atoms is increased, the contribution of an additional magnetic subsystem formed in a shell of particles smaller than ∼4 nm becomes significant, which manifests itself in the static magnetic measurements as paramagnetic contribution. © 2015 AIP Publishing LLC.
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bartolome J., Badía-Romano L., Rubin J., Bartolome F., Varnakov S. N., Ovchinnikov S. G., Burgler D.E.
Заглавие : Magnetic properties, morphology and interfaces of (Fe/Si)n nanostructures
Коллективы : International Conference on Magnetism
Место публикации : J. Magn. Magn. Mater.: Elsevier, 2016. - Vol. 400. - P.271-275. - ISSN 03048853 (ISSN), DOI 10.1016/j.jmmm.2015.07.046
Примечания : Cited References: 43. - The financial support of the Spanish MINECOMAT2011-23791 and MAT2015-53921-R, Aragonese DGA-IMANAE34 (cofounded by Fondo Social Europeo) and European FEDER funds is acknowledged. Program of the President of the Russian Federation for the support of leading scientific schools (Scientific School 2886.2014.2), RFBR (Grant no. 13-02-01265), the Ministry of Education and Science of the Russian Federation (State contract no. 02.G25.31.0043 and State task no. 16.663.2014К)
Предметные рубрики: INTERLAYER EXCHANGE
Fe/Si(100) INTERFACE
SILICIDE FORMATION
ULTRAHIGH-VACUUM
FILMS
IRON
MAGNETORESISTANCE
SUPERLATTICES
SPECTROSCOPY
DEPOSITION
Аннотация: A systematic study of the iron–silicon interfaces formed upon preparation of (Fe/Si) multilayers has been performed by the combination of modern and powerful techniques. Samples were prepared by molecular beam epitaxy under ultrahigh vacuum onto Si wafers or single crystalline Ag(100) buffer layers grown on GaAs(100). The morphology of these films and their interfaces was studied by a combination of scanning transmission electron microscopy, X-ray reflectivity, angle resolved X-ray photoelectron spectroscopy and hard X-ray photoelectron spectroscopy. The Si-on-Fe interface thickness and roughness were determined to be 1.4(1) nm and 0.6(1) nm, respectively. Moreover, determination of the stable phases formed at both Fe-on-Si and Si-on-Fe interfaces was performed using conversion electron Mössbauer spectroscopy on multilayers with well separated Si-on-Fe and Fe-on-Si interfaces. It is shown that while a fraction of Fe remains as α-Fe, the rest has reacted with Si, forming the paramagnetic FeSi phase and a ferromagnetic Fe rich silicide. We conclude that there is an identical paramagnetic c-Fe1−xSi silicide sublayer in both Si-on-Fe and Fe-on-Si interfaces, whereas an asymmetry is revealed in the composition of the ferromagnetic silicide sublayer.
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