Библиотека института физики им. Л.В. Киренского СО РАН

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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bezmaternykh L. N., Sofronova S. N., Volkov N. V., Eremin E. V., Bayukov O. A., Nazarenko I. I., Velikanov D. A.
Заглавие : Magnetic properties of Ni3B2O6 and Co3B2O6 single crystals
Место публикации : Phys. Status Solidi B. - 2012. - Vol. 249, Is. 8. - P.1628-1633. - ISSN 0370-1972, DOI 10.1002/pssb.201147518
Примечания : Cited References: 12. - This study was supported by the Siberian Branch of the Russian Academy of Sciences, Integration project no. 101.
Предметные рубрики: DIELECTRICS
Ключевые слова (''Своб.индексиров.''): antiferromagnets--crystal growth--magnetics structure--ni3b2o6 and co3b2o6 single crystals
Аннотация: Orthorhombic Me3B2O6 (Me = Co, Ni) single crystals of the kotoite family are grown from the fluxes based on a mixture of bismuth trimolybdate and sodium oxide upon spontaneous nucleation. The field and temperature dependences of magnetization of the single crystals with the magnetic field oriented along the principal crystallographic directions are obtained. Unlike Ni3B2O6, Co3B2O6 exhibits strong anisotropy of the magnetic properties. At the temperature T = 10 K, the magnetization curves of Co3B2O6 reveal an anomaly attributed to the spin-reorientation transition. Strong anisotropy of the magnetic properties of Co3B2O6 is also confirmed by the calculation of the exchange interactions within a simple indirect coupling model.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Malakhovskii A. V., Gnatchenko S. L., Kachur I. S., Piryatinskaya V. G., Sukhachev A. L., Gudim, I. A.
Заглавие : Optical and magneto-optical properties of Nd0.5Gd0.5Fe3(BO3)4 single crystal in the near IR spectral region
Место публикации : J. Alloys Compd.: Elsevier, 2012. - Vol. 542. - P.157-163. - ISSN 0925-8388, DOI 10.1016/j.jallcom.2012.07.061
Примечания : Cited References: 23. - The work was supported by the Russian Foundation for Basic Researches Grant 12-02-00026 and by the Russian President Grant SS-1044.2012.2.
Предметные рубрики: MAGNETIC CIRCULAR-DICHROISM
GDFE3(BO3)(4)
YB3+
ER3+
ND3+
Ключевые слова (''Своб.индексиров.''): rare earth compounds--nd3+--antiferromagnets--multiferroics--magnetic circular dichroism--absorption spectra
Аннотация: Polarized optical absorption and magnetic circular dichroism (MCD) spectra of the trigonal multiferroic Nd0.5Gd0.5Fe3(BO3)4 were studied in the region of transitions 4I9/2 → 4F3/2 and 4I9/2 → (4F5/2 + 2H9/2) in Nd3+ ion. Components of the crystal field splitting of the states were identified with the help of MCD and polarized absorption spectra. Splitting of the Nd3+ absorption lines caused by the magnetic ordering were observed. Splitting of Nd3+ ground state in Fe-sublattice exchange field was found to be ∼9 cm−1 at 5.7 K. The Zeeman splitting of some absorption lines in the external magnetic field and changes of the effective Landé factors in the C3-direction as a result of the corresponding optical transitions were found. Peculiarities in the temperature behavior of the absorption lines connected both with the ground and excited states were revealed. Peculiarities connected with the excited states testify to the local crystal distortions in the excited states.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Malakhovskii A. V., Sukhachev A. L., Vasil'ev A. D., Leont'ev A. A., Kartashev A. V., Temerov V. L., Gudim, I. A.
Заглавие : Nature of optical properties of GdFe3(BO3)4 and GdFe2.1Ga0.9(BO3)4 crystals and other 3d5 antiferromagnets
Место публикации : Eur. Phys. J. B: Springer, 2012. - Vol. 85, Is. 2. - P.80. - ISSN 1434-6028, DOI 10.1140/epjb/e2012-20953-1
Примечания : Cited References: 70. - The work was supported by the Russian Foundation for Basic Researches Grant 12-02-00026 and by Russian President Grant NSh-1044.2012.2.
Предметные рубрики: IRON BORATE GDFE3(BO3)4
D-D TRANSITIONS
EARTH FERROBORATES RFE3(BO3)4
ABSORPTION-SPECTRA
OCTAHEDRAL COMPLEXES
ELECTRONIC-STRUCTURE
NEEL TEMPERATURE
FINE-STRUCTURE
EXCHANGE
IONS
Аннотация: Influence of the partial substitution of paramagnetic Fe3+ ions by diamagnetic Ga3+ ions in the trigonal crystal GdFe3 (BO3)4 on its optical and magnetic properties is studied and discussed in connection with problems common for all antiferromagnets containing 3d 5 ions. Polarized optical absorption spectra and linear birefringence of GdFe3 (BO3)4 and GdFe2.1Ga0.9 (BO3)4 single crystals have been measured in the temperature range 85–293 K. Specific heat temperature dependence (2–300 K) and structure of GdFe2.1Ga0.9 (BO3)4 crystal have been also studied. As a result of substitution of 30% Fe to Ga the Neel temperature diminishes from 38 till 16 K, the strong absorption band edge shifts on 860 cm-1 (0.11 eV) to higher energy and the d-d transitions intensity decreases substantially larger than the Fe concentration does. Strong absorption band edge is shown to be due to Mott-Hubbard transitions. Correlation between position of the strong absorption band edge and the Neel temperature of antiferromagnets has been revealed. Properties of the doubly forbidden d-d transitions in the studied crystals and in other antiferromagnets are explained within the framework of the model of the exchange-vibronic pair absorption, which is theoretically analyzed in detail. The model permitted us to determine the connection between parameters of d-d absorption bands (intensity, width and their temperature dependences), on the one hand, and the exchange, spin-orbit and electron-lattice interactions, on the other hand.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Kazak N. V., Platunov M. S., Knyazev, Yu. V., Ivanova, N. B., Bayukov O. A., Vasiliev A. D., Bezmaternykh L. N., Nizhankovskii, V. I., Gavrilkin, S. Yu., Lamonova, K. V., Ovchinnikov S. G.
Заглавие : Uniaxial anisotropy and low-temperature antiferromagnetism of Mn2BO4 single crystal
Коллективы : 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 [5468GU1/2014]
Место публикации : J. Magn. Magn. Mater.: Elsevier Science, 2015. - Vol. 393. - P.316-324. - ISSN 0304-8853, DOI 10.1016/j.jmmm.2015.05.081. - ISSN 18734766(eISSN)
Примечания : Cited References:33. - The authors wish to thank to Prof. M.V.Gorev and Prof J. Bartolome for fruitful discussions, Russian Foundation for Basic Research (Projects no13-02-00958, 13-02-00358, and 14-02-31051-mol-a), Council for Grants of the President of the Russian Federation (Project nos. 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 (Grant number 5468GU1/2014) ("UMNIK" program).
Предметные рубрики: MAGNETIC-PROPERTIES
WARWICKITE
OXYBORATE
PARAMETERS
LUDWIGITE
Ключевые слова (''Своб.индексиров.''): antiferromagnets--oxides--magnetic anisotropy--exchange interactions
Аннотация: The Mn2BO4 single crystals have been grown by the flux technique. A careful study of the crystal structure and magnetic properties have been carried out The antiferromagnetic transition at T-N=26 K has been traced through the dc magnetization and specific heat temperature dependences. Magnetic uniaxial anisotropy has been found with easy axis magnetization lying in the ab-plane. The obtained value of effective magnetic moment is assigned to the non-quenched orbital moment of Jahn-Teller Mn3+ ions. The discussion of magnetic properties is based on the superexchange interaction calculations. (C) 2015 Elsevier B.V. All rights reserved.
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Вид документа : Статья из сборника (однотомник)
Шифр издания :
Автор(ы) : Val'kov V. V., Zlotnikov A. O.
Заглавие : Spin wave theory of heavy-fermion antiferromagnets in the framework of the periodic anderson model
Коллективы : "Spin Waves", International Simposium, Физико-технический институт им. А.Ф. Иоффе РАН
Место публикации : Spin Waves 2015, Int. Symp.: abstracts. - СПб., 2015
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Golovnya A. A., Korovushkin M. M.
Заглавие : Pseudogap formation in copper oxide superconductors with inclusion of spin and charge fluctuations
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 10. - P2001-2004. - ISSN 1063-7834, DOI 10.1134/S1063783411100349
Примечания : Cited References: 15. - This study was supported by the Presidium of the Russian Academy of Sciences (Program "Quantum Physics of Condensed Matter"), the Russian Foundation for Basic Research (project no. 09-02-00127), the Siberian Branch of the Russian Academy of Sciences (Interdisciplinary Integration project no. 53), and the Ministry of Education and Science of the Russian Federation (Russian Federal Targeted Program "Scientific and Scientific-Pedagogical Personnel of the Innovative Russia" in 2009-2013).
Предметные рубрики: ANTIFERROMAGNETS
DYNAMICS
Аннотация: The influence of spin and charge fluctuations on the pseudogap formation in cuprate superconductors has been studied using the diagram technique for Hubbard operators. It has been shown that the joint inclusion of the spin and charge fluctuations leads to the formation of "shadow" bands with a strong modulation of the spectral intensity and to a decrease in the density of electronic states at the Fermi level.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Golovnya A. A., Korovushkin M. M.
Заглавие : Kinematic mechanism of the modulation of the spectral intensity in the spatially uniform system of Hubbard fermions
Место публикации : JETP Letters. - 2011. - Vol. 94, Is. 3. - P.197-201. - ISSN 0021-3640, DOI 10.1134/S0021364011150148
Примечания : Cited References: 21. - We are grateful to R.O. Zaitsev and N.M. Plakida for the constructive criticism and helpful discussions. This work was supported by the Presidium of the Russian Academy of Sciences (program "Quantum Physics of Condensed Matter"), the Russian Foundation for Basic Research (project no. 09-02-00127), the Ministry of Education and Science of the Russian Federation (federal program "Scientific and Pedagogical Personnel of Innovative Russia" for 2009-2013), and the Siberian Branch, the Russian Academy of Sciences (integration project no. 53). The work of A.A.G. and M.M.K. was also supported by the Council of the President of the Russian Federation for Support of Young Scientists and Leading Scientific Schools (grant no. MK-1300-2011.2) and by the Siberian Branch, Russian Academy of Sciences (Lavrent'ev Competition).
Предметные рубрики: SPIN SUSCEPTIBILITY
ANTIFERROMAGNETS
DYNAMICS
CHARGE
MODEL
Аннотация: Using the exact representation of the Green's function constructed in terms of the Hubbard operators, it has been shown that the kinematic interaction that induces the spin-fluctuation processes in the spatially uniform system of Hubbard fermions leads to significant variations in the spectral intensity A(k, omega) in the Brillouin zone. As a result, the modulation of A(k, omega) appears in the Fermi contour. The sign of the hopping integral within the first coordination sphere is determined by the contour section, where A(k, omega) decreases according to the angle-resolved photoemission spectroscopy data.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Fedoseev A. D.
Заглавие : Thermodynamic properties of two-layer quasi-two-dimensional antiferromagnets
Место публикации : Theor. Math. Phys.: SPRINGER, 2011. - Vol. 168, Is. 3. - P1216-1224. - ISSN 0040-5779, DOI 10.1007/s11232-011-0099-6
Примечания : Cited References: 16. - This work was supported in part by the Russian Foundation for Basic Research (Grant No. 10-02-00251), the Presidium of the Russian Academy of Sciences (Fundamental Research Program "Quantum Physics of Condensed Matter"), the Siberian Branch of the Russian Academy of Sciences (Integration Project No. 53 and Lavrentiev Competition of Youth Projects, A. D. F.), the Ministry of Education and Science of the Russian Federation (Program "Scientific and Pedagogical Personnel of Innovative Russia" for 2009-2013), and the President of the Russian Federation (Grant No. MK-1300.2011.2, A. D. F.).
Предметные рубрики: HEISENBERG-MODEL
SPIN-WAVE
Ключевые слова (''Своб.индексиров.''): antiferromagnetism--high-temperature superconductor--tyablikov approximation--green's function--antiferromagnetism--green's function--high-temperature superconductor--tyablikov approximation
Аннотация: For two-layer quasi-two-dimensional antiferromagnets of type YBaCuO in the Tyablikov approximation, we investigate the dependences of the energy spectrum and the temperature of transition into an ordered state on both the quasi-two-dimensionality parameter and the intensity of the exchange coupling of spin moments located in two close planes. We assume that the exchange parameters inside the CuO (2) planes are much greater than the exchange parameters resulting in coupling between a spin located on a plane of an elementary cell and a spin on another plane of a different elementary cell. The obtained expressions for the N,el temperature and for the sublattice magnetic moment at zero temperature describe the dependences of these quantities on the parameters of interplane exchange interactions.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shaykhutdinov K. A., Popkov S. I., Semenov S. V., Balaev D. A., Dubrovskiy A. A., Sablina K. A., Sapronova N. V., Volkov N. V.
Заглавие : Low-temperature resistance and magnetoresistance hysteresis in polycrystalline (La0.5Eu0.5)(0.7)Pb0.3MnO3
Разночтения заглавия :авие SCOPUS: Low-temperature resistance and magnetoresistance hysteresis in polycrystalline (La0.5Eu0.5)0.7Pb 0.3MnO3
Место публикации : J. Appl. Phys.: AMER INST PHYSICS, 2011. - Vol. 109, Is. 5. - Ст.53711. - ISSN 0021-8979, DOI 10.1063/1.3559303
Примечания : Cited References: 20. - This study was partially supported by the Russian Foundation for Basic Research, Project No. 08-02-00259a and the Lavrentyev Competition of the Young Scientists' Projects of the Siberian Branch of the Russian Academy of Sciences, Project No. 12.
Предметные рубрики: RESISTIVITY MINIMUM
MANGANITES
FILMS
Ключевые слова (''Своб.индексиров.''): antiferromagnets--electrical resistances--ferromagnets--field dependence--inter-grain--lanthanum manganites--low temperatures--low-temperature resistance--polycrystalline--temperature dependence--tunnel contacts--antiferromagnetic materials--europium--ferromagnetic materials--ferromagnetism--hysteresis--lead--magnetic field effects--magnetoelectronics--magnetoresistance--magnets--manganese oxide--paramagnetism--superconducting materials--electric resistance
Аннотация: The behavior of temperature dependences of electrical resistance and magnetoresistance of polycrystalline substituted lanthanum manganite (La0.5Eu0.5)(0.7)Pb0.3MnO3 at low temperatures was thoroughly studied. A broad hysteresis was found in the field dependences of electrical resistance in the low-temperature region. Above 40 K, no hysteresis feature was observed. The temperature T = 40 K corresponds to the temperature of minimum electrical resistance and the temperature T-N to the antiferromagnet-paramagnet phase transition of the material of the intergrain boundaries. In this work we propose a model which explains the observed features of the rho(T) and rho(H) curves at temperatures below T-N by the formation of a network of ferromagnet-antiferromagnet-ferromagnet tunnel contacts. (C) 2011 American Institute of Physics. [doi:10.1063/1.3559303]
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gorev M., Bogdanov E. V., Flerov I. N., Laptash N. M.
Заглавие : Thermal expansion, phase diagrams and barocaloric effects in (NH4)(2)NbOF5
Коллективы :
Разночтения заглавия :авие SCOPUS: Thermal expansion, phase diagrams and barocaloric effects in (NH 4)2NbOF5
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2010. - Vol. 22, Is. 18. - Ст.185901. - ISSN 0953-8984, DOI 10.1088/0953-8984/22/18/185901
Примечания : Cited References: 17. - This work was supported in part by the Krasnoyarsk Regional Foundation for Support of Scientific and Scientific-Technological Investigations and RFBR in the framework of project 'Siberia' (Grant No. 09-02-98001), and the Council on Grants from the President of the Russian Federation for Support of Leading Scientific Schools (project No. Nsh-1011.2008.2).
Предметные рубрики: CRYSTAL-STRUCTURE
SOLID-STATE
OXYFLUORIDE
TRANSITION
ANION
Ключевые слова (''Своб.индексиров.''): antiferromagnets--ferromagnets--heat capacities--high stress--intermediate phase--pippard relations--structural phase transition--transition temperature--uniaxial pressures--financial data processing--phase diagrams--phase transitions--thermal stress--tools--thermal expansion
Аннотация: The thermal expansion along the a, b and c axes of a (NH4)(2)NbOF5 crystal was measured from 120 to 300 K. Anomalies of alpha(T) associated with previously reported phase transitions Cmc2(1) - C-2 - I a were observed along all directions at T-1 = 259.3 K and T-2 = 220.5 K. The analysis of thermal expansion and heat capacity in the frame of the Pippard relations has permitted us to determine the uniaxial pressure derivatives of the transition temperatures dT/d sigma(i). The T-sigma(i) phase diagrams have shown a tendency for the intermediate phase to disappear at high stress along the b and c axes. Intensive and extensive barocaloric effects near the structural phase transitions were found to be comparable with the caloric parameters of some ferroelectrics, ferromagnets and antiferromagnets.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Janoschek M., Fischer P., Schefer J., Roessli B., Pomjakushin V., Meven M., Petricek V., Petrakovskii G. A., Bezmaternykh L. N.
Заглавие : Single magnetic chirality in the magnetoelectric NdFe3((BO3)-B-11)(4)
Разночтения заглавия :авие SCOPUS: Single magnetic chirality in the magnetoelectric NdFe3( 11BO3 )4
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2010. - Vol. 81, Is. 9. - Ст.94429. - ISSN 1098-0121, DOI 10.1103/PhysRevB.81.094429
Примечания : Cited References: 55
Предметные рубрики: NEUTRON-DIFFRACTION
PHASE-TRANSITIONS
SLOW-NEUTRONS
CRYSTAL
NDFE3(BO3)(4)
EXTINCTION
NUCLEAR
ORDER
MNSI
ANTIFERROMAGNETS
Аннотация: We have performed an extensive study of single crystals of the magnetoelectric NdFe3 ((BO3)-B-11)(4) by means of a combination of single-crystal neutron diffraction and spherical neutron polarimetry. Our investigation did not detect significant deviations at low temperatures from space group R32 concerning the chemical structure. With respect to magnetic ordering our combined results demonstrate that in the commensurate magnetic phase below T-N approximate to 30 K all three magnetic Fe moments and the magnetic Nd moment are aligned ferromagnetically in the basal hexagonal plane but align antiferromagnetically between adjacent planes. The phase transition to the low-temperature incommensurate (IC) magnetic structure observed at T-IC approximate to 13.5 K appears to be continuous. By means of polarized neutron studies it could be shown that in the incommensurate magnetic phase the magnetic structure of NdFe3((BO3)-B-11)(4) is transformed into a long-period antiferromagnetic helix with single chirality. Close to the commensurate-incommensurate phase transition third-order harmonics were observed, which in addition indicate the formation of magnetic solitons.
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Dzebisashvili D. M.
Заглавие : Electron spectrum and heat capacity of heavy fermions in the canted phase of antiferromagnetic intermetallides
Коллективы :
Место публикации : J. Exp. Theor. Phys. - 2010. - Vol. 110, Is. 2. - P.301-318. - ISSN 1063-7761, DOI 10.1134/S1063776110020147
Примечания : Cited References: 41. - This study was supported by the program "Quantum Physics of Condensed Media" of the Presidium of the Russian Academy of Sciences, interdisciplinary integration project no. 53 of the Siberian Branch of the Russian Academy of Sciences, and the Russian Foundation for Basic Research (project no. 07-02-00226).
Предметные рубрики: PERIODIC ANDERSON MODEL
PRESSURE-INDUCED SUPERCONDUCTIVITY
KONDO-LATTICE
FERROMAGNETISM
FLUCTUATIONS
COEXISTENCE
CERHIN5
SYSTEMS
DIAGRAM
CENISN
Ключевые слова (''Своб.индексиров.''): antiferromagnetic phase--antiferromagnetics--antiferromagnets--electron spectrum--electronic heat capacity--energy spectra--experimental data--external magnetic field--heat capacities--heavy fermion--low temperatures--magnetic sublattices--magnetic subsystems--sommerfeld constant--structural rearrangement--temperature dependence--antiferromagnetism--cerium--cerium compounds--fermions--magnetic fields--phase transitions--specific heat--spectroscopy--antiferromagnetic materials
Аннотация: The energy spectrum of heavy fermions in an external magnetic field is calculated for canted magnetic sublattices of antiferromagnetic intermetallides. This makes it possible to determine low-temperature features of electronic heat capacity of heavy-fermion antiferromagnets with the metal-type ground state taking into account the structural rearrangement of the magnetic subsystem. The calculated temperature dependences of the magnetization, heat capacity, and Sommerfeld constant in the vicinity of the point of transition to the antiferromagnetic phase correlate with experimental data obtained for heavy-fermion antiferromagnets PuGa3, Ce2Au2Cd, YbNiSi3, and PuPd5Al2.
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13.

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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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : A quantum spin liquid in a two-layer triangular antiferromagnet
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 5. - P868-880. - ISSN 1063-7761, DOI 10.1134/1.2149066
Примечания : Cited References: 43
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
DIMER GROUND-STATE
MEAN-FIELD THEORY
HEISENBERG-ANTIFERROMAGNET
SYSTEM SRCU2(BO3)(2)
PHASE-TRANSITION
GAP
FLUCTUATIONS
EXCITATIONS
LATTICE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--magnetic fields--magnetization--phase diagrams--spectrum analysis--thermodynamics--analogous systems--square lattices--thermodynamic quantities--two-layer triangular antiferromagnets--quantum theory
Аннотация: The possibility of implementing a quantum-spin-liquid-type state in a two-layer triangular spin-1/2 antiferromagnet at T = 0 is investigated. The ratio of intra- to interlayer exchange constants (j) is found under which a transition from the classical state with 120 degrees triangular order to a quantum state with zero magnetization per site occurs; in this case, the spins of adjacent layers form singlets that are separated from triplet excitations by an energy gap. Compared with an analogous system with the square lattice, the range of j in which the classical ordered state is realized turns out to be an order of magnitude smaller due to the effects of frustration; in this case, the behavior of thermodynamic quantities is analogous, on the whole, to that in two-layer square lattices; a difference manifests itself in the behavior of the gap in the spectrum of quasiparticles in an external magnetic field h. For small fields h, a j-h phase diagram is constructed that determines the domains in which the 120 degrees and the singlet phases exist. It is established that, in the neighborhood of the second-order phase transition, the contribution, to the thermodynamic quantities, of longitudinal spin fluctuations, which are disregarded in the spin-wave description, is comparable to the contribution of transverse fluctuations. (c) 2005 Pleiades Publishing, Inc.
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Petrakovskii G. A., Bezmaternykh L. N., Bayukov O. A.
Заглавие : Antiferromagnetic resonance and phase diagrams of gadolinium ferroborate GdFe3(BO3)(4)
Разночтения заглавия :авие SCOPUS: Antiferromagnetic resonance and phase diagrams of gadolinium ferroborate GdFe3(BO3)4
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2004. - Vol. 99, Is. 4. - P766-775. - ISSN 1063-7761, DOI 10.1134/1.1826168
Примечания : Cited References: 16
Ключевые слова (''Своб.индексиров.''): anisotropy--antiferromagnetic materials--antiferromagnetism--phase diagrams--resonance--single crystals--antiferromagnetic resonance--antiferromagnets--crystal axis--transition fields--gadolinium compounds
Аннотация: Antiferromagnetic resonance in single crystals of rhombohedral gadolinium ferroborate GdFe3(BO3)(4) was studied. The frequency-field dependences of antiferromagnetic resonance over the frequency range 26-70 GHz and the temperature dependences of resonance parameters for magnetic fields oriented along the crystal axis and in the basal plane were determined. It was found that the iron subsystem, which can be treated as a two-sublattice antiferromagnet with anisotropy of the easy-plane type, experienced ordering at T = 38 K. At temperatures below 20 K, the gadolinium subsystem with the opposite anisotropy sign strongly influenced the anisotropic properties of the crystal. This resulted in a spontaneous spin-reorientation transition from the easy-plane to the easy-axis state at 10 K. Below 10 K, magnetic field-induced transitions between the states were observed. Experimental phase diagrams on the temperature-magnetic field plane were constructed for fields oriented along the crystal axis and in the basal plane. A simple model was used to calculate the critical transition fields. The results were in close agreement with the experimental values measured at T = 4.2 K for both field orientations. (C) 2004 MAIK "Nauka / Interperiodica".
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Static and dynamic magnetic properties of coupled spin-1/2 antiferromagnetic chains
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2000. - Vol. 12, Is. 37. - P.8191-8207. - ISSN 0953-8984, DOI 10.1088/0953-8984/12/37/316
Примечания : Cited References: 21
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
SYSTEMS
SUSCEPTIBILITY
EXCITATIONS
SR2CUO3
CA2CUO3
KCUF3
Ключевые слова (''Своб.индексиров.''): computational methods--copper compounds--correlation methods--functions--magnetic field effects--magnetic properties--magnetization--monte carlo methods--quantum theory--specific heat--thermal effects--excitation spectroscopy--interchain coupling--intrachain couplings--mean-field approximation--spin-spin correlation function--spinons--antiferromagnetic materials
Аннотация: Calculations of the thermodynamic quantities, and the spectra of spinons, triplet excitations, and two-particle spin-singlet (Delta S-z = 0, +/- 1) excitations for a weakly coupled antiferromagnetic S = 1/2 spin chain are made using a mean-field approximation for the interchain couplings (J(2)) by the quantum Monte Carlo method. The mass gaps in these excitation spectra are estimated as functions of the interchain coupling. The critical held H-c, and the temperatures at which the spinon and singlet gaps close (T-1 and T-2, respectively) are obtained. Some peculiarities of the staggered magnetization, the specific heat, and the spin-spin correlation function are found at T-1 = 0.9J(2), T-2 = 1.5J(2), H-c = 3.8J(2), as determined by linear function fitting for J(2)/J(1) 0.15 The intrachain and interchain couplings, and the staggered magnetization for KCuF3, Sr2CuO3, and Ca2CuO3 are estimated, and mass gaps are predicted to exist in the spectra of the spinons and the singlet two-particle excitations.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum spin liquid in the 2D anisotropic Heisenberg model with frustrated next nearest neighbor exchange
Место публикации : Low Temp. Phys. - 1998. - Vol. 24, Is. 8. - P.572-577. - ISSN 1063-777X, DOI 10.1063/1.593639; \b Физика низких температур
Примечания : Cited References: 25
Предметные рубрики: SQUARE-LATTICE ANTIFERROMAGNETS
VALENCE BOND STATES
SYSTEMS
SUPERCONDUCTIVITY
SYMMETRY
Аннотация: The two-dimensional (2D) Heisenberg model with anisotropic exchange (Delta = 1 - J(x)/J(z)) and with negative next nearest neighbor exchange (J(2)) with S = 1/2 is investigated by using the quantum-mechanical Monte-Carlo method. The energy, magnetic moment at a site, heat capacity, and spin-spin correlation functions are calculated. The stability regions for Neel ordering of spins as well as the strip-phase and gapless quantum spin liquid are determined in the interval Delta/2 less than or equal to J(2)/ J(1)less than or equal to 1/(2 Delta). (C) 1998 American Institute of Physics. [S1063-777X(98)00808-1].
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18.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Dimer state in the two-dimensional anisotropic alternated-exchange Heisenberg model
Место публикации : Phys. Solid State: AMER INST PHYSICS, 1998. - Vol. 40, Is. 6. - P986-990. - ISSN 1063-7834, DOI 10.1134/1.1130463
Примечания : Cited References: 14
Предметные рубрики: SPIN-PEIERLS
HUBBARD-MODEL
SUPERCONDUCTIVITY
ANTIFERROMAGNETS
Аннотация: An analysis is made of the two-dimensional Heisenberg model with S = 1/2, anisotropic exchange interaction between nearest neighbors, and alternating exchange in two directions, [100] and [010] (corresponding to condensation of the (pi,pi) mode) and in one direction [100] (corresponding to condensation of the (pi,0) mode), The quantum Monte Carlo method is used to calculate the thermodynamic characteristics and the spin correlation functions which are used as the basis to determine the boundary of stability of an anisotropic antiferromagnetic with respect to alternation of exchange delta = (1 - J(x,y) / J(z))(0.4) in the (pi,pi) model and delta = (1 - J(x,y) / J(z))(0.31) in the (pi,0) model. In the (pi,0) model a disordered quantum state exists in the range (1 - J(x,y) / J(z))(0.31) delta (0.3-0.35). The energy (E - 0.68)
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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Val'kov V. V., Mitskan V. A., Petrakovskii G. A.
Заглавие : The magnetoelastic mechanism of singlet phase formation in a two-dimensional quantum antiferromagnet
Место публикации : J. Exp. Theor. Phys.: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 102, Is. 2. - P234-247. - ISSN 1063-7761, DOI 10.1134/S106377610602004X
Примечания : Cited References: 18
Предметные рубрики: GROUND-STATE
SPIN
TRANSITION
CUGEO3
MODEL
Ключевые слова (''Своб.индексиров.''): crystal lattices--elasticity--mathematical models--oscillations--phase diagrams--phase transitions--quantum theory--two dimensional--atomic representation--magnetoelastic mechanism--quantum antiferromagnets--singlet phase formation--antiferromagnetic materials
Аннотация: A model describing the second-order phase transition with respect to the magnetoelastic coupling parameter from the anti ferromagnetic (AFM) to the singlet state in a two-dimensional quantum magnet on a square lattice is proposed. The spectrum of elementary excitations in the singlet and AFM phases is calculated using an atomic representation, and the evolution of transverse and longitudinal branches of this spectrum is studied in the vicinity of the transition point. It is established that the AFM to singlet phase transition is related to softening of the longitudinal branch of oscillations. In the singlet phase, the gap plays the role of a parameter characterizing the distance to the phase transition point. It is shown that the spectrum of transverse oscillations in the AFM phase corresponds to the Goldstone boson. Based on an analysis of the stability of the spectrum of elementary excitations, a phase diagram is constructed that determines the regions of the existence of phases with plaquette-deformed lattices.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Epikhin A. M., Ponomarev V. I.
Заглавие : Magnetic states and spin-wave excitations in strongly frustrated 2d heisenberg antiferromagnets
Место публикации : Phys. Lett. A. - 1995. - Vol. 201, Is. 2-3. - P.247-251. - ISSN 0375-9601, DOI 10.1016/0375-9601(95)00222-O
Примечания : Cited References: 19
Аннотация: It is shown that frustrations caused by additional spins result in a greater variety of phases with commensurate and incommensurate periods as well as in the appearance of nonperiodic phases. It is established that a single-e modulated phase is unstable against zero-point motions. As a result, a disordered state with zero magnetization at a site can exist in a wide range of values of the frustration parameters.
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