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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : GEKHT R. S.
Заглавие : MAGNETIC TRANSITION FROM INCOMMENSURABLE TO COMMENSURABLE INTERMEDIATE PHASE AND LOW-TEMPERATURE SPIN CORRELATIONS
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1987. - Vol. 93, Is. 1. - P255-265. - ISSN 0044-4510
Примечания : Cited References: 24
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Petrakovsky G. A.
Заглавие : Quasi-particle spectrum in copper oxides
Разночтения заглавия :авие SCOPUS: Quasiparticle spectrum in copper oxides
Место публикации : J. Supercond. - 1991. - Vol. 4, Is. 6. - P.437-448. - ISSN 0896-1107, DOI 10.1007/BF00635862
Примечания : Cited References: 0
Ключевые слова (''Своб.индексиров.''): electron correlations--electron energy structure--copper oxide--photoemission data--copper oxide--electron correlations--electron energy structure--photoemission data--ceramic materials--lanthanum compounds--fermi liquid--lanthanum strontium copper oxides--oxide superconductors--quasi particles--high temperature superconductors
Аннотация: The results of electronic structure calculations of the CuO2 layer, performed by the generalized tight-binding method, are presented. The strong electron correlations on both the Cu and O ions are included explicitly. The resulting quasiparticle band structure contains an insulator gap for undoped compounds like La2CuO4. The valence band consists of a large number of narrow Hubbard quasiparticle bands. The dispersion law of quasiparticles at the top of the valence band has a minimum at the GAMMA-point, indicating the existence of the multivalley Fermi surface in the doped La2-xSrxCuO4. The origin of the Fermi liquid behavior in the narrow quasiparticle bands is discussed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : OVCHINNIKOV S. G.
Заглавие : NOVEL MECHANISM FOR THE FORMATION OF IMPURITY LEVELS IN SEMICONDUCTORS WITH THE STRONG ELECTRON CORRELATIONS
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1992. - Vol. 102, Is. 2. - P534-540. - ISSN 0044-4510
Примечания : Cited References: 8
Аннотация: In the framework of the generalized tight binding method involving the strong electron correlations it is shown that in spite of the lattice regularity the impurity-like localized levels may arise within the semiconducting gap with the deviation of the electron concentration from the integer value. The appearance of these levels is due to the contribution of multi-electron excited terms into the single-particle density of states.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Avramov P. V., Ovchinnikov S. G.
Заглавие : Effects of the intense electron correlations on the shape of x-ray CuK absorption spectra of La2-xSrxCuO4
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz.: MEZHDUNARODNAYA KNIGA, 1995. - Vol. 108, Is. 4. - P.1479-1488. - ISSN 0044-4510
Примечания : Cited References: 28
Предметные рубрики: HIGH-TC SUPERCONDUCTIVITY
EDGE STRUCTURE
LA2CUO4
SATELLITES
ALPHA
EXCITATIONS
COPPER
OXIDES
STATE
SHAKE
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Avramov P. V.
Заглавие : Effects of intense electron correlations on x-ray and x-ray electron copper spectra of high-temperature superconductors
Место публикации : Fiz. Tverd. Tela: MEZHDUNARODNAYA KNIGA, 1995. - Vol. 37, Is. 9. - P.2559-2567. - ISSN 0367-3294
Примечания : Cited References: 22
Предметные рубрики: HIGH-ENERGY SPECTROSCOPY
HIGH-TC SUPERCONDUCTORS
SATELLITES
LA2CUO4
OXIDES
HOLES
STATE
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : OVCHINNIKOV S.G.
Заглавие : THE INFLUENCE OF THE ANTIFERROMAGNETISM ON THE ELECTRONIC-STRUCTURE OF LA2CUO4
Разночтения заглавия :авие SCOPUS: The influence of the antiferromagnetism on the electronic structure of La2CuO4
Место публикации : J. Supercond.: PLENUM PUBL CORP, 1995. - Vol. 8: University-of-Miami Workshop on High-Temperature Superconductivity - Physical Properties and Mechanisms (JAN 05-11, 1995, CORAL GABLES, FL), Is. 5. - P675-676. - ISSN 0896-1107, DOI 10.1007/BF00727473
Примечания : Cited References: 15
Предметные рубрики: OXIDES
MODEL
Ключевые слова (''Своб.индексиров.''): electron correlations--electron structure--spin fluctuations--electron correlations--electron structure--spin fluctuations--antiferromagnetism--band structure--calculations--correlation theory--electrons--lanthanum compounds--paramagnetism--perturbation techniques--antiferromagnetic phase--electron correlations--intercluster interactions--spin fluctuations--electronic structure
Аннотация: The quasiparticle approach for electronic structure calculations considering strong electron correlations is given. The exact diagonalization of a multiband Hubbard Hamiltonian for a small cluster is combined with perturbation theory for intercluster hopping. The band structure of paramagnetic and antiferromagnetic La2CuO4 are discussed.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sandalov I., Johansson B., Eriksson O.
Заглавие : From local-density approximation to strong electron correlations
Место публикации : Physica B: ELSEVIER SCIENCE BV, 1999. - Vol. 259-61: International Conference on Strongly Correlated Electron Systems (SCES 98) (JUL 15-18, 1998, PARIS, FRANCE). - P229-230. - ISSN 0921-4526, DOI 10.1016/S0921-4526(98)00789-3
Примечания : Cited References: 4
Предметные рубрики:
Ключевые слова (''Своб.индексиров.''): beyond lda--correlations--diagram technique--non-orthogonality
Аннотация: We formulate a regular approach for ab initio calculations of the band structure, ground state properties (T = 0 K) and excitations (T not equal 0) which goes beyond the local-density approximation (LDA) for systems with d- and f-electrons. A diagram technique for non-zero temperature both from the itinerant and atomic limits is developed within a non-orthogonal basis which is generated by the calculation in LDA. LDA is taken as a reference point. Local electron correlations are taken into account by exact transformation of total Hamiltonian to many-electron representation. The derived system of equations for Green's functions of coupled conduction and correlated electrons (including angular momenta, etc.) is presented in closed functional form which allows to construct accurately self-consistent approximations. The approach can be used also in particular cases of any non-commutative algebras,like different spin models with strong anisotropy, or models of correlated electrons (Hubbard, Anderson) for multiple on-site orbitals. (C) 1999 Elsevier Science B.V. All rights reserved.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aplesnin S. S.
Заглавие : Quantum Monte Carlo investigation of the 2D Heisenberg model with S=1/2
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 1999. - Vol. 41, Is. 1. - P103-107. - ISSN 1063-7834, DOI 10.1134/1.1130737
Примечания : Cited References: 33
Предметные рубрики: SQUARE-LATTICE
GROUND-STATE
SPIN-CORRELATIONS
ANTIFERROMAGNET
LA2CUO4
EU2CUO4
ENERGY
ORDER
Аннотация: The two-dimensional (2D) Heisenberg model with anisotropic exchange (Delta=1-J(x)/J(z)) and S=1/2 is investigated by the quantum Monte Carlo method. The energy, susceptibility, specific heat, spin-spin correlation functions, and correlation radius are calculated. The sublattice magnetization (sigma) and the Neel temperature of the anisotropic antiferromagnet are logarithmic functions of the exchange anisotropy: 1/sigma + 1 + 0.13(1) ln(1/Delta). Crossover of the static magnetic structural factor as a function of temperature from power-law to exponential occurs for T(c)/J approximate to 0.4. The correlation radius can be approximated by 1/xi =2.05T(1.0(6))/exp(1.0(4)/ T). For La(2)CuO(4) the sublattice magnetization is calculated as sigma=0.45, the exchange is J=(1125=1305) K; for Er(2)CuO(4)J similar to 625 K and the exchange anisotropy Delta similar to 0.003. The temperature dependence of the static structural magnetic factor and the correlation radius above the Neel temperature in these compounds can be explained by the formation of topological excitations (spinons). (C) 1999 American Institute of Physics. [S1063-7834(99)02401-6].
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Avramov P. V., Ovchinnikov S. G.
Заглавие : Effects of strong electron correlations in X-ray and electron spectra of high-T-c superconductors
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2000. - Vol. 42, Is. 5. - P788-809. - ISSN 1063-7834, DOI 10.1134/1.1131293
Примечания : Cited References: 92
Предметные рубрики: HIGH-TEMPERATURE SUPERCONDUCTORS
COPPER-OXIDE SUPERCONDUCTORS
MULTIPLE-SCATTERING ANALYSIS
HIGH-ENERGY SPECTROSCOPY
ABSORPTION-SPECTRA
PHOTOELECTRON-SPECTRA
EDGE STRUCTURE
PHOTOEMISSION SPECTRA
INCOMPLETE SHELL
SINGLE-CRYSTAL
Аннотация: The current state of theoretical and experimental studies on the electronic structure of high-T-c superconductors is analyzed. The agreement between the theory and experimental spectroscopic data is shown to be rather poor in certain cases. The reason is that the X-ray and electronic spectra reveal strong electron correlations. At the same time, no realistic model has been developed up to now in which both one-electron and multielectron mechanisms of the formation of the spectra could be described in a unified way in compounds containing transition and rare-earth elements. In this paper, particular attention is paid to a sudden-perturbation model, by which it has been possible to describe or interpret some X-ray and electronic spectra, including both one-electron and multielectron effects. (C) 2000 MAIK "Nauka/Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fransson J., Eriksson O., Sandalov I.
Заглавие : Effects of non-orthogonality and electron correlations on the time-dependent current through quantum dots
Место публикации : Phys. Rev. B: AMERICAN PHYSICAL SOC, 2002. - Vol. 66, Is. 19. - Ст.195319. - ISSN 1098-0121, DOI 10.1103/PhysRevB.66.195319
Примечания : Cited References: 46
Предметные рубрики: GREENS-FUNCTION APPROACH
TUNNEL-JUNCTIONS
LOCAL OXIDATION
ANDERSON MODEL
TRANSPORT
NONORTHOGONALITY
CONDUCTANCE
EQUILIBRIUM
TRANSISTOR
IMPURITY
Аннотация: Three issues are analyzed in the physics of time-dependent tunneling current through a quantum dot with strongly correlated electrons coupled to two external contact leads: (i) nonorthogonality of the states of electrons in the leads and in the quantum dot, (ii) non-Fermi statistics of the excitations in the quantum dot, and iii) kinematic shift of the quantum dot levels. The contributions from nonorthogonality effectively decrease the mixing interaction between the leads and the quantum dot and the width of the quantum dot level whereas the Gibbs statistics slightly changes the spectral weights of quantum dot levels, and decreases the widths, but does not introduce drastical changes to the current. The kinematic interactions are taken into account within the loop correction. For the case of block signal, the time-dependent current shows oscillations starting at the onset and termination of the bias voltage pulse.
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11.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Iskhakov R. S., Ignatchenko V. A., Komogortsev S. V., Balaev A. D.
Заглавие : Study of magnetic correlations in nanostructured ferromagnets by correlation magnetometry
Место публикации : JETP Letters. - 2003. - Vol. 78, Is. 10. - P.646-650. - ISSN 0021-3640, DOI 10.1134/1.1644310
Примечания : Cited References: 20
Предметные рубрики: AMORPHOUS FERROMAGNETS
RANDOM ANISOTROPY
NANOCRYSTALLINE
SYSTEM
RIPPLE
Аннотация: We propose a theoretically justified experimental magnetometric technique for determining the size of stochastic domains spontaneously formed in the spin system of nanostructured ferromagnets and for evaluating the effective anisotropy in these magnetically correlated regions. The method is based on monitoring the DeltaM similar to H (-2) relationship in the low-field part of the integral magnetization curve. (C) 2003 MAIK "Nauka/Interperiodica".
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12.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fransson J., Holmstrom E., Eriksson O., Sandalov I.
Заглавие : Theory of spin filtering through quantum dots
Место публикации : Phys. Rev. B: AMER PHYSICAL SOC, 2003. - Vol. 67, Is. 20. - Ст.205310. - ISSN 1098-0121, DOI 10.1103/PhysRevB.67.205310
Примечания : Cited References: 28
Предметные рубрики: DEPENDENT TUNNELING JUNCTIONS
NARROW ENERGY BANDS
ELECTRON CORRELATIONS
MAGNETORESISTANCE
BARRIER
POLARIZATION
Аннотация: Using a nonequilibrium diagram technique for Hubbard operator Green functions combined with a generalization of the transfer Hamiltonian formalism, we calculate the transport through a magnetic quantum dot system with spin-dependent couplings to the contacts. In specific regimes of the parameter space the spin-dependent tunnel current becomes more than 99.95% spin polarized, suggesting that a device thus constructed can be used in spin-filter applications. First-principles electronic structure calculations show the existence of nanostructured systems, such as, e.g., MgO/Fe/Pd(5)/Fe/MgO (001), with the desired properties in the direction of the current.
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13.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : Exotic superconductivity and magnetism in ruthenates
Место публикации : Phys. Usp.: TURPION LTD, 2003. - Vol. 46, Is. 1. - P21-44. - ISSN 1063-7869, DOI 10.1070/PU2003v046n01ABEH001235
Примечания : Cited References: 167
Предметные рубрики: ITINERANT FERROMAGNET SRRUO3
SPIN-TRIPLET SUPERCONDUCTIVITY
STRONGLY CORRELATED ELECTRONS
T-J-MODEL
J-I-MODEL
TRANSPORT-PROPERTIES
MOTT-INSULATOR
FERMI-SURFACE
LAYERED PEROVSKITE
RUTHENIUM OXIDES
Ключевые слова (''Своб.индексиров.''): electronic structure--magnetic properties--magnetism--oxide superconductors--strontium alloys--superconductivity--electron correlations--ruthenates--rutheno-cuprates--spin-triplet pairing--ruthenium compounds
Аннотация: Basic experimental and theoretical results on ruthenates and rutheno-cuprates are reviewed. The electronic structure of various ruthenates and exotic superconductivity in Sr2RuO4 with spin-triplet pairing are described. The complex phase diagram of Ca2-xSrxRuO4, involving competing magnetic phases and metal-insulator transitions, is described, as are the exotic magnetic properties of Sr3Ru2O7 and of the double perovskite Sr2YRuO6, and the coexistence of superconductivity and magnetism in the rutheno-cuprate RuSr2GdCu2O8. Possible applications of Sr2RuO4 and SrRuO3 are considered. The effect of strong electron correlations is discussed, and the properties of ruthenates and cuprates are compared.
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14.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Borisov A.A., Gavrichkov V. A., Ovchinnikov S. G.
Заглавие : Temperature and concentration dependences of the electronic structure of copper oxides in the generalized tight binding method
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2003. - Vol. 97, Is. 4. - P773-780. - ISSN 1063-7761, DOI 10.1134/1.1625067
Примечания : Cited References: 25
Предметные рубрики: SUPERCONDUCTING-GAP ANISOTROPY
BAND-STRUCTURE
FERMI-SURFACE
NORMAL-STATE
BI2SR2CACU2O8+DELTA
EVOLUTION
Ключевые слова (''Своб.индексиров.''): doping (additives)--electron transitions--electronic structure--fermi level--fermi surface--electron correlations--pseudogap--tight binding method--valence band--copper oxides
Аннотация: The electronic structure of p-type doped HTSC cuprates is calculated by explicitly taking into account strong electron correlations. The smooth evolution of the electronic structure from undoped antiferromagnetic to optimally and heavily doped paramagnetic compositions is traced. For a low doping level, in-gap impurity-type states are obtained, at which the Fermi level is pinned in the low-doping region. These states are separated by a pseudogap from the valence band. The Fermi surfaces calculated for the paramagnetic phase for various concentrations of holes are in good agreement with the results of ARPES experiments and indicate a gradual change in the Fermi surface from the hole type to the electron type. (C) 2003 MAIK "Nauka/Interperiodica".
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15.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Korshunov M. M., Gavrichkov V. A., Ovchinnikov S. G., Manske D., Eremin I.
Заглавие : Effective parameters of the band dispersion in n-type high-T-c superconductors
Разночтения заглавия :авие SCOPUS: Effective parameters of the band dispersion in n-type high-Tc superconductors
Место публикации : Physica C: ELSEVIER SCIENCE BV, 2004. - Vol. 402, Is. 4. - P365-370. - ISSN 0921-4534, DOI 10.1016/j.physc.2003.10.017
Примечания : Cited References: 32
Предметные рубрики: DOPED CUPRATE SUPERCONDUCTORS
TIGHT-BINDING METHOD
QUASI-PARTICLES
COPPER OXIDES
LA2-XSRXCUO4
SYMMETRY
MODEL
EVOLUTION
ORDER
Ключевые слова (''Своб.индексиров.''): high-t-c superconductivity--electronic correlations--electron-doped cuprates--electron-doped cuprates--electronic correlations--high-tc superconductivity--approximation theory--atomic physics--band structure--binding energy--charge transfer--correlation methods--doping (additives)--electronic structure--hamiltonians--mathematical models--mathematical operators--oxide superconductors--perturbation techniques--photoelectron spectroscopy--atomic orbitals--conduction band--electron doped cuprates--electron spins--valence band--high temperature superconductors
Аннотация: The electronic structure of electron-doped cuprates is discussed in the regions of small and optimal doping. For optimal doping we obtain the parameters from a simple tight-binding analysis by fitting ARPES data, and for small doping we study the band structure by the generalized tight-binding method that takes strong electronic correlations into account explicitly. This method has also reproduced well the ARPES data for small doping. The effective low-energy Hamiltonian is the t-t'-J model with hopping parameters t and t'. We compare both methods and find very good agreement for the value of t while t' is different because it is caused by the different contribution of the short-range spin correlations. (C) 2003 Elsevier B.V. All rights reserved.
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16.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fransson J., Sandalov I., Eriksson O.
Заглавие : A perfect spin-filter quantum dot system
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2004. - Vol. 16, Is. 16. - P.L249-L254. - ISSN 0953-8984, DOI 10.1088/0953-8984/16/16/L03
Примечания : Cited References: 39
Предметные рубрики: NARROW ENERGY BANDS
ELECTRON CORRELATIONS
MAGNETIC-FIELD
MAGNETOTRANSPORT
CONDUCTANCE
RESISTANCE
BARRIER
FORMULA
VALVE
LIMIT
Ключевые слова (''Своб.индексиров.''): electric potential--electron tunneling--magnetic couplings--magnetic fields--magnetic filters--transport properties--electron correlations--magnetic contacts--source-drain voltage--spin projections--semiconductor quantum dots
Аннотация: The discovery of a novel effect in the transport through a QD spin-dependently coupled to magnetic contacts is reported. For a finite range of source-drain voltages the spin projections of the current cancel exactly, resulting in a completely suppressed output current. The spin down current behaves as one normally expects whereas the spin up current becomes negative. As the source-drain voltage is increased the spin up current eventually becomes positive. Thus, tuning the source-drain voltage such that the spin up current vanishes will result in a perfect spin filter.
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17.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Zabluda V. N.
Заглавие : The energy band structure and optical spectra of FeBO3 calculated with allowance for strong electron correlations
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2004. - Vol. 98, Is. 1. - P135-143. - ISSN 1063-7761, DOI 10.1134/1.1648107
Примечания : Cited References: 32. - This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286) and by the “Strongly Correlated Electrons” Program of the Department of Physical Sciences of the Russian Academy of Sciences
Предметные рубрики: PHASE-TRANSITION
HIGH-PRESSURE
FERROMAGNETISM
MODEL
Ключевые слова (''Своб.индексиров.''): atomic physics--band structure--charge transfer--excitons--green's function--light absorption--dielectric gap--energy band structure--lehmann spectral representation--optical spectra--iron compounds
Аннотация: A model of the energy band structure of iron borate (FeBO3) is proposed that combines a one-electron description of the sp states of boron and oxygen with a many-electron description of the d states of iron. The Green functions of d electrons are calculated using the exact Lehmann spectral representation. The energies of the d-type quasiparticles are calculated using terms of the d(4) , d(5) , and d(6) electron configurations. The optical absorption spectrum of FeBO3 is determined by local excitons and by the electron excitations with charge transfer. The latter excitations control the nature of the dielectric gap in FeBO3 crystals. The model parameters are determined from a comparison to the exciton energies. The density of single-particle states in FeBO3 is calculated. The main bands in the calculated optical absorption spectrum agree well with experimental data for energies up to 3 eV. (C) 2004 MAIK "Nauka/Interperiodica".
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18.

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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19.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Komogortsev S. V., Iskhakov R. S.
Заглавие : Magnetization curve and magnetic correlations in a nanochain of ferromagnetic grains with random anisotropy
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2005. - Vol. 47, Is. 3. - P495-501. - ISSN 1063-7834, DOI 10.1134/1.1884711
Примечания : Cited References: 31
Предметные рубрики: NANOCRYSTALLINE FERROMAGNETS
AMORPHOUS FERROMAGNETS
FIELD
MODEL
MICROSTRUCTURE
SIMULATIONS
DEPENDENCE
SYMMETRY
SYSTEM
MEDIA
Аннотация: The magnetization curve and magnetization correlation function are calculated for a ferromagnetic chain of single-domain nanoparticles with a randomly oriented anisotropy axis for different ratios between the exchange correlation and anisotropy energies. It is shown that the coercive force decreases as the exchange correlations increase. For strong exchange correlations, the magnetization curve is described by the following three successive magnetization processes as the applied field is increased: (i) nonuniform rotation of the magnetization of stochastic domains, (ii) collapse of the magnetic solitons, and (iii) nonuniform rotation of exchange-correlated magnetization vectors of the nanoparticles. For high fields, the calculated correlation function of the transverse magnetization components coincides with that predicted from linear theory. At low and zero fields, the main parameters of the correlation function (the variance and correlation radius) tend to certain finite values rather than diverge (as is the case in linear theory). The irreversible variation in the magnetization at low fields (the hysteresis loop) and the hysteresis of the main parameters of the correlation function are calculated. (c) 2005 Pleiades Publishing, Inc.
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20.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G.
Заглавие : The mechanism of the electronic transition in ferroborates under high pressure
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 2005. - Vol. 17: 2nd International Symposium on Physics of Solids Under High Pressure Using Nuclear Probes (JUL 20-24, 2004, Cologne, GERMANY), Is. 11. - P.S743-S751. - ISSN 0953-8984, DOI 10.1088/0953-8984/17/11/003
Примечания : Cited References: 20
Предметные рубрики: STRUCTURAL PHASE-TRANSITION
MAGNETIC COLLAPSE
OPTICAL-SPECTRA
BAND-STRUCTURE
FEBO3
MODEL
Ключевые слова (''Своб.индексиров.''): carrier concentration--correlation methods--electron transitions--high pressure effects--magnetic moments--mathematical models--metal insulator transition--crystal field--electron correlations--electronic transition--ferroborates--ferromagnetic materials
Аннотация: A novel mechanism for the insulator-semiconductor transition and magnetic collapse in FeBO3 is proposed in the framework of the multielectron model with account taken of strong electron correlations. The electronic transition results from the crossover of the high spin and low spin Fe3+ states induced by the crystal field increasing with pressure. In the high pressure phase a semiconductor-metal transition is expected.
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