Alexei Grechnev - Academia.edu (original) (raw)

Papers by Alexei Grechnev

Research paper thumbnail of Crystal-field phenomena in hcp H 2 and D 2 at high pressures

Physical Review B, 2014

ABSTRACT

Research paper thumbnail of Raman scattering in hcp rare gas solids under pressure

Physical Review B Condensed Matter and Materials Physics, Jul 1, 2008

We present Raman measurements of hcp rare gas solids (RGSs) at megabar pressures together with la... more We present Raman measurements of hcp rare gas solids (RGSs) at megabar pressures together with lattice dynamics calculations. The E2g phonon was measured in Xe up to metallization near 135 GPa and in Ar up to 58 GPa. A comparative analysis of first-principles and semiempirical calculations shows that three-body forces contribute to the energetics at low pressures and that at volume compressions greater than ˜2.6 higher-order many-body forces become important. The distinct behavior of He under pressure relative to that of the rest of the RGS family is discussed.

Research paper thumbnail of Unusual manetism and MAE in CrPt$_3$

Journal of Magnetism and Magnetic Materials, 2002

Research paper thumbnail of Continuous model for exchange bias phenomenon in the ferro/antiferromagnetic layered system

Research paper thumbnail of Crystal field and related phenomena in hexagonal close-packed H2 and D2 under pressure

The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), ori... more The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), orientational order parameter, and crystal-field parameter in hexagonal close-packed (hcp) lattice of p-H2, o-D2 and n-H2 are calculated using the semi-empirical lattice-dynamic approach. It is shown that the lattice distortion in the J-even species is two order of magnitude smaller compared with that found in n-H2, and n-D2. The difference is due to the splitting of the J-odd rotational levels in the J-even - J-odd mixtures.

Research paper thumbnail of Sound velocities in H_2, He, and H_2-He solid mixtures under pressure

Bulk and shear sound velocities in solid hydrogen, helium and hydrogen-helium mixtures under pres... more Bulk and shear sound velocities in solid hydrogen, helium and hydrogen-helium mixtures under pressure are calculated using two complementary approaches: semi-empirical lattice dynamics based on the many-body intermolecular potentials and density-functional theory in generalized gradient approximation. The thermodynamics of the He-H$_2$ mixture has been treated within the additive-volume approximation. Our results are compared with the first-principle diffusion Monte-Carlo calculation of Alavi {\it et al.} (Science {\bf 269}, 1252 (1995)) and the semi-empirical work of Duffy {\it et al.} (Science {\bf 263}, 1590 (1994)) which employs the two-body Young-Ross potential. It is shown that the stiffer the potential is, the more the sound velocity is overestimated. Comparison with the data obtained from the observation of global oscillations of Jupiter is also made.

Research paper thumbnail of Poisson's ratio in cryocrystals under pressure

Low Temperature Physics, 2015

ABSTRACT

Research paper thumbnail of Elastic anisotropy and Poisson's ratio of solid helium under pressure

Physical Review B, 2015

ABSTRACT

Research paper thumbnail of Ab initio calculation of depth-resolved optical anisotropy of the Cu(110) surface

Physical Review B, 2003

... surface P. Monachesi,1,2 M. Palummo,2 R. Del Sole,2 A. Grechnev,3 and O. Eriksson3 2 ? Dipart... more ... surface P. Monachesi,1,2 M. Palummo,2 R. Del Sole,2 A. Grechnev,3 and O. Eriksson3 2 ? Dipartimento di Fisica ... Department, Uppsala University, S-7512 Uppsala, Sweden Received 7 June 2002; revised manuscript received 17 January 2003; published 29 July 2003 We ...

Research paper thumbnail of Thermodynamics of a two-dimensional Heisenberg ferromagnet with dipolar interaction

Physical Review B, 2005

Thermodynamics of quantum and classical two-dimensional ͑2D͒ Heisenberg models with long-range di... more Thermodynamics of quantum and classical two-dimensional ͑2D͒ Heisenberg models with long-range dipole-dipole interaction has been investigated using various forms of self-consistent spin-wave theory ͑SSWT͒. It has been found that SSWT gives a much lower transition temperature T c than the free-magnon ͑spin-wave͒ theory. For the classical spin, the T c from SSWT lies within 9% of the Monte Carlo value, making SSWT the best approximation among those considered. It is proven that the random phase approximation vertex corrections to SSWT are rather small. The results depend strongly on the value of the spin, emphasizing the importance of using the quantum and not the classical 2D Heisenberg model even for large spins such as S =7/2.

Research paper thumbnail of Lattice distortion of hcp solid helium under pressure

Physical Review B, 2009

... A. Freiman,1,* SM Tretyak,1 A. Grechnev,1 Alexander F. Goncharov,2 John S. Tse,3 D. Errandone... more ... A. Freiman,1,* SM Tretyak,1 A. Grechnev,1 Alexander F. Goncharov,2 John S. Tse,3 D. Errandonea,4 Ho-kwang Mao,2 and Russell J. Hemley2 Verkin Institute for Low Temperature Physics and Engineering ... 4 D. Errandonea, B. Schwager, R. Boehler, and M. Ross, Phys. Rev. ...

Research paper thumbnail of Raman scattering in hcp rare gas solids under pressure

Physical Review B, 2008

... Yu. A. Freiman,1,* Alexander F. Goncharov,2 SM Tretyak,1 A. Grechnev,1 John S. Tse,3 D. Erran... more ... Yu. A. Freiman,1,* Alexander F. Goncharov,2 SM Tretyak,1 A. Grechnev,1 John S. Tse,3 D. Errandonea,4 Ho-kwang Mao,2 and Russell J. Hemley2 1B. ... We are grateful to Yu. Ponosov for experimental help and SA Gramsch for com-ments on the paper. ...

Research paper thumbnail of Equation of state and Raman-active E_{2g} lattice phonon in phases I, II, and III of solid hydrogen and deuterium

Physical Review B, 2012

ABSTRACT

Research paper thumbnail of Theory of bulk and surface quasiparticle spectra for Fe, Co, and Ni

Physical Review B, 2007

The correlated electronic structure of iron, cobalt and nickel is investigated within the dynamic... more The correlated electronic structure of iron, cobalt and nickel is investigated within the dynamical mean-field theory formalism, using the newly developed full-potential LMTO-based LDA+DMFT code. Detailed analysis of the calculated electron self-energy, density of states and the spectral density are presented for these metals. It has been found that all these elements show strong correlation effects for majority spin electrons, such as strong damping of quasiparticles and formation of a density of states satellite at about −7 eV below the Fermi level. The LDA+DMFT data for fcc nickel and cobalt (111) surfaces and bcc iron (001) surface is also presented. The electron self energy is found to depend strongly on the number of nearest neighbors, and it practically reaches the bulk value already in the second layer from the surface. The dependence of correlation effects on the dimensionality of the problem is also discussed.

Research paper thumbnail of Multiplet effects in the electronic structure of intermediate-valence compounds

Physical Review B, 2009

We present an implementation of the Hubbard-I approximation based on the exact solution of the at... more We present an implementation of the Hubbard-I approximation based on the exact solution of the atomic many-body problem incorporated in a full-potential linear muffin-tin orbital method of density-functional theory. Comparison between calculated and measured x-ray photoemission spectra reveal a good agreement for intermediate valence systems in open crystal structures such as YbInCu 4 , SmB 6 , and YbB 12 . Spectral features of the unoccupied states of SmB 6 are predicted.

Research paper thumbnail of Sound velocities of hexagonal close-packed H<span class="aps-inline-formula"><math><msub><mrow></mrow><mn>2</mn></msub></math></span> and He under pressure

Physical Review B, 2013

ABSTRACT Bulk, shear, and compressional aggregate sound velocities of hydrogen and helium in the ... more ABSTRACT Bulk, shear, and compressional aggregate sound velocities of hydrogen and helium in the close-packed hexagonal structure are calculated over a wide pressure range using two complementary approaches: semiempirical lattice dynamics based on the many-body intermolecular potentials and density-functional theory in the generalized gradient approximation. The sound velocities are used to calculate the pressure dependence of the Debye temperature. The comparisons between experiment and first-principles and semiempirical calculations provide constraints on the density dependence of intermolecular interactions in the zero-temperature limit.

Research paper thumbnail of Effect of the exchange bias on the magnetization hysteresis of a ferromagnetic film in contact with an antiferromagnet

Low Temperature Physics, 2013

ABSTRACT The transformation of the hysteretic field dependence of the magnetization of a ferromag... more ABSTRACT The transformation of the hysteretic field dependence of the magnetization of a ferromagnetic thin layer in contact with a magnetically hard antiferromagnet is considered. It is shown that this interaction leads to a shift of the hysteresis loop from the configuration symmetric with respect to magnetic field (exchange bias). Furthermore, upon increasing the magnitude of the exchange interaction, within a narrow range of the magnitudes, there occurs a qualitative change in the hysteresis loop shape and its subsequent disappearance; hence the field dependence of the magnetization becomes monotonous and single-valued.

Research paper thumbnail of Sound velocities in solid hydrogen under pressure

Low Temperature Physics, 2013

ABSTRACT

Research paper thumbnail of Influence of magnetic anisotropy on hysteresis behavior in the two-spin model of a ferro/antiferromagnet bilayer with exchange bias

Low Temperature Physics, 2012

The influence of magnetic anisotropy of ferromagnetic film on the phenomenon of exchange bias is ... more The influence of magnetic anisotropy of ferromagnetic film on the phenomenon of exchange bias is studied. Hysteresis behavior in the 2-spin model of a ferro/antiferromagnet (FM/AFM) bilayer with exchange bias has been investigated in detail. In this model a half-space of AFM with fixed magnetic configuration contacts with a 2-layer FM film. Twelve different types of magnetization curves M(H) (both with and without hysteresis) have been found. Some of the M(H) curves demonstrate unusual features, such as plateaus and inclined segments. The hysteresis loop becomes asymmetric if the surface anisotropy is taken into account. 0 2 2 0 J J J J H .

Research paper thumbnail of Surface spin waves near a ferromagnet–antiferromagnet interface

Low Temperature Physics, 2000

Research paper thumbnail of Crystal-field phenomena in hcp H 2 and D 2 at high pressures

Physical Review B, 2014

ABSTRACT

Research paper thumbnail of Raman scattering in hcp rare gas solids under pressure

Physical Review B Condensed Matter and Materials Physics, Jul 1, 2008

We present Raman measurements of hcp rare gas solids (RGSs) at megabar pressures together with la... more We present Raman measurements of hcp rare gas solids (RGSs) at megabar pressures together with lattice dynamics calculations. The E2g phonon was measured in Xe up to metallization near 135 GPa and in Ar up to 58 GPa. A comparative analysis of first-principles and semiempirical calculations shows that three-body forces contribute to the energetics at low pressures and that at volume compressions greater than ˜2.6 higher-order many-body forces become important. The distinct behavior of He under pressure relative to that of the rest of the RGS family is discussed.

Research paper thumbnail of Unusual manetism and MAE in CrPt$_3$

Journal of Magnetism and Magnetic Materials, 2002

Research paper thumbnail of Continuous model for exchange bias phenomenon in the ferro/antiferromagnetic layered system

Research paper thumbnail of Crystal field and related phenomena in hexagonal close-packed H2 and D2 under pressure

The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), ori... more The lattice distortion parameter (the deviation of the c/a ratio from the ideal value 1.633), orientational order parameter, and crystal-field parameter in hexagonal close-packed (hcp) lattice of p-H2, o-D2 and n-H2 are calculated using the semi-empirical lattice-dynamic approach. It is shown that the lattice distortion in the J-even species is two order of magnitude smaller compared with that found in n-H2, and n-D2. The difference is due to the splitting of the J-odd rotational levels in the J-even - J-odd mixtures.

Research paper thumbnail of Sound velocities in H_2, He, and H_2-He solid mixtures under pressure

Bulk and shear sound velocities in solid hydrogen, helium and hydrogen-helium mixtures under pres... more Bulk and shear sound velocities in solid hydrogen, helium and hydrogen-helium mixtures under pressure are calculated using two complementary approaches: semi-empirical lattice dynamics based on the many-body intermolecular potentials and density-functional theory in generalized gradient approximation. The thermodynamics of the He-H$_2$ mixture has been treated within the additive-volume approximation. Our results are compared with the first-principle diffusion Monte-Carlo calculation of Alavi {\it et al.} (Science {\bf 269}, 1252 (1995)) and the semi-empirical work of Duffy {\it et al.} (Science {\bf 263}, 1590 (1994)) which employs the two-body Young-Ross potential. It is shown that the stiffer the potential is, the more the sound velocity is overestimated. Comparison with the data obtained from the observation of global oscillations of Jupiter is also made.

Research paper thumbnail of Poisson's ratio in cryocrystals under pressure

Low Temperature Physics, 2015

ABSTRACT

Research paper thumbnail of Elastic anisotropy and Poisson's ratio of solid helium under pressure

Physical Review B, 2015

ABSTRACT

Research paper thumbnail of Ab initio calculation of depth-resolved optical anisotropy of the Cu(110) surface

Physical Review B, 2003

... surface P. Monachesi,1,2 M. Palummo,2 R. Del Sole,2 A. Grechnev,3 and O. Eriksson3 2 ? Dipart... more ... surface P. Monachesi,1,2 M. Palummo,2 R. Del Sole,2 A. Grechnev,3 and O. Eriksson3 2 ? Dipartimento di Fisica ... Department, Uppsala University, S-7512 Uppsala, Sweden Received 7 June 2002; revised manuscript received 17 January 2003; published 29 July 2003 We ...

Research paper thumbnail of Thermodynamics of a two-dimensional Heisenberg ferromagnet with dipolar interaction

Physical Review B, 2005

Thermodynamics of quantum and classical two-dimensional ͑2D͒ Heisenberg models with long-range di... more Thermodynamics of quantum and classical two-dimensional ͑2D͒ Heisenberg models with long-range dipole-dipole interaction has been investigated using various forms of self-consistent spin-wave theory ͑SSWT͒. It has been found that SSWT gives a much lower transition temperature T c than the free-magnon ͑spin-wave͒ theory. For the classical spin, the T c from SSWT lies within 9% of the Monte Carlo value, making SSWT the best approximation among those considered. It is proven that the random phase approximation vertex corrections to SSWT are rather small. The results depend strongly on the value of the spin, emphasizing the importance of using the quantum and not the classical 2D Heisenberg model even for large spins such as S =7/2.

Research paper thumbnail of Lattice distortion of hcp solid helium under pressure

Physical Review B, 2009

... A. Freiman,1,* SM Tretyak,1 A. Grechnev,1 Alexander F. Goncharov,2 John S. Tse,3 D. Errandone... more ... A. Freiman,1,* SM Tretyak,1 A. Grechnev,1 Alexander F. Goncharov,2 John S. Tse,3 D. Errandonea,4 Ho-kwang Mao,2 and Russell J. Hemley2 Verkin Institute for Low Temperature Physics and Engineering ... 4 D. Errandonea, B. Schwager, R. Boehler, and M. Ross, Phys. Rev. ...

Research paper thumbnail of Raman scattering in hcp rare gas solids under pressure

Physical Review B, 2008

... Yu. A. Freiman,1,* Alexander F. Goncharov,2 SM Tretyak,1 A. Grechnev,1 John S. Tse,3 D. Erran... more ... Yu. A. Freiman,1,* Alexander F. Goncharov,2 SM Tretyak,1 A. Grechnev,1 John S. Tse,3 D. Errandonea,4 Ho-kwang Mao,2 and Russell J. Hemley2 1B. ... We are grateful to Yu. Ponosov for experimental help and SA Gramsch for com-ments on the paper. ...

Research paper thumbnail of Equation of state and Raman-active E_{2g} lattice phonon in phases I, II, and III of solid hydrogen and deuterium

Physical Review B, 2012

ABSTRACT

Research paper thumbnail of Theory of bulk and surface quasiparticle spectra for Fe, Co, and Ni

Physical Review B, 2007

The correlated electronic structure of iron, cobalt and nickel is investigated within the dynamic... more The correlated electronic structure of iron, cobalt and nickel is investigated within the dynamical mean-field theory formalism, using the newly developed full-potential LMTO-based LDA+DMFT code. Detailed analysis of the calculated electron self-energy, density of states and the spectral density are presented for these metals. It has been found that all these elements show strong correlation effects for majority spin electrons, such as strong damping of quasiparticles and formation of a density of states satellite at about −7 eV below the Fermi level. The LDA+DMFT data for fcc nickel and cobalt (111) surfaces and bcc iron (001) surface is also presented. The electron self energy is found to depend strongly on the number of nearest neighbors, and it practically reaches the bulk value already in the second layer from the surface. The dependence of correlation effects on the dimensionality of the problem is also discussed.

Research paper thumbnail of Multiplet effects in the electronic structure of intermediate-valence compounds

Physical Review B, 2009

We present an implementation of the Hubbard-I approximation based on the exact solution of the at... more We present an implementation of the Hubbard-I approximation based on the exact solution of the atomic many-body problem incorporated in a full-potential linear muffin-tin orbital method of density-functional theory. Comparison between calculated and measured x-ray photoemission spectra reveal a good agreement for intermediate valence systems in open crystal structures such as YbInCu 4 , SmB 6 , and YbB 12 . Spectral features of the unoccupied states of SmB 6 are predicted.

Research paper thumbnail of Sound velocities of hexagonal close-packed H<span class="aps-inline-formula"><math><msub><mrow></mrow><mn>2</mn></msub></math></span> and He under pressure

Physical Review B, 2013

ABSTRACT Bulk, shear, and compressional aggregate sound velocities of hydrogen and helium in the ... more ABSTRACT Bulk, shear, and compressional aggregate sound velocities of hydrogen and helium in the close-packed hexagonal structure are calculated over a wide pressure range using two complementary approaches: semiempirical lattice dynamics based on the many-body intermolecular potentials and density-functional theory in the generalized gradient approximation. The sound velocities are used to calculate the pressure dependence of the Debye temperature. The comparisons between experiment and first-principles and semiempirical calculations provide constraints on the density dependence of intermolecular interactions in the zero-temperature limit.

Research paper thumbnail of Effect of the exchange bias on the magnetization hysteresis of a ferromagnetic film in contact with an antiferromagnet

Low Temperature Physics, 2013

ABSTRACT The transformation of the hysteretic field dependence of the magnetization of a ferromag... more ABSTRACT The transformation of the hysteretic field dependence of the magnetization of a ferromagnetic thin layer in contact with a magnetically hard antiferromagnet is considered. It is shown that this interaction leads to a shift of the hysteresis loop from the configuration symmetric with respect to magnetic field (exchange bias). Furthermore, upon increasing the magnitude of the exchange interaction, within a narrow range of the magnitudes, there occurs a qualitative change in the hysteresis loop shape and its subsequent disappearance; hence the field dependence of the magnetization becomes monotonous and single-valued.

Research paper thumbnail of Sound velocities in solid hydrogen under pressure

Low Temperature Physics, 2013

ABSTRACT

Research paper thumbnail of Influence of magnetic anisotropy on hysteresis behavior in the two-spin model of a ferro/antiferromagnet bilayer with exchange bias

Low Temperature Physics, 2012

The influence of magnetic anisotropy of ferromagnetic film on the phenomenon of exchange bias is ... more The influence of magnetic anisotropy of ferromagnetic film on the phenomenon of exchange bias is studied. Hysteresis behavior in the 2-spin model of a ferro/antiferromagnet (FM/AFM) bilayer with exchange bias has been investigated in detail. In this model a half-space of AFM with fixed magnetic configuration contacts with a 2-layer FM film. Twelve different types of magnetization curves M(H) (both with and without hysteresis) have been found. Some of the M(H) curves demonstrate unusual features, such as plateaus and inclined segments. The hysteresis loop becomes asymmetric if the surface anisotropy is taken into account. 0 2 2 0 J J J J H .

Research paper thumbnail of Surface spin waves near a ferromagnet–antiferromagnet interface

Low Temperature Physics, 2000