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.
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.
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.
... 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 ...
... 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. ...
... 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. ...
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.
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.
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.
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.
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.
... 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 ...
... 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. ...
... 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. ...
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.
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.
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