Magnetic phase transformations of face-centered cubic and hexagonal close-packed Co at zero Kelvin

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Abstract

The 0K pressure-induced magnetic phase transformations of face-centered cubic (FCC) and hexagonal close packed (HCP) Co have been examined using first-principles calculations. Issues of fitting an equation of state to the first-principles energy versus volume data points containing a magnetic transformation and comparing to experimental phase equilibria are discussed. It is found that a fitting scheme employing only data where the magnetic moment decreases linearly with volume offers a physically meaningful behavior for the equation of state at metastable volumes. From this fitting, the ferromagnetic to nonmagnetic transformations with increasing pressure at 0K are at 77GPa and 123GPa for FCC and HCP, respectively, and are first order and second order, respectively, on the basis of an unambiguous measure proposed in the paper. In addition to the HCP/FCC structure transformation at 99GPa, another transformation at negative pressures is predicted, at - 31GPa. These results are shown to be consistent with the extrapolations of the experimental pressure-temperature phase diagram to 0K.

Original languageEnglish (US)
Article number096006
JournalJournal of Physics Condensed Matter
Volume22
Issue number9
DOIs
StatePublished - Feb 26 2010

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phase transformations
Phase transitions
Equations of state
equations of state
Magnetic moments
Extrapolation
Phase equilibria
Phase diagrams
extrapolation
magnetic moments
phase diagrams
Temperature
temperature
energy

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Condensed Matter Physics

Cite this

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title = "Magnetic phase transformations of face-centered cubic and hexagonal close-packed Co at zero Kelvin",
abstract = "The 0K pressure-induced magnetic phase transformations of face-centered cubic (FCC) and hexagonal close packed (HCP) Co have been examined using first-principles calculations. Issues of fitting an equation of state to the first-principles energy versus volume data points containing a magnetic transformation and comparing to experimental phase equilibria are discussed. It is found that a fitting scheme employing only data where the magnetic moment decreases linearly with volume offers a physically meaningful behavior for the equation of state at metastable volumes. From this fitting, the ferromagnetic to nonmagnetic transformations with increasing pressure at 0K are at 77GPa and 123GPa for FCC and HCP, respectively, and are first order and second order, respectively, on the basis of an unambiguous measure proposed in the paper. In addition to the HCP/FCC structure transformation at 99GPa, another transformation at negative pressures is predicted, at - 31GPa. These results are shown to be consistent with the extrapolations of the experimental pressure-temperature phase diagram to 0K.",
author = "Saal, {James E.} and Shunli Shang and Yi Wang and Zi-kui Liu",
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AU - Saal, James E.

AU - Shang, Shunli

AU - Wang, Yi

AU - Liu, Zi-kui

PY - 2010/2/26

Y1 - 2010/2/26

N2 - The 0K pressure-induced magnetic phase transformations of face-centered cubic (FCC) and hexagonal close packed (HCP) Co have been examined using first-principles calculations. Issues of fitting an equation of state to the first-principles energy versus volume data points containing a magnetic transformation and comparing to experimental phase equilibria are discussed. It is found that a fitting scheme employing only data where the magnetic moment decreases linearly with volume offers a physically meaningful behavior for the equation of state at metastable volumes. From this fitting, the ferromagnetic to nonmagnetic transformations with increasing pressure at 0K are at 77GPa and 123GPa for FCC and HCP, respectively, and are first order and second order, respectively, on the basis of an unambiguous measure proposed in the paper. In addition to the HCP/FCC structure transformation at 99GPa, another transformation at negative pressures is predicted, at - 31GPa. These results are shown to be consistent with the extrapolations of the experimental pressure-temperature phase diagram to 0K.

AB - The 0K pressure-induced magnetic phase transformations of face-centered cubic (FCC) and hexagonal close packed (HCP) Co have been examined using first-principles calculations. Issues of fitting an equation of state to the first-principles energy versus volume data points containing a magnetic transformation and comparing to experimental phase equilibria are discussed. It is found that a fitting scheme employing only data where the magnetic moment decreases linearly with volume offers a physically meaningful behavior for the equation of state at metastable volumes. From this fitting, the ferromagnetic to nonmagnetic transformations with increasing pressure at 0K are at 77GPa and 123GPa for FCC and HCP, respectively, and are first order and second order, respectively, on the basis of an unambiguous measure proposed in the paper. In addition to the HCP/FCC structure transformation at 99GPa, another transformation at negative pressures is predicted, at - 31GPa. These results are shown to be consistent with the extrapolations of the experimental pressure-temperature phase diagram to 0K.

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