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Journal of Low Temperature Physics

, Volume 139, Issue 5–6, pp 753–763 | Cite as

Orientational Ordering of ortho–para Mixtures of Crystals of Homonuclear Diatomic Molecules: Theoretical Evidence for Reentrance

  • Balázs Hetényi
  • Sandro Scandolo
  • Erio Tosatti
Original Article

Abstract

We have developed a theoretical formalism to calculate the orientational phase diagram of ortho–para (or odd-J/even-J) mixtures of homonuclear diatomic molecules in the low-pressure solid phases. In particular, our formalism allows for the explicit disorder present in such mixtrues. While the formalism is general, here we apply it to the quantum anisotropic planar rotor model, a two-dimensional model of coupled rotors. Our calculated phase diagram, separating phases of disorder and short-range order is reentrant, when an equilibrium mixture of odd-J/even-J species is considered. A reentrant phase diagram separating states of disorder and long-range order is known to exist in all-J species in both two and three dimensions. The phase diagram we find for the thermal mixture of odd-J/even-J species exhibits reentrance over a wider range of coupling constants than the corresponding all-J species. We also investigate systems where the odd-J fraction is fixed as a function of temperature. We find that even 1% odd-J mixture exhibits a phase diagram different from the pure even-J case, indicating that the even-J molecules play important role in orientational ordering.

Keywords

Phase Diagram Magnetic Material Diatomic Molecule Theoretical Formalism Orientational Order 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  • Balázs Hetényi
    • 1
    • 3
  • Sandro Scandolo
    • 2
    • 3
  • Erio Tosatti
    • 1
    • 3
  1. 1.SISSA-International School of Advanced StudiesTriesteItaly
  2. 2.The Abdus Salam International Centre for Theoretical PhysicsTriesteItaly
  3. 3.Democritos-INFMTriesteItaly

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