Uniaxial and Biaxial Quadrupolar Ordering in Magnetic Crystals: Molecular-Field Theory
- 1 January 1973
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 7 (1), 343-351
- https://doi.org/10.1103/physrevb.7.343
Abstract
The single order parameter is, in general, insufficient to describe ordering in low-symmetry magnetic crystals with quadrupolar coupling. After a brief discussion of the general situation, we study in detail the molecular-field theory of an array of quadrupoles coupled in pairs by the Hamiltonian (), . For , both and the biaxiality parameter become simultaneously nonzero at sufficiently low temperatures. We exhibit () phase diagrams and give the temperature dependence of the ordering for spins . The transitions in and may be separated by introducing single-ion anisotropy into the Hamiltonian.
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