6533b833fe1ef96bd129b730

RESEARCH PRODUCT

Nearest-neighbor Ising antiferromagnet on the fcc lattice: Evidence for multicritical behavior.

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The phase behavior of the Ising model with nearest-neighbor antiferromagnetic interactions on the fcc lattice in a homogeneous magnetic field is studied by means of large-scale Monte Carlo simulations. In accordance with the most recent of the previous investigations, but with significantly higher accuracy, it is found that the ``triple'' point at which the disordered phase coexists with both the AB phase as well as with the ${\mathit{A}}_{3}$B phase (corresponding to the model's lattice gas interpretation as a binary alloy ${\mathit{A}}_{\mathit{xB}1\mathrm{\ensuremath{-}}\mathit{x}}$ such as ${\mathrm{Cu}}_{\mathit{x}}$${\mathrm{Au}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$) occurs at a nonzero temperature. However, there is numerical evidence that the first-order jumps on the three associated phase coexistence lines tend to zero when approaching this point, which means that it is, in fact, a multicritical point. Since the Landau theory does not support this picture, and the simulation data do not definitely exclude a usual triple point with small jumps, the question about the nature of the point must be considered as unresolved. \textcopyright{} 1996 The American Physical Society.