On the existence of an intermediate phase in the antiferromagnetic Ising model on an face-centered cubic lattice

We use Monte Carlo simulation to determine the stable structures in the second-neighbour Ising model on the face-centred cubic lattice. Those structures are L1_1 for strongly antiferromagnetic second neighbour interactions and L1_0 for ferromagnetic and weakly antiferromagnetic second neighbours. We find a third stable "intermediate" antiferromagnetic phase with I4_1/amd symmetry, and calculate the paramagnetic transition temperature for each. The transition temperature depends strongly on second neighbour interactions which are not frustrated. Our results contradict a recent paper, which also reported two different AFM structures and a new "intermediate" phase exists in this system. Here we show that the assumed sublattice structure in is inconsistent with the ground state. We determine a sublattice structure suitable for solving this problem with mean field theory.

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