The phase diagram of an Ising fcc antiferromagnet in a field is investigated by a study of the ground state and Monte Carlo simulation of a lattice with 16 384 sites. At the critical field between the two "ordered" phases, the disordered phase is stable down to zero temperature due to "frustration" effects. The corresponding alloy phase diagram disagrees with all previous calculations. Order parameters and internal energy are briefly compared to experimental data on the Cu-Au system.

• Received 25 March 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.811