Phase diagram of the frustrated FCC antiferromagnet from effective-field theory

The phase diagram of a face-centred cubic (FCC) antiferromagnet is calculated from the effective field theory (EFT) of Honmura and Kaneyoshi taking into account not only the effect of interaction with nearest neighbours,J₁, but also the effect of second neighbours,J₂. The phase diagram for the nearest neighbour case away from the triple point, which in our calculations is predicted to be atH= 4 andT= 0, is close to cluster variation method (CVM) and Monte Carlo (MC) results. Similar to MC and CVM predictions, we observe that the increasing second neighbours interaction pushes the triple point towards zero field. Our calculations also show that forα= -J₂/J₁= 0.3, the triple point merges with the transition point of the L1₀phase, one of the ground states, atH= 0 and changes the nature of phase transition from first- to second-order, in full agreement with Monte Carlo predictions. The phase diagram with the effect of second neighbours calculated for several values ofαare in good agreement with available MC and CVM predictions.