On the liquid-vapour-like critical point in the model of the rare earth iron garnet

The transition between two canted phases in YbIG atH 100 is examined in the framework of the model with one saturated Fe-sublattice and six sublattices of mutually independent Yb ions. In particular, the equations determining the continuous transition point and the coexistence line of these canted phases are derived. The existence of a zero frequency mode in this second order transition point is clear from this analysis, too. The analogy with the classical theory of the liquid-vapour-like phase transition, as well as the limits of the mean field approach are discussed.