FLUCTUATION-INDUCED 1ST-ORDER TRANSITIONS IN SYSTEMS WITH SPATIALLY ISOTROPIC COMPETING INTERACTIONS

We consider a spin system with competing interactions that are isotropic with respect to the axes of a cubic lattice. In the mean-field approximation the model supports paramagnetic, ferromagnetic, and modulated phases separated by a Lifshitz point. The character of this point is investigated in the presence of fluctuations. Using a standard diagrammatic formalism, we find that the paramodulated phase transition should be first order and that the Lifshitz point should be a critical endpoint.