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 fi.rst order and that the Lifshitz point should be a criticai endpoint.
Physical review. B, Condensed matter. New York. Vol. 46, n. 6 (Aug. 1992), p. 3672-3675