INFLUENCE OF FLUCTUATIONS ON SPIN SYSTEMS WITH SPATIALLY ISOTROPIC COMPETING INTERACTIONS

We consider spin systems with competing interactions isotropic with respect to the axes of a cubic lattice. A renormalization-group analysis carried to second order in =d-4 demonstrates that the critical behavior for the para-modulated phase transition is 2m-component-like with m=3 for a uniaxially modulated phase and m=4 for a cubically modulated phase, in the same universality class as the m-component spin model with uniaxial competing interactions. Each case may describe different helical magnetic rare-earth alloys. Possible phase diagrams are proposed encompassing such compounds. © 1990 The American Physical Society.