Influence of fluctations on spin systems with spatially isotropic competing interactions

Abstract

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 E=d -4 demonstrates that the criticai 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 ditferent helical magnetic rare-earth alloys. Possible phase diagrams are proposed encompassing such compounds.