A renormalization-group study into the effects of competing biquadratic and crystal-field interactions in the Blume-Emery-Griffiths model

The Blume-Emery-Griffiths model, a spin-1 Ising model with bilinear, biquadratic, and crystal field interactions, provides a general system for the analysis of systems driven by fluctuations in density and magnetization. In this study, we consider an exactly solvable system in which frustration is present due to competing biquadratic and crystal-field interactions. Thus, this calculation models a dilute ferromagnetic material with two types of nearest-neighbor site pairs, distinguished by whether or not simultaneous occupation is energetically favored. To determine the effects of this competition, we have constructed exactly solvable frustrated hierarchical models similar to those introduced to study spin glasses. The resulting phase diagrams reveal two distinct paramagnetic phases separated by a plane in parameter space in which the biquadratic interaction and crystal-field strength rescale chaotically. Each paramagnetic phase has a ferromagnetic complement in which the unique distribution of occupied sites possesses a net magnetization. (C) 2007 Elsevier B.V. All rights reserved.