Self-Consistent Four-Particle Cluster Model of Fe³⁺ Heisenberg Chains: Spectral and Magnetic Properties of YFe₃(BO₃)₄ Crystals

The magnetic properties of antiferromagnetic quasi-1D YFe3(BO3)(4) crystals are studied based on the analysis of the measured optical spectra of the Fe3+ ions in different rare-earth (RE) iron borates and a self-consistent four-particle cluster approach to helical iron chains. The parameters of crystal fields affecting the Fe3+ ions are calculated in the framework of the exchange charge model. The parameters of the isotropic intrachain and interchain exchange interactions between the Fe3+ ions are determined from modeling the temperature dependences of magnetic susceptibilities, the phase transition temperature, and spontaneous magnetic moments. The magnetic easy-plane anisotropy is explained as the result of dipolar interactions between the Fe3+ ions in the trigonal crystal lattice. The developed model can be used to analyze and predict the properties of multiferroic multifunctional RE iron borates and highlight contributions of the iron subsystem into the magnetoelectric and magnetoelastic effects in these compounds.