Magnetic structure of ErFe3(BO3)(4): Spectroscopic and thermodynamic studies

We report on the high-resolution spectroscopic study of multiferroic ErFe3(BO3)(4). The energies of all eight Kramers doublets of the ground I-4(15/2) multiplet of the Er3+ ion were determined by the high-resolution I-4(13/2) -> I-4(15)/2 infrared luminescence spectra. The spectroscopically determined temperature dependence of the splitting of the ground Kramers doublet was used to calculate the contribution of the erbium subsystem into the specific heat and the magnetic susceptibility of erbium iron borate. The analysis of the thermodynamic properties based on these calculations allowed us to suggest the domain structure in the easy-plane antiferromagnetically ordered iron subsystem, with two magnetically nonequivalent erbium positions in each domain.