High-resolution optical spectroscopy and modeling of spectral and magnetic properties of multiferroic ErFe3(BO3)4

We carried out the high-resolution broadband temperature-dependent polarized optical spectroscopy and theoretical studies of $\mathrm{ErF}{\mathrm{e}}_{3}{(\mathrm{B}{\mathrm{O}}_{3})}_{4}$ single crystals in the paramagnetic and antiferromagnetic $(Tl{T}_{N}=39\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ phases. On the basis of the experimentally determined 45 crystal-field (CF) levels of $\mathrm{E}{{\mathrm{r}}^{3}}^{+}$ ions at sites with the ${C}_{2}$ point symmetry, CF calculations were performed, a set of physically grounded CF parameters was obtained and used to model the temperature dependences of the Er magnetic moments measured in neutron-scattering experiments, as well as the magnetic susceptibility and magnetization of the compound; the contributions of the quasi-one-dimensional iron magnetic subsystem were calculated in the frame of the previously developed self-consistent four-particle cluster model. The modeling strongly supports an easy-plane collinear structure of iron magnetic moments and excludes earlier proposed additional magnetic phase.