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 $\mathrm{ErF}{e}_3{\left(B{O}_3\right)}_4$ single crystals in the paramagnetic and antiferromagnetic $\left(T<T_N=39K\right)$ phases. On the basis of the experimentally determined 45 crystal-field (CF) levels of $E{r^3}^{+}$ 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.