Raman Scattering by Two-Magnon Excitations in FeBO₃

Abstract

An experimental investigation on Raman scattering from magnons and phonons has been made for FeBO₃. A Raman line at 537 cm⁻¹ is confirmed as due to two-magnon excitations from a comparison of the spectra of pure FeBO₃ crystals with In-substituted ones, as well as from the temperature dependence of the line of pure FeBO₃. Selection rules for the two-magnon excitations are obtained using the spin-dependent electric polarizability theory. An analysis of the two-magnon spectrum leads to give the exchange parameters in the −2J_ij(S_i·S_j) type interaction. The first neighbor intersublattice exchange interaction J_AB=−9.6 cm⁻¹. The second neighbor intersublattice interaction J_A′B and the first neighbor intrasublattice interaction J_B′B are estimated to be −0.2 cm⁻¹ on the assumption that J_A′B∼J_B′B. Thermal behaviors of the phonon lines are also studied in comparison with those in CaCO₃.