THz Absorption Spectroscopy Study of Spin Waves in Orthoferrite YFeO₃

YFeO₃ has an orthorhombic distorted perovskite structure of Pnma symmetry group. Below Néel temperature of about 655 K, the Fe spins S=5/2 arrange in an antiferromagnetic (AFM) state Γ4(G_a,F_c,A_b) with canted spins and a weak ferromagnetic component along the c axis. This complex spin structure is described by a combination of AFM nearest-neighbor couplings, Dzyaloshinsky-Moriya (DM) interactions and single-ion anisotropies.
Earlier studies show coexistence of magnetic and ferroelectric orderings in YFeO₃. Therefore, detailed description of magnetic interactions in this material is a step towards understanding the mechanisms in multiferroics, in which magnetic properties can be tuned with electric field.
We have measured absorption of THz radiation in YFeO₃ single crystals at the temperature below 4 K in magnetic fields up to B = 15 T. Two spin wave modes were observed at the Γ-point with zero-field energies 1.2 and 2.4 meV. From the B dependence of mode energies we have quantified the parameters of DM interactions and single-ion anisotropies. The obtained values of the AFM interactions are consistent with neutron scattering results.