Submillimeter wave resonance absorption in yttrium orthoferrite monocrystals

Transmission of submillimeter waves is measured in the range of 4-50 cm-1 with monocrystal YFeO3 plates in the external zero magnetic field. Plates of different thickness and orientations have been used in measurements. Resonance lines of absorption at frequences of 8.7, 35.0 and 45.2 cm-1 (+-0.3 cm-1) are found in the YFeO3 monocrystal transmission spectra. A supposition is made on the connection of the first two lines with antiferromagnetic resonance in YFeO3 in the zero external magnetic field and of the third line with excitation of optical phonons in perovskite lattice