Far Infrared Spectrum of CoCO3: High Prequency Mode of Antiperromagnetic Resonance and Two-Magnon Absorption

A high-frequency mode of antiferromagnetic resonance and twomagnon absorption at 34.6 and 54.7 cm⁻¹ (at T→O K), respectively, have been observed. Prom the experimental data we have calculated HA=115 kOe, gz=7±2 (at HE=160 kOe and g⊥=3.3). The twomagnon absorption is treated as a simultaneous excitation of two magnons near the Brillouin-zone boundary, one of which belongs to the low-frequency gapless branch and the other - to the weak dispersion high-frequency branch.