Field-Dependent Antiferromagnetic Resonance Modes in CoCl2

Results have been obtained for the magnetic field dependence of the far-infrared transmission of single-crystal antiferromagnetic CoCl2 at 4.2°K. The energy range was ħω > 10 cm−1 and fields up to 26 kOe were applied perpendicular to the hexagonal axis. The two uniform-mode antiferromagnetic resonances, ω1 and ω2, are nondegenerate in zero field with ħω1 = 19.0±0.2 cm−1. The normalized energy-field behavior follows simple curves: for ω1, a circle of radius 32 kOe centered at (0, 0) ; for ω2, a straight line crossing ω1 at 23 kOe and appearing to pass through the (0, 0) point. These results, coupled with high-field magnetization measurements, permit calculation of the isotropic and anisotropic coefficients of exchange (intra- and interlayer) and the g factors.