Magnetic Excitations in Antiferromagnetic CoF2. II. Uniform Magnetic Excitations nearT=0°K

Far-infrared absorption experiments on Co${\mathrm{F}}_2$ at 4.2 °K are extended to include all the uniform magnetic excitations below 300 ${\mathrm{cm}}^{-1\mathrm{}}$. The linear and nonlinear Zeeman effect, obtained with externally applied magnetic fields parallel and perpendicular to the spin direction, are also observed. A model of the uniform magnetic excitations derived from an effective $S=\frac{3}{2}$, ${\mathrm{Co}}^{2+}$ manifold is constructed by including a large orthorhombic anisotropy field, determined from ${\mathrm{Co}}^{2+}$ in Mg${\mathrm{F}}_2$, a simple isotropic bilinear exchange, and the independently determined spin-phonon coupling to the $E_g$ optical phonon. The model gives a satisfactory account of the energies, linear and nonlinear Zeeman effect, as well as the absorption intensities.