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

Abstract

Far-infrared absorption experiments on Co${\mathrm{F}}_{2}$ at 4.2 \ifmmode^\circ\else\textdegree\fi{}K are extended to include all the uniform magnetic excitations below 300 ${\mathrm{cm}}^{\ensuremath{-}1}$. 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.