Magnetic excitations and magnetic critical scattering in cobalt fluoride

The magnetic excitations of cobalt fluoride have been studied both theoretically and experimentally. The theory of the magnetic excitations at low temperatures has been developed with the aid of the pseudo-boson technique in terms of the crystal field and spin-orbit parameters of the individual ions and of the exchange interactions between neighbouring ions. The model with surprisingly simple forms of exchange interaction gives a very good description of many of the experimental results. Measurements of the longitudinal spin correlations near the Neel temperature have been made with slow neutron inelastic scattering techniques. The results show that the longitudinal spin correlations have a small frequency width; the width at half maximum of the quasi-elastic peak is, at all temperatures and wavevectors, less than 0.12 THz.