INFLUENCE OF LOCALIZATION ON THE PROPERTIES OF THE IMPURITY-INDUCED MAGNON IN FEF2-CO2+

The far-infrared absorption spectra of the 3-D uniaxial antiferromagnet FeF2, substitutionally doped with Co2+, exhibits a defect-localised magnon mode at 85.5 cm-1 just about 6 cm -1 above the magnon band of the host. In an external magnetic field parallel to the easy axis, the energy separation between the local mode and the top of the magnon band, and consequently the localisation of the defect excitation, can be changed considerably, with the consequence that the absorption coefficient and the effective g factor will show a magnetic field dependence.