Anomalous AFMR in some quasi-one-dimensional Mn²⁺ compounds

Antiferromagnetic resonance experiments in the range 10< nu <60 GHz have been performed on a series of quasi-one-dimensional Mn²⁺ compounds with varying anisotropy. Pronounced deviations from classical AFMR theory are observed, in accordance with the experiments at higher frequencies reported by Tuchendler et al. (1981). These deviations show a substantial temperature dependence and seem to be related to the amount of anisotropy between the preferred and next-preferred direction of spin alignment. The experimental evidence will be compared with the results of a renormalised spin wave calculation.