Short Range Order Effects on EPR Frequencies in Heisenberg Linear Chain Antiferromagnets

Abstract

The temperature dependence of paramagnetic resonance frequencies in a short range ordered spin state is studied theoretically and experimentally for two typical one-dimensional Heisenberg antiferromagnets, CsMnCl 3 2H 2 O and (CH 3 ) 4 NMnCl 3 . The present theory with the classical nearest-neighbor Heisenberg model properly predicts the shift of the resonant field from the high temperature limit for both crystals. The observed shift for CsMnCl 3 2H 2 O can be explained only by the dipolar term. For (CH 3 ) 4 NMnCl 3 , however, the effect of the single-ion anisotropy, or the D -term, has to be taken into account in the explanation of the temperature variation.