ESR in Hexagonal ABX₃-Type Antiferromagnets. I. Ground State Properties in Easy-Axis Anisotropy Case

Abstract

We study ESR modes in the ground states of hexagonal ABX 3 -type antiferromagnets with easy-axis anisotropy such as CsNiCl 3 , RbNiCl 3 , CsMnI 3 . Taking a six sublattice model for the spin structure, we investigate the normal modes for the motions of the sublattice magnetizations within the framework of mean field approximation. In general, six kinds of modes are obtained by solving the classical equation of motion, d M i /d t =[ M i × H i ]. Frequency field diagram is presented. Ground state properties of fields for resonance and line widths of ESR spectra on CsNiCl 3 , RbNiCl 3 and CsMnI 3 are reported. Calculated values of resonance fields are in agreement with experimental results. The weak interchain exchange interaction constant J 1 is estimated with good accuracy as J 1 / k B =-2.8×10 -2 K for CsNiCl 3 and -7.5×10 -2 K for CsMnI 3 .