Neutron Scattering Study of Magnetic Excitations in Pseudo-One-Dimensional Singlet Ground State Ferromagnets CsFeCl₃ and RbFeCl₃

Abstract

The magnetic excitation spectra in pseudo-one-dimensional planar ferromagnets CsFeCl₃ and RbFeCl₃ were observed using inelastic neutron scattering technique. The observed excitation spectruun of CsFeCl₃ has a gap at the magnetic zone center, while that of RbFeCl₃ has no gap with a feature of XY system. This prominent difference can be understood from the fact that they are singlet-ground-state systems. As RbFeCl₃ has a 3D LRO due to an exchange induced moment, CsFeCl₃ shows no sign of the LRO within the temperature region we measured. Moreover, from a viewpoint of the temperature dependence, it is noticeable that the excitation spectrum of RbFeCl₃ shows the feature of XY system even in the paramagnetic phase. The one-dimensionality is evaluated to be about 0.05 for CsFeCl₃ and 0.1 for RbFeCl₃ showing that they have unexpectedly poor one-dimensionality.