Local symmetry and crystalline field effects in charge-ordered Yb₄As₃

Yb₄As₃ exhibits very anisotropic magnetic properties, while its dynamic form factor of the inelastic excitation spectra at very low temperatures are well described by an almost-isotropic one-dimensional Heisenberg model, which is supplemented by the Dzyaloshinsky-Moriya interaction. To clarify the origin of this feature, the crystalline field effects in the inelastic neutron scattering and the magnetic susceptibility data of Yb₄As₃ are analyzed to separate cut the contribution of the lowest Kramers-doublet state from those of the crystalline field excited states. The isotropic excitation mode is ascribed to the former state. The excitation spectra specified by the magnetic polarization directions are also calculated to give additional information of the crystalline field states. It is also pointed out that the magnetization parallel to the c-axis is induced for the magnetic field, which is applied perpendicular to the c-axis in the c-plane. Its magnitude is proportional to the cube of the field strength. The internal field can have different values on the two Yb³⁺ sites which are connected by the glide operation. It is shown that the magnetization can give us detailed information of the local C₃ symmetry around the Yb³⁺ site.