Helical Magnetic Structure in CsCuCl₃

Abstract

Neutron diffraction measurements were made on single crystals of CsCuCl₃. The sense of Cu²⁺ ion helix was found from nuclear reflections to be predominantly right-handed. The magnetic reflection data could be interpreted satisfactorily by considering a triangular spin structure of helically modulated ferromagnetic chains: The magnetic moments lie in the c-plane and rotate by 5.1±0.1° along the chain or the c-axis, while the moments rotate by 120° in the c-plane. The magnitude of the magnetic moment is 0.58±0.01 μ_B at 4.2 K. The critical exponent of the magnetization, β was found to be 0.358±0.015 around the Néel temperature, 10.70±0.05 K. We present a model that the helical modulation along the c-axis is caused by the antisymmetric exchange (Dzyaloshinsky-Moriya) interaction characteristic of the crystal symmetry of CsCuCl₃. The model predicts a right-handed magnetic helix in the present case.