Crystal structure and magnetic properties of CoZn(TeO₃)Br ₂

Crystal and magnetic structures as well as magnetic properties have been studied for a newly synthesized system CoZn(TeO₃)Br₂. Although the system is isomorphic to Co₂(TeO₃)Br ₂, as revealed by neutron diffraction study, magnetic characteristics of the two systems are different, because the Zn atoms in CoZn(TeO ₃)Br₂ decouple the magnetic interaction among the chains of corner-sharing CoO₄Br₂ octahedra, inducing the one-dimensionality of Co spins. At temperature T_N ∼ 9:0 K, it exhibits a transition to an antiferromagnetic state accompanied by the weak ferromagnetic moment. The Weiss temperature θ_W is estimated to be -68:5K from the magnetic susceptibility data. The small value of |T _N/θ_W| (∼ 0:13) indicates the existence of the effect of magnetic fluctuation. The magnetic structure below T_N has also been determined by a powder neutron diffraction study, where Co spins within a chain are found to order basically in an antiferromagnetic way with the spins along the c direction (chain direction), but they are canted from the c-axis toward the b-axis by an angle of 17 (±3)°. Because the weak ferromagnetic components of the chains created by this canting align antiferromagnetically, the spontaneous moments stated above is considered to be due to the additional canting toward the a-axis. The existence of a temperature-linear component in the specific heat at low temperatures suggests that a significant fraction of Co spins remains in the disordered or glassy state.