Crystal structure and magnetic properties of CoZn(TeO3)Br2

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)Br2, as revealed by neutron diffraction study, magnetic characteristics of the two systems are different, because the Zn atoms in CoZn(TeO3)Br2 decouple the magnetic interaction among the chains of corner-sharing CoO4Br2 octahedra, inducing the one-dimensionality of Co spins. At temperature TN-9.0 K, it exhibits a transition to an antiferromagnetic state accompanied by the weak ferromagnetic moment. The Weiss temperature θW is estimated to be -68.5 K from the magnetic susceptibility data. The small value of |TN/θW| (∼0.13) indicates the existence of the effect of magnetic fluctuation. The magnetic structure below TN 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)deg. 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 sate. (author)