Synthesis and magnetic properties of new tellurate compounds Na4MTeO6 (M = Co and Ni) with a ferromagnetic spin-chain structure

New tellurate compounds Na4MTeO6 (M = Co and Ni) were synthesized by a conventional high-temperature solid-state reaction. The title compounds crystallize in the monoclinic system of a space group P2/c and the triclinic system of a space group P (1) over bar, respectively. Both compounds exhibit a zigzag spin-chain structure, in which Na4CoTeO6 shows uniform chains built by Co2+ ions and Na4NiTeO6 shows alternating chains built by Ni2+ ions. Magnetic measurements confirm that Na4CoTeO6 and Na4NiTeO6 possess an antiferromagnetic ordering at T-N = similar to 3 K and similar to 6.5 K, respectively, while a metamagnetic transition can be observed in the magnetization curve with an increasing field at 2 K.