Structure and magnetic properties of the two-dimensional antiferromagnet Na2TbO3

The crystal structure and magnetic properties of ternary oxide Na2TbO3 were investigated. This compound has a monoclinic structure with space group C 2/c. The cations form two kinds of layers, one of which is composed of Na and O atoms, the other consisting of Na, Tb, and O atoms. In the latter, the Tb ions are arranged in a honeycomb manner. Powder x-ray and neutron diffraction measurements show that a partially disordered arrangement has been found between Na and Tb ions (∼20%). A broad peak of the magnetic susceptibility against temperature was observed at ∼60 K, which is due to a two-dimensional characteristic of the magnetic order of the Tb ions. At lower temperatures, this compound shows an antiferromagnetic transition at 38.3 K. The magnetic structure of Na2TbO3 was determined by powder neutron diffraction measurement at 2.6 K. The magnetic moments of the Tb4+ ions (∼6 μB) order in the collinear antiferromagnetic arrangement