Study on the crystal and magnetic structures of SrTbO3 and BaTbO3 by powder neutron diffraction

Full text: We prepared oxygen stoichiometric SrTbO3 and BaTbO3 in which tetravalent terbium ions are stabilized at the B sites of the perovskite ABO3. Their crystal structures at room temperature were determined from both the X-ray and neutron diffraction measurements. SrTbO3 takes an orthorhombic perovskite-type structure with space group Pnma (No.62). On the other hand, BaTbO3 has a rhombohedral structure with space group R-3c (No.167). Magnetic susceptibility measurements have been performed for both the compounds in the temperature range between 4.5K and room temperature and at an applied magnetic field 1000G. Both the compounds show the antiferromagnetic transition at ca. 33K. The temperature-dependent magnetic susceptibilities were measured with zero-field-cooled (ZFC) and field-cooled (FC) conditions at an applied field of 1000G. A dramatic difference between ZFC and FC was observed below the Neel temperatures for both the compounds, which shows the onset of a ferromagnetic moment or a spin-glass like property below those temperatures. To determine the magnetic structures at the antiferromagnetic state, powder neutron diffraction measurements have been performed at 10K and room temperature. Both SrTbO3 and BaTbO3 have the orthorhombic perovskite-type structure with space group Pnma at 10K and the G-type magnetic structure in which terbium atoms are antiferromagnetically coupled with the six neighbouring terbium atoms. It was found that in BaTbO3 the rhombohedral-to-orthorhombic phase transition occurred when the temperature was decreased from room temperature to 10K, whereas SrTbO3 showed no crystal phase transition in this temperature range