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

We prepared oxygen stoichiometric SrTbO3 and BaTbO3 in which tetravalent te rbium ions are stabilized at the B sites of the perovskite ABO(3). Their cr ystal structures at room temperature and at 10 K were determined from both x-ray and neutron diffraction measurements. Both SrTbO3 and BaTbO3 have an orthorhombic perovskite-type structure with space group Pnma (No 62). Magnetic susceptibility measurements have been performed for both the compo unds in the temperature range between 4.5 K and room temperature. Both the compounds show the antiferromagnetic transition at similar to 33 K. The tem perature-dependent magnetic susceptibilities were measured with zero-field- cooled (ZFC) and field-cooled (FC) conditions at an applied field of 1000 G . A dramatic difference between ZFC and FC was observed below the Neel temp eratures for both the compounds, which shows the onset of a ferromagnetic m oment below those temperatures. To determine the magnetic structures at the antiferromagnetic state, powder neutron diffraction measurements have been performed at 10 K and room temp erature. Both the compounds have the G-type magnetic structure in which ter bium atoms are antiferromagnetically coupled with the six neighbouring terb ium atoms.