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

Abstract

We prepared oxygen stoichiometric and in which tetravalent terbium ions are stabilized at the B sites of the perovskite . Their crystal structures at room temperature and at 10 K were determined from both x-ray and neutron diffraction measurements. Both and have an orthorhombic perovskite-type structure with space group Pnma (No 62). Magnetic susceptibility measurements have been performed for both the compounds in the temperature range between 4.5 K and room temperature. Both the compounds show the antiferromagnetic transition at . The temperature-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 Néel temperatures for both the compounds, which shows the onset of a ferromagnetic moment below those temperatures. To determine the magnetic structures at the antiferromagnetic state, powder neutron diffraction measurements have been performed at 10 K and room temperature. Both the compounds have the G-type magnetic structure in which terbium atoms are antiferromagnetically coupled with the six neighbouring terbium atoms.