CRYSTAL AND MAGNETIC-STRUCTURE OF TBNIGE AND DYNIGE COMPOUNDS

The results of X-ray, neutron diffraction and magnetometric measurements for TbNiGe and DyNiGe compounds are presented. Both compounds crystallize in an orthorhombic TiNiSi-type crystal structure and are antiferromagnets with Neel temperature of 18 and 6 K, respectively. At low temperatures both compounds have square modulated structures with a wave vector k = (2/3, 1/3, 0). With increase in temperature a change to a sinusoidally modulated structure for TbNiGe and probably a cycloidal spiral structure for DyNiGe is observed. In both structures and both phases the magnetic moments are parallel to the c-axis. In the case of the TbNiGe compound a coexistence of two magnetic structures over a wide temperature range is observed. The experimentally determined magnetic structures are in agreement with those proposed by symmetry analysis.