Neutron diffraction studies of R2Co3Si5 (R = Tb,Dy) and Tb2Ir3Si5 compounds

The R2Co3Si5 (R = Tb,Dy) compounds crystallize in a monoclinic Lu2Co3Si5-ty pe of crystal structure while Tb2Ir3Si5 in an orthorhombic U2Co3Si5-type. T he Tb2Co3Si5 has a sine modulated structure described by the propagation ve ctor k = (0,0.0817(6),0) in the temperature range 1.6 K-T-N = 22.6 K while the Dy2Co3Si5 shows a collinear antiferromagnetic structure between 1.6 K a nd T-N = 21.9 K. For R = Tb the magnetic moment is parallel to the c-axis w hile for R = Dy it forms an angle 25.8 degrees with the c-axis. The Tb2Ir3S i5 has in the temperature range 1.5 K-T-N = 11 K, a sine modulated magnetic ordering with the propagation vector k = (0,0,0.1328(2)). The Tb magnetic moment is parallel to the b-axis. (C) 2000 Elsevier Science B.V. All rights reserved.