NEUTRON-DIFFRACTION STUDIES OF MAGNETIC-STRUCTURES OF R2NI3SI5 (R=TB,DY, HO) COMPOUNDS

Neutron diffraction studies of polycrystalline R2Ni3Si5 (R = Tb, Dy, a nd Ho) intermetallic compounds with the orthorhombic U2Co3Si5-type cry stal structure indicate different magnetic structures. For R = Tb, bel ow T-tau = 13 K, a collinear antiferromagnetic structure with a magnet ic unit cell equal to the crystal one is observed. In the temperature region between T-tau = 13 K and T-N = 19.5 K, it becomes sine modulate d with a wavevector k = (0, 1.0, 0.206(1)). In both phases the magneti c moments are parallel to the c-axis. Dy2Ni3Si5 has an incommensurate sine-modulated structure with the wavevectors k = (0, 0, 0.330(1)) at T = 2 K and k = (0, 0.159(8), 0.356(2)) at T = 5.5 K. Ho2Ni3Si5 at T = 2 K also has a sine-modulated structure with Ic = (0, 0, 0.2855(9)). This structure does not change up to the Neel temperature 7.2 K. The m agnetic structures determined have been confirmed by symmetry analysis .