INCOMMENSURATE MAGNETIC-ORDERING IN CEPTSN AND TBPTSN

The crystal and magnetic structures of CePtSn and TbPtSn were determin ed by neutron diffraction on polycrystalline samples. Both compounds e xhibit the orthorhombic TiNiSi-type of crystal structure and order ant iferromagnetically below 7.8 K (CePtSn) and 13.8 K (TbPtSn). In CePtSn a sine modulated magnetic ordering described by the propagation vecto r k = (0, 0.428, 0) has been found at 1.7 K. In TbPtSn the magnetic st ructure at 1.7 K is also sine modulated and is characterized by the wa ve vector k = (0, 0.300, 0.059). It transforms at 10 K into a structur e with the wave vector k = (0, 0.275, 0). The magnitudes of the magnet ic moments at 1.7 K localized on cerium and terbium ions are determine d to be 0.97(5) and 9.06(5)mu(B), respectively.