Neutron-diffraction study of CePtSn

We report a neutron- and X-ray-diffraction study of single crystals of CePtSn. As for the crystallographic structure, we have determined that the space group is centrosymmetric Pnma, contrary to the previously reported non-centrosymmetric ε-TiNiSi-type structure. At low temperatures two magnetic phase transitions have been observed at TN≈7.5 K and TM≈5.2 K. Our neutron-diffraction data support the previously proposed ‘spin-slip’ magnetic structures with the basic propagation vector q=(0,1/2,0) and sample-dependent spin-slips resulting in various observed incommensurate propagation vectors. Two separately prepared CePtSn single crystals were studied. In one of them we have found coexistence of the propagation vectors q1=(0,0.470,0) and q2=(0,0.422,0) below TM, while only q2 exists between TN and TM. In the other sample the propagation vector q2 also exists for the whole range T<TN and coexists with q1 below TM, but the intensity of q2-related reflections is strongly suppressed with decreasing temperature.