Neutron diffraction study of the CeFeSi-type RTiGe compounds (R=Pr, Nd, Tb–Er)

Abstract Neutron diffraction experiments were carried out on polycrystalline RTiGe (R=Pr, Nd, Tb–Er) samples. These compounds crystallise with the tetragonal CeFeSi-type structure (space group P4/nmm). This structure is closely related to the ThCr 2 Si 2 -type and can be described as “BaAl 4 blocks” connected via R–R contacts (“W blocks”). All the compounds are antiferromagnetic. PrTiGe and NdTiGe are characterised by an easy-plane sine-modulated structure characterised by a wave vector k =0,0, q z =0.242 and 0.334 below 62 and 128 K, respectively. Below 80 K, NdTiGe exhibits a commensurate arrangement, which consists on ferromagnetic (0 0 1) Nd layers coupled antiferromagnetically along the c direction with the sequence ++−−. This commensurate magnetic ordering also occurs in TbTiGe, DyTiGe, HoTiGe and ErTiGe below 312, 185, 124 and 36 K, respectively. In the first three compounds (R=Tb−Ho), the magnetic moment is aligned along the c -axis whereas it is localised in the basal plane in ErTiGe. In all the RTiGe compounds, the magnitude of the ordered moments at 2 K amounts nearly to the free ion magnetic moment ( gJ ) values for the respective R 3+ ions.