Magnetic structure of the La3NiGe2-type Tb3NiGe2 and Mn5Si3-type Tb5NixGe3−x (x=0 and 0.3)

We present a neutron powder diffraction investigation of the magnetic structure of La3NiGe2-type Tb3NiGe2 and Mn5Si3-type Tb5NixGe3−x (x=0, 0.3) compounds. It is found that below∼135K Tb3NiGe2 exhibits a commensurate b-collinear ferrimagnetic ordering with C2h′={1, mz, 1′×2z, 1′×1̄} magnetic point group. The Mn5Si3-type Tb5Ge3 and Tb5Ni0.3Ge2.7 compounds are found to present a flat spiral type antiferromagnetic ordering at 85 and ≥89K, respectively. The Ni for Ge substitution is found to decrease the flat spiral ordered magnetic unit cell from a×a×40c of Tb5Ge3 (below 40K) down to a×a×5c for Tb5Ni0.3Ge2.7 (below ∼10K).