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

Abstract We present a neutron powder diffraction investigation of the magnetic structure of La 3 NiGe 2 -type Tb 3 NiGe 2 and Mn 5 Si 3 -type Tb 5 Ni x Ge 3− x ( x =0, 0.3) compounds. It is found that below∼135 K Tb 3 NiGe 2 exhibits a commensurate b -collinear ferrimagnetic ordering with C 2h ′={ 1 , m z , 1′× 2 z , 1′× 1 } magnetic point group. The Mn 5 Si 3 -type Tb 5 Ge 3 and Tb 5 Ni 0.3 Ge 2.7 compounds are found to present a flat spiral type antiferromagnetic ordering at 85 and ≥89 K, respectively. The Ni for Ge substitution is found to decrease the flat spiral ordered magnetic unit cell from a × a ×40 c of Tb 5 Ge 3 (below 40 K) down to a × a ×5 c for Tb 5 Ni 0.3 Ge 2.7 (below ∼10 K).