Magnetic structure of the La3NiGe2-type Tb3NiGe2 and Mn5Si3-type Tb5NixGe3_x (x=0 and 0.3)

摘要

We present a neutron powder diffraction investigation of the magnetic structure of La_3NiGe_2-type Tb_3NiGe_2 and Mn_5Si_3-type Tb_5Ni_xGe_(3-x) (x=0, 0.3) compounds. It is found that below~135 KTb_3NiGe_2 exhibits a commensurate b-collinear ferrimagnetic ordering with C_(2h)'={l, m_2, 1' × 2_2,1' × 1} magnetic point group. The Mn_5Si_3-type Tb_5Ge_3 and Tb_5Ni_(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 ax ax 40c of Tb_5Ge_3 (below 40 K) down to a × a × 5c for Tb_5Ni_(0.3)Ge_(2.7) (below ~ 10 K).