On the magnetic structure and magnetic phase transitions of Tb5Ge4. A Neutron diffraction study

Tb₅Ge₄ crystallizes in the orthorhombic space group Pnma, and orders antiferromagnetically below T_N = 91K. Neutron diffraction powder data at 4.2K reveal a ten-sublattice canted antiferromagnetic arrangment. The structure, which is described by the magnetic space group Pnm'a (Γ_8u) with propagation vector k = 0, has three-dimensional components for the atoms in the 8(d) positions, and is almost colinear for the atoms in the 4(c) positions. The magnetic interaction in the layers formed by the Tb atoms in the (010) plane is mainly ferromagnetic, in agreement with the high paramagnetic Curie temperature of 85K. The structure is antiferromagnetically compensated through an antisymmetry center. The main axis of antiferromagnetism is parallel to z. Magnetic phase transitions have been observed by applying a magnetic field in the (010) plane. The structure is stabilized through exchange interactions via conduction electrons. Because of the low symmetry, the Hamiltonian may contain anisotropic terms that result in a canted arrangement.