Magnetic measurements on Tb₅Ge₃

Tb₅Ge₃ is a weak antiferromagnet, which orders at 83 K. It crystallizes in Mn₅Si₃-type hexagonal structure with two different positions for the Tb³⁺ ions. The hexagonal ab-plane is the easy plane of magnetization. Magnetization and magnetostriction measurements have been done on a single crystal in static fields up to 30 T and in pulsed fields up to 50 T. In addition to the antiferromagnetic phase, three more phases were found in fields in the ab-plane at low temperatures. Surprisingly, the measurements along the b-axis do not resemble the a-axis properties which indicates an anisotropy in the hexagonal plane. Initial model calculations reveal the anisotropy of the magnetic exchange, which is dominant over the crystal electric field effect, as cause. The hard c-axis shows only one phase transition at 5 T followed by a nearly linear magnetization and magnetostriction slope which is attributed to a steady-going rotation of the moment.