Synthesis and magnetic properties of binary boride REB₂₅ compounds

Binary REB₂₅ (RE = Gd, Tb, Dy, Ho, Er) B₁₂ icosahedral compounds were successfully synthesized and magnetic properties were measured. Measurements down to 1.8 K revealed that an antiferromagnetic-like transition occurs in TbB₂₅ at 2.1 K. This transition temperature is almost one order of magnitude lower than that of the transition in the more magnetically dilute TbB₅₀. The structure of TbB₂₅ is refined and, from the differences of structure, the previous conclusion that B₁₂ icosahedra are indicated to play an important role in the transition of TbB₅₀ is further supported. The other magnetic rare-earth compounds show Curie-Weiss behaviour down to the lowest temperatures, with values of the effective moment close to that expected for trivalent rare-earth compounds.