Magnetic and transport properties of single crystal TbB44Si0.7, a B12 icosahedral cluster compound

Good quality single crystals of the new B₁₂ icosahedral cluster compound TbB₄₄Si_0.7 were successfully grown and magnetic and transport properties investigated. Magnetic measurements showed that this compound has an antiferromagnetic transition temperature at 18.5 K and metamagnetic transition critical field of 33 kG, comparable to the transition observed in TbB₅₀. These compounds exhibit the first magnetic transitions ever observed in the higher borides, and are particularly interesting since T_N is Similar to that of the much more magnetically dense TbB₆ in which the magnetic interaction is further mediated by conduction electrons. The material shows a sizable magnetic anisotropy. While the magnetic moment of polycrystalline TbB₅₀ and sintered TbB₄₄Si_0.7 show a saturation of the magnetic moment around 4.5 μB/Tb atom at 55 kG and 2 K, a magnetically aligned TbB₄₄Si_0.7 crystal sample reached a value of 6.6 μB/Tb atom. The resistivity of TbB₄₄Si_0.7 was measured and no evidence of good metallic conductivity was found, i.e., a sufficient number of conduction electrons does not exist in TbB₄₄Si_0.7, and therefore it is further indicated that the B₁₂ icosahedral clusters play an important role in mediating the magnetic interaction in this new series of cluster compounds