Ternary gallides RE4Rh9Ga5, RE5Rh12Ga7 and RE7Rh18Ga11 (RE=Y, La–Nd, Sm, Gd, Tb) – intergrowth structures with MgCu2 and CaCu5 related slabs

Fourteen ternary gallides RE4Rh9Ga5, RE5Rh12Ga7 and RE7Rh18Ga11 (RE = Y, La-Nd, Sm, Gd, Tb) were synthesized from the elements by arc-melting, followed by different annealing sequences either in muffle or induction furnaces. The samples were characterized through Guinier powder patterns and the crystal structures of Ce4Rh9Ga5, Ce5Rh12Ga7, Ce7Rh18Ga11, Nd5Rh10.44(4)Ga8.56(4) Nd4Rh9Ga5 and Gd4Rh9Ga5 were refined from single crystal X-ray diffractometer data. The new gallides are the n = 2, 3 and 5 members of the RE2+nRh3+3nGa1+2n structure series in the Parthe intergrowth concept. The slabs of these intergrowth structures derive from the cubic Laves phase MgCu2(Mg2Ni3Si as ternary variant) and CaCu5(CeCo3B2 as ternary variant). Only the Nd5Rh10.44(4)Ga8.56(4) crystal shows Rh/Ga mixing within the Laves type slabs. Magnetic susceptibility measurements reveal Pauli paramagnetism for Y4Rh9Ga5 and Curie-Weiss paramagnetism for Gd4Rh9Ga5 and Tb4Rh9Ga5. Low-temperature data show ferromagnetic ordering at T-C = 78.1 (Gd4Rh9Ga5) and 55.8 K (Tb4Rh9Ga5).