Synthesis, structure, and magnetism of Tb{sub 4}PdGa{sub 12} and Tb{sub 4}PtGa{sub 12}

Single crystals of Tb{sub 4}MGa{sub 12} (M=Pd, Pt) have been synthesized. The isostructural compounds crystallize in the cubic space group Im3-bar m, with Z=2 and lattice parameters: a=8.5940(5) and 8.5850(3)A for Tb{sub 4}PdGa{sub 12} and Tb{sub 4}PtGa{sub 12}, respectively. The crystal structure consists of corner-sharing MGa{sub 6} octahedra and TbGa{sub 3} cuboctahedra. Magnetic measurements suggest that Tb{sub 4}PdGa{sub 12} is an antiferromagnetic metamagnet with a Neel temperature of 16K, while the Pt analog orders at T{sub N}=12K.