CRYSTAL-CHEMISTRY AND MAGNETIC-BEHAVIOR OF THE TERNARY COMPOUNDS RE3(AU,PT)XGA11-X (RE=Y, GD, TB, DY, HO, ER, TM AND YB)

Phases of composition RE3AuxGa11-x (RE=Y, Gd, Th, Dy, Ho, Er, Tm and Y b) and RE3PtGa11-x (RE = Y, Th, Dy, Ho, Er, Tm and Yb) have been synth esized from the elements by arc- or HF-melting followed by heat treatm ent at 600-degrees-C. Yb3Au5.5Ga5.5 crystallizes with a unique structu re type, all other compounds belong to the La3Al11 structure type. Iso typism of the new compound Yb3Au4.8Ga6.2 with La3Al11 has been establi shed from X-ray powder diffraction data using full profile refinement (space group Immm, a = 4.3684 angstrom, b = 12.976 angstrom, c = 9.468 6 angstrom). Only partially ordered substitution of the Al-sites by Ga and Au has been found. The magnetic properties have been studied over the temperature range 4-550 K. Above liquid nitrogen temperature (LNT ), the magnetic behaviour of all compounds investigated, with the exce ption of the ytterbium phases, corresponds to the paramagnetism of tri positive rare earth ions. Below LNT, antiferromagnetic ordering has be en found for Gd3Au3.6Ga7.4 and (Tb, HO)3Pt2.2Ga8.8; a metamagnetic tra nsition occurs for (Tb, Dy, Ho)3Au3.8Ga7.2 as well as Dy3Pt2.2Ga8.8, w hereas (Er, Tm)3Au3.8Ga7.2 appear to be ferromagnets. The yttrium comp ounds are very weak, temperature-independent paramagnets. For both Yb3 AuGa11-x compounds, ytterbium atoms adopt the non-magnetiC Yb2+ ground state, resulting in temperature-independent magnetic susceptibility o ver the whole temperature range studied. Yb3PtGa9, however, reveals a small magnetic moment (1.1 mu(B) per Yb atom), possibly due to interme diate valence behaviour.