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Abstract:
Phases of composition RE3AuxGa11-x (RE=Y, Gd, Th, Dy, Ho, Er, Tm and Yb)
and RE3PtGa11-x (RE = Y, Th, Dy, Ho, Er, Tm and Yb) have been
synthesized from the elements by arc- or HF-melting followed by heat
treatment at 600-degrees-C. Yb3Au5.5Ga5.5 crystallizes with a unique
structure type, all other compounds belong to the La3Al11 structure
type. Isotypism of the new compound Yb3Au4.8Ga6.2 with La3Al11 has been
established from X-ray powder diffraction data using full profile
refinement (space group Immm, a = 4.3684 angstrom, b = 12.976 angstrom,
c = 9.4686 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 exception of the ytterbium phases, corresponds to the
paramagnetism of tripositive rare earth ions. Below LNT,
antiferromagnetic ordering has been found for Gd3Au3.6Ga7.4 and (Tb,
HO)3Pt2.2Ga8.8; a metamagnetic transition occurs for (Tb, Dy,
Ho)3Au3.8Ga7.2 as well as Dy3Pt2.2Ga8.8, whereas (Er, Tm)3Au3.8Ga7.2
appear to be ferromagnets. The yttrium compounds are very weak,
temperature-independent paramagnets. For both Yb3AuGa11-x compounds,
ytterbium atoms adopt the non-magnetiC Yb2+ ground state, resulting in
temperature-independent magnetic susceptibility over the whole
temperature range studied. Yb3PtGa9, however, reveals a small magnetic
moment (1.1 mu(B) per Yb atom), possibly due to intermediate valence
behaviour.
