Crystal chemistry and magnetic behaviour of the ternary compounds RE 3(Au, Pt) xGa 11− x (RE = Y, Gd, Tb, Dy, Ho, Er, Tm and Yb)

Abstract

Phases of composition RE 3Au x Ga 11− x (RE = Y, Gd, Tb, Dy, Ho, Er, Tm and Yb) and RE 3Pt x Ga 11− x (RE = Y, Tb, Dy, Ho, Er, Tm and Yb) have been synthesized from the elements by arc- or HF-melting followed by heat treatment at 600 °C. Yb 3Au 5.5Ga 5.5 crystallizes with a unique structure type, all other compounds belong to the La 3Al 11 structure type. Isotypism of the new compound Yb 3Au 4.8Ga 6.2 with La 3Al 11 has been established from X-ray powder diffraction data using full profile refinement (space group Immm, a = 4.3684 A ̊ , b = 12.976 A ̊ , c = 9.4686 A ̊ ). 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 Gd 3Au 3.6Ga 7.4 and (Tb, Ho) 3Pt 2.2Ga 8.8; a metamagnetic transition occurs for (Tb, Dy, Ho) 3Au 3.8Ga 7.2 as well as Dy 3Pt 2.2Ga 8.8, whereas (Er, Tm) 3Au 3.8Ga 7.2 appear to be ferromagnets. The yttrium compounds are very weak, temperature-independent paramagnets. For both Yb 3Au x Ga 11− x compounds, ytterbium atoms adopt the non-magnetic Yb 2+ ground state, resulting in temperature-independent magnetic susceptibility over the whole temperature range studied. Yb 3Pt 2Ga 9, however, reveals a small magnetic moment (1.1 μ B per Yb atom), possibly due to intermediate valence behaviour.