Crystal chemistry and magnetic behaviour of the ternary compounds RE₃(Au, Pt)_xGa_11−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 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

Crystal Chemistry and Magnetic Properties of the Ternary Compounds RE₃Ag_xGa_11-x (RE = Y, Gd, Tb, Dy, Ho, Er, Tm, and Yb)

Ternary samples with the composition RE3 AgxGa11-x, RE = Y, Gd, Tb, Dy, Ho, Er, Tm, and Yb, have been synthesized from the elements by arc- or HF-melting and annealing at 600°C. In all cases isotypy with the La3Al11-type has been confirmed from X-ray powder data. The homogeneity region of the Yb3AgxGa11-x phase has been established by X-ray powder diffraction analysis and ranges at 600°C from x = 2.6 to x = 3.8. Unit cell parameters in this region reveal a remarkable positive deviation from Vegard's rule corresponding with a partial composition-dependent atomic ordering in the various sites of the La3Al11-type structure. The occupation mode in the Yb-containing alloys has been studied in detail by full profile X-ray powder analysis for compositions x = 2.55 and 3.65 and by X-ray single crystal counter data refinement for the alloy with x = 3.0, confirming in all cases full consistency with the La3Al11-type structure with the space group Immm. Throughout the homogeneous range Ag was observed to preferentially occupy the (2c) sites. The relative increase of the Ag occupancy in (2c) with increasing content of silver, however, decreases and for compositions x > 3.0, Ag was found to enter the (81) positions. In correspondence with magnetic susceptibility measurements the peculiar lattice parameter variation observed is due to this complicated mode of Ga/Ag-substitution rather than to a valence change on the ytterbium atom. Magnetic susceptibilities were determined over a temperature range from 4 to 550 K. Above LNT, magnetic behavior of Gd (x = 2.8), Tb, Dy, Ho, Er, and Tm compounds (x = 3.8) corresponds to the paramagnetism of ideal tripositive rare earth elements. Below T = 25 K antiferromagnetic ordering of the RE-moments is encountered for the Yb3AgxG11-x alloys. The Yb-atom was found to be in a nonmagnetic Yb2+ ground state throughout the entire homogeneous range. The susceptibilities are practically temperature independent paramagnetic down to 20 K. Y3Ag3Ga8 is a diamagnet