REAuAl4Ge2 and REAuAl4(AuxGe1−x)2 (RE=rare earth element): Quaternary intermetallics grown in liquid aluminum

The two families of intermetallic phases REAuAl4Ge2 (1) (RE=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm and Yb) and REAuAl4(AuxGe1−x)2 (2) (x=0.4x=0.4) (RE=Ce and Eu) were obtained by the reactive combination of RE, Au and Ge in liquid aluminum. The structure of (1) adopts the space group R-3m (CeAuAl4Ge2, a=4.2384(7)Å, c=31.613(7)Å; NdAuAl4Ge2, a=4.2258(4)Å, c=31.359(5)Å; GdAuAl4Ge2, a=4.2123(6)Å, c=30.994(6)Å; ErAuAl4Ge2, a=4.2074(4)Å, c=30.717(5)Å). The structure of (2) adopts the tetragonal space group P4/mmm   with lattice parameters: a=4.3134(8)Å, c=8.371(3)Å for EuAuAl4(AuxGe1−x)2 (x=0.4x=0.4). Both structure types present slabs of “AuAl4Ge2” or “AuAl4(AuxGe1−x)2” stacking along the c-axis with layers of RE atoms in between. Magnetic susceptibility measurements indicate that the RE atoms (except for Ce and Eu) possess magnetic moments consistent with +3 species. The Ce atoms in CeAuAl4Ge2 and CeAuAl4(AuxGe1−x)2 (x=0.4x=0.4) appear to be in a mixed +3/+4 valence state; DyAuAl4Ge2 undergoes an antiferromagnetic transition at 11 K and below this temperature exhibits metamagnetic behavior. The Eu atoms in EuAuAl4(AuxGe1−x)2 (x=0.4x=0.4) appear to be in a 2+ oxidation state.

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