2D crystal structure and anisotropic magnetism of GdAu_6.75-xAl_0.5+x (x ≈ 0.54)

Exploration of the gold-rich part of the ternary Gd-Au-Al system afforded the intermetallic compound GdAu_6.75-xAl_0.5+x (x ≈ 0.54) which was structurally characterized by single crystal X-ray diffraction (Pnma, a = 18.7847(4) Å, b = 23.8208(5) Å, c = 5.3010(1) Å). GdAu_6.75-xAl_0.5+x crystallizes in a previously unknown structure type featuring layers of Gd₂(Au, Al)₂₉ and Gd₂(Au, Al)₂₈ clusters which are arranged as in a close-packing parallel to the ac plane. The Gd substructure corresponds to slightly corrugated 3⁶ nets (d_Gd-Gd = 5.30-5.41 Å) which are stacked on top of each other along the b direction with alternating short (5.4, 5.6 Å, within layers) and long distances (6.4 Å, between layers). The title compound has been discussed with respect to a quasicrystal approximant (1/1 AC) GdAu_5.3Al in the same system. The magnetic properties of GdAu_6.75-xAl_0.5+x were found to be reminiscent to those of some ternary ACs, with sharp peaks in the temperature dependent magnetization, and metamagnetic-like transitions. The material becomes antiferromagnetic below 25 K; magnetometry results suggest that the antiferromagnetic state is composed of ferromagnetic ac planes, coupled antiferromagnetically along the b direction.