RE₂MAl₆Si₄ (RE = Gd, Tb, Dy; M = Au, Pt): Layered Quaternary Intermetallics Featuring CaAl₂Si₂-Type and YNiAl₄Ge₂-Type Slabs Grown from Aluminum Flux

Six new intermetallic aluminum silicidesGd2PtAl6Si4, Gd2AuAl6Si4, Tb2PtAl6Si4, Tb2AuAl6Si4, Dy2PtAl6Si4, and Dy2AuAl6Si4have been obtained from reactions carried out in aluminum flux. The structure of these compounds was determined by single-crystal X-ray diffraction. They form in space group R3̄m with cell constants of a = 4.1623(3) Å and c = 51.048(5) Å for the Gd2PtAl6Si4 compound. The crystal structure is comprised of hexagonal nets of rare earth atoms alternating with two kinds of layers that have been observed in other multinary aluminide intermetallic compounds (CaAl2Si2 and YNiAl4Ge2). All six RE2MAl6Si4 compounds show antiferromagnetic transitions at low temperatures (TN < 20 K); magnetization studies of the Dy compounds show metamagnetic behavior with reorientation of spins at 6000 G. Band structure calculations indicate that the AlSi puckered hexagonal sheets in this structure are electronically distinct from the other surrounding structural motifs.