Structure, chemical bonding, magnetic susceptibility, and Gd-155 Mossbauerspectroscopy of the antiferromagnets GdAgGe, GdAuGe, GdAu0.44(1)In1.56(1),and GdAuIn

GdAgGe, GdAuCe, GdAu0.44(1)In-1.56(1), and GdAuIn were prepared as single-p hase materials from the elements by arc-melting and subsequent annealing at 970 K, The indium compounds were investigated by X-ray diffraction on both powders as well as single crystals. GdAu0.44(1)In-1.56(1) adopts the CaIn2 structure, a puckered version of the AlB2 type: P6(3)/mmc, a = 478.9(1) pm , c = 740.3(1) pm, V = 0.1470(1) nm(3), Z = 2, wR2 = 0.0278, for 149 F-2 va lues, and 8 variables. GdAuIn crystallizes with a ternary ordered variant o f the Fe2P type: P (6) over bar 2m, a = 769.8(3) pm, c = 397.8(2) pm, V = 0 .2032(1) nm(3), Z = 3, wR2 = 0.0562, for 505 F-2 values, and 14 variables. GdAgGe crystallizes with the same structure, and GdAuCe adopts the NdPtSb t ype, a ternary ordered version of the Cain, structure. Chemical bonding in GdAuIn was investigated by semiempirical band structure calculations. The s trongest bonding interactions are found for the Au-In contacts, followed by Gd-Au and Gd-In, while the Gd-Gd interactions are much weaker. The four ga dolinium compounds are antiferromagnets with Neel temperatures of 13.0, 16. 9, 21.0, and 12.5 K for GdAgGe, GdAuGe, GdAu0.44(1) In-1.56(1), and GdAuIn, respectively. No field-induced magnetic transitions are evident from the l ow-temperature magnetization data. The magnetic hyperfine interactions in t hese intermetallics were studied in detail by Gd-155 Mossbauer spectroscopy . (C) 1998 Academic Press.