Transition from antiferromagnetic ordering to cluster-glass behaviour in the solid solution Gd 4NiMg 1− xAl x (0 ≤ x ≤ 0.9)

Abstract

Various samples of the solid solution Gd 4NiMg 1− x Al x were synthesized from the elements in sealed tantalum ampoules in an induction furnace. These gadolinium-rich compounds crystallize with the cubic Gd 4RhIn type structure, space group F 4 ¯ 3 m . All samples were characterized on the basis of Guinier powder patterns. The lattice parameter decreases with increasing aluminium content in a Vegard-like manner. The structures of two crystals were refined on the basis of diffractometer data: a = 1359.3(1), w R2 = 0.0711, 481 F 2 values, 20 variables for Gd 4NiMg 0.52(1)Al 0.48(1) and a = 1351.40(6), w R2 = 0.0665, 478 F 2 values, 21 variables for Gd 4NiMg 0.10(1)Al 0.90(1). The main structural motif is a rigid three-dimensional network of edge- and corner-sharing Gd 6Ni trigonal prisms and isolated (Mg/Al) 4 tetrahedra in fcc packing. The edge length of the tetrahedra drastically decreases from Gd 4NiMg (309 pm) to Gd 4NiMg 0.10(1)Al 0.90(1) (294 pm). The Gd 4NiMg 1− x Al x samples show Curie–Weiss behaviour with slightly higher magnetic moment values than the theoretical one for a free Gd 3+ ion. By substitution of Gd 4NiMg with aluminium the cell volume decreases and the atomic disorder (Mg/Al) induces a random distribution of the magnetic interactions. This leads to a shift of the Néel temperatures to lower values when increasing the aluminium content. Already for Gd 4NiMg 0.4Al 0.6 the long-range antiferromagnetic ordering no longer exists and the system comes into a cluster-glass state.